Wheel test.... how much do deep rims save

Just came across this on ST, it’s one of the more sensible answers/arguments to the disc vs deep rim debate. It’s from Josh at Silca who seems fairly well regarded.
I put disc wheels into the category of highly asymmetric marginal gains.

At low yaw angles the aero drag is a wash compared to the best deep rear wheels and your primary advantage is the reduced wattage to spin… call it a few watts. If your frame has an extreme rear wheel cutout, the advantage here becomes even greater for a disc as there is increased airflow over the wheel which is other wise directed into the spokes and across the system, call it 4-5 watts with normal yaw angle distribution.

However, at certain cross and cross-tail wind conditions, the effects can be pretty unbelievable… like 20-30 watts over a good deep wheel… and in these conditions, the wheel also helps to move the center of pressure of the bicycle rearward leading to this sort of stability effect that others are mentioning.

So for maybe 100 extra grams and some money you have a gain that generally on the order of 1-2x that of one of those oversized ceramic pulley systems, BUT can unexpectedly be worth 8-10x that in some special cases.

I generally analogize it to the no-lose charity wine pull that my kid’s school does. For $20 you get to pull a random bottle of wine off of the wall… the guarantee is that the cheapest bottle on the wall is worth $20 but some are worth $50, 100, 200, and one is a $400 bottle, seems like a pretty good deal. So if you spend $2000 on a disc and plan to use it 100 times over the course of its life, you need to be comfortable in accepting that it will only return the expected $20 of value 80% of the time and then you can be thrilled for the 20% of the time that you get $100 or $200 worth!

However, if in any of this you are thinking 3-5 watts ‘most of the time’ is not worth $20 per race over 5 years (or whatever your math is…) then keep doing what you’re doing.


There used to be a hierarchy and wheels used to come 2nd to an aero helmet. Not sure if that’s changed.

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The first thing is to buy a Cube Aerium SLT C:68 :rofl:

Did you miss the memo? :stuck_out_tongue_winking_eye::see_no_evil:

  1. Position
  2. Clothes (non-flappy jersey, shoe covers, duct tape)
  3. helmet
  4. bike
  5. wheels
  6. Are you a pro? Give over

But it probably depends, doesn’t it?
If I do 5km on my shopping bike on jeans and a hoody, I’m probably going to be quicker on a TT bike in the same clothes, even if position is similar?
(Like sat up…like most people I pass on the second lap of an IM :rofl::rofl::rofl: gets me every time)


I’m 8-10kgs over race weight. Flappy clothes isn’t an issue these days!


I see it has been spotted. Wind angle has a huge effect. Straight speed with both frame and wheels give totally different efficiency readings at different wind angles. What works one day, or in the wind tunnel won’t work the next.

Wheel go whomp whomp whomp.


You should hear them when going through a tunnel :grinning:


Discs do.
My deep sections don’t :sob:

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I love that sound…

I remember back in the early 90s when I first heard one come up behind me in a TT. Thought I was being attacked by a pterodactyl!


It’s a great noise isn’t it? It’s the only reason I ride disk if I’m really honest with myself.

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Trouble is, you only get the noise with the expensive ones!


And definitely not with a wheel cover :rofl:


That info has saved me a few £££ :slight_smile: