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.
Update, more wheels added 01 June 2019
Update, more wheels added 06 July 2019
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
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.