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Old 07-28-11, 02:36 PM   #1
jacampb
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Replacing Shimano 105 Superglide Double Chainring

I just bought a road bike with Shimano 105 crankset which has a superglide double chainring that is the "B" series (the one with 42/53 teeth). I need a smaller inner ring to fight off knee problems on these hills, and I've learned that in 130mm the smallest I'm going to find is 38T. Smallest Shimano 130mm I've found is 39T.

First question - Do I have to use a shimano chainring here?

Second question, if the answer is yes, do I have to use a chainring from a shimano 105 superglide or can I use a chainring from an ultegra crankset?

So far about all I've been able to find is some steel 9 speed 105 superglide chainrings and some aluminum 10speed ultegra chainrings both at 130mm 39T. My bike has a 7speed cassette so I should be able to use either chainring since i have a 7sp chain right? (guess that's third question).

Thanks!
Josh
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Old 07-28-11, 05:40 PM   #2
joejack951
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Some Shimano cranks use offset chainrings where the teeth are in a different plane than the mounting tabs. In those cases, you are far better off using the same Shimano ring for replacement otherwise you will likely end up with shifting problems. The 105 7 speed crank, from memory, is not one of those cranks though. I am not certain about either of the two chainrings you've asked about. If you can sit them side by side with your current ring and confirm the offset either is not present or matches your current ring (I might be wrong about the offset) then I don't see an issue with using one of those rings. Your 7 speed chain should be fine as well.

Assuming your ring is flat though, you could use a Sugino (or Salsa, or Vuelta) flat chainring and get the 38T size you prefer. See here: http://www.universalcycles.com/shopp...&category=3160

The lack of ramps or pins means nothing on an inner chainring. Your current ring shouldn't have any. Any of the above manufacturer's rings should be cheaper than Shimano too.

With all that said, you'll get a far bigger boost in gearing going with a wider MTB cassette, or my preference, a triple. You could even combine both if your knees/terrain called for it. If your bike has RSX brifters, they should be compatible with a triple crank. If you have friction shifters, you are definitely good to go. If you'd like to explore either path, just say so and we can help you through the swap.
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Old 07-28-11, 09:33 PM   #3
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Will the offset be enough that I'll be able to eyeball whether it's there pretty easily? I know there's something slightly special about the superglide chainrings because on Sheldonbrown it says shimano recommends you stick with either the "A" set (39/53) or the "B" set (42/53) because they somehow work together for optimally smooth transfer. But it also says you can switch out and rough shifting won't be a very big deal. Now that you say it i don't know why the bottom ring would need any sort of a special feature since the chain just drops onto it. And I really can't understand how there would be a difference in the A/B set. I'll prob just order one of those other 38ts and if it doesn't work I'll just be sad.

The previous owner changed the 13/26 cassette out for a 13/30 cassette so I'm a little better off than stock. I do have friction shifters but I don't know that I can afford to switch to a triple just yet. I think I read about a shimano 7sp cassette on Sheldonbrown that's 11-34. I'd sure like to have it.
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Old 07-29-11, 06:59 AM   #4
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Quote:
Originally Posted by jacampb View Post
Will the offset be enough that I'll be able to eyeball whether it's there pretty easily? I know there's something slightly special about the superglide chainrings because on Sheldonbrown it says shimano recommends you stick with either the "A" set (39/53) or the "B" set (42/53) because they somehow work together for optimally smooth transfer. But it also says you can switch out and rough shifting won't be a very big deal. Now that you say it i don't know why the bottom ring would need any sort of a special feature since the chain just drops onto it. And I really can't understand how there would be a difference in the A/B set. I'll prob just order one of those other 38ts and if it doesn't work I'll just be sad.
The difference between A and B only applies to the outer ring. If you look around, you'll see that you can only find 42T "A" rings and 39T "B" rings. 52T and 53T rings come in "A" and "B" types. It has to do with the location of the shifting ramps and pins. They are located differently for a 42T inner ring than for a 39T ring.

The offset should be enough to eyeball, and like I said, I'm pretty sure your inner ring is flat.

Quote:
Originally Posted by jacampb View Post
The previous owner changed the 13/26 cassette out for a 13/30 cassette so I'm a little better off than stock. I do have friction shifters but I don't know that I can afford to switch to a triple just yet. I think I read about a shimano 7sp cassette on Sheldonbrown that's 11-34. I'd sure like to have it.
You might like the sound of a 11/34 7 speed cassette but I doubt you'd like the jumps between cogs. As far as a triple conversion is concerned, a Shimano Sora triple plus Tiagra bottom bracket will run about $100. Considering you'll be spending ~$30 for just a tiny change in gearing, the triple is well worth the cost in my opinion. With the triple, you can also swap out the small chainring for a 24/26/28 ring and get some ultra low gearing, or go back to a closer spaced cassette, again depending on how much extra gearing you need.
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