Flexy wheels?

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JoeFlan
Posts: 102
Joined: Tue Jan 28, 2014 8:06 am

by JoeFlan

Background: I used to ride a set of American Classic sprint 350 never had any problems until I dented the front rim riding over a cuddle grate

I replaced the front wheel with a m5 straight pull hub laced the a 20h stans alpha 340 rim and now on some descents my rim hits the brake pads

So do these parts have history of being flexy?

Is there any fix?

PS: less than 60kg rider
Current Steed
Supersix Evo 6.25kg
Giant TCR SLR 6.8kg
Past Lovers
Focus Izalco Pro
Cervelo S1

Marin
Posts: 2664
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

The rim is a low profile rim @ 380g so it's gonna be flexy even with more than 20 spokes.

Stiffness is a function of bracing angle (wider is stiffer), spoke number and weight (heavier are stiffer) and rim weight (heavier -> stiffer). At the same weight, a wider rim will flex more than a taller one very generally.

The simplest option would be to get a front wheel with a heavier rim or more spokes.

by Weenie


eric
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Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
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by eric

Try a deeper section rim. The rim is a tube, and the stiffness of a tube is mostly determined by its diameter.
Unfortunately the deeper section rim will also be heavier.

Another solution would be to run your brakes with more clearance. Many riders set their brakes too tight. All you need is for the lever to not bottom out on the bars when you squeeze hard. On may brake caliper designs the leverage ratio is not linear- the leverage is less (pads move more for X amount of lever travel) in the initial travel, to take up
the clearance. In the middle range the leverage ratio is increased to make the brakes more powerful. Setting the clearance too tight means that the pads contact the rim before the caliper gets to the more powerful ratio, so you have to squeeze harder for a given amount of braking.

Geoff
Posts: 5093
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

What spokes?

For riders of our weight, nobody should be saying a 20-spoke wheel will be any kind of problem. It sounds like something else is wrong.

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Zen Cyclery
Shop Owner
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Location: McCall, ID
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by Zen Cyclery

Theh 340 is an inherently soft rim especially if you have the 1st rendition of that hoop. I'd say that erics suggestion of opening up your brakes a bit is the best one. If you don't want to do that they you will need to switch to a stiffer (ie heavier) rim.

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