Upgrading Chainset - a few questions

DanJS

Hello,
I'm thinking about upgrading the my chainset and would like to tackle it myself if I can...
At the moment, I'm riding a 2007 Giant SCR 3 - with Tiagra Rear Mech and Sora(triple) front. I'd like to upgrade to Shimano 105 (compact). So nothing flashy, but reliable.
Is this likely to cause me any big problems?

For instance....

- Will I be able to fit a new 105 Hollowtech bottom bracket (with outboard bearings) to my frame, or is the width of the BB shell likely to cause issues?

- Anything else I should bear in mind?

- And what are the pros and cons of a compact versus standard chainset? Aware that this is probably a whole other thread / can of worms...
Any advice gratefully received,
D

BG2000

Your BB shell width will be fine (68mm) but you'll need to get a bike shop to 'face' the shell to ensure the ends are perfectly flat and perpendicular to the length of the shell (threads to be exact).

There's nothing stopping you installing a new 'outboard' bearing chainset straight away, but it's recommended you get the shell faced first.

The triple front derailleur will be fine with a compact chainset, and if anything, is better than a standard double version, as you'll be less likely to drop a chain when changing to the 34 ring.

As for benefits...well everyone's got their own view. I did just change from triple to compact but that was mainly because I wanted a Campag chainset, and the model I wanted isn't available in triple.

So far, I'm liking it. There are only 2 rings to think about, which simplifies things. I've needed to get a slightly larger cassette to give me similarly low gears to what I had previously. This is a negative in my opinion, as with a triple, I could run a close ratio cassette before.

Overally, if I was renewing the same make and model of components, I'd probably stick to a triple if a bike is already setup for it. Don't fall into the trap of worrying about what some roadies think of people using triple chainsets.

Bozman

Face? I'll be amazed if it needs facing.

BG2000

If it shipped with an internal bearing BB, then Giant probably painted over the ends of the shell, so facing would still be required. And knowing this, Giant would have had no reason to chase/face the shell flat in the first place. Even if the shell was cast nicely, facing simply ensures that the ends are at 90° to the threads, regardless of how symetrical and neat the shell might look to the human eye.

Monty Dog

Modern bike frames used machined BB shells not cast ones and the dimensional and geometric tolerances are pretty good. It's almost impossible to distort a external BB cup unless the thread is mis-aligned - the whole facing thing is often a scam by bike shops to justify an uneccessary expense. As any quality bike is going to use an external BB anyway, you can expect it to leave the factory fit for purpose.