Classic & Vintage - Question on cranks - your expertise is much appreciated!
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09-19-08, 07:42 PM
As you can see from my sig., I have a 1991 Miyata that runs ultegra 600 tranny, all around. At the time, ultegra = 7 speeds at the back. The crank is 53-42, and although I already have a relatively large cassette (13-28), I'm just rather unfit and would prefer something closer to compact gearing.
My question is this. If I simply change the crank to a 50-36 compact, claimed to fit for 9 and 10 speeds only, will I have issues running the 7 speeds in the back? Will the chain be too loose for the crank's teeth?
09-19-08, 07:50 PM
There's info on sizing a chain on the Park Tools website.
09-19-08, 08:23 PM
You can run a 36 on a 130 BCD crank. You will need a compact crank or a 110 BCD mountain/touring crank. You can get 130 rings in 39 or maybe 38 if you are lucky.
he's wondering about his 7-speed chain working with crankset teeth and spacing designed for 9-speed.
As far as I know, I think it would probably be ok, but I'm no expert.
09-19-08, 09:27 PM
I've run 8s and 9s rears with anywhere from 7s to 10s cranksets and never had a problem. Size the chain to your rear cogset, so in your case, use a 7/8 speed chain.
I'd probably just look for an older 6/7/8 speed 38t chainring for your 130BCD crankset. Lots cheaper than changing out the crankset and bottom bracket.
09-19-08, 10:11 PM
Thanks for the answers so far. So my takeaway is the following: claimed 7 speed chain should run fine on a claimed 8/9/10 speed cranksets. I appreciate the suggestion of trying to find 39 chainring. Since my other bike is on compact, I guess I can force myself to try something closer to a standard double.
You know what - I posted the same message on the mechanics forum, and have had zero answers. The vintage people are definitely the nicest :)
09-19-08, 10:41 PM
The smaller chainwheel will make a significant difference, but you can do almost as well with a Megarange freewheel or cassette in 13-34 or 11-34, in terms of getting a bailout gear.
09-20-08, 05:10 AM
38T chainring 130bcd, $18 (http://harriscyclery.net/itemdetails.cfm?ID=1188)
09-20-08, 07:26 PM
Just a hunch, but since the diameter of a 50/36 chainring is smaller than your current 53/42, you may find that the current chain will be too long - you may need to take a link or two out of it. Not that you would ride like this, but you'll know when you put the chain on the new small chainring and small cog in the back. If the chain is dragging on the chainstay, the chain is too long. As for the width of the chain, I would think it would be OK on the new chainring.
09-20-08, 07:53 PM
You are saying "compact," but all I keeep hearing is "triple."
The fact is, if you stay with a double, changing to a smaller toothed ring up front will not do much at all.
The equation is rather simple: For every 1 tooth out back equals 3 teeth up front. So, a 30T in the back with your current crank would be the equivalent of a 36T compact and a 28T out back. But a better solution that will keep your gearing tight will be a triple.
I vote to replace the 53-42 ringset with 48-38, a 10% reduction. You can keep the same crank, the same freewheel, the same derailleurs, and the same chain, although you may want to remove a link. If this doesn't do the trick, try a 13-30, 13-32, or 13-34 cogset.
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