53/39 to 50/34 Chainset

[Edge705]

Hi All I want ot shove a compact chainset on my scott cr1 its about 5 years old and I beleive has a hollowtech II bottom bracket

Its ultegra and so is my potential compact chai.onset

Unfortunately I can get the 175m for half price and to replace the exisitng 172.5 I would have to stump up another 50 quid

Questions are do I need to modify anyhting going for a compact ie: anyhting on the rear and would the extra 2.5ml cause me any issues ie: clearence from the ground

Thanks in advance

 

[TheDoctor]

I doubt you'd notice a 2.5 mm difference. I didn't.
You won't need to change anything at the back. I didn't even bother shortening the chain. You'll need to move the front mech down by a few mm, but that's all. Go for it!!!

 

[Edge705]

Brill I will many thanks for your quick reply

 

[Will1985]

You should also lower the saddle if you are changing crank length.

 

[User482]

A problem with compact chainsets is the jump between the front rings - I find that if you need to shift to the inner ring, you also need to shift several gears at the back to get the right ratio.

If you need lower ratios you might be better off changing the cassette.