# Aero Benefit - front wheel or back



## Ericv2010 (Nov 30, 2010)

Am considering purchasing a deeper aero section wheelset (no more than 46mm) and was wondering what the ideal combination of wheel depths are. I am a pure road racer with no TTs or Tri's in my future.

1. both wheels 46mm
2. back wheel 46mm and front wheel 32mm (front more stable in cross winds?)
3. front wheel 46mm and back wheel 32mm

Essentially, I'm trying to find the sweet spot between maximizing aero advantage while at the same time not sacrificing stability. I ride in a mostly flat area with a significant amount of cross winds (can get pretty strong at times).

I used to have a set of Mavic Cosmic Carbones (52mm depth) but ended up selling them because whenever I rode the wheelset my bike would get really twitchy and lose a significant amount of stability. I'm wondering if the optimal compromise is to go with an aero wheel on the front or back and something closer to standard depth for the other wheel.

Has anyone come accross any articles that support one approach vs. the other? Any opinions or experiences that would help me decide?

thanks,
eric


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## Gilarider (Jan 11, 2011)

Can you give more info?

What is your weight(re getting blown around)?

Are these race wheels only, bc if you are training on them deep rims bug.

How long do your races last-do you have a need to take both hands off the bars, then you need shallower.

What is your price range-can you afford the supposedly more stable wheels (Zipp and Hed)?


Aeroness is way more important in a front wheel, so buying a deeper front makes sense, except that getting blown around is influenced by front rim depth mostly, so catch 22. 

My opinion: based on you getting blown around on carbones I would think you should get a shallower front this time around (32) unless you are looking at Zipp or Hed. I would say get a matching rear just for the sake of fashion, deeper front than rear looks really weird, deeper rear than front looks only a little weird.


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## coachboyd (Jan 13, 2008)

The front wheel is going to be the one that has the most benefit aerodynamically, but going super deep in the front will also add to the decreased handling if there's a cross wind. In my experience, I have found that staying at or under 50mm in the front will have little impact by heavy crosswinds. Even my wife uses 50mm clinchers as her everyday training wheelset.

One of the reasons why the Cosmics probably felt twitchy is because of those big thick bladed spokes. When the crosswind hit them it's almost like you're riding with the spokes all turned at a 10-15 degree angle (it's not very aerodynamic). Going with smaller spokes like the CX Ray will help with aerodynamics especially in a crosswind. Looks like with the depths you have listed you are thinking about Reynolds. I believe they use the DT aerolites which will have similar shape as the CX Rays.

I would go with the 46mm on both the front and back. If you want the benefit of an aero wheelset, you may as well go aero where it matters.


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## Ericv2010 (Nov 30, 2010)

I'm 5-10" with mid-season race weight around 155-160. Not the biggest guy, so that plays a role as well. My races are generally 1.5 to 2hrs and no, I don't generally have a need to take my hands off the bars

Yes, I'm considering Reynolds - mostly for the value proposition. approx $1000 for a nice/quick and light 46mm profile wheel is a pretty sweet deal. Last check the Assaults come in at 1525g with the UL version at 1410g. Doubt that I'd pay the extra $$ for the UL for only a 115g weight differential. Of course, if I do decide on a full carbon clincher, I've got all the related safety considerations to take into account.

thanks guys,


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## cdhbrad (Feb 18, 2003)

Assualts are built with DT Revolution spokes and the UL have DT Aerolites, so $.75 vs. $4.00 per spoke. Considerable difference in hub quality too. That said, I would agree with Boyd and go with the 46s front and rear if you want carbon rims. If you only want a 32, you may as well choose a 30mm alloy rim, with Sapim CXray spokes, and better hubs, for about the same weight but considerably less money than the Assaults, and none of the "all carbon clincher" concerns.


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## rruff (Feb 28, 2006)

You can even go with the XR380 rim and not have to deal with carbon rims at all. ~1600g and $1000 with Alchemy hubs and CX-Rays.


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## euro-trash (May 1, 2004)

I'd go 32 front, 46 rear with cx rays. Any advantage (.07mph?) you'd gain with the 46 in the front you'd loose via 'stress energy' worrying about the next crosswind gust. I'd also really consider rruff's advice and look at Kinlin's 38mm rear rim and their 30mm front rim. You can build a decently light, super reliable pair for $500 with good spokes. They'd serve you well. 

I'd also recommended borrowing/buying some rollers. If you're nervous in crosswinds, there is no better way to get more comfortable. In just a few up-front hours, combined with 10 minutes of every-other week 'maintenance time' they work wonders.


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## Zen Cyclery (Mar 10, 2009)

What Ron said. Anyways, regardless of what you do, don't go with option 3. Having a deeper wheel up front than in the back would be impractical especially if your lighter. That front wheel can feel a bit squirrely in strong crosswind conditions.


