Hambini Engineering https://www.hambini.com Hambini Engineering Mon, 03 Feb 2020 15:22:14 +0000 en-GB hourly 1 https://wordpress.org/?v=5.3.2 https://www.hambini.com/wp-content/uploads/2019/12/favicon.png Hambini Engineering https://www.hambini.com 32 32 172902428 Specialized OSBB – Engineering Guide https://www.hambini.com/specialized-osbb-engineering-guide/ https://www.hambini.com/specialized-osbb-engineering-guide/#disqus_thread Tue, 24 Dec 2019 12:11:57 +0000 https://www.hambini.com/?p=1316 A question that crops up frequently is with regards to Specialized’s OSBB bottom bracket and what size it is exactly. The short answer is OSBB comes in 3 variants which are all called OSBB. 46×61, 42×68 and 46×73. A summary table is below, with the detailed drawings below that. Variant (Diameter x Width) (mm) Application […]

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A question that crops up frequently is with regards to Specialized’s OSBB bottom bracket and what size it is exactly.

The short answer is OSBB comes in 3 variants which are all called OSBB. 46×61, 42×68 and 46×73. A summary table is below, with the detailed drawings below that.

Variant (Diameter x Width) (mm)ApplicationDescription
46 x 61RoadFrame tolerances are the same as PF30. It is extremely narrow
42 x 68RoadThis has exactly the same dimensions as BB30 and is designed for 6806 or 61806 bearings and a 30mm axle.
46 x 73MTBThis the same as PF30 MTB

46 x 61mm OSBB Road Applications

This is a shortened version of PF30. It uses the same type of cups to encapsulate the bearings which then push into the bike frame. The bearings are usually 6806. it was designed for 30mm axles.

This is technically a poor standard because the bearing stance is very narrow. It lends itself to quite a lot of flex which would require significant material in the bike frame to regain the lost stiffness. OSBB in this guise has the narrowest stance of any modern BB standard.

OSBB 46 x 61

42 x 68mm OSBB Road Applications

This is the same as BB30. It uses two smalley VHM 42 circlips to hold in a pair of 6806 bearings. It was designed for 30mm axles. A schematic of this is shown below

The only real quirk of this against BB30 is the use or non use of circlips. Some OSBB bottom brackets have an integrated lip in the bottom bracket and do away with the Smalley VHM 42 circlips.

42 x 73mm OSBB MTB Applications

This is the same as PF30 MTB.

Cranksets and OSBB

If a 30mm crankset is being used, 6806 bearings should be used with inboard bearings. The use of 6806 bearings in an outboard sleeve configuration is not recommended due to the small width of the bottom bracket.

If a different crankset is used such as Shimano or SRAM GXP. then a Hambini Bottom Bracket with 6805 based bearings can be used.

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Testing to Find the Fastest Bicycle Wheels https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/ https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheels/#disqus_thread Thu, 12 Dec 2019 00:28:58 +0000 https://www.hambini.com/?p=607 Precursor – The critics and those with a vested interest I have added this section to the start of this blog post. The method this test uses is called transient state and it is used when aerodynamics are constantly changing. This is difficult to explain in detail in one blog post so I have linked […]

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Precursor – The critics and those with a vested interest

I have added this section to the start of this blog post. The method this test uses is called transient state and it is used when aerodynamics are constantly changing. This is difficult to explain in detail in one blog post so I have linked to a youtube video.

Forward to 10m20, this shows the clear difference between steady state and the real world

The important part of the video is at 10m20 and this shows the difference between airflow that exists in the real world, airflow that manufacturers test at and a (turbulent) transient test. The flow that is generated in a steady state wind tunnel rarely occurs in real life and is borderline acceptable for a velodrome.

Be aware that a lot of wheel companies use internet forum users as a method of subversively selling a reality that does not exist under a premise of an impossible power saving. I DO NOT SELL WHEELS SO I HAVE NO VESTED INTERESTS and remain impartial.

In short, the wheel companies are exaggerating their power savings and testing using methods THAT ARE INAPPROPRIATE FOR ROAD USE. If they tell you otherwise, they are categorically lieing and I would be more than happy to prove that in a court of law.

Introduction

In terms of drag caused by a bicycle rider, the biggest loss is caused by the rider themselves followed by the wheels and frame.

The drag caused by wheels is significant because of two fundamental reasons. The first is they hit the air first as they are the most forward part of the bike and second because they are rotating. The effective air speed at the top of a wheel/tyre is double the indicated speed of the bike.

In the bike industry, wheel aerodynamic testing has generally been conducted by two groups of people – Wheel manufacturers and journalists. Wheel manufacturers will usually adjust tests to make their particular wheels look more favourable than their competitors in testing. This is usually achieved by a combination of adjusting speeds and angles. The reality is this type of test is not impartial.

Journalists on the other hand tend to visit their local university and ask some clever boffin to conduct their testing for them and give them the results or go to their local velodrome, hold a speed and see how much power the wheels consume.

Both of the above testing methodologies are not representative of the real world. A comparative analogy would be fuel consumption for a car driving along a perfectly smooth glass like road surface with no wind and no change in speed – it is totally unrealistic.


The testing that has been carried out is usually steady state. A steady state analysis assumes the wheels, bike and rider are in a nice environment where air is hitting them at a perfect speed and perfect angle. The drag is then recorded.

In the real world, very few riders have the ability to maintain a speed of 50km/h for a length of time as they are simply not fit enough. The reality is on the open road, wind does not come in from a perfect angle, it’s speed changes and things like street furniture (hedges, kerbs, passing cars, rider rocking from left to right) upset the airflow over the rider. Modelling this type of situation is called transient analysis. It is technically more difficult to carry out transient analysis both in CFD and in a wind tunnel. Most wind tunnels are not geared up to carry out transient analysis.

Wheel manufacturers are now using a weighted analysis of yaw angles and speeds to give an overall rating for their wheels. Bare in mind they can adjust their weighting to make their wheels look better!

A superior method of analysis is to carry out a transient analysis in a wind tunnel. This requires a wind tunnel with Horizontal and Vertical Louvres to add Swirl to the air before it hits the bike and rider. This allows a much more realistic estimate of drag to be estimated as it simulates road conditions.


