Different depth wheels for aero advantage - relieve my confusion, please...

[dd74]

I've been researching the aero advantages of different depth wheels. My basic question is if one has a 42mm & a 60mm wheel, would there be an advantage and/or more stability against crosswinds if the 60mm wheel is the rear wheel? Or should the 60mm wheel be the front wheel and the 42mm the rear for more of an aero effect? As importantly, is there an aero advantage at all from having a mixed wheel set such as 42mm & 60mm?

Thanks for the help & advice.

[ultraman6970]

Are we talking about weekend rider or racer here?

[dd74]

Are we talking about weekend rider or racer here?
A little of both.

[kramnnim]

Enve probably has a reason for the mismatched rim depths on their "Smart" wheels...

[Louis]

As best I can tell the deeper the aero section of the rim the more drag reduction you will get. However, that larger area makes the wheel more likely to be affected by crosswinds, particularly on the front.

[dd74]

Enve probably has a reason for the mismatched rim depths on their "Smart" wheels...
Yeah, but does anyone onboard have any real world experience with mismatched rims. That's what I'd like to know.

[dd74]

As best I can tell the deeper the aero section of the rim the more drag reduction you will get. However, that larger area makes the wheel more likely to be affected by crosswinds, particularly on the front.
So a shallower front wheel is probably the way to go. Okay, that's what I wondered as opposed to a deeper wheel in the front and shallower wheel in the rear.

[Louis]

mismatched rims

deeper rim has less of an effect on handling in crosswinds if it's on the back, so less deep in front for better handling and deeper in back for less drag

[Louis]

a deeper wheel in the front and shallower wheel in the rear.

That would be backwards.

[kramnnim]

I have 3.4s, they've fine in gusty crosswinds. I don't think I could tell how much of an aero advantage they have, I bet riding in the drops instead of the hoods makes more of a difference...

[Louis]

Every little bit helps.

[dd74]

Okay, cool. I'm coming off of 50mm rims front and back, and might be going to 42mm front and 60mm rear, with the second set of rims (42/60mm) being .4-pound heavier. I wonder if there will be an aero difference with such, and less blowing around via the crosswinds. The .4-pound difference I believe I won't notice much. Another set I have are 47mm, and they are .8-pound lighter than the 42/60mm set.

[ANAO]

I'm coming off of 50mm rims front and back, and might be going to 42mm front and 60mm rear...

I doubt you'd notice the 8mm in the front and 10mm in the rear....but perhaps.

When I went from 82/110 to 60/60, I definitely noticed. I felt fastest on 88/88, probably because the 110 was just a bit heavier, more sluggish and slightly flexier on climbs/sprints.

Now, I'm on Open Pros and feel like a snail 0.o

[AgilisMerlin]

i ride openpros

hard telling not knowing

if anything

would make me quicker, :eek:

ex cept a tailwind

like the sound of carbon wheels, though

[Shortsocks]

Go as deep as you can go with feeling comfortable in a crosswind. For me that's 38-40mm. You will generally get more "aero-benefit" with a deeper wheel. But if it loses it's fun...then don't. Pretty easy. I'm 5'9 135, and for a daily wheel you couldn't pay me enough to ride a deep wheel. I get blown away by crosswinds and it takes all the fun out of cycling.:bike:

[fogrider]

I'm riding 46s in windy sf bay area without any problems. since the rear wheel gets about 60% of the weight and the front is where the steering happens, deeper in the rear is typically more stable.

[zap]

If aero data supplied by manufacturers are to be believed, one or two 35 rims are more aero than 50-58 rims. New aero shapes and wider rims/tires make a difference in crosswinds too.

[Ralph]

I ride almost daily (or at least 4-5 days a week) with pretty much same group of guys, in mostly flat to slightly rolling terrain. Some of ride usually some head and side winds, and some of ride some tail wind. But winds not usually strong, but are noticeable.

I usually ride wheels with 32 round DT spokes, black Record hubs, with one wheel set being very light with IRD 400 gram Cadence rims. These are very responsive (1500 grams) good riding wheels. However, both my wheel sets have low section rims. I weight 155 or so.

Our group usually rides in the 16-20 MPH range, and occasionally, if we have some tail wind, maybe up to 25-26 or so under pedal power. Never more than that, or I'm coasting.

Would I benefit from some lower spoke count deeper section wheels? Have been a fan of some of the Campy medium section wheels for a while, but never bought any. I'm not a fan of heavy wheels, no matter how "deep" they are. Prefer responsive over aero. Also capable of getting built abount any combination of hand builts. For me, and my riding, anything really better than some 24/28 spoke A 23 or similar rims? Apologize for butting into your post.

