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I have three gears in the front and 8 in the back, but I always use the highest gear (I live in a flat place) I might drop down one or two gears occationally but this is only a small fraction of the time.

I want to buy new gears and re-center this distribution around something I find useful, I probably only need the top three ratios from my current setup, and I would like to have maybe 5 more ratios above that. Is this type of modification ever performed?

Sorry I don't know any of the relevant cycling vocabulary. Also, what are power ratios measured in and how do I determine the ratio of my current highest gear?

Where should I buy these parts? Can I make this modification for under $100?

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It sounds like you probably have a hybrid or mountain bike. Could you give any more detail about the bike or the specific components on it? – amcnabb Jul 27 '12 at 21:06
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One thing that's been neglected in the answers so far: you may be over-gearing. If you find your cadence is slower than 80–90rpm, then the solution is to just use your lower gears. Riding in too high a gear is inefficient and bad for your knees. – Stephen Touset Jul 30 '12 at 2:44

1 Answer

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To get higher gearing, you'll need either a chainring (front gear) with more teeth or a sprocket with fewer teeth. Mountain bikes usually have smaller chainrings because off-road speeds are generally slower. For example, a mountain bike with a triple crankset with 24, 34, and 42-teeth chainrings would be limited in its top speed by the largest (42-teeth) chainring. In constrast, the largest chainring on a road bike may have 50 or 53 teeth, giving 19% or 26% higher gearing respectively.

Unfortunately, upgrading probably won't be as cheap or easy as you hope. You can't just replace a single chainring, so you would need to get a whole new crankset (the crank arm plus chainrings) and also a new front derailleur. Depending on how much your bike is worth, it may be better to get a new bike.

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I'm not sure why you couldn't change a single chainring or the cassette... Can you explain why not? – Benzo Jul 29 '12 at 23:29
Increasing the size of a chain ring may mean a new derailleur, or sometimes a new crankset (depending on the PCD of the existing crank set) and a new crankset may mean a new bottom bracket... It's easy in concept- unbolt this and bolt on that - but it's something a novice bike mechanic is better getting the LBS involved in - at least get there advise for your bike. – mattnz Jul 30 '12 at 5:04
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It's more likely that the OP needs to learn to ride with a higher cadence. There are not many out there that will run out of RPM on the flat on a "normal" 24 speed bike and last more than a 1/2 mile - and most of those would know the answer to the question. – mattnz Jul 30 '12 at 5:06
Additionally, if it is a mountain bike it might not have an 11-tooth sprocket in the back as the smallest one. depending on what is current ratios are he could see greater ratio increases by replacing a cassette with a smaller small sprocket than by replacing the a crank. Just depends on the current set up though. – Brad Jul 30 '12 at 13:39

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