Wheel Mythology?
Being a bit of a sceptic & scientifically trained I am continually amazed at the almost supernatural powers attributed to bike wheels.
I know this one will cause a bit of a stink for some but here goes.
The weight of your rim only has a very small effect on how you perform on a bike.
Check out this site:
http://biketechreview.com/reviews/wheels/63-wheel-performance
To summarise:
"So, what do all these numbers mean? It means that when evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant."
There are other references out there citing the same thing.
So, beware the marketing hype and even worse the reviews both online and in bike mags, does the phrase "these wheels spin up really fast" sound familiar.
Personally I think most of what people attribute to increased performance (read speed) is actually more to do with differences in wheel stiffness, aesthetics, sound (e.g. zipps) & cost.
Remember I am not talking about aerodynamics & total weight (bike + rider) here...more to come on that.
Cheers Chris
Tags: wheels
Replies to This Discussion
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Permalink Reply by Graham Gower on -
While I agree that aerodynamics should be more important than rotating wheel mass, the model presented doesn't give the whole story. In particular, it doesn't take into account the constant acceleration required to maintain velocity due to rolling resistance (one of the comments on that page hints at this). I don't know whether this would show anything significant for typical tyres/roads at e.g. 100 psi. Also, I would have liked to know what assumptions where made when he derived his "easily manipulated" equation from Newton's second law.
Anyone got a copy of "Bicycling Science"? Does it have anything more definitive to say on the matter?
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Permalink Reply by Chris Adams on
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Hi Gemma, will read. Have plenty of time as I got knocked off my bike 10 days ago by a car and broke hip. Driver's fault.
Cheers Chris
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Permalink Reply by Chris Adams on
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Hi Gemma,
Yes I have seen this site. I am going to work out a few familiar scenarios & determine the numbers. i'm sure it will interest a few.
Cheers Chris
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Permalink Reply by Chris Adams on
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Hi graham,
Yes rolling resistance is significant and the choice of tyros and tubes have an effect. Plenty of discussion about this on TT & tri sites. Latex tubes offer better rolling resistance than rubber tubes, prob is you have to pump them up all the time. Needless to say rolling res has nothing to do with rotating mass. Also tyre pressure has a significant bearing on rolling resistance. On smooth surfaces, like the velodrome go for v high pressures. For rough road surface, dep on body weight, more like 100 psi or even lower is optimal. On rough surfaces you tend to bounce along the surface, esp with high tyre psi, which means energy is wasted in the wrong direction.
There are other sites out there by physics/engineering geeks who all come to the same conclusion.
Cheers Chris.
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Permalink Reply by Simon Lownsborough on -
Easy test - glue some weights around a wheelset and see what difference it makes.
I would have thought more mass = more energy required to spin up to and maintain speed?
Anyone got a wheelset they don't care much about?
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Permalink Reply by Graham Gower on
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I'd like to see someone with a dyno hub do this for descents. If a 500g weight on the rim makes a difference to energy production it might be worthwhile having quick release weights on the rim that you attach before descending.
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Permalink Reply by Gemma K on -
It's called grabbing a bunch of water bottles from the team car as you go over the top of the hill.
I'd prefer the mass on the rider or near the BB, rather than on the wheelset affecting handling.
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Permalink Reply by Chris Adams on
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Hi Simon, it does but the effects are v small, unless you get silly and start adding several kg to the rims.
Cheers Chris
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Permalink Reply by Kevin White on -
Speaking from personal experience the weight of a wheel set does make a significant difference, heavier wheels use more energy to push up to a particular speed. I have noticed the performance difference on several occasions fitting mag wheels to cars and lighter aluminium rims and mags to motor bikes. good tyres also have an effect, being the connection with the road. On a bicycle the single most noticable upgrade you can make is fitting a better wheel set.
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Permalink Reply by Chris Adams on
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Hi Kevin,
I agree that it makes a difference but I would like to see proper scientific data that shows that it is significant beyond a few fraction of a second. This of course can be significant when going for Olympic medals are sometimes measured in fractions of a second.
Good tyre definitely have a bearing, see above.
In terms of bike upgrade, it depends on the type of riding. For tt/tri learning to ride in a more aero position with aero bars is more significant than wheels. Approx 80% of drag is due to the rider. Of the remaining 20% wheels make up approx 1/3, bike 1/3 and clothes, helmet,etc 1/3. Aerodymanics is the most imp factor when considering wheels, unless all you do is ride up corkscrew every day where weight is more impt (not rotating weight, though). :)
Cheers chris
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Permalink Reply by Kevin White on
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You are correct. I was taking position as a constant and looking at upgrades as components. As for scientific data I'm only going on personal feel. It would be a fairly straight forward experiment to conduct, I have seen an electric motor connected to a flywheel using an ammeter and tacho we measured the power used to spin up to speed and moved weights along the radius of the flywheel. You could do the same thing with various bicycle wheels. Aerodynamics have more effect the faster you are going. When I used to race old motorbikes it was generally accepted in the paddock the easiest way to reduce lap times is to fit lighter rims. I can't be bothered racing push bikes so aero wheels don't effect me much. I just like my wheels to be easy to ride. Car wheels are balanced by attaching weights to the rim not the hub.
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