General Guidance

Yaw Angles
Wheel manufacturers tout their wheels as having fantastic drag at varying yaw angles. The effectiveness of their marketing is remarkable as many posters on the Internet also believe this.

Due to the laws of physics, for an average rider, the maximum yaw angle before complete separation occurs is around 12 degrees. A more blunt (toroidal) cross section might get to 15 but that’s really the limit. This limit of separation is affected by a variable known as Reynolds number (A combination of Speed, density, profile of the shape and viscosity)

Aerodynamic design is always a compromise, increasing the separation point at high yaw angles will always negatively impact drag at very low (<5 degree) yaw angles.

In repeated testing, wheels with very good transient performance work best for the average rider.

Tyres
This guidance is uniform across the board. It is vitally important to install tyres that are slightly narrower or inline with the brake track of the wheel rim. A ballooning tyre will impact the drag significantly.

There has been a trend towards wider tyres on bikes of late. From an aerodynamic perspective, the width of the rear tyre has little effect but the width of the front tyre has much more impact and therefore a 23mm front tyre is recommended irrespective of whether the wheel was designed for 25mm tyres. At speeds above 30km/h, it is more beneficial to have 23mm tyres than 25mm front tyres for aerodynamic benefit.


Testing Protocol

The test protocol is the product of “weekend work” by a group of Aerospace Engineers from Bristol, England. The testing protocol is very different to manufacturer tests. It is fundamentally impartial and mimics real world riding conditions in the sense it models transient air movement. Emphasis is placed on wheels which handle the separation and reattachment of airflow efficiently, very little emphasis is placed on riding a bike straight into a head wind at zero degree yaw – this is not realistic so why bother testing it. The wind tunnel used was temperature and humidity controlled.

The graph below shows a sample of one ride where a rider was riding along a straight road at an almost constant speed. It is clear that neither air speed or yaw angle were constant.

Road Test Data

The real world basis for this protocol are based on two subsets of bike riders in the Bristol (UK) area. Riders who are good club riders averaging 30km/h and time triallists averaging 50km/h. Data from their rides in terms of effective yaw angles, speed and air pressure distribution was recorded over 6 months. This was assessed, aggregated and mapped to a protocol suitable for a wind tunnel. The method of transformation was to statistically analyze the road conditions, apply a Fast Fourier Transformation to the data and run some test simulations for validation. The two discreet protocols are shown below.

THE GRAPHS DO NOT REPRESENT A RIDE CYCLE, THEY INDICATE THE PARAMETERS THE WHEELS WERE TESTED TO. Wind tunnels have limitations and part of the data gathering exercise is to validate data as it’s being processed. It is expensive and time consuming to rectify errors later. To replicate transient conditions, pulsing velocity or pulsing angle are both acceptable. The ramp tests were used to validate one against the other for each wheelset.

Test Protocol 30 Km/h
Test Protocol 50 Km/h

Through investigation it was found that micro corrections from the riders and the somewhat random nature of wind speed and deviation in yaw angle produced transient response of the bike and rider combination. This was much worse on the wheels as they were rotating into an oncoming airstream. In effect, a rider riding in a perfectly straight line into an oncoming wind was generating turbulence/buffeting/flutter by the bike rocking from side to side. What would be considered a zero degree yaw angle in steady state analysis behaves more like 5-6 degrees when the transient effects are factored in.

This protocol mimics the buffeting nature of the rider in the airstream configuration and produces an overall average drag value against time and consequently average power. It is designed to weed out the wheels that have poor transient performance. The lines on the protocols are shown for completeness, they do not mean this protocol favours blustery conditions.

Transient vs Steady State drag

The concept of transient drag effects have been well noted in low speed Aerospace applications such as military reconnaissance drones. This transient concept has not been applied to bicycle related products despite the overwhelming sensitivity of the velocity vectors involved. As an example the crosswind velocity on a bike often exceeds the forward velocity (Ratio > 1). A comparison for a car would yield a forward to crosswind ratio of 0.25 at 100km/h typical cruising speed.

A significant hurdle with trying to accurately measure the drag of a bicycle and rider is the discontinuation of the body. There are large areas with no solid body (eg wheel rim to hub, frame tube triangles, clearances between tyres and frames). This leads to inevitable separation of the freestream from the body surface and results in aerodynamic buffeting or aeroelastic effects (flutter). This causes the flow to take a long time to settle out and inevitably in that time, another variable has changed and the process repeats.

To illustrate the impact of transient drag, the graph below shows the yaw angle which is incremented in step inputs by 2 degrees every 10 seconds (data labels shown). This is plotted against drag force in steady state and in transient states.

The steady state line shows the drag performance of the wheelset when readings are allowed to settle and then noted.

The transient lines are more representative of real life. In the case of this data acquisition, a datum yaw angle was established and 2.5 deg/s of movement was overlapped. As the oscillation was introduced, there was an immediate increase in drag on both sets of wheels. At 4 degrees of yaw, there was a noticeable difference between the Reynolds and FLO wheels. The Reynolds wheels were able to deal with the instability and buffeting much better than the FLO wheels. Beyond 12 degrees, neither wheel was able to effectively contain the buffeting and full separation occurs.

In almost every case, the drag in the real world is much more than in a steady state scenario. It is particularly prevalent on the wheels because they are rotating and the net velocity at the top of the wheels are double the forward velocity.

Transient vs Steady State Drag

Time spent at varying Yaw Angles

Whilst the primary aim of this study was to establish a wind tunnel protocol to depict road analysis. Some of the data gathered could be used for generic calculations.

The instrumentation used for the road analysis had a sampling rate of 1024 times per second. Combining this level of accuracy with standard filtering protocols, it was possible to ascertain the effective yaw angle of the bike and rider. By reducing the resolution, the data was converted into a format that aligns with wheel manufacturer marketing departments for yaw angle vs time at that angle. In doing so, it reduced the accuracy of the results but has been shown for comparison purposes.

