Rear Wheel Flex

8kvscdpglqnyr4

I was recently in Pyrenees on a cycling trip with a mate of mine and we noticed something about our rear wheels that we wouldn't have expected. On some of the climbs when we were out of the saddle, the wheels were flexing enough to allow the rim to rub off the break blocks! Breaks rubbing is the last thing you want to hear when you're on some of the bigger Cols in the Pyrenees!!! I have never noticed this at home.

For the climbs I had to reach back and open the back breaks using the release mechanism that I use to take the wheel off. I had to ensure I closed this again for the decent:eek:

The break blocks are not tight on the rims - probably 4 or 5mm gap on each site of the wheel.

I'm 88kg and my mate is about 82kg.

I have Mavic Ksyrium Elites on my bike and he has Mavic Ksyrium SLs. It was happening on both bikes.

Since coming home, I've checked the flex on a set of Mavic Aksiums and Shimano WH-R500's I have on other bikes and they too suffer from a similar amount of flex.

It's something I've never noticed before - is it normal? If it is normal, is there much power loss in this flex?

If you want to test your wheels, just grab the tyre near the break blocks and push/pull the wheel towards the break blocks. I'm amazed by the amount of flex!!!

ednwireland

yep my rs10 does the same but its not that noticable , just a slight rub now and again (and i'm just back from the alps)

Lumen

A well built stiff wheel is much less prone to this.

In my experience:

Mavic Open Pro 32h -> pass
Soul C5 24h -> pass
Planet X model B 24h -> pass
Planet X model C 32h -> pass
HED Ardennes 24h -> fail

CramCycle

Maybe this:

http://www.sheldonbrown.com/cone-adjustment.html

If the cones are not screwed on far enough, the bearings will have "play": the wheel will be able to shake back and forth on its bearings. This is an unpleasant sensation, and may cause control problems.

I had the same problem and thought I'd have to get the wheels repaired at my LBS till a guy in work showed me the error of my ways, took 5 minutes to tighten up, just don't do it to tight or your wheel can seize.

8kvscdpglqnyr4

Thanks for the replies.

As I was saying, it's not something I noticed while riding at home, only getting out of the saddle on big climbs.

Is there much power loss resulting from this flex (assume it's not rubbing off the break blocks)?

Thanks for the link CramCycle - the cones are not my problem. I've had that before on an old bike and I know what it's like.

Lumen - any experience with the wheels I've mentioned?

Lumen

Tatiana Old-fashioned Sunbonnet wrote: »

Lumen - any experience with the wheels I've mentioned?

I had Aksiums and I don't recall any brake rub. Ksyriums have a good reputation for stiffness, though I've never owned any.

doozerie

I have Ksyrium SL's but haven't noticed any perceptible flex in the few months that I have been using them. I've only used them on Irish roads though so the climbs obviously don't compare to what you will have been doing in the Pyrenees. Having said that, I've deliberately stayed away from my lowest couple of gears on a few steep-ish climbs here and not detected any noticeable flex then either.

However, at 63kg I'm not sure I'm ever likely to stress a wheel to any great extent. Rider weight, and power output, do contribute to flexing of wheels, as does how much you move the bike from side to side during a climb.