Bicycle Mechanics - triple chainwheel spacing on 9 vs 7/8 speed

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pierce
10-27-12, 01:59 AM
is there a difference in the chainwheel spacing on triples meant for 9 speed systems vs the traditional ones used with 7/8 speed ?

I have a bike with a nasty tourney riveted steel crankset, that I'd like to replace with something nicer like a deore 'trekking' crankset (48-36-26), but I know 9 speed chains are thinner (although not as thin as 10 speed), so I don't know if the chainring spacing is the same, so my SiS shifter will work.

cs1
10-27-12, 06:09 AM
On Campagnolo the spacing is the same for 7 - 9. But Campy shifters all have basically a friction front shifter. So spacing isn't as important as Shimano which is indexed. Can you measure the spacing and compare to the crank you are looking to buy?
HillRider
10-27-12, 08:16 AM
Shimano spaces the two larger chainrings slightly closer together for their 9-speed cranks than their 7/8-speed ones so the narrower chain can't "skate" between the rings. When 9-speed cassettes and chains first came out, Shimano said they would work with 8-speed cranks but recommended not front shifting under load.

pierce
10-27-12, 10:31 AM
I suppose I can always use chainring spacers. in fact, I did exactly that with a 50-34 FSA compact crank on my old hybrid, that I was using friction shifters with. When on the 34, the chain rubbed on the iinside of the big ring in almost any gear but the lowest rears, so I added about 2mm of spacing. I basically left that bike on the 50 and treated it as a 7 speed until it was hill climbing time, then I'd drop to the 34, and could use about the lowest 4 gears, which worked out nicely for what it was. I also used a slightly too short BB (these were square post cranks), so the big ring was almost centered on the cassette.

But, my new hybrid has trigger shifting, and I'm liking it. I can see /eventually/ switching to a 9 speed rear but thats new shifters + RD + chain on top of the front stuff.

FWIW, I'm looking at this crankset,
http://www.ebay.com/itm/SHIMANO-DEORE-FC-M590-48-36-26t-175MM-BLACK-Mountain-Bike-Crankset-w-BB-Crank-/290794714365#vi-content

to replace one of these cheap tourney cranks..
http://www.amazon.com/Shimano-M191-170mm-Black-Chainguard/dp/B001GSOHO0