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I used to live in quite a hilly area but managed well with a single speed Mango aluminium bike on most of these hills. I wanted to know if it is possible that due to extra pressure being exerted on the pedals and therefore on the crank and bottom bracket system, the bottom bracket might need replacing more often than a bottom bracket in a bike with multiple gears? I feel like I do damage to my bottom bracket way more quickly than I should. Perhaps the bottom brackets I have had were of low quality? I don't currently know what of bottom bracket I have installed.

In general what factors are involved in the usual degradation of the bottom bracket?

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    If you were riding fixed gear and using skid-stops then your bearing life would be even shorter due to shock-loadings. – Criggie Jun 27 at 1:48
  • Bearings wear out faster if the chain tension is too high! The chain needs at least 1-1.5 cm slack. Reason for this is among others that chainrings are never perfectly centered and a taut chain puts high load on the BB, and the (right) hub bearing. Check chain slack at different positions of the crank. – Carel Jun 27 at 13:14
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It is inevitable than with more radial load, bearings will have lesser lifespan. The only alleviation to this is to get good quality bearings.

If you notice a decrease in your bearings' lifespan, check if you've fitted your bottom bracket properly and specc'd everything to more or less proper torques indicated. If bearings fail regardless, there may be misalignment either on your bottom bracket unit or the BB shell itself. (more likely the latter)

Due to the larger forces inputted, the misalignment's effect of degradation is aggravated.

@juhist 's option for outboard-bearing bottom brackets only serves as a non-direct solution and masks any genuine issue the drivetrain has.

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Bottom brackets have a fundamental flaw that the most typical shell size is too small for a good quality axle and good quality bearings at the same time. All bottom brackets fully inside the shell thus fail very often, usually due to bearings or axle breaking.

Typically, the higher the load is, the more likely is the failure of axle or bearings. So, gearing affects but your weight affects too.

Shimano has outboard bottom brackets in Hollowtech II components. These have the bearings outside of the bottom bracket shell. Thus, with Hollowtech II, you can have both good axle and good bearings.

I think that with Hollowtech II, your bottom bracket worries should be mostly gone. What is left is crank failure. The crank-pedal attachment has a fundamental flaw too, it cannot keep the pedal non-moving. Microscopic motions slowly damage the pedal eye of the crank, to result in a fracture of the crank. The pedal eye design should be modified to have a countersink and the pedal spindle should be modified to fit to the countersink. With traditional pedals, the crank can be modified by adding the countersink in a machine shop and a split collet can be made to fit to the pedal spindles: http://pardo.net/bike/pic/fail-001/FAIL-016.html

The countersink and manufacture of the split collet is probably more work that you are willing to do, so eventually your crank fails -- especially in a single speed bike, if you are a heavyweight rider. If the bottom bracket is of the Hollowtech II style, it will probably outlast your cranks.

You might be interested in this online museum of broken bicycle parts: http://pardo.net/bike/pic/fail-001/000.html

Perhaps the bottom brackets I have had were of low quality?

Were they of the square taper type? If so, they are low quality by design. Toss those away and select Hollowtech II.

In general what factors are involved in the usual degradation of the bottom bracket?

  • Engineering (type of your bottom bracket)
  • Price (affecting the quality of bottom bracket materials available for the price point)
  • Your weight
  • Gearing
  • Your riding style, spinning at high speed versus mashing at low speed
  • Tire size and air pressure (affecting suspension characteristics)
  • The non-uniformities of the road
  • Whether you approach non-uniformities of the road sitting on the saddle or standing on the pedals
  • Whether or not you ride in a hilly / mountainous area
  • Whether or not you use drop bars from which you can pull up using considerable force allowing you to pedal with more force
  • Whether or not you use clipless pedals allowing you to push up using the rear foot to result in more force at the front foot.
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    "All bottom brackets fully inside the shell thus fail very often, usually due to bearings or axle breaking." -- I think that's being a bit dramatic. – whatsisname Jun 26 at 18:54
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    Well, you have to have some reason to sell new stuff. It's not like square taper BBs break in reality that often. To me it sounds like the OP hasn't actually broken a BB but is looking for an excuse to buy new toys. – ojs Jun 26 at 19:21
  • I wonder if "All bottom brackets fully inside the shell thus fail very often, usually due to bearings or axle breaking." includes various oversize standards. I have let myself be told that for press fit the main failure mode is creaking. – ojs Jun 26 at 19:23
  • How inboard or outboard the bearings are only results in variation of stiffness. Bearings (and axles/spindles too) are trashed with improper fit and misalignment, which is aggravated in inboard bearings. – Gregory Leo Jun 27 at 0:42

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