BB axle length

stubs

I am a MTBer and dont know much about roadbikes but I am tinkering with a Specialized Allez for a friend. I need to replace the BB because its rumbling got it out and its a brand I have never heard of called RPM. I want to replace it with a good Shimano square taper BB. I know what shell width I need 68mm but when I measured the axle it came out as 108.5 I went onto CRC site and they do a UN 55 in 107mm or 110mm :?

Which one do you guys reccomend I get, worried if I get the 107 there might be crank and heel clearance issues.

Monty Dog

The 107mm should easily fit unless you've got less than 1mm clearance between the inside of the crank and the chainstay. Even if you go to 110mm, you're only moving the chainline out by 0.75mm, well within the tolerances of the drivetrain. FWIW RPM are a Taiwanese OEM brand whose owners also make FSA stuff.

keef66

You should also check that the original axle is symmetrical, ie that the same amount sticks out on both sides. I have occasionally encountered them with a longer axle on the drive side.

247cycleshop

What make of chainset is fitted?

jimothy78

stubs wrote:

I know what shell width I need 68mm but when I measured the axle it came out as 108.5 I went onto CRC site and they do a UN 55 in 107mm or 110mm

Don't assume current one is necessarily correct - the important factor is to get the right one for the crankset, so look it up on Sheldon brown's table:
http://sheldonbrown.com/bbsize.html

stubs

Decided to go for the 110mm BB the cranks are pretty close to the chainstays with the original BB and to my eyes I wouldnt like to go any closer. As its from CRC its no biggie to get it swapped for the 107mm if it looks wrong.

I think this is the crankset Shimano 2300 8 speed not the greatest of cranks I reckon and heavier than my SLX twin and bash MTB crankset but good enough for a student who is skint.