MTB Cassette & Derailleur with STIs

davidj525

I have a Shimano XT M780 10sp Rear Mech but can’t it to work with all gears on my Shimano XT M771 10 Spd Cassette. I can get it to work with the top, bottom or middle 8 gears by adjusting cable tension but not all gears.

My LBS told me this is because the derailleur’s parallelogram design isn’t compatible with the amount of cable pulled by my Shimano 105 STi Levers 10sp 5700 shifters, but a 9 spd XT derailleur would work fine. I have a 50/36 double on front.

The web site I bout the derailleur from said:
“
Road and MTb 10 speed shifters cannot be used together as even though the cable pull ratio is the same at 2:1 the amount that the Dyna-Sys XT rear mech moves is further than a 10 speed Shimano road rear mech would shift.
You cannot use a 9 speed rear mech with Shimano 10 speed shifters as the older 9 speed rear mechs have a different leverage so for the same amount of cable pull a 9 speed mech will move less than a 10 speed one. You click the shifter and it'll move a different distance to a 10 speed shimano mech with the same shifter. We have tried mixing and matching 9 and 10 speed components but it does not work at all.
”

Given that I need 2 shifts to move 1 sprocket in the middle of the cassette I think the mech is moving less not further per shift as they say.

If older 9spd mechs moves less for the same cable pull than a 10 spd, isn’t this actually what I need?

Does the mention of “older 9 speed” mean there has been a design change, what’s the difference?

What is Dyna-Sys?

Is there anywhere I can get a list of specs such as cable pulls, distance between sprockets, mech movement etc?

Can anyone clear up my confusion?

Thanks,
David

cycleclinic

Given you have found all this info I am not sure what your confusion is? I think this would work if you have a 10 speed MTB rear mech and 10 speed STI's
http://jtekengineering.com/shiftmate.php

nicklouse

You will need to use a MTB 9spd rear mech. 10spd shimano MTB rear mechs are not compatible with shimano 10spd STIs.

PS that site you found is not very good.

In fact it is just wrong.

Dynasys is a shimano term. See their webby.

Shimano MTB work close to 1:1 ratio as you have found.

davidj525

Thanks, I mainly want some confirmation I need a 9spd mountain mech before buying one. I presume "old 9 spd" rrefers to 10spd being more recent than 9 spd rather than there being an old and new version of 9spd?

nicklouse

all MTB rear mechs have had the same pull since about 1980.it is just the new MTB 10spd that have changed.

mister p

I can confirm that you need a 9 speed XT mech to get your set up working correctly.

samsbike

Sorry to drag this up, but would the 9 speed mechanism give the full range of 10 gears?

Monty Dog

Yes, as it's the shifter that determines where the rear mech stops - a 10 speed road cassette is in fact narrower than the 9 speed one i.e. the sprockets are closer together and the chain is narrower.