It should be noted that the transient data was a better reflection of actual time at an angle as it took into account the micro corrections for rider input steering and the instantaneous corrections for wind speed. Filtering for steady state by reducing the sample rate removed the instability. In summary the drag response against rate of change of yaw angle is a better predictor of response in a free stream at angles below the separation point of the section.

When considering an entire bike and rider combination, the effect of the wheels are comparatively small compared to the drag caused by the rider so the transient nature of the wheel drag becomes diminished. The rider drag is by far the dominant part of the system. The effects of transient response diminish as the ratio of forward to swirl (crosswind) velocity becomes greater. Thus the faster the rider goes, the less effect the transient behaviour becomes.

Time at Yaw Angle 30km/h
Time at Yaw Angle 50km/h
Time at Yaw Angle Combined

The effect of Tyre width on Aerodynamic performance

There has been a general trend towards wider tyres in the bicycle industry over recent years. This has been largely pushed by tyre and wheel manufacturers heading towards tubeless designs on the premise that a wider tyre has lower rolling resistance. Whilst the effects of rolling resistance and a more favourable contact patch have been well documented, the effect on aerodynamic drag has been disputed. Some wheel manufacturers have claimed their wheels were more aerodynamic with wider tyres – for this claim to be valid the wheels would have required a lower combined drag coefficient to overcome the increase in frontal area.

The graphs below show the comparison between two wheels, a narrow bodied Shimano C60 and a wider bodied Enve 7.8. It was clearly evident that a ballooned tyre (25mm on a Shimano C60 rim) had a significant impact on drag, especially at higher speeds. In contrast the effect on the wider bodied Enve wheel was much less dramatic. In both cases a narrow tyre reduced the drag. The continental tyres tended to measure slightly wider than their stated width when mounted.

Tyre width Drag 30km/h
Tyre width Drag 50km/h

Interpretation of the data

This data should be interpreted like those of fuel consumption figures for a car. They are designed to give a typical indication of how much power is absorbed over an ENTIRE ride loop at a given speed. It is important to note that wheels that are fast at 50km/h aren’t necessarily the fastest at 30km/h.

  • The MAXIMUM EXPERIMENTAL ERROR has been calculated at +/- 2.5%, the middle of the range is plotted for each of the values to maintain consistency
  • The rim depths are split into classes to make it easier for comparison, they may not agree with the stated size from the supplier.
  • The Power rating in a transient analysis is much worse than a steady state analysis
  • Comments are indicated for anything noteworthy
  • The rider position was within +/-10mm for each run, this was backed up with a reverse mounted pressure rake to remove any spurious data. There have been comments suggesting a rider could not keep a fixed position for the entire cycle duration – the protocol does not require them to, error checking is built in. Although unusual for the cycling industry, removal of appendage drag is commonplace in the Aerospace industry so the same technique was applied
  • Control Tyre was a pair of Continental GP4000SII 23mm with a pressure of 8.25BarG, there are a couple of wheel and tyre combinations that are highlighted in yellow showing a variation from the control tyre, these have been included for reference
  • The ROTATIONAL Drag required to spin the wheel up is included (Most manufacturers do not include this figure which is around 25 to 30 percent, a notable exception is Swiss Side)
  • The riding position (relaxed hoods) remained unchanged irrespective of speed. In reality high speeds would necessitate a different riding position but doing so would have invalidated the test.
Power Average 30km/h
Power Avearge 50km/h

Who tests in Transient Conditions?

To date, the only company that has confirmed they test for and include turbulence (transient conditions) when designing is SwissSide. Jean-Paul Ballade of SwissSide commented on the Youtube video shown above.

Although unconfirmed, there are certain features on Mavic wheels which suggest they either design for or test in Turbulent conditions.

Conclusions

Riders have long been fed a diet of wheels being tested at 50km/h, this speed is inappropriate for the vast majority of riders as they cannot maintain the power required for that velocity. There has been a general thought process that most riding happens at yaw angles of less than 10 degrees. Whilst this may be a valid statement if you are doing 50km/h, at more modest speeds this does not occur. In both 50km/h and 30km/h riding, the effect of micro corrections to the steering, turbulence from the wind itself and external objects causes unsteady turbulent flow over the wheels. This phenomena causes the effective yaw angle experienced by the wheels to increase.

  • Wheels that performed well were noticeably resistant to generating areas of turbulence
  • Wheels that performed well mitigated generated turbulence quite well
  • Wheels that performed well had a lower rotational drag compared to their competition
  • Wheels with a deeper rim section are generally more aerodynamic than shallow sections
  • The difference between wheels of a similar depth is very small and it would be difficult for a human to be able to detect this during riding
  • The difference between a low profile wheel and a deep wheel would be picked up by a human riding.
  • The FLO cycling and Hunt wheels performed badly, they appear to have been designed by individuals with a limited understanding of aerodynamics of rotating objects. As such they generated unnecessary separation and could not deal with the separated airflow
  • The Aerocoach disc and 75mm deep section front wheel showed quite interesting results. This wheel was essentially an aluminium wheel with a clip on fairing. At low to moderate speeds, the wheel performed reasonbly but as the speed was increased the wheel started to perform quite erraticaly. The front wheel construction is agriculturual and large gaps exist between the spokes and the non structural fairing. These gaps generated pressure disturbances and caused the flow to behave erratically. As the speed was increased, it’s performance became quite poor in comparison to the immediate competition and this was mainly due to the poor front wheel design. A picture of the problem is shown below
Aerocoach Aeox Wheel

If you are considering using the data from this article to influence your purchasing decision then please use this with caution. Some aspects of wheels like their general build quality, braking performance, hubs and ease of maintenance are not measured. These factors should be taken into account accordingly.

Flo Cycling examined in more detail…

After publishing this data, some people commented the data was controversial. In the sense the brands they expected to be good weren’t. Of note was Flo Cycling. A brand that is run by two Canadian Entrepreneurs from their base in Las Vegas, they buy in rims from the far east and sell them with their markup to consumers around the world. Some further anlysis was conducted into the aerodynamics by Airbus aerodynamacists and the conclusion was unanimous.

It appears that Flo Cycling did not model or take into account the effect of the spokes on their wheels. The spokes and internal geometry contributes up to 40% of the total drag – the amount decreases as the wheels get deeper. Their wheels had very poor aerodynamic behaviour aft of the wheel rim.

