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FSA ISIS Bottom Bracket Failure

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by Sheldon "Ouch" Brown
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The I.S.I.S. (International Spline Interface Standard) splined bottom bracket system is a response to the Shimano splined bottom brackets, supported by a number of independent makers of cranks and/or bottom brackets. This is being pushed as an alternative to Shimano's proprietary spline pattern.

Most of the bikes we sell use Shimano components, so we haven't had a lot of dealings with the I.S.I.S. system. Even though we don't feature these, we decided that it would be a good idea to bring in a selection of replacement bottom brackets, so that we would be able to offer prompt service when bikes would come in that used this type of bottom bracket.

Accordingly, I ordered in all 4 different sizes. I didn't want anything superlight and chi-chi, so I went with the basic FSA unit, retailing for US$40.

When a pair of long-distance touring cyclists showed up at our door with a worn out ISIS bottom bracket, I was very glad to have a correct replacement in stock.

Unfortunately, about 3 days later, we got a phone call from New Hampshire, reporting that the end had snapped right off of the brand new bottom bracket unit, the first we have sold! Although the rider is over 70 years old, he's a tough bird and was not seriously injured.

We overnighted a replacement to the New Hampshire shop that our customer had limped in to, and got him back on the road again. He sent the busted unit back to us, here's what we saw:


It appears that the fracture was caused by poor design...there is a sharp corner running all the way around the spindle which seems to have acted as a stress riser. I do not believe that this represents any shortcoming in the general ISIS spline system, merely an engineering error on the part of FSA.

In any case, I sent the rest of these back to my supplier, I don't want to take a chance on dumping another customer on the road. A product that fails after a couple of hundred miles for a 70 year old tourist does not inspire confidence!

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