[JetSpeed]

Have a set of 03' Kysriums SL's and I cracked the rim where the spoke nipple meets the rim. My LBS replaced the rear Kysrium w/a Mavic Cosmos I had that is about 2 years old and has only a few hundred miles on it.

Today for the first time I had a chance to ride my bike (frame and components are 1 month old) w/this mixed wheel set-up and I never though I'd feel such a difference!!?

The front Kysrium felt fast and twitchy as normal (in a good way). BUT, the rear of the bike (w/the Cosmos) felt sluggish and VERY slow to respond. In summary, It felt like this was my first time riding a road bike. My balance was thrown-off for the entire ride and the bike seemed VERY unbalanced!!?? I'm now a bit nervous about trying to group-ride tomorrow because of it.

Am I crazy or is this exactly what I was feeling? WHY was I feeeling this?

Now I'm totally bummed. I'm thinking of just buying a new wheel set instead of waiting 4-6 weeks for my cracked wheel to return from Mavic and having to ride is wobbly set-up.

 

[rruff]

Check for loose rear hub bearings or something else like that... can you wobble the wheel with your hand while it is mounted?

 

[JetSpeed]

Can't wobble the wheel while mounted. I'm still a bit weirded-out by this. (???)

 

[foz]

i'm not sure because from what you say it's not 100% clear, but was this your first ride on this bike, or the first ride on this bike with the newly fixed wheel? if it was the first ever ride then look no further - the bike will obviously feel different to your previous one.
if it wasn't your first ride on this bike then make sure you've checked everything - hub ok, spoke tension, tyre mounted correctly and with the correct pressure, wheel centered in the frame (have you checked the rebuild before mounting the wheel?), brakes not rubbing? I wasn't even aware that a cosmos rim is compatible with the ksyrium hub and spokes, but simply changing the rim shouldn't have that much effect. it might make the bike heavier or lighter overall, but there is no way it can throw your balance if it's installed correctly and the wheel is straight in the frame. as for being slow to respond - slow to respond to what? if you think that when you pedal harder it doesn't accelerate as fast as the old wheel well then it's pretty much all in your head. a few grams more or less on the rim will not make much noticeable difference, if any at all.

foz

 

[Deoxy]

I guess he means that his LBS gave him a wheel (cosmos) and sent his ksyrium rear wheel to Mavic.
I know what you mean Jetspeed.. I didn't know wheels can make such a difference..
The first time this season I rode my shamals (those old, silver colored shamals, wich are very stiff and responsive), I almost fel because I accelarated while being not complete out of the turn..
I've heard complaints about cosmos' before being very "unstiff" and wobbling, therefore not reacting directly.
I always take care that in a race my rear wheel is at least as stiff as my front wheel. Whenever your fontwheel is not so very stiff, but your rear is, it won't really bother because the bike handles pretty good.. (I often use cxp33 rim/ultegra hubs front and Shamal rear)

I you do it other way around (like you've got right now) the rear won't really be able to follow you as directly as the frontwheel does.. so the bike gets unstable..

Conclusion: If I were you I'd put anoter rear wheel in (stiffer) or ask wheter you can borrow the front cosmos wheel also, so your front and rear wheel are both a bit wobbly (your bike wil be in better balance then it is right now, even with 2 wobbly wheels)

It might be a little confusing as I say it here, but I'm not very good at English..
Good luck

 

[cmg]

so did the LBS replace the rim with a cosmos and re-tighten the spokes or did they send the k's back to mavic and he put cosmos wheel in its place? if the LBS just replaced the rim and re-laced it then the weight difference between the K's and cosmos rim is what he's feeling.

 

[rruff]

I you do it other way around (like you've got right now) the rear won't really be able to follow you as directly as the frontwheel does.. so the bike gets unstable..

Eh??? That's an ok theory you have going there... but unfortunately it doesn't square with reality.

Ksyriums are *not* stiff! They are among the most flexible wheels you can get. Damon Rinard took the time to measure a bunch of wheels awhile back. Check #96 and #97:
http://www.sheldonbrown.com/rinard/wheel/data.htm

He didn't test the Cosmos, but just looking at other conventional wheels with 28 spokes, they are all stiffer than the Ks.

I'm pretty sure that the Cosmos uses an OP rim... which is surely lighter than the Ksyrium rim... so added inertia isn't the problem either.

Bad tire? Too little tire pressure... too much? Misaligned wheel? Cracked frame?

 

[Kerry Irons]

Say what?

The first time this season I rode my shamals (those old, silver colored shamals, wich are very stiff and responsive), I almost fel because I accelarated while being not complete out of the turn.

Interesting story, but I'm going to have to raise the question of operator error rather than anything to do with the wheels.

 

[Deoxy]

I got an explanation for it, but don't really know how to translate to English...
Here's a try:
Because I wasn't competely out of the turn, I was still hanging a little to the right. With accelarating I pulled my left shifter to hard (because that was the force I usually use with other wheels). Because of that I almost pulled my front wheel to the left (while I was still hanging a little to the right).. It's very hard to explain in English, but I hope you guys understand..:?

About the cosmos being stiffer than k's.. I really don't think so, I rode them once but didn't dare to go through turn fast, because they were so very wobbly and stuff.. Also when accelarating I could hear the rims touching my brakepads, while the wheel was true when I stopped and spinnend it around...:S

 

[JetSpeed]

O.K., well. Took the bike to my local shop. I have only put a few hundred road miles on my Cosmos wheels AND most of it's miles have been on my Cyclops stationary trainer. So, the spokes needed tightening and just a hair of trueing. Problem solved.

The wheel was flexing enough that when I would apply power to it, it would ever so gently rub the rear brake and create a bit of noise as well.

Was I feeling a difference in wheels? Maybe-Probably not. Was I feeling the Cosmos flex? Yes. Was it that obvious from simply touching each spoke for tension? Somewhat.

Simple lesson, simple fix.

 

[Mr. Versatile]

Deoxy - Your English is just fine. Good job.