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Every new bike in my price range comes with a compact crankset, which I want for climbing, but I race and I need to keep the same top speed that I've had for sprinting and descending (I live in the mountains). So I'm just wondering what rear cassette I would need to use with my compact cranks to equal the same gearing as using a normal crankset (53/39) with a 11-28 cassete.

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That's a bit unusual for a compact crankset... Sure you don't mean 50/34? – freiheit Jul 10 '13 at 22:28
You could just swap a mid-compact crankset on the new bike running 53/36 or 52/36 chainrings. This is an option for Shimano 105, Specialized S-Works and other brands. It wouldn't be super cheap with race level components. Adjust the rear cassette size to get the range you need for climbing. – Benzo Jul 11 '13 at 3:07
@freiheit not so unusual, I'm using one from sram. – imel96 Jul 11 '13 at 22:18

It's not possible. You'd gain lower gears, but lose your very highest gear. If you want to keep that highest gear, maybe you should look at a wider-range cassette to get there, instead?

If you were switching from a 53/39,12-28 setup to a 50/34,11-28 setup, it would work out well.

Switching your largest chainring from 53 to 50 basically shifts all your high gears about 1 notch lower.

11 teeth is the smallest cog you can get on a road bike cassette, currently. I've seen BMX bikes with a smaller gear on the back, but they're not cassette based.

You can compare gear ratios on a given bike (where wheel diameter, tire width and crank length can all be assumed to be a constant with simple division.

Assuming your 11-28 is 11-12-13-14-15-17-19-21-24-28, or similar:

53:11 = 4.8
53:12 = 4.4
53:13 = 4.1
39:21 = 1.9
39:24 = 1.6
39:28 = 1.4   

50:11 = 4.5
50:12 = 4.2
50:13 = 3.8
36:21 = 1.7
36:24 = 1.5
36:28 = 1.3
... or if it's the more common 50/34:
34:21 = 1.6
34:24 = 1.4
34:28 = 1.2
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Use bikecalc to calculate the ratios or gear inches for yourself. Then you can figure out range equivalent setups for any combination of chainrings / cogs.

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Keep in mind, you'll never get as fast of a ratio using a crankset with a 50t big ring vs a 53t big ring. You just can't get a rear cog any smaller than a 11 tooth on standard 9 or 10 speed cassette that will match the 53x11 since your fastest possible combination will be 50x11. – Benzo Jul 17 '13 at 13:00

Since you are interested in top speed I assume that means you really want to replicate the 53/11 combo. One way of finding a similar combination is by looking at a ratio of the front and back gear.

A 53/11 gear ratio will give you a gain of 4.81. A 50/11 gear ratio will give you a gain of 4.54.

To recover the .27 difference you would need to run a 10.4 (or 10) tooth top gear.

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I don't think I've seen too many 10 tooth cassettes. It would probably be too small to fit on the freehub body. 50/11 is faster than 53/12, so you're right it's only that very bottom gear that matters. I think that you really have to analyze how often you are in the 53/11 gear, and if you're really maxing out the RPMs in that gear. I think you could probably go just as fast in both gears, you'd just need to spin slightly faster. – Kibbee Jul 10 '13 at 12:31
I've never seen a ten tooth either. That wasn't really the question though. Figuring out speed, gear inches, and anything else is really a trivial exercise for excess detail. – Ritch Melton Jul 10 '13 at 16:25


You can't get higher gear combination than 53/11 with a 50, 11 is the smallest cog available. And 53/28 is about equal to 50/26. Hopefully it will be more comfortable because the tighter gear ratios.

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The Shimano Capreo system goes down to a 9 tooth cog, but it only works with the Capreo hub, and it's designed for small wheeled bikes like folders, not normal road bikes. cf. (9 tooth MTB cog, prototype only),… (Moulton hub with 10 tooth cog). – armb Jul 11 '13 at 9:39

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