FPSDavid

What's the practical riding difference between a wheelset that is 20mm deep vs 30mm deep vs 40mm deep?

e.g. Soul S2.0 vs Soul S3.0 vs Soul S4.0

Jed19

Aerodynamics is the short answer.

pallen

nothing - its all in your head

merlinextraligh

about 10-15 seconds in a 40k tt.

Triguy

And to make things much, much more complicated when it comes to aerodynamics of wheels: whether a 20 v. 40mm wheel is more or less aero depends on about 5 other factors (tire selection, rim shape, rim width, spoke count, spoke selection, hub flange width).

As an example the 23mm deep Corima Winium+ was more aerodynamic than the 52mm deep Mavic Cosmic Carbone SLR in the recent Tour Aero tests with a 23mm Conti clincher tire.

In general a well designed set of aero wheels can save up to 2 minutes in a 40k tt for someone riding about 20mph. Those time savings are for a disc and 808 front though. Something more reasonable, say the difference between a set of Ksyriums and a Hed Jet 5 or Zipp 303 firecrest or Bontrager D3 Aura 5 is more likely 60-70 seconds in a 40k tt.

Soul, even by their own admission, has done no aerodynamic designing, so I would expect the savings to be a bit less than the 60-70 seconds quoted above for 50ishmm wheels from data driven manufacturers.

Velonews has been running a lot of tire aerodynamics v. rolling resistance articles lately and this has something that has been well known to some of us for years but I'm glad it's getting more light. But the importance can't be stressed enough in aero wheel discussions. It's really quite worthless to buy most "aero wheels" and put 23mm tires on them, except companies that really design for such a tire. In the end though you'll pay a premium for such design emphasis.

Dan333SP

Ignorant question- what tire width do pro riders use when they have deep rims on TT bikes, if 23mm isn't effective? 19?

tagaproject6

Depends on the crosswinds...

carpediemracing 

To me 20, 30, and 40mm rims are virtually identical. I haven't ridden the new wide shallow rims (Zipp 303 etc) but I went from Reynolds 46mm to Stinger 6s because I felt the Reynolds, although light, didn't give me much aero benefit.

Tires make a huge difference in aero, as pointed out above. The Stinger 6s and other wide rims (typically 28mm wide rim at max) are usually designed for a particular width tire. The Stingers are made for a 23 tire.

Faired tires make a huge difference I think. I know that there are mechanics that put clear caulk along the seam of the rim and tire, to smooth out air flow there. The further out on the wheel the more important the aerodynamics. Hubs don't count for much.

My understanding, based on talks with a wind tunnel person, is that a narrow rim and narrow tire would be fastest, but since most people won't run an 18 or 19mm tire, designers have gone to wider rims to properly "fair" the wider 21-22-23mm tires.

UCIMBZ

Headwind they all suck. Crosswind deepest profile is the worst. Tailwind they all jolly. Wind in any direction from 90 degrees on backwards the deeper the wheel the faster you go. 50mm is pretty much the best compromise.

Triguy

23mm and thats why Hed, Zipp, Enve, Bontrager, etc have all started designing their wheels around 23mm tires. When I said "aero wheels" I meant a 19mm wide, 50mm deep v rim. But to that end, pros keep using 23mm tires and that why Mavic and others are finally starting to go wide ~3 years after Hed and Zipp.

Lets face it, pros and consumers are in a tough spot. 20mm tires don't feel as fast and they aren't produced by many companies. Even Vittoria, which makes a narrow version of their Corsa CX, isn't a great option because the narrow tire uses the same tire on a smaller casing making it a poor rolling tire.

However, smart pro riders do tend to go narrower. Jordan Rapp, is an engineer by education but a triathlete by profession, and he runs a 21mm tire up front even on his Firecrests. Tony Martin was running a 22mm Conti on his front wheel at the world champs TT if I'm not mistaken.

When I had the privilege to be provided wheels (and subsequently a tire) by Hed, they gave me the new at the time 19-20mm Bontrager Aerowing TT tire. Apparently, it was a combination of the narrowness, shape and filling in the rim/tire gap that made it a spectacularly fast tire; particularly on a wheel like the Hed 3 which features a 20mm wide rim. However, they admitted at the time that their big time pros weren't riding it due to sponsorship obligations and general distrust of such narrow tires.

There is a very old adage which is not necessarily outdated that the best tire width for aerodynamics is one which is no wider than your brake tracks.

StanSeven

Triguy,

Thanks for the information and insight. Your posts are really helpful.