Can I use a 3 x 10 front mech?

[NeilM]

I'm pretty handy when it comes to matters bike and I've built a fair few in the last year or two, but this one has me puzzled, so I thought I'd ask to see what you all think.

I have a few bikes set up 3 x 7/8/9 using Shimano mechs F&R and I have never really given the front mech much thought. I also have a 3 x 9 on my Yates and a 2 x 10 set up on my Roberts DB, both using SRAM. In both cases I carefully bought the 'correct' front mech.

A forthcoming build has got me thinking about front mechs (again SRAM) as I prefer the style of the newer front mechs, but they are all marked 2 or 3 x 10, so...

Is there any real functional difference between a 3 x 9 and a 3 x 10 front mech?

I know the 3 x 10 may be used on a smaller chainrings, but I'm only after 44 teeth, and I really can't think of any other differences, but you may know better.

 

[Elysarian]

you may have issues with shifting as 10-speed front Mechs are optimised for the narrower chain used (most likely issue I can think of is chain rubbing on the side plates and indexing issues)

that said, I'm running a 9-speed XT front mech on my otherwise 10-speed Shimano setup, It's just more sensitive to indexing adjustment so YMMV on this.

 

[NeilM]

I'll be using gripshift, which allow me a small amount of adjustment in each gear, so if that's the only issue, I'll get front mech I'm after.

 

[Chopper the ex Copper]

You will have problems with a 10sp front mech on an 9/8sp rear set up. As you change gear on the rear the chain will eventually touch the front mech cage. Try to adjust it out and it simply moves the point at which the chain touches the cage to a different gear, you'll never eradicate it. Dunno why this is and I've never had the tape measure or verniers out to figure out why. My guess is because the cage width is for some reason narrow than a.9 or 8 speeder, and the 10 speed changer has an extra half-click of movement to trim the position of the cage, which 8 and 9 speed STIs lack (though some road shifters have it).

I know this because I acquired a smart New XT front mech for free-earlier this year and just had to have it in a bike, so true it on my 9 speed Trance and then my 8 speed Diamond Back (RIP) and it just would not run quite right on either.

 

[NeilM]

Good point, but I do have to wonder why that is, as 8, 9 and 10 speed cassettes all occupy the same space on the freewheel, it is just the sprockets that are narrower and spaced closer together.

If I could see some technical drawings with dimensions of the mechs, I could probably work out what was going on, but I don't think anyone lets that info out.

 

[jimplops]

As the 10 speed chain is narrower the t fm cage needs to be narrower, as on a wider cage it would have to travel further before moving the chain, so inversely a wider chain will sit closer to the plates of the 10 speed fm.

 

[NeilM]

Thar she blows!

See I could have worked that out for myself if I had just been and bit more cleverer. :mrgreen:

 

[Chopper the ex Copper]

By Jove, that make perfect sense!