ROJA

Front: Shimano Compact Double (R700) w/ Ultegra FD
Rear: Shimano 12-27 and RD (all Ultegra)

I know you are not supposed to cross the chain (biggest CR/biggest cog or vice versa). But can I use all but the 2 sprockets that would be crossed over (e.g., big CR, can I go to the second largest cog, or third largest, or what)? This seems like an answer I should know, but I'm not sure.

One other thing: Does the answer depend on how much torque I am applying?

Psimet2001 

I find that on my 53/39 12-27 Ultegra setup that I can use all cogs while in the big ring (yes even the largest) without too much of a problem. I find that when I get to the top 3 cogs while in my small ring that the chain starts picking up some rub on the shift pins on the big ring. The last 2 cogs will rub and or not run at all. So really there are only 2 combinations that I can't really use:

39X13
39X12

MB1

Chainstay length makes a big difference here.

On my wifes Rivendell with very long chainstays she uses all 30 gears without any problems or bigtime rubbing. On her Waterford with shorter stays she gets rubbing but I am not about to tell her how to shift. I would rather she is happy riding and I will just replace parts a little sooner.

Psimet2001 

Great point about the chainstay length. A lot of builders will try to at least keep the chainstay length equal between sizes, but there is a huge variation. For reference I ride a Giant TCR C2 (compact Geometry) in a size "S" or small. It is pretty close to what most would consider a small 52.

mayukawa

On my 50/34 with 12-27 cassette, I can't use the 34x12 and 34x13 (chain rubs against the shift-assist ramps on the big chainring).

merlinextraligh

Aren't you in the best position to answer your own question? Try them and see.

corny

Use 8 out of 10 from each end as long as it doesn't rub.

caloso

Merlin has the best answer, but if you want others' experiences, here's mine:

Campy Record 53-39 crankset, Centaur 10spd RD, 12-25 cassette: Can use all 10 cogs on the big ring, but I get some rub on the 39-12 combination.

ROJA

I thought that it could do damage if I went too far due to the big angle when crossing the chain. But it sounds like I should just use any gear so long as it doesn't rub.

jeremyb_nz

Even if you did try and use all the gears, theres plenty of overlap that makes some of them redundant

twahl

That's my general rule of thumb as well. As has been mentioned, chain stay length makes a big difference though, the longer the chain stays, the more likely you are to be able to use the full range without too much trouble. Not using the last two on either end will help things last longer though, even if all of the gears can be used without making noise.

el twe

2x10=16.

I mean, didn't you take high school math?!

ADlBOO

Kinda a good question though by the OP, It is nice to get other peoples experience cause depending on who tuned the bike, you may be able to get all ten gears on one ring, or only 6-7 before rubbing, dependin on how its set up. I get slight rubbing when in the small chain and the second from smallest in rear, and no probs in big chain ring...