[shovelhd]

CDR rides HED and mixes and matches his wheels according to wind conditions. Maybe he will chime in here. I have two sets of wheels and do not mix because one is tubular and one is clincher. The training wheels are 50mm and the racing wheels are 58mm, and the deeper wheels are better in crosswinds because of the rim shape. Both are very fast. Another point of reference is the Zipp 606 set, which is a 58mm 404 front with an 80mm 808 rear. Triathletes use them in windy conditions where they would normally run an 808 front.

[verticaldoug]

The irony here is you probably will shave more drag by removing your water bottles and cages from your bike then going from 10mm of rim depth.

As people have pointed out, the smaller wheel in front is just convention for handling. An 808 in the front with 404 in the back, will ride faster than a 404 front808back. But windy conditions will make the 808 a handful in the front before the 404 plus it looks stupid. Since you can't switch hubs, the logical choice is to buy the 404 front 808 back for the most riding conditions. But in our imaginary world of unlimited wheel funds, you have a set of 303s , 404s, 808s and disk for your bikes. (You might as well have a tt bike to run disk on too)

[Ti Designs]

I spent last season trying out carbon wheels to get an idea of the advantages or disadvantages. To be consistent I role all carbon clinchers, while my own set is a 2005 pair of 303 tubulars. I tried out Roval 60's, Enve 4.3's, Enve 45's, Zipp 303's, Zipp 404's, Mavic Cosmic carbon's and Easton EC90sl's.

To compare the two wheels which should be somewhat similar shows the gains made in design. I compared my old 303's with newer 303 carbon clinchers and found the new Firecrest design is better in just about every way. Side winds on the new 303 is hard to notice, side winds on the old air foil shaped rim is horrible. Zipp and Envy seem to be on the same page with cross section design, they've both come up with designs that are fast in all sorts of wind conditions. If you're looking to do steady state efforts, I would have to point you in that direction. One other thing I noticed, which I can't yet explain is the ability for the air foil shaped rims to accelerate. I'll admit that I haven't looked at rim weights, but the wheels that accelerated well were all of the narrower air foild shaped rims.

[sailorboy]

I was shopping the zipp firecrest offerings a couple years ago and by their own published data, over a 40k course, the 303 saved something like a minute over 'standard' box profile rims with 32 spokes etc. Interestingly when you went up to the 404s you only dropped another 8 seconds or something over the same 40K course.

While that may be a tangible difference for a pro or in a TT, for most situations the 303 would be a better all-around wheel IMO. The rotational weight savings over those 404s is not insignificant compared to the little aero gain.

So to answer your question if it's not dead flat where you ride and not a triathlon/ TT specific situation, I'd go with the wheels in the 38-45mm depth range.

[bluesea]

I was shopping the zipp firecrest offerings a couple years ago and by their own published data, over a 40k course, the 303 saved something like a minute over 'standard' box profile rims with 32 spokes etc.


I wonder at what average speed, or does that not make a difference?

[Louis]

or does that not make a difference?

Yes it would, but there are multiple factors at work:

The faster you're going the more the drag reduction helps (since drag force is nonlinear - it's proportional to the velocity squared, and the power required proportional to the velocity cubed.)

But the faster you're going the shorter the total time, so that will also have an effect on the delta time.

[carpediemracing]

Yeah, but does anyone onboard have any real world experience with mismatched rims. That's what I'd like to know.

A tall front wheel affects control. A tall rear wheel simply stabilizes bike.

Being a poor FTP rider (horrible at TT - PR is 23.5 mph with full aero including disk wheel + TT bars + skin suit + aero helmet, worse at RR - never finished a RR in the main field and most of them I got shelled in the first climb or two), a decent sprinter (how else would I ever have earned a Cat 2 upgrade), and a geek/nerd when it comes to equipment, I've been riding aero wheels since about 1988 or so. By 1989 I was regularly racing with a disk rear wheel, low spoke count wheels, etc. I was using Zipp wheels after they first came out, the Zipp 340 and 440 (the predecessors to the Zipp 303 and 404), laced on to Campy NR/SR hubs (24H, x2). I've been using aero wheels for a while.

I think that aero wheels help me more in cross-tailwinds than in headwinds or crosswinds. I'm looking for a massive delta in speed, not "10%" or some percentage. Going 20% faster when I'm going 15 mph means I'm going 18 mph. That's not going to make a difference in a race where everyone can just sit in at either speed.

However if I can go 2 mph faster because of the wheels at 35 mph then it becomes a bit more interesting. If the sprint is in a cross-tailwind then the wheels are ideal. If the bit just before the sprint is in a cross-tailwind then it's almost as ideal since I can use the wheels to help me move up (since I'm almost always moving up until the sprint due to me choosing to save energy vs holding good position).

Front counts more for aero benefit. A ratio that I read somewhere a long time ago is 2/3 front, 1/3 rear. Since that's easy to remember that's what I go by. It's about right, maybe a bit overly biased to the rear, meaning if anything it's even more front wheel. It might be more like 70% front, 30% rear.

