- 1 Are all MTB bottom brackets the same size?
- 2 How do I determine bottom bracket spindle length?
- 3 What bottom bracket is on my bike?
- 4 How do I know what size crankset to buy?
- 5 Will BB30 crank fit PF30?
- 6 What do the numbers on a bottom bracket mean?
- 7 Will a 68mm bottom bracket fit a 73mm shell?
- 8 Does bottom bracket spindle length matter?
- 9 How do I know what size bottom bracket I need?
- 10 How long does a bottom bracket last?
- 11 Can you remove a bottom bracket without tool?
With mountain bikes, 68mm is most common too, but sometimes the wider version with 73mm width can be found. The diameter of the bottom bracket is 41.96mm, and the bottom bracket bearings are always pressed into the frame separately.
The best way to find out which spindle length you need is by looking up the specs. (The alternative is trial and error…) Spindle length and the resulting chainline have some leeway. If you are within 2-3 mm of the “correct” 43.5 mm or 45 mm, you are doing quite well.
The bottom bracket is the bearing system between the cranks. It sits inside the part of the frame called the bottom bracket shell. The bearings are held in the shell by an adaptor or a cup.
How do I know what size crankset to buy?
The crank length represents the distance between the centre of the bottom bracket and the centre of the pedal axis. The most common lengths are 170, 172.5 and 175 mm, but it is possible to find cranks between 165 and 180 mm in the market.
Will BB30 crank fit PF30?
BB30 and PF30 are completely different, from the frame perspective. In other words, a PF30 frame needs a PF30 BB, and a B30 frame needs a BB30 BB. However the cranksets are identical, so a BB30 crankset fits a PF30 BB/frame (this was my CX setup for last season).
The numbers numbers ranging from 86 to 132 refer to the nominal width of the shell in millimeters, which is not related to the press fit of the bearings. These bottom brackets will vary in the width of the dust sleeve used for that different widths.
You could install it, but it will shift your chainline, shift the centerline of your feet, clearance issues might arise on the non-drive side, and you might be leaving some BB shell threads exposed on the non-drive side as well.
The critical thing is your spindle length: as long as you can set up the correct chainline you will be good to go. But, again, best never to mix standards if you can at all avoid it. If you are looking to replace a cottered crank setup with a square taper setup, then look no further than a cartridge bottom bracket.
To find out the size of bottom bracket needed, measure the inside of the bottom bracket shell in your frame, it will be 73mm, 70mm or 68mm. Some older frames may have Italian threaded bottom brackets, instead of the more modern English.
As for a bottom bracket, on the low end, maybe 5000 miles. The basic Shimano one most people use (UN51/55/similar) can reasonably expect 10k+ miles. But sometimes you get unlucky and get a bottom bracket that lasts maybe 500 miles.
Almost anything can be taken apart without proper tools, including bottom brackets. it, but it can be done. The right tool for the job(any job) makes life much easier and will lower your frustration level by leaps and bounds. If it is a Square taper, isis or octalink then no.