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## cwg_at_opc (Oct 20, 2005)

for non-matching rim depths: the reason you want the deeper rim in the back is that it shifts the center-of-pressure to the back and actually helps to stabilise the bike in crosswinds.

some rim designs are better(more tolerant) of cross-winds than others; i have a set of flashpoint fp-60(the Real Design version) and depending on the angle of the cross wind i can feel some 'lift', like a wing, but it's not hard to handle for me(5'9, 170).


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## stevesbike (Jun 3, 2002)

keep this in mind:

0.1 lbs (50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr 

Eyeballing drag numbers from Hed's website for a Zipp 404 clincher vs. a 'typical OEM alloy wheel' the difference is roughly 70 grams of drag so about 7 watts. I don't know what the typical OEM wheel is, but to make the differences as large as possible, it's likely something like an open pro with 32 round spokes. Based on the rouesartisanales numbers, the difference between a 404 and a Shimano Dura-ace c24 shallow rim but low spoke count (and aero spokes) the difference is only 3.2 watts. I don't know what the drag #s for a Strike or Assault look like (round spokes) but they are likely not much better than the c24. A c24 and an aero water bottle on a seattube vs. a round bottle probably results in less drag than a 56mm deep front wheel like the 404. Diminishing returns?


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## Ericv2010 (Nov 30, 2010)

Stevesbike,

While I'm not as up to speed on the aero / drag numbers as you are, I can appreciate the point that (I think) you are trying to convey. At a certain point, it doesn't make sense to keep spending $$ chasing the elusive 'aero advantage'. You'll eventually reach a point where the minimal benefit you gain by spending the extra cash is outweighed by the negative impact on your bank account.

Question is: has my personal point of diminishing returns already been hit with the purchase of the set of wheels I run now (Reynolds MV32Cs) or does it make sense to spend the extra coin on a set of more aero wheels? At this point, I'm tending more towards sticking with what I've got...especially considering that the majority of my races will include some measure of climbing (where the lighter the wheel is the better)...

Looking at some of the wheelsets that the Pro Tour riders use for climbing (or even the mixed stages with some climbing and some long, flat sections), it looks like they're all using between a 32mm and a 44mm rim depth...basically the rim depth of a 202 or a 303. I'm at 32 now...and likely sticking with what I've got

thanks for the input guys...
eric


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## cdhbrad (Feb 18, 2003)

You already have a nice set of wheels that, I assume, are working for you so far. Going to a Reynolds 46 won't give you a noticeable change in performance, only a significantly lighter wallet. Unless you could get a killer deal on the 46s, I'd stay with what you have.


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## mimason (Oct 7, 2006)

Those Reynolds wheels are nice. I have the MV32ULs and at 175lbs they are a great option for weight,aero and stability. They spin up wicked fast and handling is very nimble. I think the ones you have also have the DT aero spoke IIRC. This is a good thing.
This morning was very windy with winds at 20mph and riding north with NW winds was not a problem, even gusts are manageable. Granted, I can ride 80mm depth in the same conditions but it is definitely not as fun.

The Mavics you mentioned are pretty poor in the winds with those bladed spokes. I have ridden them and a buddy has the SLR version.

A good choice for wheels that are good in cross winds are the Zipp 303s but since you already have the 32s why bother. Unless you are getting rid of the 32s and will go for a new wheelset I would think that getting a significantly deeper wheel for those nonwinds days would be best in order to compliment your current wheel inventory. This would be something greater than 45 in the 50-58 range or a 65/66 for the rear.

If it helps I am 12-15lbs heavier than you and have three sets of wheels for my road bike that allow me to cover a wide range of conditions:
Alu clinchers
MV32UL
Enve 65 - coming soon

If I only could have one set of the above it would be the 32s.


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## Ericv2010 (Nov 30, 2010)

Mimason,

Thanks for your post - definitively reassuring. I haven't had the 32s out on the road yet - picked them up over the christmas holidays and, being in canada, I'm not really in a position to ride them until the first / mid March. I've got a PRO+ Cycleops power meter laced into the back wheel and have been spending alot of time on the trainer with them in preparation for the upcomming season.

I've got a set of Ksyrium SL's as well for a tough, tough training wheel. In my personal opinion, everyone should have a training wheel as tough as the SLs. I've even heard of guys riding cross with these. I know you mentioned an alum clincher set in your wheel inventory but I'm not familiar with toughness / weight / etc.

Yeah, I'm not really in the market for another wheelset at the moment but, you never know, if the deal is right, I might just pull the trigger. I'd likely go for something in the 404 depth...

In terms of the spokes, I'm not sure what's in there. It's not their 2011 wheelset, migth not even be their 2010 wheelset. If I had to guess, I'd say either 2010 or 2009. Not sure how to tell without pulling tire and rim strips off and looking for a serial number...

thanks again for everyone's feedback...I'll be sure to watch inflation pressure and break use over the upcomming season...

eric


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