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Old 02-25-06, 07:14 PM   #1
Abbey
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Cassette for a MTB

I use my Giant NRS3 on the road most of the time and I was wondering about changing the cassette to more of a road bike type set up. Would the change in gearing help in terms of speed? Thanks.
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Old 02-25-06, 07:33 PM   #2
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It depends on how strong you are.

Most MTB cassettes have a smallest cog of 11T or 12T so a road cassette won't give you a higher top gear. You will have closer intermediate steps and a higher low gear.

To get a higher top gear, you will have to change the chainrings (or the entire crank) and get a larger big chainring. Most MTB cranks have a 44T "big" ring while most road cranks have a 52 or 53T big ring.

Have you changed the tires from knobbies to slick road tires? That will help a lot all by itself.
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Old 02-25-06, 08:53 PM   #3
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I concur with Hillrider, the easiest way to make your bike go faster on the road is to switch to slicks. If you do a bit of both road and trail, you could try a tire like the Continental Double Fighter. When comparing your gear ratio to other bikes, you have to consider the tire size. a 12 - 52 is going to be a higher gear, if your bike is 700c or 27" than on the 26".
52X11 on a For 700 X 23 / 23-622 tire with 170 mm cranks = 124.2 with a 26 inch tire the gear-inch would be 121.7.

Note that switching from a 12 to an 11, will get you another 10 inches!

Changing the front rings gets you less change per tooth then a one tooth difference on the rear. 109.4 vs 111.6 for a 51 vs 52 respectively.
Play with the "gear inch" setting at Sheldon's gear calculator.

http://www.sheldonbrown.com/gears/
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Old 02-26-06, 09:13 AM   #4
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Quote:
Originally Posted by Abbey
I use my Giant NRS3 on the road most of the time and I was wondering about changing the cassette to more of a road bike type set up. Would the change in gearing help in terms of speed? Thanks.
If it was my bike, I'd do it.

Changing your cassette probably won't make your top speed any faster. Most mountain bike cassettes already start with an 11 tooth cog, which is the smallest that's commonly available. Switching to a cassette that lacks a 32 tooth big cog will give you smaller steps between gears so you'll be more likely to be able to find a gear that's right in the "sweet spot" when you're riding on the flats. That's an advantage that's well worth sacrificing hill gears that you don't use.

Be sure to replace your chain when you get your new cassette and resize it to match your new gears.
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