I’m a road racer, but I thought I’d get on here, because I think triathletes are much more serious about their equipment. I see wind data comparing different wheels, and they have between them a range of different wind resistances that’s around 200g or so (aeroweenies), between a regular aluminum wheel and a high end pair of zipps. what does this translate to in a 30 mph paceline? how much watts do I actually save if I were to race on 50 mm carbon wheels vs 26 mm aluminum rims?
(50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr = 20seconds per 40k.
Commit the above to memory as it’s quite useful
also, it’s actually 7.3W at 30mph, but the above will do for a quick mnemonic
savings of 200g is way blown out of proportion; maybe you get that when comparing a wheelset to a 32H box section. Most likely saving btwn a wide 50mm deep front wheel and a wide 30mm deep front wheel is 60-70g of aero savings at 30mph. Saving of rear about 40% that of front.
(50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr = 20seconds per 40k.
Even easier:
50 grams of drag at 50 kph = 5 watts = 0.005 m^2 = 0.0005 Crr = 0.5 seconds/km
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(50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr = 20seconds per 40k.
Commit the above to memory as it’s quite useful
also, it’s actually 7.3W at 30mph, but the above will do for a quick mnemonic
savings of 200g is way blown out of proportion; maybe you get that when comparing a wheelset to a 32H box section. Most likely saving btwn a wide 50mm deep front wheel and a wide 30mm deep front wheel is 60-70g of aero savings at 30mph. Saving of rear about 40% that of front.
Agreed, the flo data indicates that a worst case scenario between flo 30s and 90s is 100 grams at 30 mph. Extrapolate out the watts required to go 30 and 100 game of drag isn’t the greatest concern. It matters in a tt but in group rides on road bikes the advantage drops off.
How much less important could aero be in a pack? The old truism is that drafting saves up to 40% of your energy. Would it be fair to say that your 100g aero wheels should be worth at least 60g even in the pack? I’ll take 6 watts any time.
Besides, in pretty much every race or group ride I do I eventually take a pull, attack, or get spit out the back.
The only issue I see with your post is that the flo 30 is an pretty darn fast wheel in itself.
well, as you mentioned, it becomes important when you attack OTF. if i’d spend my money differently, i’d get a road aero helmet first, as they are probably worth at least the savings of a wheelset, followed by narrow aero handlebar, and followed by wheelset. The savings from these three items would be worth about at least 15W at 25mph; not insignificant.
It matters in a tt but in group rides on road bikes the advantage drops off.
If you’re in the group it might not matter but if you are in a group because at some key point you are planning on coming out of the group, ever little bit can help 
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The difference between the 30 and 90 is nil until you get past 5 deg of yaw. At high yaw most people will have handling issues with the deep rims. The bottom line as I’ve been saying for 15 years is that a decently shaped 25-30mm aluminum-rimmed wheel with minimal aero spokes is an aero wheel. The gains to be had going deeper are minimal, and usually a poor speed/$ ratio.
For the OP’s question regarding road racing in a pack, I see no reason to go past 40-50mm and only got that deep if you think you will go solo or in a small break. An aero frame, helmet, and skinsuit will yield bigger gains without the potential handling problems.
much appreciated, fellas
I’m usually super frugal about my energy, and rarely go into breakaways, and almost never initiate them. 20W may seem significant over a longer race, but not nearly enough to matter in a p/1/2 crit, in a pack no less, where the 20W turns into 10W (I guess). the other difference I was concerned about is whether it will affect my sprint. someone on bikeforums emphasizes the sailing effect, or flywheel effect, illustrated in the above figure, where the aerodynamics is drastically improved at non-zero yaw angles. however, I’m wondering if this is all placebo, considering the differences are no more than 300g of drag reduction.
otoh, gcn did a real world test, where they had simon do a 20 min FTP test, and then he put on 808’s, and was able to hold that same speed for 54 minutes. I believe the watts he used in those two tests were 379 and 344W, so around 35W difference at ~45-50 kph. that seems a lot higher than the 20W assumption, and echappist’s numbers match much more closely to this. 35W is getting into major savings category for me. But then again, 808’s are top of the line, and what I have are generic chinese ones, and there’s no way in hell I would pay $2k+ for a set of wheels. So the actual delta definitely diminishes for me. i guess it depends on how you want to argue this…
right now, I have 50mm wheels, aero road helmet, and skinsuit. the handlebars never really appealed to me, because they’re the first to touch the ground, and crashed carbon is not to be trusted. the wheels only get used for races, which I’m not sure is a very good investment of the money. most people who get the wheels seems to go after the look anyway. I see all the time people riding deep wheels with regular jerseys and non-aero helmets.
