Bicycle Mechanics - Road STI shifter with MTB crank

Specifically SORA 8x3 shifters with an old (really old) Deore XT triplecrank. Sora front derailer also.
Will this setup work or is it a try and see thing?

pretty sure you needed a shimano MTB FD that pulled the cable at road ratios since the sora FD is not shaped correctly to allow it to shift through all the rings smoothly.

Indexed pull on the FD is the same road to MTB. Depending on your chainrings though the Sora you have may be the wrong curvature for the chainrings, ie: road 52 versus mtb 44 on the large ring which will cause shifting issues.. Pick up a Deore FD for like $25 (less on eBay) and run with it if that's the case.

actually the RD is the one with the same cable pull ratio, the FD is different between road and MTB so you will need a MTB FD that's designed to work with the road cable pull ratio.


http://www.sheldonbrown.com/front-derailers.html#indexing

Indexed pull on the FD is the same road to MTB. Incorrect.

This is only true of rear shimano derailleurs.

Using an MTB derailleur with a road STI shifter won't work all that well.


Specifically SORA 8x3 shifters with an old (really old) Deore XT triplecrank. Sora front derailer also.
Will this setup work or is it a try and see thing? What are the sizes on the chainrings?

The curvature of the Sora derailleur may not be ideal (probably designed for 30-39-52), but if it's say, 26-36-48 it's similar to a touring crankset, and many of those work with a sora FD. With a 22-32-44, your mileage might vary.

I say just try the sora derailleur with your XT crankset; if it doesn't work well then you can consider the next step, which may require you to replace both your left shifting and front mech at the same time.

Chainrings are 48-38-26. I'll try it out and see. I'd rather replace the front derailer than the crank. It might be easy to just find an older, cheap road triple crank though and then everything would work well.

Incorrect.

.

That's what I get for answering posts at near 1am after a long day riding *thwock* I knew that ! :P

Chainrings are 48-38-26. I'll try it out and see. I'd rather replace the front derailer than the crank. It might be easy to just find an older, cheap road triple crank though and then everything would work well.

It will work fine. I have 3 bikes set up with similar chainrings...or at least close to it. My touring bike has a 46/34/22 set up with a Tiagra FD, my cross bike has exactly what you have with an Ultegra FD and my daughter's bike has a 48-38-24 with Sora (I think:rolleyes:). All of them shift just fine. The argument that you need to match the diameter of the rings to curve of the derailer isn't one that you need to pay too much attention to. I even ran the touring bike with a 44 tooth outer for a while and never had problems.

It'll work.

It will work fine.
+1. Road front derailleurs work remarkably well with MTB cranks and their "too small" chainrings.

My son's '98 Trek 1220 came factory stock with an RSX triple crank with 46/36/26 chainrings and an RX-100 road front derailleur intended for a 52T big chainring and it shifted (and still does) very well.

It will work fine.

+1. You may have to lower the FD a little for the smaller outer chainring, but the cable pull will be good.