When I ordered my bike, I had a clear idea what I wanted for the gear ratios; I didn’t want a compact set of chain rings, and instead wanted a standard double of 53/39. Also, for the cassette, I was getting a 10 speed, and wanted a bigger range than the standard 12/25, so went for an 11/28.
Afterwards, I wondered whether I’d made a mistake, especially regarding the compact chain rings, as the guy in the shop had assumed I would want a compact for climbing hills. I investigated how much it would cost to get a replacement compact chainset of comparable quality to what is on the bike right now, and the RRP of £250 was beaten by Chain Reaction at £167. A lot of dough, but if the bike is unusable going up hills, at least the option was there.
But then I remembered about the cassette I was getting, and started wondering whether it would be ok after all. So first, for those of you who don’t understand these numbers, a description.
The chain rings are the big rings on your cranks (those things that your pedals are attached to). You will have one, two or three of them. I have two. There are 53 teeth on one, and 39 teeth in the other. You can now work out why I referred to it as 53/39. When you are wanting to go faster, you put the chain on the larger chain ring.
The cassette is the set of smaller chain rings on your back wheel, but they are not referred to as chain rings; it’s your cassette. I mention chain ring here merely to allow people to know what to look for. On a road bike, you will typically have anywhere from 6 to 11 individual rings, getting bigger the nearer to the spokes you go. The one I have is 11/28, which means the smallest ring has 11 teeth, the largest has 28. The others are somewhat evenly spaced, although this specific cassette isn’t that even, as it goes 11 12 13 14 15 17 19 21 24 28. Completely opposite from the chain wheels, you go in smaller rings the faster you want to go.
What appears to be a normal cassette is 12/25. I wanted a bigger range, 11 meaning I could go faster, 28 meaning I could get up steeper hills (and thus go slower). A compact set of chain rings, on the other hand, is only for going slower, and thus up hills. It’s not much use once you get close to 30mph on the flat, as you run out of gears.
So, to that end, I went to Sheldon’s site to use his gear calculator. I first put in what I’ve got, and then put in what I would have got by default. And hey presto, the gear ratio for the smallest gear is the same! Hurrah! See above screen grabs from Sheldon’s site, showing the two ratio calculations. Therefore, I have the same lowest gear as a standard cassette with a compact set of chainrings, but a significantly higher ratio at the top end. Unless I’m completely mis-reading this, but from common sense calculations in my head, I figured that it was going to be pretty close, so I’m reasonably sure it’s right.