Your advice please...

Rob1 · May 13, 2009

Going to buy a new bottom bracket: ISIS SKF cross country.

What size should I get? I am running a middleburn duo RS8 with 9sp at rear.

I *think* I've got a 118mm on there at the moment. Would a 113 make any difference to the chainline (better/worse?). Not really sure and would like the smaller length if it doesn't have any negative repercussions...

Whadayallthink?

Cheers,

R

mtbfix · May 13, 2009

113 would be better I would imagine. On my SS I run a 108mm axle but your chainstays and chainring sizes will have some bearing on what fits.

Rob1 · May 13, 2009

thanks, there's easily 5mm between crank arm and chainstay but what's the science here? how do you figure what's best for chainline/shifting?

kaiser · May 13, 2009

The middle ring should be 47.5mm to 50mm from the centre of your seattube. Also bear in mind that 5mm from the axle is 2.5mm each side. You should also measure the clearance from crank arm to chainstay if you intend to fit a smaller bb.

Rob1 · May 13, 2009

he heh... i don't have a middle ring! this is why it's all a bit confusing. I suppose the space between the duo's rings should be at 45-50mm then?

I'll just take the plunge I think...

dyna-ti · May 13, 2009

kaiser":3eslh64n said:
The middle ring should be 47.5mm to 50mm from the centre of your seattube. Also bear in mind that 5mm from the axle is 2.5mm each side. You should also measure the clearance from crank arm to chainstay if you intend to fit a smaller bb.

:shock: :?

Take it to your LBS

besides they need your money in this horrid financial climate

Tallpaul · May 13, 2009

http://www.middleburn.co.uk/tech_faq_cranks.php

Your advice please...

Rob1

Old School Hero

mtbfix

Senior Retro Guru

Rob1

Old School Hero

kaiser

Rob1

Old School Hero

dyna-ti

Tallpaul

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