aero advantage of deep section rear wheel only?

Discuss light weight issues concerning road bikes & parts.
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by neeb

I'm looking at getting a powertap rear clincher wheel built up, and as it's going to be expensive anyway I thought I might go for the new enve smart 3.4 rim (45mm deep at the rear). My thinking is that I could use this pretty much all of the time for training etc - it would be stiffer than an alu clincher wheel, the same weight or less, and as I'd just stick with an alloy clincher on the front there would be no real problems with braking in the wet.

What I'm wondering is, how significant would the aero advantage be if this was coupled with a campagnolo eurus alloy clincher at the front? I know that the rear wheel is in a turbulent area in any case and that there is more aero advantage with a front wheel (at the expense of stability), but the enve 3.4 is designed to run with a shallower rim at the front in any case (albeit significantly wider and more aero than a campag eurus..). Would there be a real-world aero difference (something I'd notice) over a standard alloy rear clincher rim?

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by Valbrona

It would be a sod in a strong cross wind.

by Weenie

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by neeb

Valbrona wrote:It would be a sod in a strong cross wind.

Even with just a rear wheel? I thought that crosswinds were mostly a problem at the front due to interaction with the steering.

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by Dalai

Wont be an issue in winds as it is on the rear. I rock my disc in all winds on the back when TTing, only swapping the front from a Hed Stinger 90 to Zipp 404 if windy.

As to aero - studies I've seen suggest 30 seconds over 40km going from a high spoke low rim depth wheel to a disc. So I'd be factoring less than that for the Enve.

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by notsoswift

I race 46 mm front and rear in nearly all conditions, it just will not be an issue this side of 30 kph cross winds and if it is a head or tail you will be way in front
Just my opinion

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by Pantani

The aero advantage will be small but you might as well have it anyway.

I agree with other posters - even at 58kg riding a Zipp 808 on the rear, I've never had an issue with crosswinds and its windy here most of the time.
Not everything that counts can be counted. Not everything that can be counted counts.

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by neeb

I'm vacillating now..

I could get a velocity a23 rim built on a powertap G3 for quite a lot less. The enve rear would probably have only a tiny aero advantage without the front wheel. I'm also pretty sure that if I got it, at some point in the following months I'd just have to have the front wheel too, and an enve 3.4 powertap wheelset is a much more significant purchase than an a23 rear powertap... :wink:

It might come down to what the enve rides like, aero properties aside. I've heard that it's very stiff and responsive, but then I've also heard something about a test in Tour magazine saying something like the opposite.. I'd be interested to hear informed comparisons of this rim with a decent alu clincher, aero properties aside and bearing in mind it would be built on a G3 hub.

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by davidrichardson

Most aero gains come from from. The velocity would make more sense if its a training wheel.

I was planning on getting exactly the same set up for the winter bike later in the year. The a23 is a nice riding training rim.
Tester for PMR@cing /

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by highwater

I agree with the logic of going with the Enve 3.4 to save weight in the rear wheel w/ powertap. But why not just use the 3.4 as a set, and keep an alloy clincher as backup? You would have a definite aero advantage, and lower weight overall. I recently started riding the 6.7s, and while it's not coming from a lot of experience, the braking quality has been completely satisfactory so far with Red brakes and Enve pads. Braking in the wet has been about the same as an alloy clincher. I would generally rather use Bike #2 for 'known-adverse' weather situations, but getting caught in the rain with the SES wheels isn't a big deal. Stability with the 3.4s would not be an issue - I've been really impressed with the 6.7s and I am not a heavy rider. Aside from aero, the wide rims also contribute to ride quality. Don't neglect the benefit of that for the front wheel.

Yes, it is much more expensive, but wouldn't you want nicer rims than the A23 down the road anyways? It would just cost more to have your powertap built into a second custom wheelset later on.

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by Mikmik

Valbrona wrote:It would be a sod in a strong cross wind.

Please, don't answer if you have nil experience in using a disc wheel.

To the OP. That German magazine that keeps doing all those cool tests but only release their literature in German have found a simple answer. When they were aero testing different TT frames and wheels they found that the biggest difference 'in equipment only' (remember the rider produces the largest amount of drag by a fair margin) is what wheels you use. There was little difference between the leading aero frames but the wheel choice made the biggest difference in numbers. So the short answer is yes. Definitely a yes for the rear wheel and even a disc on blowy days is easy to control. I've ridden a TT in 40km/hr crosswinds with 60km/hr gusts and I am very thankful I took my bonty xxx lights at the front, the disc was not a concern. So, since rear wheel has very little affect on handling of your steed the deeper dish you get the more aero benefit you will get. Double check though as somewhere along the grapevine I heard that UCI does not allow you to ride with as deep as the 1080 wheels but 808 is fine. Remember Highroad a couple years ago? They road with 808 rear and 404 front.

Your concern will be windy conditions and the front wheel.....always.

Keep in mind that when there are crosswinds there are several factors that will affect your control. The strength of the wind of course, how much weight you have over the front wheel as well as your weight, how deep are the rims, how many spokes are in the front wheel are the big ones. Another is weather you have bladed spokes, they can make a difference. Also your speed. When travelling at high speeds even a low spoked wheel will get a disc like effect.

Hope that helps.
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by ave

I've no experience with disc wheels myself, but Schleck supposedly crashed because of the wind-disc wheel, no?
Also I have a friend who was blown off the road sporting a disc in a 20km TT.
And he is certainly no Schleck in bike handling.

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by mjduct

the deeper wheels also transfer power better on the rear, but the aero advantage is less than a deep dish on the front (dirty air bask there and alot of it is shielded by the frame/you)

also since all your weight is on the rear, it doesn't move in the crosswinds, where as a deep on the front has less mass holding it down.

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by Ypsylon

Well, it depends.

IIRC the difference between a 32spoke box section and a disc was quite a bit larger on a standard road bike than on a p3c, which shields the rear wheel better.

Then the UCI allowes discs at all times but makes your saddle end 5cm behind the bb, while the triathletes ban discs for certain windy races but you could sit on your handlebar if you wanted to.

So, if this is about a rear wheel on a "regular" road bike with a "regular" road position it will not cause problems and will be a bit more aero and likely stiffer, but more expensive.

I have 5 on you buying a matching front before the season's over, though. :mrgreen:
"Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.

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by neeb

Still vacillating.. :)

This Tour Magazine test is really throwing a spanner amongst my decision processes:

If you are paying for these extremely expensive wheels instead of some alu clinchers, you are paying for perceptibly better aerodynamics, stiffness and performance for the same or less weight. So it is somewhat disconcerting to have a test suggest that they might actually be less stiff and less aero. I'd really like to see this definitively refuted by something other than the manufacturer's marketing. I have seen one or two very favourable opinions from apparently unbiased and knowledgeable sources suggesting that the enve 3.4 clinchers ride extremely well, but I'd like to see more.

by Weenie

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by Ypsylon

Tour tested wheels, not rims. If the ENVE rim with unknown spokes and DT hubs didn't test overly stiff, that doesn't have to have too much to do with the rim.
"Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.

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