If I get a pair of road cranks and put a 1/8 chainring and use them on a fixie, what are the implications of doing this? Because it’s designed for double chainrings I should put the chainring on the inside rather than the outside? And what about chainline? Any other things I should be thinking about.
Thanks tech heads. :evil:
Outside looks better. Chainline is dependent on the BB spindle-crank combo.
Standard road double puts 42mm in the centre of the two rings, standard triple puts it on the middle ring (I think, check Sheldon). Thus a shorter than normal BB will bring the outer position to 42mm.
3/32 to 1/8 doesn’t matter, the body of the ring is (usually?) the same thickness regardless, the teeth are just machined down on 3/32.
Thanks Blakey.
You make it sound quite straightforward…
I’m putting a double Sugino Mighty Competetion crankset on my next build. I’m putting the inner chain rink on the outside, hopefully it won’t be too much of an issue once I replace the bottom bracket. I can’t see why it would cause terrible problems.
It is. In theory.
It’s the finding the right spindle length, removing and reinstalling cranks part that’s annoying.
Again, theoretically, you should be able to measure the chainline from a given spindle and calculate what length spindle (correcting for symmetric/asymmetric spindles) will move the chainline the right amount.
Eg: 48mm chainline on a 126mm symm spindle needs to more 6mm, so take 12mm off overall spindle length = 114mm spindle for 42mm chainline.
Or you can ask people what’s worked for them, hence the table of chainlines for different cranks/bbs on sheldon’s site. (Campy AC-S & Sugino Super Mighty = ~42mm on outer position)
Or… you can do this:
Won’t the type of cranks play a part in this as well?
Chainline is dependent on the BB spindle-crank combo
eg, Suntour Superbe Pro road double works well on a 111mm ISO, but Sugino Super Mighty strada gives a 42mm line on the outer ring, and you can’t mount an inner ring.
Blakey you’re dangerous, you know too much random stuff! :evil:
What type of cranks have you got/got in mind Hor?
Oh I’m just dreaming at this stage Christof :evil:
But I’m thinking of changing the cranks on my road fixie away from a strictly track cranks to road.
You can make it work quite well and get a perfect chainline, but make sure you don’t use shitty poor quality cranks! Or else…
Or you could run 3/32" and save yourself a buck or two on chainrings (as I have without incident on about 4 consecutive fixies). Still might involve the same tinkering with bottom brackets (or chainring spacers etc etc etc) to get chainline right. I’m currently using old campag chorus cranks with a 111mm bb and chainline is spot-on.
Some chaps say that a 3/32" road chain will be more forgiving of chainline imperfections because they’re built to not run straight, but don’t go silly. Chain strength won’t be an issue. Someone once told me I should use 8sp chain in preference to 9 or 10. Can’t remember why - something to do with thicker plates (?) - it sounded plausible at the time.
Also, your road crankset’s chainring bolts might be a hair too long for running one ring, you might need to scrounge/buy some spacers or track bolts or do what blakey did.
Helpful stuff here:
http://sheldonbrown.com/chainline.html
where’s my decaf…