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.
For the past few months I have been working with NTN and one of my racing teams in developing a bottom bracket suitable for SRAM dub cranksets. SRAM's Dub is their current bottom bracket standard which uses a 29mm (28.99mm) axle with a bearing landing spacing of ~90mm. The 29mm bore diameter is non standard and no tier 1 bearing manufacturer makes a bearing with a bore of this size.
In order to accommodate the axle a thin delrin insert was required. This had the advantage of prolonging crank life because the hardened bearing did not come into contact with the relatively soft crank axle. The technical difficulty was manufacturing an insert of only 0.5mm wall thickness at a nominal diameter of 30mm. My competitors were using blow moulded nylon inserts but I found the tolerances on these to be quite poor. Instead I elected to machine the adaptors in delrin. New jigs
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.
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.
Due to a large number of customer requests. Racing Bottom Brackets will be available in Silver colour shortly. This is an addition to Black and Hambini Orange.
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.
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
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 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.
I was recently invited to appear on the GCN Tech YouTube Channel. You can see my performance below. I had a great day there, it was fantastic!
Some of the content was edited out, the original recording was probably in excess of 1.5 hours so I will make a video to cover some of the questions that had not been answered as thoroughly as some of the commenters wanted
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
In this video, I take you through the engineering that I went through to fix a Trek Madone BB90 bottom bracket. You get to see some of the real engineering decisions involved in trying to get a fix at a reasonable cost.