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

I have been helping my son with his Baccalaureate science project - basically looking at the savings achieved by different rim depths

We compared 5 different wheelsets on my TT bike
Walker Brothers Disc Rear and 80mm Front
Reynolds 88 rear 66 front
FFwd 40mm rear (no front)
Fulcrum 32mm rear 32mm front
1980’s Mavic 10mm rear 10mm front

We tested different combinations of front and rear wheel, and complete wheelsets

The test comprised of creating 2, 500m Strava Segments along a flat road alongside the lake (1 segment out and 2nd segment return). I then rode my TT bike 5 times, at 40kph, for both segments, with each wheel combo

The results were taken from the Strava segments, and were normalised by creating a W/kph

So here are the results
Rear Wheels:
Disc blows everything else away completely 6.6% lower power than the 88mm Reynolds, 8.2% lower than FFwd, 10% lower than Fulcrum, 10.1% lower than 1980’s Mavic

Front Wheels
80mm Walker is 1.1% better than 66mm Reynolds, (no FFwd front), 6.1% better than Fulcrum and 6.0% better than Mavic

Wheel Sets
Most efficient, Walker Brothers 249.7w @ 40kph
Second Reynolds 66/88 277.5w (10% more power at 40kph)
Third Fulcrum 295.6w (15.5% more power at 40kph)
Fourth 1980’s Mavic 297.4w (16% more power at 40kph)

Walker Brothers and Reynolds had same tyres: 25mm Vittoria Corsa G+ Tubulars
Fulcrum has 25mm GP4000 Clinchers
Mavic has Schwalbe One 23mm Tubulars
All tyres were run at 90psi

Big surprise for me was the rear disc: I have read a lot recently that made me wonder whether a disc really made a difference… the answer is massive.

When I have enough energy I will go back and repeat the test to see whether I get similar results


What tyre did the rear disc have on?

25mm Vittoria Corsa G+ Tubular

It is a more modern wheel with a wider rim than the Reynolds, but same width rim as the Fulcrum

That’s weird!
Like you - the disc thing is now being proved to not be as much as people once thought it was.

Add to that handling and stuff.


What’s the Hamburg wheel choice?

Hamburg will be Disc

In terms of Deep Vs Disc, Swiss Side told me that the difference at 40kph is 5w with the 80mm Hadron Ultimate, I am seeing 19W difference from the rear disc. Now some of that may be down to the older design of the Reynolds wheels, The question is whether the latest Swiss side rear wheel is 14W better than the Reynolds, it is possible

You might find companies that claim discs aren’t faster, don’t make disc wheels. Swiss Side for example :thinking::smirk:


It’s interesting information, and certainly a worthwhile experiment for your own analysis of wheelsets you have, but with a variety of different tyre types (clincher v tubs), tyre brands, tyre widths, etc, I’m not really sure how valid this is as a takeaway more widely.

You say you ran them all at 90psi, but with 23mm and 25mm tyres in the mix, that would create different crr results even if they were otherwise the same brand and tyre type, would it not?

Also, how accurate does strava say you were in holding precisely 40kph for each run along the segment?

That said, I don’t know how much a difference some of the inconsistencies would be expected to make, and your results indicate substantial benefits of certain wheel types, so whilst maybe there is some additional noise in there, the underlying conclusions may well still be valid.

Didn’t Enve go down that road, then made a disc? :thinking:

Not related directly to wheels but this is interesting on is wider faster?


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You are correct, and in the write up, my son will use data from bicyclerollingresistance.com tests to identify the different CRR, all of the tyres have been tested

However, the difference will be a couple of watts per tyre, where we saw much bigger differences


I was pretty pleased with the distribution curve of the speeds achieved 75% of runs were between 41 and 44 kph, the data was normalised by dividing the number of watts by the speed to calculate w/kph… now you can certainly argue that riding at 41kph is more efficient that riding at 44kph. There are also other factors, like being overtaken by a large car or van will create a decent draft, but it was a quiet road.

I was amazed by how clean the data was, I did over 100 runs in total. Each rim came out in the correct depth order. I was really surprised by the disc, and actually went back and retested against the Reynolds yesterday, and came up with an almost identical result, I also tested at 33kph and 2 runs each at 49kph (I couldn’t hit 50), and had similar results

That’s really interesting data , thanks. Hitting the same speed at 249W v 297W just by changing the wheels is absurd.

I’m off to the disc shop, don’t tell her indoors.

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And tyres. And tyre widths.

I wonder what a wheel cover is worth?

Any reason why you chose a constant speed, instead of constant Watts?
More speed, same Watts = TTing
Same speed, less Watts = Triathlon

Isn’t it?

I’m going with 404 front and Super 9 rear clincher. Tyres are corsa g+ 2 on the front 25, and GP TT 23 on the back

I’ll let you know which tyre is the quickest, my money is on the front wheel getting there first :joy:

I’ve only really started riding 25’s in the last year, with no scientific backing I think they are slightly quicker than the equivalent 4000’s 23.

My favourite front wheel was always the HED3 but terrifying in the wind :grimacing:



My front 808 ended-up being fine in Hamburg; I think that’s because the wind was behind us over the suspension bridge! I actually felt it tugging away less on race day than the Friday before. But it was still very windy on race day, and long :relieved:

Hey everyone - I think @Jorgan is letting us know the Hamburg bike course is a bit long.

That extra 5.5km would be the final straw for any Hamstring injuries.

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Hammy in Hamburg :rofl::rofl::rofl:

If it’s a given that a rear disc is the way to go, where do wheel covers lie when it comes to aero performance? Closer to discs, or closer to deep section rims?
Can’t really afford a rear disc, so covers are a great solution. Any input would be great.

My understanding is that, as long as they are well fitted, they are as good as a “real” disc. Also that there is very little between different discs, some shapes (lenticular, flat) favouring a particular frame but unless you test all of them you wouldn’t know which.


As long as the cover is a tight fit, and doesn’t flap/trap air where it joins the rim, then hypothetically there should be no difference.

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