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I have a Trek road bike (although you might call it a hybrid since it has straight handlebars. I do about 3,000 miles per year on it for general health reasons (up to 30 miles at a time and averaging 13 mph) and I'm not into racing, cycling clubs etc (I'm coming up to 70). I've just replaced the front chain wheel with an identical version (Shimano Acera FC-M361 48-38-28T) and also the chain. I need to replace the rear chain wheel but before I do I thought I might ask for some advice.

The supplied rear chain wheel is a Shimano HG-51 8aw (i.e. 11-32T). Virtually all of my riding is on levelish ground and UK roads (as bumpy as hell!) with pretty shallow inclines - no off road riding. I find I rarely use the high and low front gears and virtually never use the bottom two rear gears. So what would be your advice on what gearing I should buy for the rear chain wheel replacement, and if you feel so inclined could you comment on the overall front and rear gearing - I feel its probably not optimal since I only seem to use 5 or so of the 24 gears!

  • You should have done the rear at the time rather than break the chain again. – paparazzo Jun 14 '15 at 20:25
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If you aren't using many of the gears, then you should definitely go for something with a smaller range. The triple crank will give you plenty of range even without a wide range cassette. They sell 12-25 and 12-23 cassettes which may be closer to what you are looking for. I have an 8 speed cassette with a 52-42-30 crankset and I opted for the 12-23 cassette. I find there is plenty of range for climbing hills. The nice thing is that the gears are so much closer and I find that it's a lot easier to find the right gear in order to maintain an optimal cadence.

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  • +1: 28/23 (new lowest gear) gives same gearing as 38/32 (current middle chain ring/lowest). This is a good guide for the OP to decide if he should go 12/23 or 12/25. – mattnz Jun 14 '15 at 22:05
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It sounds like you already know the range of high and low gears that work for you on your normal rides – an 11-24 cassette with a 38 tooth chainring, which covers a range of 93.1 to 42.7 "gear inches." The closest standard 8-speed cassettes are an 11-23 or a 12-23 (Sheldon Brown has a list of available cassettes).

Both are pretty close to the range you're using now, but with closer steps. This would give you more options for finding a comfortable cadence. Your small ring would give you an overlapping range 32.8 to 62.9, use it when you're tired or riding into a headwind. The big ring would give you a range of 61.6 to 118 (assuming an 11 tooth small cog) which you might use with a tailwind or if the ride is predominantly down hill. Both of the ranges on the outside rings of the front omit the extreme cog of the rear (e.g., small ring front to small cog in the rear or large ring in the front to large cog in the rear).

The only other advice I'd offer is to notice the front and rear combination where pedaling feels the best on the current setup and select a new cassette that includes that same ratio – and ideally also gives you something very close to that ratio when you're using the large and small rings as well.

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