FLO were asked if this accusation was true on several occasions, and on each occasion, they have declined to respond.

FLO’s marketing has a heavy engineering bias and to the untrained eye, this reads well. However when looking at their hub design, the calculations behind them and their engineering practices some gaping holes were noted.

When looking at this page Flo Cycling. It was quite obvious that the engineering behind flo wheels is commercially driven and not mechanically driven. Topics of note

  • The choice of measuring tool – a vernier caliper is totally unsuitable for measuring down to 0.01mm
  • The L10 calculation does not account for any axial loading in the bearing, to put this into layman’s terms, it does not account for the wheel going around corners or being subject to road vibration
  • If the bearing met ISO, JIS or DIN standards, it would not measure an exact mm reading, it would be slightly under (i.e. 20mm nominal is 19.99mm). This highlights the use of a poor measuring instrument or poor quality bearings
  • EZO bearings have only been chosen because the hub supplier in Taiwan uses them as an upgrade over the no name standard bearings they use. EZO bearings have been chosen for commercial reasons not technical reasons.

Here is what NTN technical had to say

The calculation provided from this page does not approximate the road behaviour of a wheel bearing with sufficient accuracy. One would expect to see the axial loads applied with a ramp or step input along with sinusoidal input for the radial loading. We would not expect the wheel bearing to last as long as the L10 life predicts because the boundary conditions for the data are inaccurate. Further, vernier calipers are not recommended by NTN for the measurement of our bearings, we cannot comment for other manufacturers.

FOLLOW UP… Letters from Lawyers

Shortly after writing this blog post, I received a letter from a firm of solicitors representing FLO cycling which was addressed to the HR department of my employer. They complained this page depicted their wheels in a poor light, the test protocol was not openly published and they did not like the statement that they had a limited understanding of the aerodynamics of rotating objects. They wanted their power figures removed from the data along with threats of court action. Furthermore, they requested I was dismissed from my Engineering position for misuse of company resources.

It should be noted that FLO Cycling have a somewhat questionable strategy of paying prominent forum members in a number of popular cycling/tri forums to endorse their products. They usually do this under the premise of supplying wheels.

FLO cycling’s behaviour has been disappointing as when the wheels were originally tested and an issue was found, FLO were contacted. This was 6 weeks prior to the data being uploaded. Once the data had been uploaded, they were first to comment and question every aspect of the testing in surgical detail, even going so far as to suggest an adjustment of 5% in tyre pressure would make their wheels more aerodynamic. As time has progressed, they have come out and openly stated that these results were fabricated.

Link to Letter from FLO Cycling

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Hambini vs Flo Cycling https://www.hambini.com/hambini-vs-flo-cycling/ https://www.hambini.com/hambini-vs-flo-cycling/#disqus_thread Wed, 11 Dec 2019 23:22:03 +0000 https://www.hambini.com/?p=602 I do not usually write this type of post but I wanted to clear a few things up. I am an engineer by training and one of my weaknesses is I am unable to articulate myself as well as I would like. This is mainly because English is not my native language. There have been […]

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I do not usually write this type of post but I wanted to clear a few things up. I am an engineer by training and one of my weaknesses is I am unable to articulate myself as well as I would like. This is mainly because English is not my native language. There have been a lot of negative words exchanged between myself and FLO cycling about their wheels and I wanted to clear a few things up.

My engineering is Genuine

A key fact that seems to have been glossed over is when a set of FLO wheels was originally tested, the results were kept private and I went to lengths to contact FLO cycling to inform them that their wheels had performed badly. I waited a number of weeks and received no reply. I took the view that as a comparative nobody in the cycling industry they did not really care. So I proceeded to publish the results on my blog.

At this point FLO got interested – they did not want the negative publicity and asked me if I was using the same tyres for all wheel tests. A bizarre question but nonetheless I answered.

As this saga progressed…

Myself and my colleagues who are all engineers became subject to somewhat aggressive questioning complete with racism and the answers provided were not deemed to be satisfactory. The line of questioning was down a steady state test path when the test carried out was in transient state. The main point which stands firm to this day is that FLO cycling and others test in a steady state condition with what is colloquially called Utopian airflow.

Wheels are ridden in conditions which are much more chaotic and random. In random and chaotic (turbulent) conditions, the effectiveness of aerodynamic shapes diminishes and you can experience this first hand when flying on an aircraft as it goes through turbulence – the wings lose lift. Testing in a steady state will give a power absorbed but it is 100% not indicative of the real world.

The understanding of unsteady airflow in the aerospace industry is a specialist subject, understanding of it in the cycling industry is almost zero and the majority of aggressors are essentially ignorant of it despite all of the visual clues that point to transient turbulent unsteady flow.

As the situation with FLO progressed. A letter was received by my employer from a firm of solicitors representing FLO cycling. FLO have strenuously denied they sent this letter but neither myself or my colleagues are convinced for the following reasons:

  • This letter was sent to a company address in the wrong country. Post to receiving this letter, a member of the Slowtwitch forum called Dan Empfield sent me an email asking where I worked and eluded to the incorrect said country. I did not respond. Days before, a letter was received at the address in the wrong country. Pure Coincidence – unlikely?
  • I made a statement in my blog; “The FLO cycling and Hunt wheels performed badly, they appear to have been designed by individuals with a limited understanding of aerodynamics of rotating objects”. It is difficult to prove correct methods in aerodynamics as there are few recognized codes of practice. Hence, I elected to cite their use of bearing engineering (tribology) as a basis for the statement. I included written responses from SKF, FAG and NTN. This was sent to their solicitors The page in question was deleted from the FLO website shortly afterwards. I thought this may happen so I took a copy of it, which you can view HERE. Coincidence once again? – Unlikely.
  • Flo have been called out on multiple occasions for using CFD as a marketing tool. They neglected to nipples or even the spokes in their models! To date, they have not responded

What is in it for me and my colleagues

The answer to this question is nothing. All testing is done for free and performs part of a training programme for young engineers. Where a manufacturer requests a test, then we do this for free and ask they make a donation to a charity of their choice – usually the Red Cross. Despite what you may read on various internet forums.

