mtb_man_14

I have a motobecane fantom cx and want to upgrade the drivetrain. I can get 105 or XT for nearly the same price. I do each road cycling and cross racing with the bike but am torn at which to get. I dont care about weight too much so thats not a deciding factor to me. I also have sora levers/shifters. Should I upgrade those too? And I know those components are too good for the bike but its a 49cm and I'm 5'6 and still growing so im going to carry those components to a new frame later. Thanks!

4SEVEN3

I think there are a few factors to determine. Are you going to go to 10 speed? if so I dont think your shifters will work being that there 9 speed. As for what group, I asked the same thing and one point was brought up about the MTB derailer hanging down more than the road derailuer, but if your going to run a MTB casette then a longer derailuer cage may be needed so the XT may be the way to go. Plus if you go 10s, youll need a new casette. It all turns into a nice big snowball....and I may have forgotten a thing r three!

mtb_man_14

im going to keep it 9 spd with the cassette that is already on there. I just wanted new derailleurs and didnt know if it was worth it to upgrade the shifters

Andy_K 

You'll need to use 105 for the front derailleur because the XT doesn't work well with road shifters (you can make it work, but it won't work perfectly). I'm not sure how much difference you'll notice between the Tiagra rear derailleur you have and either 105 or XT. Replacing the cables would probably give you more of an upgrade in shifting performance.

Personally, I do think it's worth upgrading the shifters, but if you want to stay 9-speed you can't go above Tiagra. There's a difference in mechanism between Sora and Tiagra that I think makes the Tiagra shifters a nice upgrade. Unfortunately, they're a low-enough level component that it can be hard to find good deals on them. Check Ribble Cycles.

My advice would be to upgrade the shifters, replace you cables while you're doing it and leave the derailleurs alone. Other things I'd upgrade on that bike before the derailleurs are the front brakes, the wheels and the crankset (in that order).

mtb_man_14

thats pretty solid advice. thanks! Ive decided that I may just buy a nicer bike when I outgrow that one which will be soon. After pricing everything, it really isnt worth it to me.

Andy_K 

That sounds like a good call. There's really nothing wrong with what you've got.

pretzelface

If you're doing both road cycling and cross racing, you're better off with the 105. There's no reason you need the kind of gear range you'd get with a mountain bike cassette and RD on the road. In a cross race, anything you can't climb in 38 x 23 is a run-up anyway. Even if you could spin up it in a near-1:1 gear, running would be faster at that point.

Upgrade the Sora if you can, but be aware that changing from 9-speed shifters to 10-speed will require a new chain and cassette. If it were my bike, I'd strongly consider SRAM Rival, if you can stretch the budget. You'd need new derailleurs too if you went that route, but it's an Ultegra-level gruppo. It's also more desireable for CX than Shimano, because it uses a different cable pull ratio. It pulls more cable for each shift, making it less sensitive to cable friction. This is important when your cables are all gunked up!

Don't worry about the components being too good for the bike. You need something besides Sora if you want a usable bike, especially if you're racing. Nothing wrong with the frame. As you said, if the shifters are still usable when you upgrade the frame, sweet. FWIW my first CX bike was an old Haro with an aluminum fork, Dura-Ace shifters, and an FSA Gossamer crank.

Andy_K 

That really depends on your fitness level and the length of the hill. There aren't a lot of hills I can run up for more than 50 feet or so. Anything longer than that tends to turn into a walk-up. I'm working on it though.