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Discussion Starter · #1 ·
How can I tell what part on my bike is flexing when riding? I hear of guys talking about flex, but how do they know what part is doing it?

I am asking because I am feeling what i think is flex when I ride my bike. I feel it when cornering the bike hard. I am thinking it may be the wheels, but really have no idea.

Any thoughts on this?
 

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What bike/fork/wheels? Are you running 26/27.5/29 wheels? Need to know a bit more about your bike to have a better idea as to what is going on.
 

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Bikes flex: frames, wheels and tire deflection, fork, seat post, bar.

Unless you're getting serious and consistent wheel rub or the bike is so noodly that it doesn't go where you point it when pushing it harder, not much to worry about.

Yep, more info.
 

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Discussion Starter · #5 ·
Its a 2010 Specialized FSR XC Comp. Rock Shox Tora SLite 120mm fork, 26in Alex RHD rims, no name 1.8mm spokes, Specialized hubs.

I am running 30 PSI in the front tire and 32 in the rear tire. I am getting tire rub in the rear a few times a ride, but the bike does go where I want it to.

I am not really worried about, rather I am just curious.

Thanks
 

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Small amount of rear tire rub can be some rear triangle flex that is normal because aluminum and the pivots do flex some, or perhaps some wheel flex due to slightly loose spoke tension, or both.

With my Al hard tail, I get some tire rub even with correctly tensioned wheels because when I'm on the power, the bottom bracket and lower half of the frame flexes the chain stay into the tire. Pretty normal. I could probably eliminate it with a narrower tire but I like the extra grip, cushion, so the small amount of rub doesn't bother me.
 

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That's a pretty stiff wheel, assuming it's tensioned adequately, and quite a lot of air pressure.

I can't say I can put my finger on where flex is coming from. On my old bike, I'm on my third suspension fork. The OEM fork was an RST something. Flexy garbage, anyway. I was having trouble holding a line over roots and major trouble with diagonal roots. But since those are problematic for me anyway, I thought it was just me. When that fork seized and I stuck a Manitou R7 (thanks, EBay) on the front, I was suddenly and magically better at holding a line! So I think it was really that the fork was flexy. Something similar happened when I wore out the R7 and stuck an old Marzocchi on the front.

Since we're talking about an older full suspension bike, though, you should also check for play in the rear triangle. Hold the main triangle steady and try to move the rear hub laterally, and to twist it. Since all materials in real life bend, it's possible that you'll get a little flex. But you shouldn't have any free motion.
 
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