The situation in the bicycle wheel industry is smoke and mirrors gone mad. A product is being sold on misinformation that the end user has no way of verifying. Added to this, there are various individuals who are actually wheel company employees sticking up for their testing methods because they know they are fundamentally flawed.

And finally…

Before purchasing a set of wheels, the question that you need to ask of the manufacturer is:

Please explain to me how your test method is indicative of real world turbulence.

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Bottom Bracket Pressfit and Creaking, an Engineering Analysis https://www.hambini.com/bottom-bracket-pressfit-and-creaking-an-engineering-analysis/ https://www.hambini.com/bottom-bracket-pressfit-and-creaking-an-engineering-analysis/#disqus_thread Wed, 11 Dec 2019 23:21:24 +0000 https://www.hambini.com/?p=600 If you are reading this you will have probably already come across the numerous posts by various individuals in Internet forums across the web. The issue of creaking bottom brackets has been blamed on the introduction of pressfit and directfit bottom bracket standards, where bearings either push directly into the bike frame or push into […]

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If you are reading this you will have probably already come across the numerous posts by various individuals in Internet forums across the web.

The issue of creaking bottom brackets has been blamed on the introduction of pressfit and directfit bottom bracket standards, where bearings either push directly into the bike frame or push into cups which are then pushed into the bike frame.

General guidance varies from taking everything out and regreasing it to installing with extreme measures such as epoxy resin.

Pressfit is not the problem and threaded is certainly not the answer…

The reality is pressfit has nothing to do with creaking. There are many areas of a bike where bearings have a pressfit and there are no problems. For example, wheels, freehubs, pulley wheels and some headsets are pressfit yet they don’t generally creak.

The basic reason for the creaking is one of two reasons, either a poor fit or misalignment. Often, the two occur at the same time. Modern bicycle frames are now readily available in lightweight materials and more specifically made of carbon. The manufacturing techniques associated with composite structures produce frames which have multiple parts that have been glued (manufacturers will say bonded) together. Bottom brackets are commonly glued together in two halves. A lack of suitable alignment dowels means these parts have a high tendency to be misaligned.

Once a misalignment in a bottom bracket is evident, the hardened bearing surfaces wear the bottom bracket down and the shell becomes a slack fit and thereby causing creak.

The drawing below shows parallel misalignment

Parallel Misalignment

The drawing below shows angular misalignment

Angular Misalignment

Another route to bottom bracket problems is through issues in the carbon fibre manufacturing process. Carbon is placed into moulds and with pressure and heat, it is cured to produce rigid carbon fibre frames. Unless carefully controlled, this process can produce wildly varying dimensional fits. Practically, the frame manufacturer must allow for expansion and contraction to occur through the autoclave and make allowances for this.

If the expansion and contraction effects are ignored or miscalculated which is a common occurrence, the bike frame could end up with a fit that is too slack and once again a creaking problem may occur.

As a lot of manufacturers sub contract this manufacturing out to companies in China and Taiwan, they are at the mercy of the sub contractors quality control.

The Video below, talks through some of the issues with creak

The chart below is a box and whisker plot showing the dimensional variation between a number of different frame manufacturers. For those who are unfamiliar with box and whisker plots, the box and whiskers represent an entire range, the smaller the boxes and whiskers – the more accurate the frame is. This chart has been normalized to a BB30 or 6806 bearing standard as there are a number of different BB standards on the market.

Bottom Bracket Tolerances

Conclusions

Look and Time have very good manufacturing tolerances, their frames are unlikely to creak. These two companies control their manufacturing in their own factories and this is reflected by very good dimensional stability.

Conversely, of the large manufacturers, Cannondale and Boardman bikes have poor manufacturing tolerances and this is affirmed through numerous posts in multiple bike forums with lots of users reporting bottom bracket problems.

The worst performer in this chart is Filament Bikes. A boutique bike brand run by one individual called Richard Craddock. His bottom brackets are usually much slacker than they should be due to his inability to use accurate measuring equipment and understand the limitations of it. As a result of this, I do not warranty any Hambini bottom bracket in a Filament frame.

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Aero Bike Wheel Test… The Fallout https://www.hambini.com/aero-bike-wheel-test-the-fallout/ https://www.hambini.com/aero-bike-wheel-test-the-fallout/#disqus_thread Wed, 11 Dec 2019 23:19:54 +0000 https://www.hambini.com/?p=598 Those of you who are avid viewers of a number of Internet forums will have noted that some results from my bike wheel wind tunnel testing have been contested and criticized. The ultimate result was I ended up getting banned from weightweenies for a week for calling Tom Anhalt of bike blather a spec of […]

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Those of you who are avid viewers of a number of Internet forums will have noted that some results from my bike wheel wind tunnel testing have been contested and criticized. The ultimate result was I ended up getting banned from weightweenies for a week for calling Tom Anhalt of bike blather a spec of shite on the anus of humanity and a letter went from Flo Cycling to my HR department to ask for me to get the sack.

One of the advantages to not being in the bike industry full time is I don’t really give two hoots about brand perception and I’m more than happy to tell someone where to poke it when they are talking from their rear end.

The Background

This story starts off with an innocent enough beginning. One of my colleagues was doing an IronMan race and needed the fastest wheels. So some testing was performed. The difference was as a group of aerospace engineers, we probably have a better understanding of airflow than bike companies whose primary aim is to sell more equipment and not really care if what you buy is slower than what you had last year.

The results of this wind testing were published on the internet, mainly to help people decide which wheels to buy. There was a general perception amongst my colleagues that testing of any aero bike component was subject to bias in favour of a particular brand so as an impartial body with a wind tunnel this removed that bias.

What happened after this is what I can best describe as a violent welcome to the shady world of Bike marketing. Instantly, people were questioning the validity of the study and the methods that were used. They were quite entitled to do this so some increased data was provided. At this point, I was starting to think something ropey was going on because the data that was being asked for was being heavily skewed in a particular direction and a number of users wanted data in a format that is not how Aerospace Engineers represent data, it’s how bike marketing departments represent data. There were also accusations that the data was made up – reasoning for publicity – these accusations mainly came from people associated with poorly performing wheels.