The rear wheel stabilizes your bike, at least in a straight line. Wind merely keeps the bike going in a straight line. Therefore in the rear I run the deepest light wheel I can run. Since it's about rotational weight I will run a heavier wheel if it means the rim is actually lighter. The disk I used to use was built with a 280 gram FiR Alkor rim so it accelerated nicely. In fact I'm trying to buy it back from the guy who owns it now, I think it would be fun to have it again.

I've bought up a nice selection of HED wheels over the last 4 years. 46mm front (2010 Stinger 4, bought used in 2014), 60mm F&R (Stinger 6, bought new in 2010), 75mm front (2012? Stinger 7, used, bought in 2013), 90mm rear (2012 Stinger 9, used, bought in 2013).

For fast courses or where I think it'll be strung out single file for a while I'll go to the 7/9 set first. Wheels are fast at speed but not ideal for a jumpy race. For something with a short steep hill or hard corners where I think I'll be jumping a lot out, where it probably won't be super strung out, I'll go to the 6/6 set. Slightly lighter, better in a sprint, but the top end isn't quite the same. In heavy wind I've used the 6/9, so the tall rear for stability, the shallowest front I had at the time for control.

I tried using the 7/9 at Bethel which has a short steep hill to the line (6-8%? 10% according to Strava, 150m). Didn't do great in sprints with them. Put the 6s on. Won 3 field sprints, racing against basically the same guys each week.

I just bought the (used) Stinger 4, have not even put it on my bike yet. My thought was to use it in extremely windy conditions where even the 6 is a bit much. It would take a lot for me to do the 4 up front, maybe 30+ mph gusts.

I have yet to run the 7 up front with the 6 in the rear. If I'm running the 7 I'm thinking there will be very fast sections and therefore I want the 9 in the back.

Today, with gusts up to 20+ mph I decided to use the 6s front and rear. Jumpy corners plus wind. Wind seemed stronger - the wind knocked over bike or two in the parking lot leaned up against cars, wheel covers flew away, blew the baseball cap right off of my 2 year old's head, and my 7/9 set stayed at about a 30 degree angle when I carried them back from the pits. The 6s were absolutely fine in these conditions.

With heavier wind I think the 4 front would have been good. The 7 front would have been a handful.

One exception to all this. I found that even a 46mm front wheel (v-profile, not u-profile) was a handful on descending speeds over 50 mph. I was on a Jet 60 front wheel I was drafting a truck at 50 mph. It was pretty brutal when I dropped back out of the draft. In high speed situations (going to looking for trucks to draft, 50+ mph descents) I'll use a box section front wheel. In the few RR I've entered I've gone out with a 28H box front wheel and a super aero rear wheel (Trispoke or 440), Scott Drop Ins, and TT'ed behind the field. Super fast on descents, stable, and I'm set up to TT behind the field :)

In the past (1995 - 2005 or so) I tried to run a TriSpoke up front all the time, also known as the HED3 (they bought the rights from Specialized). I trained on a TriSpoke front clincher, regardless of the rear wheel (box section clincher usually, like Eurus or a Fir Zenith or similar). I got used to the TriSpoke up front so I could use it in most wind conditions, including 20-30 mph gusts. Same course as today, similar conditions, I used a disk rear and a TRiSpoke front, no problems. That day I was in a break in the 123 race for 10 laps with 2 other guys, strong both (Amos and Leigh, for those from the area). I couldn't contribute much but I was there :) We got caught and I barely hung on for the rest of the race.

As an extreme example I used a pair of TriSpokes on a training ride when I flew to FL to visit a friend's family for a crit (Coconut Grove, FL). The crit got canceled due to Hurricane George hitting the area, I think it was 1999. With steady wind of 50 mph and gusts over 80 mph according to the TV/weather that day (top speeds recorded were 120 mph but I don't think I ever saw anything even close to that), my friend, his gf (and racer), and I went for a training ride to see what such powerful wind was like. Since we only had our race wheels, since the crit was a p123 race, I brought the "high speed" TriSPokes (for strung out fast race conditions). Although I had to lean a lot to stay upright we got in a pretty fun (and probably stupid) ride. We headed into the wind on the way out so we'd have a tailwind back. On a causeway bridge I sprinted over the top - I was already going something like 35 mph with the tailwind just hammering before I sprinted. I held 60 mph on the flat for about a minute after that, totally spun out. Sitting up coasting we'd go 15-20 mph, it was nutty. Tons of wind, Trispokes front and rear, no problems with control. I wouldn't have ridden no handed but it was fine otherwise.

Finally all this matters not one bit when I race against the better racers. A Cat 1 and former pro went to the front of a Tues Night Crit, drilled it for 4 or 5 laps, dropped back, looked at me suffering, went to the front, drilled it again, and I was gone. I could have been on any wheel in the world and I'd have gotten shelled. He was on Ksyriums, about the most unaerodynamic wheel you can get.

So it's all relative. I play in a very small sandbox but it's fun when it applies :)