cgates66

First some background. I'm a 95kg rider on a Cannondale SystemSix and I had been running the old 20/24 spoke Ksyrium Equipe wheels with Conti GP4000s (25 rear, 23 front due to fork clearance and handling issues - the 25 measures about 27 on these wheels, and with the narrow Ksyrium rim the 25s up front squirm around a lot - fast in a straight line but unsettling over 50kph if you have to turn - and they were very occasionally rubbing the fork which seemed like a bad thing). I figured I'd get some cool deep-dish wheels, and given my good experience with a lower-end wheelset, I figured I'd be okay running the CXRs. The aero on all of these wheels is similar - within a few watts - they look awesome to me and the Exalith braking works great. And while heavy-ish, they are about the same weight as my old Ksyriums. Plus, 95kg up top.

Anyway here's my issue: my times on a few "well known" routes on which I have pretty consistent performance are whole minutes slower, and I'm certain I'm not suddenly less fit. Different day, different track - I know - but my sample size seems reasonable enough. So a few things occurred to me:
1) Are the 23mm Mavic tires slow? This is possible - I was running Gatorskins before the GP4000s (same pressure) and those things are just horrible. Some guy ran a roller test on the *prototype* CXR tires and got similar results to the GP4000s - but the non-CXR Mavic tires seem slow, and the tubular CXRs are also supposed to be...let's keep it positive and say "well built".
2) Am I getting a super-crappy pressure reading with valve extenders? I'm heavy so I run higher pressure (120psi) - just like a truck. It's possible that I'm not getting sufficient air in there, but I'm wondering maybe if my pressure is WAY off, because 10psi one way or the other shouldn't matter. For example, if I thought I had 120, and I had say 80...yeah that would probably make a difference. But I don't see how to get a good reading.
3) The spoke count on these wheels is low - 16/20 - and it's possible that they just eat up my super fat-guy power - I can make the rim kiss the brake pad out of the saddle (Exalith is loud so you hear it, even with a delicate touch although it doesn't feel like its dragging).

It seems that it's *possible* that the fat GP4000s have sufficiently lower rolling resistance, despite the "lightbulb" aero penalty, that 25mm GP4000+Ksyrium (aero-wise, among the worst setups you can build) is faster than 23mm Yksion+CXR (aero-wise, among the better 60mm options).

Anyone have any thoughts here? I'd love Mavic Zack to weigh in - Mavic is pretty good about their aero data (although they haven't released anything without the UCI-illegal blades ahem), but their tire data is let's say not so good. I'd hate to have to sell these things, because they look awesome, and the bearings, brakes and build are gorgeous.

canam73

Couple thoughts:

Valve extenders shouldn't change psi readings.

I don't know the width of your new rim, but if is wider than the Ksyrium you might do better to lower your pressure 10psi or so.

Do you still have a set of GP4000s you could swap in? Isolating the issue could save you a lot of guess work.

Spin tests are usually useless, unless a hub is obviously stiff because of some problem. I'm guessing you have checked, right?

cgates66

That's good advice. I'll try a few combinations and see what happens.

Dean V

Rolling resistance is a bigger factor for larger people as it increases with the weight and the aeroness (is that a word?) of the wheels is less of a help than normal (%) due to the increased wind drag of a larger rider. So you would be correct in looking at things that effect rolling resistance.

rpenmanparker 

First and foremost you must compare apples to apples. Trying to sort out multiple variables at the same time requires a design of multiple experiments. It is a lot like solving simultaneous equations in algebra class way back when. Just limit things to one variable at a time and put the Conti tires on and try them on your test route before you jump to any other conclusions.

cgates66

This is excellent advice and I appreciate the responses! I'll run some tests and share. I might run some scienc-y roll-down tests also (I have a clean hill and run-out I can use).

cgates66

I installed the Contis and did a test ride (I'm going to run a few samples obviously - one ride is insufficient). Here are a few practical notes:
1) The bead track is very narrow - 13mm, while the brake track is very wide - 25mm+ - but the 25mm and 23mm GP4000s fit fine. The 25s are a little fatter than 25mm, and so don't line up perfectly with the rim width, but it's pretty close, so I'm guessing the aero penalty is small. The 23s seem to fit pretty well, though.
2) The Mavic CXR tires are TINY - very low apparent air volume. For the heavier rider, I suspect that this is a disadvantage.
3) The gap-filling blades fit fine, and are "soft" - I doubt they will cause any excess wear on non-Mavic tires, despite the marketing claims, unless maybe some grit gets in there.

I checked / adjusted the bearings and there are no obvious issues, and there is no brake drag.

Ride-wise, the GP4000s *feel* like they roll better - the CXR tires are comparatively plush and have plenty of grip, but they *feel* slow (they remind me somewhat of the old Schwalbe ZXs - I haven't ridden those for a few years though). I suspect this is partially a weight issue - for the same pressure, they deform more. Again, though - I'm 95kg running a 25mm tire that's actually more like 27mm at 120psi in the back, and a "bigger" 23mm tire in the front.

There is enough noise in a one-ride sample to avoid drawing tire-based conclusions just yet, although it does seem like - despite good rim stiffness - the total wheel stiffness is not super-high (spoke count). I have only butt-dyno data for this - although the evidence appears to be that up to 350w this is not that relevant.

I might - although it's a pain - try running my old wheels with the CXR tires. That would be interesting...

Anyway, thanks for the suggestions - I should have some more useful information later this week.

cgates66

I've now done a couple of rides and looked at the data little more closely. I'm not riding on a closed track, so there are variables that can't be controlled (weather esp.). In general though I'd say these perform as advertised - although mind the tires if you're heavier and the Topeak valve extender is miles better than the Mavic pipes. If you get these wheels, either get extra-long valved tubes or get this Topeak thing. It's genius.

Summary:
1) Mavic tires offer an aero benefit, maybe, but I prefer to run GP4000s - 25 out back and 23 out front. You lose some but not all of your aero probably, but you get RR if you're a heavy rider. If you're a littler guy, the Mavic stuff is probably good.
2) Make sure your brakes are wide enough.
3) You probably get about 1 minute / hour of benefit vs. Ksyriums, maybe a little better (the data says 0.9MPH @ 25MPH - which is quite a lot for wheel) in the real world but it's very hard to quantify. They feel faster though, and in a crosswind, you could feel the drag from the traditional wheels tugging a little more. Over an hour, it adds up. Directly into a headwind, though, the gains are modest. You need a positive angle of attack to really get the major gains.
4) They look awesome and sound awesome decelerating due to the track.

Thanks for the suggestions on testing etc. Much appreciated.