Bicycle Mechanics - Help my fixie get a 42mm chainline!

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.



PDA
Autobus
10-23-08, 08:19 PM
Or whatever ideal is with 120mm rear hub spacing:o

Right now, I use a 68x103mm and when the chainring is on the inside, the cl is 38/39mm. When I stick the ring on the outside of the crankset, it is about 45mm.

Do I need to go to a 107mm or 110mm to get the chainline to the 42mm I'm looking for (chainring on inside I assume is the only way)?

operator
10-23-08, 08:31 PM
Assuming your crank is JIS and ignoring chainring/spider frame clearance issues then if you can obtain a ISO bb, say Phil (or any ISO bb) 68x104.5 will set your crank up with the ring on the outside with 42mm chainline.

If you want a cheaper option then, run the ring on the inside and get a 68x107 bb for a 42/43mm chainline.
Autobus
10-23-08, 08:36 PM
Assuming your crank is JIS and ignoring chainring/spider frame clearance issues then if you can obtain a ISO bb, say Phil (or any ISO bb) 68x104.5 will set your crank up with the ring on the outside with 42mm chainline.

If you want a cheaper option then, run the ring on the inside and get a 68x107 bb for a 42/43mm chainline.

It's a generic JIS crankset as I recall. How is the ISO bb different? From what you describe, the pedals arms seat more deeply onto an ISO spindle??:wtf:

sfclearwater
10-23-08, 09:52 PM
Or whatever ideal is with 120mm rear hub spacing:o

Right now, I use a 68x103mm and when the chainring is on the inside, the cl is 38/39mm. When I stick the ring on the outside of the crankset, it is about 45mm.

Do I need to go to a 107mm or 110mm to get the chainline to the 42mm I'm looking for (chainring on inside I assume is the only way)?

Chainrings on a normal road double crank are spaced 5mm apart. So if you think you might have had a 38mm chainline on the inside position, you will have a 43 on the outside. Close enough to 42. Might want to measure again to see if it is really 38/43 or 39/44.

Also, yes a JIS crank will slide farther inboard on the same length ISO spindle.