Crankset interchange?

yamahafx1 said:

Hi. I have a 1999 5500 trek 9 speed that has a Dura-Ace square tapered crankset currently. My question is will a Dura-Ace 7800 crankset fit my bike and will it work with my 9 speed cassette? Will the bottom brackets interchange?

A 7800 crankset will not work with a square taper bb or any other bb except the outboard bearing bb (SM FC7800) that it is designed to work with. As you have a Trek, it will need the BSA (English thread) version. You should, AFAIK, have no probs with a 9 speed cassette.
BTW, I doubt that a 1999 9 speed Dura Ace crank would be square taper...are you sure it isn't Octalink? That would make more sense.....unless you had upgraded to 9 speed and had the crank from before that? In any case, no, the new Dura Ace crank won't work with any of those bb's.

BikingBrian said:

A 7800 crankset will not work with a square taper bb or any other bb except the outboard bearing bb (SM FC7800) that it is designed to work with. As you have a Trek, it will need the BSA (English thread) version. You should, AFAIK, have no probs with a 9 speed cassette.
BTW, I doubt that a 1999 9 speed Dura Ace crank would be square taper...are you sure it isn't Octalink? That would make more sense.....unless you had upgraded to 9 speed and had the crank from before that? In any case, no, the new Dura Ace crank won't work with any of those bb's.

Hi. Thanks for the reply. My bike came with an 8 speed and I upgraded to a 9. I wasnt planning on using the same bb though. I was wondering if I bought a 7800 crankset with a new bb, will the bb fit in my bike? Do the older bikes have the same size housing and threads as the newer ones? Also what is different on a 10 speed & a 9 speed 7800 crankset? Do they use different rings? Sorry if I wasnt clear on the first post.

yamahafx1 said:

Hi. Thanks for the reply. My bike came with an 8 speed and I upgraded to a 9. I wasnt planning on using the same bb though. I was wondering if I bought a 7800 crankset with a new bb, will the bb fit in my bike? Do the older bikes have the same size housing and threads as the newer ones? Also what is different on a 10 speed & a 9 speed 7800 crankset? Do they use different rings? Sorry if I wasnt clear on the first post.

Ah, I see. Nope, no difference between older bikes and newer bikes in threading: a 68 mm BSA thread will be the same no matter the age of the bike. As for the crankset differences, theoretically the rings should be a bit narrower, however in actual practice there are people who use 9 speed chains without any problems. Not sure about any other real diffs between the cranks....except for Shimano advertising which will tell you that the 10s cranks are supposedly stiffer....unless you are planning to upgrade to a 10s system, I'm not sure there will be any advantages over the older cranks?

BikingBrian said:

Ah, I see. Nope, no difference between older bikes and newer bikes in threading: a 68 mm BSA thread will be the same no matter the age of the bike. As for the crankset differences, theoretically the rings should be a bit narrower, however in actual practice there are people who use 9 speed chains without any problems. Not sure about any other real diffs between the cranks....except for Shimano advertising which will tell you that the 10s cranks are supposedly stiffer....unless you are planning to upgrade to a 10s system, I'm not sure there will be any advantages over the older cranks?

Thanks for your help Brian!!

BikingBrian said:

As for the crankset differences, theoretically the rings should be a bit narrower, however in actual practice there are people who use 9 speed chains without any problems.

9 and 10 speed chains are the same width on the inside. It's only the outside that's narrower. The chainrings are the same thickness and are interchangeable.