Bottom bracket - ISO or JIS

lastpubrunner Posts: 108
edited February 2010 in Workshop
I have a Stronglight 80 chainset (Double, NOT triple) for which I require a bottom bracket.

A well known bike shop has recommended that I fit either a 118mm ISO or a 115 JIS bb.

Which should I go for and why ?

Thank you for any comments/advice.


  • Wooliferkins
    Wooliferkins Posts: 2,060
    The tapers between the two are slightly different they both start and finish at the same dimension but one is longer getting there than the other. Stronglight take JIS BBs (edit) now but I'm not 100% on the 80 . Where are you going to get 86BCD chainrings from when the time comes?
    Help I'm Being Oppressed
  • Wooliferkins
    Wooliferkins Posts: 2,060
    Help I'm Being Oppressed
  • Where are you going to get 86BCD chainrings from when the time comes?

    Luckily, I've got a few in stock and Spa Cycles sell them; besides, I'm not sure that I'll do enough miles (on that bike) to wear them out.

    Thanks for taking the trouble to reply !
  • Monty Dog
    Monty Dog Posts: 20,614
    Just to confuse you, older model Stronglight chainsets were made in France and take an ISO BB e.g. mod 80, whereas more recent models are in fact made in Japan by Sugino and have JIS tapers.
    Make mine an Italian, with Campagnolo on the side..
  • Mike67
    Mike67 Posts: 585
    The Stronglight 80 is most likely an ISO taper being quite an old model.

    I have some Stronglight Speedlight cranks which are also ISO taper.
    There are quite a range of Campag BBs around which are ISO square taper. Token, Tifosi, Ambrosio are other ISO brands which I've come across in my many searches for the right axle length :(

    I have sucessfully used the cranks on both ISO and JIS taper bottom brackets with no loosening issues. (Make sure they're done up really tight from the off though :)

    From my calcualtions (quite rough), I worked out that to keep the same chainline I had to use a 4mm shorter JIS axle than I did for ISO as the cranks go approx. 2mm further onto the ISO taper.

    I guess this works out to about the same as you were recommended by your LBS.

    Hope it helps.
    Mike B

    Cannondale CAAD9
    Kinesis Pro 5 cross bike
    Lots of bits
  • Mike67 wrote:
    The Stronglight 80 is most likely an ISO taper being quite an old model.....
    Interesting to note that Stronglight now use a JIS BB taper. TA were for many years ISO though, they changed to JIS. like TA the older Stronglight were also ISO, TA still being listed as ISO on that chart and even they have been JIS for a few years, first used on their Alize and Zephyr chainset and they are no longer made, so possibly what you actually have is a JIS BB anyway, which is why it doesn't creak perhaps.

    Although they look similar they are very slightly different, they both use the same two degree taper, the main difference is in the actual length of the taper, the JIS version is slightly longer, so if you try and put a crank designed for a JIS BB onto an ISO shorter tapered BB which would happen if you use a Shimano Chainset onto a Campagnolo BB, then the crank may go to far up to the end of the taper, so you will be tightening the axle bolt against the axle, as apposed to the crank onto the axle taper, not such a problem vice versa of course as the crank depth will not reach the end of the taper; still not to be recommended.