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I've been weighing up some options over wheels and in doing my research I've noticed that rim depth may be a bigger factor than I had previously considered. On the one hand, shallow rims are typically lighter and less susceptible to cross winds than deep rims - obviously the choice if doing lots of riding in hilly or windy areas. On the other hand, deep rims offer great stiffness (so more stability/handling improvements) and better aerodynamics, seemingly then the choice for flat low wind areas.

But then I thought about group vs solo riding - when riding solo obviously the deep rims provide a maximal aero advantage. However, when riding in a group there is more slipstreaming going on, so aero performance should theoretically become less important (at least when not leading the bunch). This depends on how much slipstreaming advantage reaches the bike, I assume the biggest "hole in the air" comes at body level and that the bikes only punch a small hole which is unlikely to reach the bike behind unless very close.

My question is, does the aero performance of a wheel become dramatically less important when group riding?

I ask because I do a lot of solo training but want to maximize my speed for big group (~20-30 riders) riding events (vätternrundan and skandisloppet in Sweden), if the aero benefit is not reduced greatly then I think it makes sense to take deep rims.

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So what if the aero benefit shrinks in groups? You said yourself that you do a lot (most?) of your training solo, so that's what your bike should be good at. OTOH, the aerodynamic gain from a more aerodynamic riding position (tri bars, deeper drops) is far greater than the rims. –  arne Mar 7 at 9:43
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@arne Group riding is where I care about speed though - I don't want to let the group down... "but want to maximize my speed for big group (~20-30 riders) riding events" and already I work on riding position by getting recorded occasionally and have the bars set pretty low. –  GriffinEvo Mar 7 at 10:02
    
I don't think the Deep-V rims will have any adverse effects as long as you're not constantly climbing. But during climbs, groups usually break up anyway, so I don't see any problems. –  arne Mar 7 at 10:24
    
@arne cool, I will bear that in mind for any cycling holidays to the alps/mountains and switch back to my existing low profiles if they are lighter than my new ones (hoping for a trip to Canaries this winter/autumn!) –  GriffinEvo Mar 7 at 10:30

2 Answers 2

up vote 4 down vote accepted

The aero benefits of deep rims come from reducing the spoke length. Imagine that you're drafting behind a large truck at 25 MPH; you're not experiencing any headwind, but your spokes are still going around in a circle and slicing through the air. So reducing the total length of all the spokes (by using less spokes or shorter spokes) will give you better aerodynamics no matter what.

Look at what the pro road racers do (I mean besides the doping.) They use moderately deep rims on flat races, and only use shallow ones for climbing (when weight is a more important consideration).

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Thanks, that's a really good explanation of the reasons behind aero benefit of deep rims. I've almost settled on a pair of fulcrum red wind h50's but want to read some more reviews! Oh, and no doping too of course. –  GriffinEvo Mar 8 at 20:10
    
Theres an additional point there though - train harder. –  Batman Mar 9 at 23:20

You get aero benefit when you ride at the front and at the back. So it depends on how big is the group. Or more to the point, how long you spend time at the front and at the back. If you ride in two lines in group of four the you get the aero benefit 100% of the time (in different amount).

If there are 6 in a group riding in two lines then 67% of the time you get aero benefit, assuming equal time spent in every position. If the group forms 4 rows then you get benefit 50% of the time, and so on. It diminishes as the group gets larger.

If you're a protected rider or just a passenger, then you don't get any benefit at all. But you could also spend 99% of them in the middle of the pack conserving and wishing you have all aero advantage when it comes to the sprint.

I think when riding in bunch (forming more than 2 lines) the aerodynamic is a bit different for the guys in the middle because it's not only there's less air resistance but it also sort of move in the same direction as the group. Kind of like there's no advantage of being aero when having some tailwind. Positioning might be the key there.

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