replica9000

I have a new GT Aggressor 1.0. From what I can find, it comes with the SR Suntour XCC-T102 42/34/24T crank. I was interested in upgrading to a 48/38/28T crank. I see the GT Tachyon 2.0 comes with the Shimano FC-M311 48/38/28T crank. Would this be a simple swap?

eicca

I swapped a Suntour for a Shimano. I'd highly recommend swapping the bottom bracket too so the Shimano fits right (speaking from experience). Very easy job, I bought the tools and did it myself. It cost the same for the tools as it would have for the shop to do it. Just remember: the threads on the bottom bracket are reversed on the chain side (speaking from experience again )

replica9000

Thanks for the reply. How do I know what bottom bracket I'll need? Most of the cranks I've looked at are listed "Compatible bottom bracket: Square type" or "Spindle Interface Type: Square Taper JIS". I'm not seeing anything more specific than that.

eicca

Square taper is a pretty common type of bottom bracket. There are a few different types of square tapers within that class, all using different lengths and stuff (such as Japanese International Standard, or JIS). If you pair the Shimano crankset with the Shimano bottom bracket it specifies in the crankset instructions, you'll have no issue. As long as you get the size right. The axle and body lengths are variable. A local bike shop should measure it for you for free and tell you what size you need.

hybridbkrdr

That's a good question. The way the Shimano Technical Documents are made, you can't always align the model number of the crank to the length of the bottom bracket recommended. It depends on the model but what I do is search and look at a number of sites to try to confirm what I've found.

Gnosis

Shimano’s FC-M311 48/38/28 crankset requires a BB-UN26 (-K) square taper bottom bracket which has a spindle length of 123mm. The crankset’s offered in 170mm & 175mm crank arm lengths.