Fast forward a couple of months and what has become apparent is bicycle wheel companies and frame suppliers have people parading on internet forums convincing forum users to buy their products and other commenters believing these individuals are informed. This is apparently called a “shill” in north america and would probably be more like a tout in the UK.

I will categorically state this on my blog, the majority of aerodynamics engineers who work in the bike industry are not well trained and not well versed in aerodynamic principles. Most bicycle and wheel manufacturers sub contract their Aero out to third parties like Siemens or Fluent/Ansys for this very reason.

The Informed… aka the bell end

There are also a category of forum goers that some might consider to be informed. You should apply caution to these individuals because spending 2 hours in a wind tunnel does not suddenly make them an expert. They talk a very good game but when data is supplied like Aero engineers look at it, they discredit it. Mainly because they don’t understand it.

The Fake Wheel Companies an example.

There are a lot of companies who buy in cheap far eastern wheel rims and then build up wheels to sell in the west. While the aerodynamics is difficult for an end user to question because they rarely have access to a wind tunnel. It’s quite obvious when mechanical engineering is exposed. If we take this example from Flo Cycling, they comment on how their EZO bearings are of top quality and their L10 ratings are amongst the best.

To the casual observer, it’s a good sales pitch and being open is a modern marketing ploy. To the experienced engineer some of their methods are frankly shocking. If one of my graduate engineers did the following, they would be disciplined

  • They have calculated their bearing loads assuming a pure radial load. No axial – cornering load had been used. 6000 series bearings fail much faster in axial loading.
  • They have used a vernier caliper (and a cheap one at that) to measure bearings to 0.01mm accuracy. This is a completely inappropriate measuring instrument. A micrometer would be more appropriate
  • Quality bearings will never measure exactly on the bore and outer diameter, they always measure under so these readings are 100% fake, they are cheap bearings or they cannot use their equipment properly.

The Conclusion

This is mainly a statement that the buyer should be aware of some of the practices of bike suppliers and manufacturers, a lot of them have vested interests in a shady form of social media advertising but it goes undetected.

As a practicing engineer, I will continue to provide commentary but will pay careful attention to the individuals that are asking for it.

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Testing to Find the Fastest Bicycle Wheel Hubs https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheel-hubs/ https://www.hambini.com/testing-to-find-the-fastest-bicycle-wheel-hubs/#disqus_thread Wed, 11 Dec 2019 23:19:15 +0000 https://www.hambini.com/?p=596 The aerodynamic performance of wheels often grabs the headlines and the marketing budget but the reality is the hubs and the bearings within them will have more of a performance differential for the average cyclist. As an example, the power differential between wheels of an equivalent depth at speeds of less than 35km/h will only […]

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The aerodynamic performance of wheels often grabs the headlines and the marketing budget but the reality is the hubs and the bearings within them will have more of a performance differential for the average cyclist. As an example, the power differential between wheels of an equivalent depth at speeds of less than 35km/h will only be 1-2W, the difference in bearing friction can easily exceed that.

Wheel hubs and freehubs account for around 60% of the rotational friction in a bicycle drivetrain. The remaining friction is from the pedal bearings, bottom bracket and pulley wheels. The total amount of friction is small but a cost effective marginal gain.

The term rotational drag has been used of late to describe the amount of power required to spin a wheel up to speed. This loss is a significant aerodynamic loss of about 25 to 30 percent. Rotational drag is not the same as frictional drag which comes from the mechanical components.

Wheel Hub Design methodology

There are a several engineering considerations to be made when designing hubs which have been discussed below

  • The most obvious is the choice of bearing type. The vast majority of hubs use 6000 series ball bearings which are deep groove. A notable exception are Shimano and some Campagnolo/Fulcrum wheels which use cup and cone bearings. A cup and cone bearing is a type of angular contact bearing. A cup and cone bearing will always have more friction than a radial bearing because of an axially oriented contact angle. A loose cup and cone bearing allows for fairly slack manufacturing tolerances.
  • The bearing material (ceramic or steel) is often credited with lowering the friction in a hubset. The reality is the seal and choice of grease will have more effect.
  • The axle size determines the friction torque from the bearings. Axle sizes of between 10mm and 17mm are common on bicycle hubs. The smaller axles will always have lower frictional torque because the moment lever is shorter, the negative effects are the wheel hub will have more flex and the bearings will not last as long.
  • Machining accuracy, a lot of hubs are manufactured in Taiwan by forging aluminium 7075 alloy and then machining bearing landings afterwards. This is a standard process but it can be riddled with quality control issues. Having bearings that are misaligned due to slack jigs and holes that are too tight due to worn cutting tools will severely hamper friction levels.

The chart below shows the friction loss through hubs which were loaded. These tests results have some limitations

  • They do not take into account Road Vibration
  • A sample size of one for each hub set does not take into account any natural variation
  • Some of the hubs had completed an unknown mileage, they were checked for vibration to ascertain any bearing fault frequencies.
  • The power figure has some factors for calculation and it’s advisable to use this as a relative reference rather than an absolute figure

Upgrading Wheel Bearings

It is not cost effective to replace OE bearings straight from the factory unless the rider requires the ultimate in marginal gains. It is more advisable to wait until the bearings have worn out first and then retrofit.

Conclusions

Generally speaking, the Hambini recommended hubset to use would be the Carbon-TI. These have low levels of friction, are well made and use decent quality bearings from the factory. The Miche Primato hubs are a good budget option but the small axle diameter is not favourable in the longer term despite having the overall lowest friction, it should be noted that the test example had retrofitted bearings so the exact figure from the factory may be higher or lower. The angular contact Shimano hubs do quite badly in this test because the contact angle lends them to high levels of axial load, these wheels will be extremely stiff and predictable when cornering but the trade off is the higher linear friction.

In the longer term, bearings will wear out and for this reason, Shimano hubs are not recommended unless the cyclist is willing and able to carry out regular maintenance. The bearing surfaces are costly to replace and are a proprietary component.

