My I had a Shimano XT X-type BB in the shed, when I need to replace the one on my singlespeed road commuter I stuck it on. With one spacer on each side it looked bang on the same size as the old one. Am finding the cranks start to come loose, start to wobble, I have to tighten them every day.
Can a MTB BB go on a road bike?
IIRC Shimano road external bbs have a smaller diameter axle than their mtb equivalents. Maybe length okay but, erm, girth not right and hence causing the wobbling?
I think the BB screws in fine, pretty sure its the cranks working loose, not the BB. Can it be that I need to fit another spacer?
I've got a shimano XT (MTB) BB on my road bike with FSA cranks...never had a problem (touch wood). Its a Specialized allez elite if that helps...
Yeah, sounds like it might need the extra spacer, however in a moment of madness I missed one out once and it didnt come loose, I only noticed because I couldnt get the front mech to work right, there was float on the cranks but they did stay tight.. Try the spacer you have nothing to lose.
To test if the cups are the right width appart you can try pushing the cranks from side to side (might need a gentle tap) any movement and its because it needs the spacer so you can preload the bearings.
I use road BBs on my MTB. bearings/cups are identical, just use the spacers that came with your frame/bike/crankset.
IIRC Shimano road external bbs have a smaller diameter axle than their mtb equivalents. Maybe length okay but, erm, girth not right and hence causing the wobbling?
I think the BB screws in fine, pretty sure its the cranks working loose, not the BB. Can it be that I need to fit another spacer?
I don't think breatheasy is implying the BB cups are coming loose, but I too also remember reading somewhere that the axle diameter for HTII road and MTB are 19mm and 24mm respecively..... so you may be able to wind the preload up each time so the crank are pressed against the bearings, stopping the wobble, but ride a bit and the wobble will come back as there is free air betwene the inside of the bearing and the axle.
Could all be bollox though 
thanks, will give the spacer a go, will post back.
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