double cassette to triple?

I agree with John O,

You would have to replace a lot of parts. I am in the process of taking off my tripple front set up and installing a double. I am going to use the older frame (2000 model year) for Time Trial Compatition the cheap way.

The bike currently has Shimano Sora components wich are two steps lower on the Shimano quality list from your 105 group. I do have left over though the Tripple front crank with 170mm arms and the Shifters/brake levers ( I am using bar end shifters and TT Bars) I may also be getting rid of the rear Derailleur to accomadate the smaller front ring.

What part of the world do you live in perhaps we can work a deal if you would like to go down to the sora parts yours are a little better quality than mine.

Wally

I'm new to cycling (so sorry if my language is a bit off) and have a querie regarding my new bike. I recently purchased a second hand giant tcr 1(1999 model i think). It has a double front cassette, shimano 105 groupset and 8 cogs on the rear hub.

Although i love my new bike dearly i find dealing with the steep hills in my area really challenging - especially compared to my old mountain bike.

I was wonderring whether i could add a third, smaller, cog to the front cassette to make climbing easier. if so, would it be expensive, difficult, require me to change or adjust my derailers/shifters. Could i do it myself? if so how? Where would i buy the parts.

All opinions or advice welcomed.

Thanks Tom

I put on a triple when I built a bike up last summer. There's a killer hill in front of my house, figured that I'd need the granny gear. Sure enough, I needed it.

Yes, you can install a triple crankset on a bike that has a double, but you have to replace quite a few parts. Typically, you would replace:

Crankset
Bottom bracket
Front derailler
Front shifter - with 105, this means the whole STI lever/shifter, which means both, shifters, because they don't sell them individually
Rear derailler

You have to replace the bottom bracket, because triple cranks need to stick out further to make room for the third ring. 105 front shifters aren't indexed for a triple, and they don't sell just a triple front STI shifter, so you end up buying both. You might watch ebay and hope you get lucky on that one. Rear der. has to go because with a small chainring on the front, you need a long cage derailler to take up the slack.

It's more parts and work than you might think at first. Just guessing here, but with labor, replacing all of those parts could set you back $400-500.

It may be cheaper to check with the LBS's in your area for a bike with a triple, and see if they will work a trade.

Logun - the cheaper solution to your situation is to put on a mountain bike derailleur and mountain bike cassette on your bike. You could probably do it for about $75 US with LX components. You can put a cassette (rear gears) on with a 32 tooth low gear and your existing 105 shifter will work fine with the LX derailleur. You should probably have your shop do this since you're new to cycling - they'll make sure you get the right combination of components (8-speed vs 9-speed, etc.)

If you divide the number of teeth in the front by the number of teeth in the rear, you get the ratio of wheel revolutions per pedal revolutions… ie if your low gear now is 39-25 you have a ratio of 1.6 (you'll travel about 3.3 meters per pedal revolution). With a triple you'd have a 30-25 gives a ratio of 1.2 and 2.5 meters of travel per pedal revolution. With a 39-32 LX derailleur/cog setup you'd have almost the exact same low gear as with your triple. There are a lot of guys who make this switch rather than going to a triple.

By the way - in front you have chainrings, in back you have a cassette… other than that your terminology was fine.