hybridbkrdr

I was doing research between square taper vs splined (which is Hollowtech right?) and came accross the FC-M660 which uses a bottom bracket I can't even find. If I can't find the name for it, how does someone go about replacing the bottom bracket if it needs replacing? Do they last forever? lol

reptilezs

https://www.jensonusa.com/store/produ...g+Bb+Htii.aspx the road and mtb ones do not have the same dimensions

HillRider

I believe the M6XX series of MTB cranks were Octalink, not external bearings like the M7XX and were called Hollowtech, not Hollowtech II. In that case they would use the V2 Octalink type bb, not the V1 road (and XTR) Octalink.

hybridbkrdr

Well, the point of the thread is, does the Hollowtech I use Octalink V1 and V2 and Hollowtech II use external bearings?

From what I read, Octalink V1 and V2 uses smaller bearings than square taper cranksets so the V1 and V2 bottom brackets don't last as long. So, I figured maybe I'll try finding out whether a Hollowtech II crankset with external bottom bracket would be worth it. But, I prefer 8 speed cranksets so it's kind of meh...

mechBgon

Regarding the terminology, Hollowtech actually refers to the hollow-forged crankarms. There are Hollowtech square-taper cranks out there (e.g. Deore FC-M510), and there are Octalink and external-bearing non-Hollowtech cranks like my current Deores, which are external bearings but not hollow arms.

Regarding longevity, Octalink BBs are pretty durable in real life. If you find the crank you want and it's Octalink, don't let it bug you.

If you get the SLX FC-M660, it (should) come with the external BB cups included, they're part of the package.

hybridbkrdr

Yes, but I mean in theory, do the bearings on the external bottom brackets last longer than the Octalink V1 & V2? I'm wondering if I could get an 8 speed crankset like that. (I mean external bb.)

HillRider

Theory is ok but practice is the final decider. I have an Ultegra 6500 crank on a V1 Octalink bb and the bb has over 31,000 miles on it and is still in great condition and in daily use. Do you expect better than that?

mechBgon

I don't think they do. If you find a good Octalink setup that does what you want, go for it.

hybridbkrdr

Well, thanks for those who tried to help. As for me, I think I'm going nuts with choices. My inseam was measured in a shop at 83.5cm. So, I decided maybe the 175mm cranks I bought (which I may sell on eBay) with 52/42/30 are maybe too long. So, I figured maybe I could go with 172.5mm or even 170mm because a doctor told me I have a bit of condromalasia (spelling?) in my knees. I'm tempted to believe the 172.5mm are maybe ideal but can't really prove it. Besides, I recently read 175mm means more leverage but means more pedaling to go the same speed.

I initially wanted to go with a max. 52T chainring so I could save a lot of time if I'm going a long gradual downhill against the wind. And now I believe I'd go faster with 170mm cranks. But, since I do live in a hilly area, I find I'm often on the 38T middle ring (on my cheap hybrid which was a little heavy with hardshell, multi-tool and extra lock which I recently unloaded because of the weight) with the 28T in the rear when I arrive home. And it's nearly flat there with a slight incline. So, I figured maybe I need a 34 or 36 middle chainring which means I'll end up having maybe 42, 46 or 48 big chainring. Whatever, hahaha, I'm going to go nuts...

You guys will never believe this but after doing research for months and months, I ended up buying two rear derailleurs, two front derailleurs, two handlebars, two stems, two seatposts, two saddles, etc. So, I ended up deciding I'll eventually build two touring bikes. One will be a back-up rain/city bicycle which I may not load with a backrack, fenders, kickstand, panniers, whatever. But, it may still have a dynamo hub at the front. Oh well, just talking out loud I guess. I suppose eventually I'll make up my mind. ha

bradtx

hybridbkrdr, Chondromalacia patella is pretty much what I have with my left knee. I put 175 mm crankarms on my distance road bike so that I'd have a bit more leverage. It worked well. Now with the touring bike I have 170 mm crankarms, but a greater selection of low gears to keep the stress off of the knee when I need to torque up a hill. So far, so good.

As far as the BB lifespan goes, don't worry about the design, they'll all last a long time. While I have read of some external BB issues, I've read more about every other design over the years.

Brad