Shim STI 8/9-speed compatibility

[Audax67]

Hello all,

I have an unused MTB that I want to fit with bullhorn bars for long-distance touring. The bike is fitted with an 8-speed Shim Acera transmission. I have an old set of Shim 105 9-speed shifters lying around the workshop. Does anyone know if these will work with the 8-speed rear mech and chainshift?

Failing that, can I replace cassette & chain with 9-speed versions and keep the 8-speed chainset?

TIA

JohnE

[CJ]

They'll move the rear mech to the right places to index a 9-speed cassette, but the mech, as it's not made any more precisely than it needs to be for 8-speed, might be a bit sloppy. So it'll most likely shift like an old and slightly worn-out 9-speed mech, which is probably good enough - provided you renew the cables (don't forget the casings) and also get a new 9-speed chain to go with the cassette.

Moving up front: the chainset will be fine but the front mech will not shift anything like far enough. MTB mechs need more cable than road shifters pull. So you'll need either an in-line Shift-Mate or a road front mech. But the road mech might not be very happy with your MTB-sized chainrings, which will be much smaller than it's designed for and with a different outer-middle difference, which is not mentioned in any front mech spec sheets but is absolutely vital to the proper function of a triple mech!

[Audax67]

Thanks, CJ. Sounds like a can of worms. I'll think of something else.

Cheers.

[rjb]

Sheldon Brown shows how to use a 9 speed sti shifter to change across an 8 speed cassette by using an alternative cable clamping arragment here. http://sheldonbrown.com/derailer-adjust ... #alternate
I have used this quite successfully with Tiagra 9 speed sti's and a sora 8 speed mech and cassette.

[Audax67]

Thanks, RJB. Interesting... leaves me with the chainshift problem, though.

If I could get the Acera shifters onto a 24mm-diam bar then there wouldn't be a problem. I even have an old set of drops I can cut down to bullhorns. But the Aceras are 22mm with a cast alloy bar clamp that won't spread far enough. Heigh ho...

[531colin]

I managed to ream out 8 speed (I think) Alivio shifters to fit 26mm bullbars...Profile aero base bars....never used them.....I'll look for them if you are interested

[Audax67]

Thanks, Colin - I'll keep it in mind. I still have a couple of other things I want to try.