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I have a Specialized HardRock from the '90s. It's seen better days, but I got it for cheap. I had a bike shop look it over, but for some reason the guys missed the rounded off teeth on the front gears. Whenever I ride it, the chain slips every few rotations. I'd like to get a new crankset, but i'm not quite sure what will work and what won't. Any and all advice would be greatly appreciated.

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Nope. But you can figure it out by observing how many front sprockets you have, how many rear sprockets, how many teeth on the largest and smallest front sprocket, and maybe one or two other details. – Daniel R Hicks Mar 28 '12 at 21:47
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Definitely consider just replacing the chainrings. This will be much cheaper and simpler than replacing the whole crank (especially since that might lead to replacing derailleurs, shifters etc) – Mac Mar 28 '12 at 22:24

3 Answers

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The main intercompatibility issues with cranksets are the connection between the crank arms and the bottom bracket spindle.

Most bikes from that age (not to say all mountainbikes) use square taper bottom bracket, for which is very easy to find good quality cranksets.

These look like the leftmost spindle in the picture above (which also show newer types, that are less likely to be what you need):

enter image description here

You might also take a look at the page from where that image came, in the excelent website of Sheldon Brown:

http://sheldonbrown.com/bbsize.html

Other compatibility issues might be related to the length of the bottom bracket and the length for which the crankset was designed. Using different-sized bottom brackets and cranksets might result in a misaligned chainline, an ill-working front derailer, or in extreme cases a chainring running too close to the frame. This is so for tapered square, but I am not sure about the other types.

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And, of course, you might swap only the worn chainrings, that is not so difficult or expensive. The only drawback is perhaps the gear shifting not being so "automatic" as with a fully-matching, brand-new indexed crankset (in my experience, not big problem) – heltonbiker Mar 28 '12 at 21:54
The other dimension to take into account is the length of the crank arm. They tend to be 165-175mm (commonly 170mm). – Colin Newell Mar 28 '12 at 23:31
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Don't forget cranks with outboard bearings and fixed spindles. – Stephen Touset Mar 29 '12 at 19:20
@StephenTouset You are right. I think I skipped that because it seems the OP wants to keep the BB and change only the crankset. Thanks for reminding! – heltonbiker Mar 29 '12 at 20:32
Thank you so much. That is exactly the information I was looking for. – JustinTheTransporter Apr 14 '12 at 1:26
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It looks like this bike likely came with a square taper bottom bracket and crankset. I'd recommend taking the dust caps off your crank arms and verifying this first. You may also need to remove the bolt holding the crank on the bike. If it is indeed a square taper (you'll see a square box sized hole in the crank where the bolt was), then that's good news. It's really easy to find cranks that will fit a square taper bottom bracket.

Something like this FSA Crankset would probaby be a decent replacment for not a lot of cash http://www.amazon.com/FSA-DynaDrive-Sqare-Crankset-22-32-44/dp/B001PT7TM2/ref=pd_sim_sbs_sg_3

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Thanks for the tips! You all have been a great help. – JustinTheTransporter Apr 14 '12 at 1:26
up vote 2 down vote

From the description of the problem --- rounded teeth on the chainring --- there is no need to be replacing the crankset. Simply replacing the chainring in question should take care of the problem. It's almost certainly a 5-bolt 110mm BCD chainring which should be available in any bike shop.

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