How much less important could aero be in a pack? The old truism is that drafting saves up to 40% of your energy. Would it be fair to say that your 100g aero wheels should be worth at least 60g even in the pack? I’ll take 6 watts any time.
Besides, in pretty much every race or group ride I do I eventually take a pull, attack, or get spit out the back.
Agreed, I’ll take 6 Watts if I can get it, but it’s a very small percentage of the power required to go 30 mph.
The only issue I see with your post is that the flo 30 is an pretty darn fast wheel in itself.
Agreed, and reasonably priced too. There is lower hanging fruit that people usually ignore. We as cyclists put a crazy amount of time and money into wheels and don’t put nearly as much into tactics, position and kit (among others).
If you’re one of those who has every detail figured out, great, but basic observation tells me the majority of cyclists don’t.
well, as you mentioned, it becomes important when you attack OTF. if i’d spend my money differently, i’d get a road aero helmet first, as they are probably worth at least the savings of a wheelset, followed by narrow aero handlebar, and followed by wheelset. The savings from these three items would be worth about at least 15W at 25mph; not insignificant.
You forgot skinsuit! Notable in the pro tour how everyone is effectively wearing a skinsuit now. Where would you rank that? On a level with or maybe even ahead of the aero road helmet? Depends what it is being compared against I guess.
It depends on the specifics but by and large the skinsuit is worth more savings.
so for shallower wheels, like the flo30, is it mostly the width that makes it more aero than the mavic open pro that it’s compare to? or is it more the depth?
well, as you mentioned, it becomes important when you attack OTF. if i’d spend my money differently, i’d get a road aero helmet first, as they are probably worth at least the savings of a wheelset, followed by narrow aero handlebar, and followed by wheelset. The savings from these three items would be worth about at least 15W at 25mph; not insignificant.
You forgot skinsuit! Notable in the pro tour how everyone is effectively wearing a skinsuit now. Where would you rank that? On a level with or maybe even ahead of the aero road helmet? Depends what it is being compared against I guess.
You are quite right, and from personal experience, a good skinsuit makes a lot of difference. But finding such a skinsuit is non-trivial (viz. the generic ones one could by off the rack are rarely good enough). What works for me is a Bodypaint skinsuit, but i’m told that one gets about 20-25 wears out of it, and i personally can’t justify using it in a road race.
so for shallower wheels, like the flo30, is it mostly the width that makes it more aero than the mavic open pro that it’s compare to? or is it more the depth?
I suspect that 20 aero spokes versus 32 round ones is the most significant factor.
Hugh
so for shallower wheels, like the flo30, is it mostly the width that makes it more aero than the mavic open pro that it’s compare to? or is it more the depth?
As the poster above mentioned the spokes play a part, but the fully toroidal shape with angled brake tracks play a big part too. When we started the design we were using flat brake tracks. We kept drafting and drafting trying to fit what we learned from our 60/90 design into the FLO 30. The flat brake tracks really limited what we were able to do in only 30mm of depth. A flat brake track is about 11mm deep and then you’ve only got 19mm left to create the right curves for a rim profile. On top of that, you can’t transition a toroidal curve into a flat surface smoothly.
Once we started adjusting the brake tracks, the shapes we could create became vastly more expansive, and as a result faster.
(50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr = 20seconds per 40k.
Even easier:
50 grams of drag at 50 kph = 5 watts = 0.005 m^2 = 0.0005 Crr = 0.5 seconds/km
I’m not sure how P=DU=1/2 rhoU^3CdA turns
rho=1.225 kg/m^3 (standard atmosphere)
U=13.41 m/s (30mph)
D= 50 gram-force (0.050kg*9.80665 m/s^2) ~= 0.4903 N
into a power 5W, or CdA of 0.005 m^2…
I get DU=0.5rhoU^3CdA → CdA=2D/(rho*U^2) = 0.04 m^2 (order of magnitude higher CdA)
or 0.49N*13.4 m/s = 6.6 W = P (if somehow you’re rounding to 5’s maybe this is “close”, but it’s slightly worse if using 50kph)
Yes, rounding…only number you need to remember for this ROT is 5. Very handy when doing back-of-the-envelope calculations in your head - just ask Cervelo.