On one 456 bottom bracket width

Joesimp

Hi there,

I'm currently building up a 456 using parts from my freeride hardtail.

I originally wanted to just take everything off the old bike and put it on the new, but as i'm finding, it's really not as simple as that!

My latest issue is that I have a 118mm isis bottom bracket that I want to swap over, but i'm not sure whether this will work.

My old hardtail has a double chain ring up the front, which i'll also be transfering over, and an 8 speed cassette at the back on a 150mm hub.

I've had to get some new wheels with a 135mm rear hub for the 456, and i've also invested in a 9 speed xt cassette.

So my question is, will the chainline on the 456 be ok with a 9 speed cassette on a 135mm rear, and a double chain ring on a 118mm bottom bracket up front?

Has anyone done this? Any problems?

What width bottom bracket are you running on your 456??


Thanks very much for any help you can give!

Joe

nicklouse

BB width is not your question.

what chainline did your old set up have? and what does the new bike want?

as the old bike had a 150 rear i would guess you will need a shorter BB axle. BUT without knowing the chainlines it is not certain.

Joesimp

Well so far as i can tell, with a rather crappy tape measure, the middle of the two front rings is 50mm from the centre line of the seat tube.

The rear, using more rough numbers and parktools calculations, works out to be approx 52.5mm.

I've no idea what chainline is needed for a 456 though!

Can anyone help with that?


Thanks

the phantom pieman

The BB on a 456 is 68mm

You then need to apply spacers to suit the chainline ...

nicklouse

50mm is fine.

butcher of bakersfield

The BB width is dependent on the chainset, as I recently found out. And what a nightmare that is when no one can tell you the right answer.

The way I figured it out in the end was to fit an old BB with the new chainset and measure the chainline. I played it safe and got a smaller BB, and now need to find some spacers.* Which is preferable to going to big and needing a new BB.

*I don't trust the string that I used to bodge it to last too long, and it still needs another mm or so to get it running smooth.

nicklouse

butcher of bakersfield wrote:

The BB width is dependent on the chainset, as I recently found out. And what a nightmare that is when no one can tell you the right answer.

The way I figured it out in the end was to fit an old BB with the new chainset and measure the chainline. I played it safe and got a smaller BB, and now need to find some spacers.* Which is preferable to going to big and needing a new BB.

*I don't trust the string that I used to bodge it to last too long, and it still needs another mm or so to get it running smooth.

Errm.

BB width is frame dependant.

Axle length is crankset and frame dependant.

not all frames want a 48.5 or a 51 or a... Xmm front chainline. and not all cranks give the same chainline with the same axle length.

Adding spacers will just cause more issues as it will move the opposite crank arm in and it may contact the Cup or the arm on the frame.

all the above is only for the internal BB and separate crank arms.

butcher of bakersfield

nicklouse wrote:

[

Axle length is crankset and frame dependant.

not all frames want a 48.5 or a 51 or a... Xmm front chainline. and not all cranks give the same chainline with the same axle length.

I could be wrong, but it seems the OP was about axle length

I just know I had a nightmare trying to figure it out and I wish someone had told me about spacers a month ago.. Yeah, it'll not work for everyone, but if you fit an old BB in there you'll get a good idea.

Joesimp

Thanks for the replies guys!

Well I managed to get through to someone at on one who said that the 456 needs a 50mm chainline and a 113mm long bottom bracket axle (68mm BB).

My 118mm BB axle though seems to give a 50mm chainline with my twin rings and bash up front so i think i'm just gonna swap it straight over! Happy days!

Though I was eying up a rather tasty crank brothers isis BB from chain reaction... next time I think!


Thanks again!

Joe