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Ceramic Bearings vs Steel Bearings… An Engineering Analysis https://www.hambini.com/ceramic-bearings-vs-steel-bearings-an-engineering-analysis/ https://www.hambini.com/ceramic-bearings-vs-steel-bearings-an-engineering-analysis/#disqus_thread Wed, 11 Dec 2019 23:18:29 +0000 https://www.hambini.com/?p=594 One of the most controversial topics in the cycling industry is with regards the topic of Ceramic bearings and whether they do or do not reduce friction dramatically in riding. This article will address some of the concerns and topics associated with this debate and quantify the numbers. Internal Bearing construction – Ceramic bearings are […]

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One of the most controversial topics in the cycling industry is with regards the topic of Ceramic bearings and whether they do or do not reduce friction dramatically in riding. This article will address some of the concerns and topics associated with this debate and quantify the numbers.

Bearing Terminology

Internal Bearing construction – Ceramic bearings are not 100% ceramic

Ceramic bearings are in actual fact hybrid. They use ceramic balls and usually a steel inner and outer race. The ceramic balls are often silicon nitride or equivalent. Steel Bearings are commodity items that are composed of hardened steel balls and a steel inner and outer race. Geometrically, the contact points, inner and outer dimensions and thickness between steel and ceramic bearings is the same so they are interchangeable. The only real big noticeable difference between the two is the bearing clearance. On ceramic bearings, this is usually a C3 clearance whilst on steel it’s usually CN.

The bearing clearance is a measurement given to the small gap between the inner race, outer race and balls. It is required to prevent bearing seizure when it warms up and expands.

Another common difference in bearing construction is the cage type. The cage is required to keep the ball spacing even all of the way around the bearing. On steel bearings (usually by Japanese manufacturers NSK, NTN) the cage is a ribbon that is made from a piece of pressed metal and riveted between balls. This is a comparatively costly method of construction but improves friction characteristics at low speed and stiffness.

An alternative method of cage construction that has become popular is a composite or rubber cage. This cage snaps in and holds the ball spacing. Under high loads, the cage can often pop off or deforms and causes more friction. Almost all ceramic bearings use a composite or rubber cage.

External Bearing Construction – the Seals

Bearing seals come in 4 generic types. There are open bearings – these have no seals, metal shielded bearings – these have a metal strip over the bearing cage, non contact seal bearings and fully contacting sealed bearings.

In the bicycle industry, bearings generally have non contact or fully contacting seals. This is in light of the real risk of contamination from dirt and other ingress. In theory, non contacting seal will have the same friction level as a completely open unsealed bearing, in practice this is not quite the case because the seals generate a barrier for lubricant to ride up against and this is a frictional loss. Fully contacting seals touch both the inner and outer races to maintain the seal. This is definite frictional loss and they will always appear to be draggy when rotated in the hand. At operating speeds this loss from friction is still there but not so noticeable.

Basic bearing seal technology has not changed dramatically since the sixties and is largely governed by manufacturing costs rather than performance. Over time, the main improvements have come from sealing materials rather than geometrical differences.

Bearing Production

Bearing production in volumes is an almost entirely automated process and was pioneered by the Japanese. The big four (SKF, NTN, NSK and FAG) produce thousands of bearings every second with little human intervention. The bearings are usually made on one site from raw material to boxed finished product. These bearings are almost always steel.

In contrast, the smaller ceramic suppliers (Enduro, Kogel, Ceramicspeed) have much more human intervention and often complete assembly of bearings by hand. The smaller companies do not have the ability to carry out the entire manufacturing process on site and typically subcontract the manufacturer of one or more parts of the bearing to a third party and then complete the final assembly in house.

Some suppliers of ceramic bearings buy in a generic hybrid assembly and laser etch their own brand name onto the side of the bearing. These bearings are purchased at very low sums ($5/£5/€5) from the far east and then sold on for 10 or even 20 times the price to consumers in the US and Europe. It’s easy to spot these manufacturers as they are usually sold by one supplier only and lack technical data.

Bearing Friction

The large manufacturers have lots of people working specifically in their engineering departments whom end users can consult for technical advice.SKF, NTN, NSK and Schaeffler (FAG/INA) provided the graphs shown below which show the proportion of frictional loss for each component of a bearing.

Whilst the proportion of friction associated to each component of a bearing varies slightly, the overall values and order are the same. The bearing seal is the biggest loss, followed by the lubricant. The rolling friction is extremely small.

Power Loss Distribution NTN NSK SKF

Schaeffler (FAG/INA) went a stage further and gave the breakdown into the constituent components

Power Loss Distribution FAG/INA

Schaeffler’s data is useful because it shows how small the potential gain by switching from steel to ceramic bearings is. The maximum improvement is a potential 3%. In practice, rolling friction cannot be eliminated so the likely figure is more like 10% of the 3% ie 0.3%.

The cage friction is worthy of attention because ceramic bearings almost always have snap in cages. These have consistently been shown to have more friction than pressed metal cages. So whilst ceramic bearings could reduce the rolling friction (3%), they will inevitably increase the cage friction (7%). The net result is a steel bearing will have lower friction.

To illustrate this practically, a small experiment was carried out to neutralize the effects of grease and seals. Two bearings, an Enduro ceramic and an NTN LLB (Non Contact) steel bearing had their power loss measured at different stages of disassembly. The graph below shows the process

Power Loss Grease and Seals

There are three states. The first is out of the box. The second is the removal of grease and replacement with oil. The third is removal of grease, replacement of oil and removal of seals.

In out of the box configuration, the Enduro bearing has fractionally lower power loss. Once the grease has been removed, the power loss of both bearings is equal. After the seals have been removed, the NTN bearing has comfortably lower friction. This correlates well with the data provided by NTN, NSK, SKF and Schaeffler.

Bearing Friction vs Life

An often neglected part of tribology is how a bearing responds as it wears out. The graph below shows a comparison between two steel bearings (SKF and NTN) and a Ceramic bearing (Enduro). Initially the Enduro bearing has lower friction, at around 600km of use, the ceramic bearing has worn a track into the comparatively soft steel races and the bearing friction starts to increase dramatically. It is comfortably higher than steel bearings after a modest running in period. Hybrid ceramic bearings are the equivalent of trying to run a locomotive on an asphalt road – the hardness differential causes the road (raceway) to become damaged.

