Bicycle Mechanics - Ok to mix chainrings?
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03-11-09, 08:05 PM
I have a Shimano crankset with rings that are getting worn out. I swapped in a new chain and it's skipping. So I need some new rings. The problem I'm seeing is i cannot find replacement shimano rings for my Deore XT M751 crankset.
I plan to make a large order through Universal Cycles and they only have a middle ring for a m752. Will it work?
And since the granny gear is just a flat ring i assume i can slap anything there, correct?
03-11-09, 08:08 PM
If the new chain is skipping it is more likely your freewheel or gear cluster that is worn out.
03-11-09, 08:09 PM
If you are going to replace your drivetrain start with the rear gears and then get chainrings if that doesn't fix the problem
03-11-09, 08:37 PM
Sorry, forgot to mention that I had changed the rear cassette/chain at the end of the last riding season.
03-11-09, 09:07 PM
Tight link in the chain ? Mismatch between sizes of cassette & chain ? Rear derailleur adjustment needed ? The chainrings are the last thing to cause skipping.
03-11-09, 09:12 PM
Then you need to measure the distance between the holes on your crank arm to determine what size chain rings will fit your crank. You should be able to find out on google how to do the conversion. You also need to be sure that the rings you buy are designed for the number of chainrings you will have on your crank. As to the Granny Gear Question you can't have too great a difference between your large ring and the granny ring unless your front derailure has a very long cage. Basically the top of the cage goes just above the chain on the largest chainring, and the bottom of the cage is just below the chain on the granny gear. It is best to use the same number of teeth that is already on your bike so you don't have to muck around with that front derailuer, otherwise you will need a mechanic.
C'mon guys, front rings do wear out. Wear there isn't easy to detect visually, either.
Divinitous, is it skipping in all front gears? If so it isn't a front wear problem.
The middle gear on a triple is usually first on a road bike, but sometimes a heavily-used granny goes too. (Fewer teeth means more wear per tooth, but some gears are used more frequently than others.)
There are definite differences in front chainrings. I have an old thread here where I measured several models of road cranksets and few were identical. Some were radically different. However, between versions of the same model - like M751 and M752 - they should be interchangeable. Did you look at the interchangeability chart on the Shimano exploded drawings? So long as you stick with 32T, the middle rings are 'A' rated for interchangeability.
One can't make blanket statements about the granny. Two of the variables are plate thickness and tooth offset (from the spider mounting surface). Also ring bolt countersink. Unless you know what you're doing, best to stick with the spec'd parts.
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