Hello I’ve just about finished converting my mountain bike from a 21-speed to a 27-speed. I thought I’d write about what it involved, and maybe it’ll help someone who wants to do the same thing.

First thing’s first. The bike. In 2006 I purchased myself a Trek 3700 MTB. At the time it was the most expensive bike I had ever owned and I thought it was fantastic. This was true for the first year or so, then components started to break. I realised the quality of the gear on the bike was not meant to take the punishment I was giving it, so I eventually had the idea to replace the components with higher end gear that would hopefully last longer and take more punishment.

The majority of the high end components were all in the 9-speed rear cassette setting, so I had to do some work to get this accomplished. The rear wheel already on the bike had been buckled too many times so it needed to be replaced. Also, the gearset on this bike was a freewheel type, and I was putting on a cassette type. Basically the two systems are incompatible with each other. Before I go into the work I did, here is a list of the components I used.

• New rear wheel, hub compatible with Shimano 9-speed cassette
• New rear derailleur Shimano XT Long cage type (you don’t always need to replace this, but mine was the wrong type and I had destroyed it anyways)
• Shimano 9-Speed Saint/Deore LX gear cassette
• 9-speed Shimano Deore LX gear shifter
• Shimano Deore XT Chain 9-speed compatible (you can’t use a normal chain for 9-speed as a normal chain is too wide)
• Shimano Acera V-Brake lever (some may not have to replace this, but my original shifter was a shifter/brake combo so I needed a new brake lever)
• New shifter and brake wire
• Lock ring tool to screw the cassette onto the wheel hub
• Chain breaker tool to remove old chain and install new one

Now onto how to complete the conversion.

1. Remove rear wheel.
2. Remove old chain using a chain breaker tool (or if you don’t want to re-use the chain you can just use bolt cutters).
3. Remove old derailleur and install new one (Note: if your old derailleur is compatible with 9-speed gearsets you won’t need to do this, but if you want the higher end gear you may as well). Simply requires a set of metric Allen keys and a Phillips head screwdriver. Refer to the instructions that come with your new derailleur for more details on how to adjust it.
4. Detach shifter cable from derailleur and then remove shifter from handlebars, carefully pulling the wire through the sheath.
5. Attach shifter cable (preferably a new one) to new shifter and bolt onto handlebars. Run cable through old sheath (or make new ones if you are inclined) and guides down to the new derailleur. Run cable into holder but do not tighten it yet.
6. Screw 9-speed cassette onto new hub or wheel. I am not going into how to replace the hub, but there’s probably a youtube video on how to do this. Requires a lot of time. Might be easier to just buy a new wheel + hub combo. Tighten cassette using the lock ring tool. NOTE: you want it tight, but not so tight that you can’t remove it later if required.
7. Install wheel back into frame.
8. Install the new chain using the chain breaker tool to join the links. When doing this, run the chain along the largest gears on both cassettes and through the derailleur to make sure you have used enough chain. You want the derailleur to still have some play with it outstretched. When joined, move chain onto the smaller gears to make sure that the derailleur can pick up all the slack. If the chain is sagging noticeably, you may need to shorten the chain using the chain breaker again.
9. Follow the instructions for your derailleur on how to adjust it and connect the cable.
10. Reconnect brakes and then take your bike for a test ride. Adjust the derailleur as necessary if you have clicking between gears.

There you go, hope that helps some people out there. When I did this information was pretty scarce so hopefully this can assist someone doing the same thing.

The completed bike.