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I have a 9 speed specialized sport comp road bike. my chainrings are 50 x 34t and i wanted to possibly change them to a 53 x 39t to increase my speed. it has shimano cassette/components and a truvativ iso flow crank arm. my question is would most 53x39t chainrings match up with my crank? or would it be better just to get a whole new crankset?

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2 Answers 2

Yeah, you should be fine just to replace the chainrings. Make sure you replace them with Shimano (road) kit that is compatible with your 9-speed setup and you'll be fine.

Note that rings designed for a 10-speed setup will strictly speaking be incompatible, since the 10-speed chain is narrower than the 9-speed chain. I have been told that you should be able to get away with this mismatch, although it will be suboptimal.

As a side note though, I'm not at all sure that this change will make you faster. Sure, riding on the large ring going downhill might give you a little more "oomph" (5% tops) but would you likely lose that advantage because climbing would be that much harder? And how much time do you spend in top gear anyway?

I mean obviously the wisdom of this change is entirely your call, but if it were me I'd think hard before I'd part with my cash on this particular upgrade. For hard numbers as regards the gear ratios of what you have and what you're thinking of buying, check out Sheldon's Gear Calculator.

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It's also important to note the limits of the front derailleur. All derailleurs have an upper and lower compatibility limit for each chainring. –  jimirings Jul 31 '13 at 23:08

You have to check if the chainrings have the same Bolt Circle Diameter (BCD). I think compact cranks have 110 mm BCD and normal one usually 130 mm BCD. See also http://sheldonbrown.com/gloss_bo-z.html#bcd to see BCD in detail.

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If the op is going to change to 53/39, this is a standard double setup so he shouldn't have problems. But I agree, worth checking. –  PeteH Aug 6 '13 at 10:06

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