Bishop4

I want to upgrade to carbon cranks but would prefer to keep same bb (shimano bb-5500). Any suggestions? I like FSA but I'm unsure if ISIS is compatible with Octalink. Could I switch to an external bb and go with a two piece crankset? Will it fit?

fietsbob

Frame threads are pretty standard , falling into either British 68 W or Italian 70 W thread.
so if you feel carbon compelled , go for it.


nope,
either or.. ISIS was an attempt at a non shimano spline.
then shimano dropped that and gave the others another 'standard' to chase.

jimc101

FSA is just about your only choice if you want any crank in the Octalink format other than Shimano, as fietsbob notes, it was a Shimano design to compete with ISIS, both designs which are now obsolete. They are not compatible with each other, so if you do buy one, make sure it is the correct design.

What are you hoping to achive with this change? although the carbon will be lighter than a alu crank, you won't get any benefit from any added stiffness, you really need to change to an external bearing BB crank to get any real noticeable increase in stiffness.

Kimmo

You know a crank upgrade is total fail when it comes to bang for buck, right?

I assume you already have a nice pair of wheels, a sweet drivetrain, etc... cause cranks are about the last thing you should throw money at.

HillRider

Not quite correct. Shimano designed and patented the Octalink interface first and for a long time, refused to license the design to other makers. ISIS (International Splined Interface Standard) was created to work around the Shimano patent and was released as a public domain design so anyone could use it and several makers did. As a result, Octalink bottom brackets were generally very good and reliable while ISIS varied all over the place from very good to terrible.

And, yes, they are not at all compatible or interchangable.

Bishop4

It's a project bike and I need cranks so that's why the carbon idea. The BB is new so I didn't want to replace but I don't know of any carbon cranks that are BB-5500 octalink compatable. Suggestions?
Will external BB fit a 05 Trek?
Will the additional BB width affect the drivetrain?
Thanks for all the good info

HillRider

AFAIK, Shimano never made carbon cranks and certainly not in Octalink form so if you must have carbon, you will need a different bb also.

Yes, external bottom bracket cups will fit your Trek and it has standard English threading.

The "additional bb width" is a non-issue since the cranks that use external bb cups are designed to compensate.

jimc101

Yep, FSA are the only company to make carbon cranks for Octalink AFAIK, I had some FSA MTB carbon cranks, and although they looked nice, I always got chainstuck with them, which went away when I changed to a Shimano crank.

They were light but nowhere near as stiff as an external bearing BB.

CACycling

And if you go FSA, do your homework. The FSA SL-K carbon cranks had a lot of issues. Mine failed at about 250 miles. Eventually, they started shipping the cranksets with Locktite as they had a tendency to come loose without it (which is what did mine in). The LBS gave me the option to have it replaced with Ultegra and I jumped on it.

Soil_Sampler

There were a few others,AC, Zipp,Stronglight,Pinnarello,Deda,...Stella Azurra,Ergomo,Kuota,Token(these were probably made by FSA)and Ritchey made carbon Octalink cranks.

and some others I missed...