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On a new mountain bike, the brake pad seems to touch the rim only at some parts when I apply the brake, not the entire rim. It still stops the wheel or touch all parts if I press hard enough. Does this mean the rim is not centered, or warped? Or could be brake pad position issue that I can adjust to resolve?

Thanks

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  • It definitely sounds like something is off, perhaps a couple of things. Can you post a video? That would help diagnose. – jimchristie Oct 29 '20 at 21:42
  • Thanks for chiming in. I haven't figured out how to post a video here. As suggested below, it is probably the wheel out of true, which I am going to bring it to a bike repair shop. – foxinsocks Oct 30 '20 at 18:02
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If you have to pull hard on the brake lever to get the pads to full engage on the rim, the brake caliper is not adjusted properly. Rim brakes can only generate stopping force when both pads are applying opposing 'gripping' forces to the rim.

New bike should be set up correctly, if you bought from a dedicated bicycle store take it back and and ask for the brake calipers to be adjusted. If you bought from a 'big box' store or general sports store the staff probably do not have expertise to do this properly, so you should seek out a bicycle repair shop to help you.

If you want to address this yourself, there is plenty of guidance on-line. Park Tool Repair Help is particularly good.

It also seems from you description that your wheels may be out of true. This can prevent the pads from being adjusted closely enough to the rim. First check the wheel is properly seated in the fork or frame drop-out slots before the quick-release or axle nuts are tightened. You can visually check the trueness of the rim by spinning the wheel slowly and observing the distance between the rim and a brake pad. If the distance varies by more than a couple of millimeters the wheel may need truing. This is not a trivial process so enlist the help of a bike repair shop

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  • Thanks for your help, Argenti. I should have clarify that this is the front wheel, which I put on myself, as this bike was delivered from online purchase. I have tried to adjust the brake caliper so that it is not too tight or too lose. I can fully stop the wheel by pressing the brake to about 3/4 of the full range. but before it fully stops, the brake pad have been touching the rim at some part, but not all. Which is why I am wondering if the wheel is out of true, though it is brand new. – foxinsocks Oct 29 '20 at 17:57
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    @foxinsocks sounds like your wheel is in fact a bit out of true. See updated answer. – Argenti Apparatus Oct 29 '20 at 18:11
  • Could also be rim brake pads that are toed-in a little bit aggressively ? – Criggie Oct 29 '20 at 21:37
  • I tried to spin the wheel and do see the distance between the rim and pad varies between 1 to 3 mms, how do I know that is due to out of true, or the wheel not seated in the fork properly? – foxinsocks Oct 30 '20 at 0:20
  • @foxinsocks if the distance between the pad and rim varies, the rim is out of true, that’s basically the definition of ‘out of true’. A few mm deviation is probably livable, but as I said a bike repair shop can re-true the wheel – Argenti Apparatus Oct 30 '20 at 0:36

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