Shimano crank length label?
 

Crankset is FC-6500 - Ultegra 9-speed. I've measured the crank length (center to center) on these and although I'm eyeballing the centers, I'm getting about 172.5 mm. Stamped on the inside of each crank on the shaft side of the pedal hole is "170". There's other stamping, but no part numbers that I can see.

Are these 170 mm cranks? Would a 172.5 mm arm be stamped "172.5"?

Yep, the stamping indicates the length. I have shimano cranks stamped 170 mm and 175 mm. I'm not sure exactly where Shimano measures from/to, but a 172.5 mm crank should definitely be 2.5 mm longer than a 170 mm crank :)

the 170mm may be measured along a theoretical axis parallel to the centreline of the bike. Most crankarms will have some outward splay in order to clear the chainstays. A quick pythagoras tells me that IF your 172.5mm measurement is correct, AND shimano's 170mm parallel to the centreline is correct, the pedal hole is some ~29.26 mm from the theoretical axis shimano is measuring along. Which seems like a lot.

Someone's not right - and as here is the only place in which this thread is active AND it's 2am I suspect that someone is me!

- Joel

Um... your math is fine :) It's just that the OP says he is "eyeballing" the centers of the bottom bracket and pedal holes, that's the likely cause of the 2.5 mm error. Additionally, 30 mm from the "theoretical axis" isn't so far off... the cranks may have a fairly large Q factor, and 30 mm is not unreasonable.

oh good. It seemed like a large splaying (I know that's not the right word, but I like it) for a road crank. I suppose the OP's measurement error is, in fact, the most obvious confound this time around.

- Joel

"Splay" or "splaying" IS a good word!!!

It makes a lot more sense than Q factor, which is in my opinion a ******** term for something so simple as "the horizontal distance between the pedals" :rolleyes:

but labeling things that way is so COOL! It's like an X FACTOR ! But a little more engineered. As soon as you say "Q factor" people know straight away that you're clever, even if they don't know what you're talking about. It's great. I, in my modesty, just call it "tread" like old people do.

- Joel

Yeah, I believe the measurement error is mine.

And I'm disappointed. This bike was built for a 6'2" rider. It should have 175 mm cranks. It would make climbing a mite easier...

Q typically represents a damping factor. There's gotta be a better term for it. I like "splay".

Is this an 80s Japanese bike? According to Sheldon Brown, the Japanese makers at that time didn't really have a good idea of the body proportions of tall American guys, despite making very good products.

Hence my 60 cm Fuji Allegro (1985?), which came with 39 cm handlebars and 170 mm cranks. The 39 cm Nitto Olympiade bars were beautiful and stiff, but way too small for me. The 170 mm cranks are shorter than I prefer for a geared bike, but just perfect for a fixed gear :)

Well fella, if I was speccing your bike it would have 175s. But hey, you can't say no to bulk OEM discounts right? And if the manufacturer only has to buy 170s to put on all their bikes they can get it to YOU for a couple of bucks less. Or pocket the couple of bucks. I think the difference is called "integrity". Me - I'm struggling to understand why my 1977 57cm Raleigh grand prix came with 165s. One answer is "everything did back then" and the other is "some things never change".

moxfyre, 9 speed ultegra suggests pretty modern. Specced by American or European cats I guess, assembled by Taiwanese cats.

- Joel

tomacropod, you nailed it. Custom-built in 2005 in America with OEM bits (on a '03 Raleigh Professional 59 cm frame). Not for me but for a guy my size.

Related question: I'm now shopping for longer arms (or maybe a triple). I see Dura-Ace arms for sale. Are they interchangable with the Ultegra arms? Can't think why they wouldn't be.

if you're talking 9 speed, I'm pretty sure you can put the dura-ace octalink cranks onto the ultegra bottom bracket. It's a common downspec in there where you can't see it on the showroom floor. You've just got to find some - I keep meaning to pick up some 9 speed dura-ace crankarms to keep in storage simply because they look so much better than the 10 speed stuff. Ack !

- Joel

DMF, I don't mean to kill your plans but... have you tried longer cranks before on a similar bike? In my experience, longer cranks make an almost imperceptible difference in most cases.

If you know what you're doing, by all means go ahead... but don't expect the crank swap to make a huge difference on the hills. For the money it will cost, there are probably other adjustments or upgrades that would make a bigger difference for hill-climbing. In other words, I wouldn't personally make this change unless my bike was otherwise 100% perfect ;)

Yeah, I realize that it won't make much difference, but this is going to eat at me until I get it fixed. :rolleyes:

I see lots of cranksets out there, but few arms. If I'm going to buy a crankset, I might as well go to a triple. I know there are issues with the derailleurs etc. but in for a penny, in for a pound. And while I gather the various bits for the conversion I can use the arms and get rid of that jones. :D

There's a nice FC-6603 (10-speed) triple available. Can 10-speed rings be used with a 9-speed chain?

Yes! Shimano changes the chainring width ever so slightly every time they narrow the chain... but the 9-speed rings are fine. They mostly do it to make people think they hafta upgrade :rolleyes:

Hmmm. I see the drive arm is different between double and triple. (Duh!)

Makes sense, but puts the kibosh on my plan. Oh well, two distinct projects, then.

Just so readers won't get confused, moxfyre does not mean that 6600 cranksets (esp. arms) can be used with 6500 bottom brackets. It's only the chainrings themselves that are backward compatible.