Bottom bracket tapers

[hesh0925]

Howdy y'all!

I've asked a few of my friends about this, but am curious to hear where you guys stand on the subject matter. The question is regarding bb taper interchangeability.

With square taper bottom brackets, you have ISO and JIS. Now some people say if you ever use an ISO crankset with a JIS bb, you should never go back to using ISO bbs and vice versa. Personally, I think it would be fine as long as the cranks haven't been taken off and put back on a bunch of times since this tends to stretch the crank hole.

Anyway, just wanted to see what you guys thought about it. Do you think it's okay to go back, or would you just keep using the mismatched bottom bracket from that point on? :banana:

[Ralph]

There is more to it than that. One way (can't remember which) the cranks go onto the BB axle more than they should, and the other way less than they should. So you get a incorrect chain line....in addition to possible hurting the cranks. It's so simple to match them correctly....why interchange them?

[spartanKid]

There is more to it than that. One way (can't remember which) the cranks go onto the BB axle more than they should, and the other way less than they should. So you get a incorrect chain line....in addition to possible hurting the cranks. It's so simple to match them correctly....why interchange them?


ISO crank on a JIS taper sits further outboard, Sheldon claims by ~4.5 mm, and thus a JIS crank on an ISO taper sits ~4.5 mm further inboard.

[wallymann]

tapers are the same 2deg angle, but ISO is "skinnier" of the 2...which results in the aforementioned differences in width when mixing.

installing a *worn* ISO-taper crank onto a JIS-taper BB is a great way to continue getting many more miles/years out of an otherwise unusably-worn ISO-taper crank.

as tapers of a JIS-taper crank get worn, once the crank-bolt "bottoms" on the spindle the cranks are basically done.

this image from VO sums up the 2 tapers perfectly:

http://1.bp.blogspot.com/_C1XrRVl3W8k/StiSOxN7uvI/AAAAAAAAJRw/dEypSsGcQwc/s320/BB+taper.jpg

[ultraman6970]

You have short iso... the 102 campagnolo bottom brakets are short iso :P

Honestly ok? If you arent expecting that crankset to last 50 years, and dont care... you can comeback to the original tapper... but at some point the craknset tapper will just give up, how long it will take?? in a cheappy crankset probably a couple of years, in a campy or a shimano will take a while as long you dont have add/adhd and dont remove and install that crankset like 500 times in a year.

You always can get away mixing tappers, as long as you arent taking that thin in and off like 5 times a day.

[oldpotatoe]

Howdy y'all!

I've asked a few of my friends about this, but am curious to hear where you guys stand on the subject matter. The question is regarding bb taper interchangeability.

With square taper bottom brackets, you have ISO and JIS. Now some people say if you ever use an ISO crankset with a JIS bb, you should never go back to using ISO bbs and vice versa. Personally, I think it would be fine as long as the cranks haven't been taken off and put back on a bunch of times since this tends to stretch the crank hole.

Anyway, just wanted to see what you guys thought about it. Do you think it's okay to go back, or would you just keep using the mismatched bottom bracket from that point on? :banana:

Well, both are 2 degree 'slope' but JIS is alrger in actual millimeters in thickness. 'Forcing' a ISO crank onto a JIS BB 'can' enlarge the crank flats. And it 'can' have an effect on chainline and front der action.

As for 'going back', install, torque(dry spindle, proper torque), and see how far the spindle is into the crank flats.

[11.4]

Well, both are 2 degree 'slope' but JIS is alrger in actual millimeters in thickness. 'Forcing' a ISO crank onto a JIS BB 'can' enlarge the crank flats. And it 'can' have an effect on chainline and front der action.

As for 'going back', install, torque(dry spindle, proper torque), and see how far the spindle is into the crank flats.

If you torque to the right level, this shouldn't be a problem. Where mixing tapers got a bad reputation and made everyone paranoid was when people would fit an ISO crank onto a JIS bottom bracket and then force it into chain alignment. The only way to do that was to deform the crank. I've seen lots of ways to work around a taper mismatch, some good, some bad. As long as you stick with proper torque you can't really screw stuff up. You may have a chainline problem (or in the opposite direction, have a crank that gets too close to the frame and has chainring or crank arm contact with the frame) but you can work that problem out or acknowledge that you don't have the best alignment. I've seen worse things done to bikes. I'd do it properly, and a replacement spindle isn't all that expensive. This is where Phil Wood is your friend -- you can fix a multitude of problems with square tapers if you work with their bottom brackets (either the cartridges or the bare axles).