Do you need a new front mech with compact chainsets?

otherself

Would you need to buy a knew front mech if choosing a compact chainset. Say 50/34 chainset (Shimano R600) and 12-26 cassette, would the chain rub on the front mech's bridge when in the 34 ring with 12 cog out back? Or even 14, 16t?

Mech is a braze-on Ultegra 6500 for double.

chriskempton

I didn't, you shouldn't

shazzz

kno.

Mister W

Some you do and some you don't. You need to find out the largest difference the mech can cope with. Some will only manage a 15 tooth difference but you'll need 16.

alfablue

Shimano's website says that their compact C/S have special ramps on the inner ring meaning that no special mech is required. This compatibility chart suggests that it is compatible

Mister W

I've had a quick peek on the Shimano website and the spec for that mech gives a maximum difference of 15, so it may not work.

Smokin Joe

Doesn't matter what Shimano or Campag claim, any front mech will work.

alfablue

ah, the chart shows FD5600 compatible, not 6500 (misread your post), however Shimano specs are a little conservative so I would expect it to work with just 1 tooth outside the range. I know I have got away with exceeding specs on the rear mech capacity with no problem.

John.T

I am running a Sora 8sp front mech on 50/34 and 12/27 with no trouble and also an Ultegra 9sp one on the same set up in 10sp. Again works fine. Both have less chain rub than a full 10sp setup.

Monty Dog

No - need a bit more care setting them up and upshifts not quite as sharp because the compact mech has a slightly different shape to the iner cage plate.

John.T

That is on Campag Monty. I am pretty sure we are talking Shimano here. They do not do a compact specific front mech. There are no problems with the standard ones. Like most things they do need to be set up right.

Mettan

I moved from a Double to Compact with no front mech change needed (Shimano 2200) - on mine, there is chain rub in certain combinations - never been overly happy with the setup. but it will do for now and it works "ok" without being "very good" (my lack of setup know-how). I tend to stick to 6 of the 8 sprockets mainly (8 speed).

Meds1962

My 50/34 works fine with the same Ultegra mech I had when I was on 52/39. The shifting is spot on although it took a couple of attempts to get right. What I haven't been able to cure yet is chainrub at the extremes of gears which I didn't have a problem with when the standard chainset was on. For some reason I tend to find myself using the large / large ring combination more regularly with the compact but I'm still getting used to it really.

John.T

There should be no more rub on the 50 than there was on the 52. You may get some rub on the inside of the 50 ring when you are on small/small but you would not normally use this. It does depend on the crankset a bit. %0/34 with 12/27 is right at the limit of Shimano and will need to be carefully set up including chain length which should be as long as possible.

maddog 2

as above, the Shimano double mech is fine with a compact

however, the Campag CT mech does work better IME, but isn't quite compatible with Shimano shifters, which is a shame.

I run a CT mech with Shimano shifters but you need to do some fettling/drilling to get it to work together.

otherself

Sounds like if you want the best range of gogs one would be much better off investing in a front mech intended for triple chainsets when going compact then?

Don't know whether to keep the old chainset (Ultegra 600 with 52/42t; circa 1995) and just buy a 38t Stronglight chain ring for £14.00, or invest in stiffer and slightly lighter outer bearing chainset + triple front mech. Is it worth it? Is there much difference say between 34t/38t? I'm still a fairly young man (30) but there's some monster hills here and I find my self in the 42:26 a lot which is not ideally keeping a straight chain line.


P.S would a chainset intended for 8sp work with 10sp chains If i ever upgrade other parts? Likewise if I run my current 8spd on a compact intended for 10. It says the R600 works with 8, 9, 10 on DHCyclesports lsiting.

otherself

I think the rings ona 10sp chainset are cut thinner, so 8spd chains on them might slip a bit?

John.T

The only problem you would have with 10sp rings is perhaps more chain rub on the inside of the outer ring on small/small due to the chain being a bit wider and the rings being a bit closer together. It would not slip.
As for using a triple mech there is no advantage and as Shimano ones have slightly different geometry it may work less well.

redddraggon

I'm currently running a 07 STD campag mech with a 50/34 on my winter bike, shifts fine.

John.T

I would say that from the comments on here that the best way forward is to try the mechs you already have and if they work OK stick with them. They will always work well enough until you can get the correct one if you need it.