Swiss Side Wheels spend a lot of time in front of the fan, and some of the things they find out might not be what you'd expect



Swiss Side Wind Tunnel 25.jpg


Swiss Side Wind Tunnel 22.jpg






Well, up to a point.



Swiss Side Wind Tunnel 29.jpg
Drag v yaw angle (click image to embiggen)


What's yaw?





More speed, less yaw

Swiss Side Wind tunnel 10.jpg



Swiss Side Wind tunnel 5.jpg



2. Fit the wrong tyres and your wheels won't be aero



Swiss Side Wind Tunnel 28.jpg


And how much difference does it make?




Swiss Side Wind Tunnel 27.jpg


Well, no. because...

3. Weight is a secondary issue almost all the time




Swiss Side Wind Tunnel 31.jpg

Well, it would increase it.

By three seconds.






Swiss Side Wind Tunnel 30.jpg


A final note on disc brakes

Disc brakes, in their current incarnations, aren't aero. I'm sure we all guessed that. The magnitude of the difference is fairly significant.

"We've measured a 16% increase in wheel drag between a disc-braked wheelset and a standard wheelset", Jean-Paul told us. "We performed a direct back to back test of the Zipp 303FC in standard version and disc brake version, for our own competitor comparison purposes. That 16% is a constant offset in the performance curve across the entire cross wind angle range."

So there's work to be done there, but how much can actually be done? The extra drag essentially comes from three sources. The rotor itself adds drag, and because disc wheels need more spokes to cope with braking forces there's more drag there too. On top of that, a disc hub contains more material and needs to be built to withstand torque across the hub body, as the braking forces are on one side only. Because of that, the hub body is generally bigger and that increases drag as well.

What can be done about those three sources of extra drag? In reality, probably not a huge amount, and disc systems will likely continue to be at a disadvantage in terms of aerodynamics. So if you want to be as slippery as possible, it's rim brakes for the time being. And hide them, if you can.




fukawitribe [2955 posts] 1 year ago
1 like
mrchrispy wrote:

you guys are totally missing the biggest take away from this article. 

we now have empirical evidence to justify buying some 40-50mm section carbon wheels to overcome the drag effects of my disc brakes.  re-fecking-sult! 

You'll also need to set aside some cash for beer for the ultimate performance set-up



(GCN - Why A Beer Belly Actually Makes You Faster)

madcarew [1002 posts] 1 year ago
1 like

Dave, just wondering if you could look at the more recent iterations of discs and aero testing and include that in the last part of your article. Re-cycling (sorry) old articles is fine, but it'd be of more interest to many of us if they were updated along the way.



MarkiMark [107 posts] 8 months ago
1 like

I rode the Tour de Yorkshire Sportive on Sunday. The 'race' (against my mate) culminated with a sprint finish for (our) 1st and 2nd place. The crowd were roaring. Long short, I came second by a wheel, and now I learn that I could have gained a valuable 3 seconds over the course if I'd had more aero tyres!!!!! Marginal gains indeed.

rws [2 posts] 8 months ago

This article seems to have been written for time triallists - for a road racer it’s not the overall course gradient that matters, it’s where you plan to attack, and 4% or higher gradient is not unusual. Furthermore, when it comes to attacking, it’s not all about weight - inertia matters too.

crazy-legs [1228 posts] 8 months ago
1 like
tritecommentbot wrote:

Generally in favour of disc brakes, but if drag really is that bad then it's quite a step back in terms of aerodynamics.

Ah but they're more powerful so you can brake later which means you can carry speed for longer so overall they're still faster.   3

Hobbanero [4 posts] 8 months ago

the guys at Deceunink Quickstep apparently didn't get the memo about disc brakes being slower.

Simon E [3927 posts] 8 months ago
rws wrote:


No, it wasn't written for time triallists, but they benefit most and care most about the subject. Does nobody use aero bikes, wheels & clothing in your races?

You might want to launch your attack on a 6% gradient but unless it's really steep and you're going very slowly then the aero benefit is still there, and it will be even more effective on any subsequent descent, when you definitely won't want to be using your weight-weenie climbing wheels!

Hobbanero wrote:


Things have improved on this front since the article was published, as madcarew's post might suggest. And if your rivals also run disc brakes...

davewyman [3 posts] 7 months ago

I like riding uphill. I like the feel of acceleration on the flats and reaching a high speed. As my last official race was decades ago, I don't care about setting any speed records on descents. 

That why I've got a climber's bike that, with pedals, weighed less than 15 pounds when I bought it. Now my bike has a set of aero wheels in place of the wheels that came with the bike, that make it even more lightweight. 

So I think I have the ideal bike for what I most like to do (not, somewhat regrettably, that this is my only bike.) 

TrueFalcon [1 post] 1 month ago

It's more than a bit annoying to read an article dated today and after reading a dozen or so comments, you noticte they are TWO YEARS OLD. When Conti 5000 tyres weren't being mentioned, I wondered why. I'm riding TLs and wondered how they fared in this tunnel.

How can 2 year old comments be relevant to an article written today? They can't be commenting on something written after their comments?

Why does road.cc redate old articles and publish them as new??? I've noticed this happens a lot and it's a disservice to the readers.

It looks like it's time to dump this tab from my batch of open-all-the-time tabs.

Griff500 [461 posts] 1 month ago

"100g is 1.25% of the wheel weight"

Those are some heavy old wheels!