Changing the rear cassette on your bike can be a great way to get a bit more speed, or keep your cadence at a more efficient rate. Here is a rough guide on how to do it yourself.
First, you’ll need a couple of tools. A chain whip and a cassette remover (lockring wrench) http://www.wiggle.co.uk/lifeline-shimanosram-cassette-tool-and-chain-whip-bundle. If you don’t want to buy them, you shouldn’t have too many problems finding someone who you can borrow them from.
You’ll need to remove the rear wheel and the QR skewer from the hub.
Wrap the chain whip around the smaller end of the cassette, about the 2nd or 3rd ring, with the chain going anti-clockwise, then place the cassette tool into the hole where the skewer was. Line them up like in the photo.
Putting them like this allows you to just squeeze them together with your hand and makes it a lot easier to keep it stable while putting pressure on to loosen. Once loosened, you can just easily unscrew the lockring from the front of the cassette and pull the cassette off.
Take note of any spacers at the back of the cassette. The freehub on this particular wheel (Campagnolo Vento) is compatible with 11 or 10 speed cassettes by using a spacer with 10 speeds. That spacer has to stay on there.
Now the new 105 10 speed cassette goes on. We’re going from a 12-30 Tiagra cassette to a 11-25 105. The 105 comes with an additional 1mm spacer so we’ll have 2 spacers on there, the Campagnolo one supplied with the wheel and the Shimano one supplied with the cassette. Just read the instructions and do what they say and you’ll be fine.
Next, get the new cassette and start putting it onto the freehub. You can’t really go wrong here; the cassette and freehub are keyed so can only go on in the correct way. Look for the larger key on the cassette and slot on the freehub and line them up to install
Then carry on laying the cogs on top of each other with the writing facing outwards. The blank side faces behind.
Between flat cogs you’ll have spacers to correctly space them out. These don’t need to be correctly keyed
Eventually you’ll end up with the cassette on and the lock ring ready to tighten. Use the cassette tool again but you won’t need the chain whip this time as you’re tightening against the freehub.
That’s the new cassette on and ready to go. Next is to reinsert the QR skewer and put the wheel back on the bike.
If you’ve bought a shiny new cassette, you’re probably going to want to put a new chain with it, otherwise an old chain is going to wear a new cassette quicker. If you’re lucky enough to have a chain with a missing link, simply squeeze and remove the old chain.
Then thread the new chain around the rear derailleur jockey wheels and the front crank.
Note : Make sure not to thread the chain around the rear derailleur the wrong way like I did last time..
I was all ready to email Shimano about their poor design that ran the chain over a metal lug and made it very noisy and inefficient. Then I realised what I’d done after about 3 months riding like that.
Finally, trim your indexing if required, but I find it doesn’t generally need doing if staying on the same number of gears.