Bearing Friction vs Life

Total Power saving

The graph below shows how much power could be saved over 1000km between different bearing brands and their seal types. NTN, NSK and SKF dominate this chart and that is largely due to efficient seals and metal cages. The ceramic bearings which are coloured in red are not quite as efficient over a prolonged distance. If the evaluation window was extended to 10,000km, the ceramic bearings would perform much worse as a more significant track would have worn into the bearing races thereby increasing friction.

Projected Power saving

Watch the Video!!

You can see a bit more of the bearing internals in this video I have made

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BB86 Bottom Brackets with a 30mm or SRAM DUB Crankset https://www.hambini.com/bb86-bottom-brackets-with-a-30mm-or-sram-dub-crankset/ https://www.hambini.com/bb86-bottom-brackets-with-a-30mm-or-sram-dub-crankset/#disqus_thread Tue, 10 Dec 2019 18:13:35 +0000 https://www.mikoyangurevich.com/?p=407 30mm cranks into BB86 bike frames – Avoid if you can… A common question I am often emailed about is asking if I can supply a bottom bracket that will allow a 30mm crank to be fitted into a BB86 bike frame. This post will talk through the many problems associated with this. BB86 uses […]

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30mm cranks into BB86 bike frames – Avoid if you can…

A common question I am often emailed about is asking if I can supply a bottom bracket that will allow a 30mm crank to be fitted into a BB86 bike frame. This post will talk through the many problems associated with this.

BB86 uses a bottom bracket with a diameter of 41mm and a width of 86.5mm (Drawing shown below). In practice these are nominal dimensions and have a tolerance on them that makes them slightly smaller. BB86 is a Shimano standard and is used by lots of frame manufacturers (BMC, Canyon, Look etc). BB86 is effectively the pressfit version of an ISO threaded bottom bracket.

BB86 Shimano OEM Shell

The size of Shimano and it’s market share allows them to dictate standards and as such to an external engineer looking in, it appears that Shimano designed BB86 to try and exclude (or make it very difficult) to run a 30mm crank. Shimano uses a 24mm crank as standard which is a combination of 6805N bearings and nylon inserts to make up the difference in the bore.

A lot of people have 30mm / DUB cranks and a large number of those individuals have power meters attached to them and understandably don’t want to purchase a new power meter, they would rather find a solution to allow fitting in a BB86 shell. As a result a number of companies have produced bottom bracket solutions. I use this term loosely because there are some severe performance limitations that they omit from their product pages.

There are two popular methods of BB86 30mm / DUB bottom bracket design. I will cover them both

BB86 30mm Drawing

From left to right. A 6805, 6706 and 6806 bearing. Note how slender the 6706 bearing is in comparison to the others

6805 6706 6806 Comparison
6805 6706 6806 Comparison

Method 1 – Modified 6806 bearing

The original BB30 specification and 30mm cranks as a whole, are designed to run inside 6806 bearings. Irrespective of BB30, PF30, BBright or BB386EVO etc – there may be a cup between the bearing and the frame but all of these standards use 6806 as a design basis. Unfortunately this bearing is fractionally too large to fit into a BB86 shell. A BB86 shell is 41mm and a 6806 bearing is 42mm on the outside diameter. Hence a rather crude solution is to machine or grind 1mm from the outer race of the bearing.

This might sound like an easy and perfect solution but it has some implications for performance. Grinding down the outside of a 6806 bearing by 1mm reduces the strength of the outer race and it is much more likely to deform. Any rider that is putting a large amount of torque through the cranks – typically going up hill, will be deforming the bearing outer race significantly.

At a torque of 50Nm (~500W at 100RPM) the deformation is over 9 times worse than an unmodified 6806 bearing.

Correspondingly the bearing life is also reduced.

Method 2 – Use 6706 bearings or a Double row bearing

BB86 30mm Drawing

6706 bearings have an outside diameter of 37mm so they will comfortably fit inside a BB86 bottom bracket shell. They are however quite difficult to obtain and of the tier 1 manufacturers, only SKF have them readily available. Several bottom bracket suppliers use these bearings inside machined cups.

These bearings have an EXTREMELY low load rating, it is about 25% of the load of a 6806 bearing which is the next size up (used in BB30). Realistically, a rider would expect to achieve only 25% of the life or could only put through 25% of the peak torque before the bearing would fail.

A minor modification to this method is by using a double row ball bearing. This increases the life marginally but it is still far short of either a 6805 or 6806 bearing.

Performance

In every criteria of performance, running a 30mm crank in a BB86 shell is suboptimal. Friction, bearing life, stiffness and load rating are all significantly worse than running a 24mm crank or using a bike frame with a larger diameter bottom bracket

The graph below shows the relative friction against distance travelled for each type of bearing. Having had a discussion with SKF technical support, their conclusion was the 6706 and ground down 6806 were in an overloaded state due to the sinusoidal loading. Their firm recommendation was to avoid using these bearings in this application.

BB86 30mm Friction Graph

The Life chart speaks for itself

BB86 30mm Life Chart

Load rating can be obtained from bearing handbooks. They are an effective way of predicting bearing life using an L10 calculation. The slender 6706 and ground down 6806 bearings have a substantially reduced load capacity in comparison to the 6805 and 6806 bearings.

BB86 30mm Load Rating

An often overlooked parameter is bearing stiffness. When using 6806 and 6805 bearings, this is not usually a problem because the bearings are robust and stiffness can be ignored until very large torque is encountered at which point they flex and deform. In a 30mm to BB86 application this deformation limit occurs much earlier and even a modest rider will be able to feel spongeyness at power levels of ~250W.

BB86 30mm Stiffness

Conclusion

Using a 30mm crankset in a BB86 should be avoided. The likelihood of a failure is very high. I receive countless emails every week about people having problems with their 30mm cranksets in BB86 bike frames. My usual recommendation is to try a different crankset with a smaller diameter axle.

There will inevitably be anomalies in any data analysis and plenty of people will be able to use their 30mm crankset without having seen any problems however the engineering analysis clearly demonstrates this practice should be avoided.

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