Bottom Bracket...What size???

JAKBLADE

Just got a new frame and want to put a Un54 BB in it...(Don't want Ext.BB as it would mean extra cost)...and UN54 suits my purposes just fine.....

The problem is how do i know what length the BB should be...as they reange from 107mm to 127mm...Obviously need to get the chain run somewhere close to 50mm.....

Help please as I am building this bike up for my daughter, who is anxious to ride off road.....Jak.

W00DENT0P

What chainset / bike is it ?

shm_uk

http://www.sheldonbrown.com/chainline.html

warpcow

+1 what Woodentop asked. BB axle length tends to be fairly unique to the chainset, though the most common by quite some way is 113mm.

JAKBLADE

Haven't got a clue what the frame is.....but the chainset is the old Specialized from me Hardrock

W00DENT0P

Without knowing the frame or exact chainset then it'd just be guess work, as said 113mm is pretty common, but doesn't mean to say thats what size is needed, some.
Pics of the backside of the chainset would help, still not guarenteed to get the exact size tho.
Best bet isto pop down to your local bike shop, they'd be able to measure it up for you no probs.

warpcow

The easiest thing to do if the frames' BB shells are the same width is to just measure the old BB axle and buy the same size. That's assuming you still have the old one of course.

JAKBLADE

don't know how much use this, does anyone know what frame this is??

http://img.photobucket.com/albums/v228/The_Fretboard/IMG_5636.jpg

My LBS is, shall we say, not the best, Woodentop.......for instance :just had a hub relaced in my front wheel and after 20 mins of riding had to return home as most of the spokes on LHS were loose, so had to set to and tighten everything up myself.....good experience at wheel truing though....

Needless to say don't think I will be using them again........hence the search for knowledge on here...

supersonic

Impossible to tell from that I am afraid. Needs to be measured for the width, then the axle to match whatever chainset you plan to use.

JAKBLADE

Yep, i know that Sonic, but don't have an old axle to measure ....What i need to know is what to measure and how, to find out length off BB I require.

supersonic

The axle depends on the chainset lol. Rarely the frame. Two different chainsets may require totally different axle lengths for a given chainline.

You got a chainset in mind?

JAKBLADE

It's an old one, sq. taper from my Spesh hardrock listed at bottom of posts...

Don't know if that helps...

supersonic

Will need to know the exact model I am afraid.

JAKBLADE

Afraid that's it Sonic....Chainset is the original Spesh own brew that was fitted onto bike from new...

supersonic

I'd have to take a punt and say 113mm, but is a shot in the dark.

JAKBLADE

That does seem to ring a bell now I've thought about it. Think that was the original size that was in the Spesh......and i'm not sure but that BB could be chucked in the bottom of abox in the shed or in the Carrera at the mo...think i will measure the new frame and the spesh and go from there..

Cheers for the help Sonic...and everyone else...

By the way Sonic the frame is the one you enquired about in the small ads in the week....bought it to build a bike up for my daughter...

Thanks again ...Jak....

W00DENT0P

Any pics of the back of the chainset ? Is it branded as a Specialized chainset ? does it have any other brand stamped on it, on the back of the arms ? Sugino ?
A lot of early Spec chainsets ran a short axle, like a 107 / 110.
Its all just guess work tho, unless you can see it.

cooldad

CRC have BB's for £7.99. Basic but adequate, so not too much of a loss if the size is wrong. You could probably check the chainline without actually fitting it, and they are pretty good on refunds or exchanges if it comes back unused.

supersonic

Looked a nice frame for the money!

Shotsaway

According to Bikepedia the 1999 Hardrock had a 110mm BB

http://www.bikepedia.com/QuickBike/Bike ... pecialized

Crankset Specialized ForeArm Sport, 22/32/44 teeth
Bottom Bracket Specialized Sport, 110mm spindle

JAKBLADE

I thought so to Sonic, especially for the £30 i paid for it....

Woodentop, will have a look later and if I can will post some pics later..

Shotsaway, that site was a great help, looks like mine is a 2000 model,it's the black and silver one, even though it doesn't list sizes for the BB it gives a name (tange Seiki) which is the same make of BB in the 2001 model, which it does have sizes for....so......looks like I may opt for the 68x113mm as most peoples guesses seem to be that size and the evidence strongly points in that direction...

Again, THANKYOU ALL for your help and advice....GREATLY APPRECIATED....Jak....