2

Problem is that during off saddle sprint my rear tyre touch the frame and makes small 'hole' in it. Any idea how to prevent this issue? It is normal or with the frame itself is something wrong?

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Many thanks for any response


EDIT:

  • My weight: 74kg

I noticed that is quite common problem in Cervelo forum even in top models like S5 forum

  • OK, how do you know it happens during out-of-saddle sprints? I know when I'm hammering in such an effort, I wouldn't notice the sound of my rear tire rubbing nor feel it at all. Worst case is you think it's happening when you sprint, but it's not, you don't look for other problems, and this then gets worse and ruins your frame. – Andrew Henle Feb 11 at 23:16
  • @AndrewHenle Hi Andrew, Is very easy to hear that something rubbering the frame during strong sprint. – Robert Feb 12 at 7:57
5

Possible causes may include:

a. The tyres are too wide for the frame, check the clearance between the tyre and the stay. Be aware that there are dynamic shape changes under load.

b. The wheel is too soft. Does it suit your weight? Are the spokes properly tensioned, even though the wheel is true?

c. The rear triangle and/or the bottom bracket housing are too soft and move sideways. This is the case on certain frames. It happens with powerful riders who may put a high load on pedals especially off saddle. You research on cycling magazine sites who tested the bike. To check the sideways flex: Stand over the bike, put the left foot on the pedal, lean the top tube against the right leg, pull both brakes and push the foot down hard. You'l see how far the BB moves to the right.

d. The wheel axle has play. You can check this if you lift the rear wheel or, better, put the bike on a stand and try to wiggle the wheel sideways.

I'd say that the most likely cause is 'c', combined maybe with 'a'.

[edited]

  • 1
    It's a 20-spoke rear wheel. My bet is 'b' contributes quite a bit, too. – Andrew Henle Feb 11 at 23:11
  • I can't really think how a flexible wheel would deviate into the stays under power or load. The rim the road surface would deviate radially or laterally, but that would not drive the point between the stays laterally – Argenti Apparatus Feb 12 at 0:14
  • 'b' seems very unlikely to me. Its common (with large/powerful riders) for a wheel to flex by 1-2mm at the rim and rub on the pads, but certainly not enough to rub the frame. – Andy P Feb 12 at 9:01
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    @AndyP Some frames have miniscule clearances. I have a Merlin frame where 23mm tires are about 1.5mm off of the chainstays when totally true. This means I need to true the wheels constantly or run smaller tires. To minimize flex, I decided to tension the spokes a bit over spec and it does help although I never know when something will break. – Gabriel C. Feb 12 at 15:59
  • @GabrielC. Wow, have never seen that with 23mm before, usually only when trying to fit 25/28mm's into an older frame. Seems a bizarre design choice for a manufacturer to make. – Andy P Feb 12 at 16:07

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