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Questions and answers about sports

Unusual bottom bracket shell

5 min read

Asked by: Jason Fuhrer

Are all bottom bracket shells the same size?

There are 4 widths available with BSA bottom brackets; 68mm, 73mm, 83mm or 100mm. This bottom bracket clearly shows you on the outside what bearings have been fitted to the bike. For road bikes, a BSA bottom bracket is always 68 mm wide. Other sizes, and particularly the 73 mm width, is commonplace with mountain bikes.

Can I use a 68mm bottom bracket in a 73mm shell?

Multiple spacers are included in order to fit both sizes meaning if you see a BB for sale that says 68/73 it means it will fit both but it includes a couple spacers in the box to make it fit the 68, those spacers (or fewer of them) are not needed if the shell is 73mm wide.

How do I know which bottom bracket I have?

Quote from video: Found at any point here by hitting the information icon in the corner. The bottom bracket is the bearing system between your bicycles cranks.

What are the different types of bottom bracket?

There are two main types of bottom bracket design, one with a threaded shell which the bearings screw into, or a press-fit design which the bearings press into the shell.

How long should a bottom bracket last?

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.

How many spacers should a crankset have?

If your BB shell width is 68mm wide then you need three 2.5mm spacers to properly align your BB/crank and get a proper chainline (two on the left side and one on the right). If your BB shell is 73mm wide you need one 2.5mm spacer (on the right) to properly align your BB/crank.

What’s the difference between English and Italian bottom brackets?

The key difference is in how the two thread into the bottom bracket shell. Like pedals, one side of a BSA standard bottom bracket shell is reverse (left) threaded, while both sides of an Italian standard bottom bracket shell are regularly (right) threaded.

Are bottom brackets interchangeable?

Threaded bottom brackets shells have been made over time in various thread standards that are not interchangeable. The common threaded bottom bracket uses cups or adapters with the thread specification of 1.37″ x 24 threads per inch (approximately 34.8mm diameter).

Why is my bottom bracket creaking?

Most of the time, the true cause is a loose chainring bolt—tighten them up and that’ll quiet most creaks. After you check the chainring bolts and if you still hear the noise, look at your pedals, crank bolts, seatpost, and seat. By checking these first, you’ll save an hour of digging into your bottom bracket.

How often should you grease bottom bracket?

Around the three month mark is normally enough time, even in the best conditions for dirt to work its way into the small gaps and contact points around the crankset and bottom bracket area.

Do ceramic bottom brackets make a difference?

The Bottom Line: Quality hybrid ceramic bearings are better than steel bearings in a bicycle bottom bracket application because they have rounder balls for lower resistance, better races for lower resistance, and are grease-efficient in low RPM, low heat environments for lower resistance.

Why does my bike click when I pedal hard?

The chain will rub against the derailleur only in some gears since it changes its angle as you shift gears. That’s why your bike makes a clicking noise when pedaling hard. So, you need to shift your bike into the gear where you hear the clicking.

How many spacers does a 73mm bottom bracket have?

one 2.5mm spacer

For 73mm Shimano HTII bottom brackets

If your bottom bracket shell is 73mm wide, you only need one 2.5mm spacer fitted to the drive side.

What are bottom bracket spacers for?

Bottom bracket spacers are used to adjust the spindle position to add extra clearance, or to fine tune chainline. For example, if your inner chainring is too close to the chainstay you can add spacers to move the crank outward just a bit. They are really great if you want a perfect chainline on a fixed gear bike.

What is crank spindle size?

Crank spindle diameter is 30mm from end to end. Crank spindles are 30mm and then have a step-down to 28mm to lock on the non-drive side bearing. Road version designed to work in frames shell width from 68mm to 86.5mm. Mountain version designed to work in frames shell width from 73mm to 92mm.

Does spindle length matter on bottom bracket?

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.

What bottom bracket spindle do I need?

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.