Compatibility of XT shifter with Tiagra C/set and mech

[theboykidney]

Hi everybody,
I'm a first time bike builder and Im down to what i hope is my last big problem.
Im building a flat barred road bike. I have Tiagra crankset (double) and Tiagra front derailleur. Problem is I have XT shifters so the pull ratio is all wrong.
Ideally I'd like to keep the shifters so it means Im after a new front derailleur thats compatible with XT shifters.
Does anyone know if such a thing exists?
Cheers,
TBK

 

[alfeng]

I'm a first time bike builder and Im down to what i hope is my last big problem.
Im building a flat barred road bike. I have Tiagra crankset (double) and Tiagra front derailleur. Problem is I have XT shifters so the pull ratio is all wrong.
Ideally I'd like to keep the shifters so it means Im after a new front derailleur thats compatible with XT shifters.
Does anyone know if such a thing exists?

The 9-speed XT shifters will work with any 8-or-9-speed Shimano rear derailleur ... and, the 8-speed XT shifters will work with any 8-or-9-speed Shimano rear derailleur.

I have substituted XT-and-XTR rear derailleurs for Shimano Ultegra-and-105 9-speed rear derailleurs without noticing any difference in the indexing.

In the past, I have mismatched a 9-speed 105 triple-compatible shifter with an 8-speed XT front derailleur & a double crankset on an otherwise 9-speed Shimano drivetrain ... this probably worked because of the extra indexing indent in the left shifter allowed the front derailleur to be moved the necessary extra distance (if any) between the two chainrings.

Because the XT shifter is triple-compatible, you should theoretically be able to use it with your Tiagra front derailleur on a double crankset BECAUSE the extra indent should allow you to move the derailleur any extra distance that may be needed.

A lot of Shimano stuff works with stuff that the engineers don't want you to mismatch ...

BTW. I don't know how much (if any) additional stress there is on the shifting mechanism by using a triple-shifter with the an unauthorized front derailleur; but, I would certainly give it a try ...

Whether or not a double-only (i.e., "road") Shimano shifter will work with an unauthorized front derailleur is unknown to me.

 

[Peter@vecchios]

Hi everybody,
I'm a first time bike builder and Im down to what i hope is my last big problem.
Im building a flat barred road bike. I have Tiagra crankset (double) and Tiagra front derailleur. Problem is I have XT shifters so the pull ratio is all wrong.
Ideally I'd like to keep the shifters so it means Im after a new front derailleur thats compatible with XT shifters.
Does anyone know if such a thing exists?
Cheers,
TBK

Yep, road front derailleurs generally aren't compatible with MTB LH shifters. Look for an older XT front derailleur when shimano MTB cranks had a bigger(46-48)t big ring. In other words, a shimano MTB FD where the arc of the outer cage approximates the arc of your big chainring.

 

[theboykidney]

Because the XT shifter is triple-compatible, you should theoretically be able to use it with your Tiagra front derailleur on a double crankset BECAUSE the extra indent should allow you to move the derailleur any extra distance that may be needed.

It looks like a single gear change with the XT shifter pulls the cable more than the derailleur is capable of moving. So the entire travel in teh derailleur is less than one indexing on the shifter.

 

[theboykidney]

Yep, road front derailleurs generally aren't compatible with MTB LH shifters. Look for an older XT front derailleur when shimano MTB cranks had a bigger(46-48)t big ring. In other words, a shimano MTB FD where the arc of the outer cage approximates the arc of your big chainring.

Hey Peter,
good tip. Thanks. How old is an old derailleur?!
also, is there any difference between the gaps on road and mtb chainrings?
thanks for the posts guys, much appreciated.

 

[alfeng]

It looks like a single gear change with the XT shifter pulls the cable more than the derailleur is capable of moving. So the entire travel in teh derailleur is less than one indexing on the shifter.

I haven't checked to see how much more pull a Shimano MTB shifter has than a road shifter, but try setting up the front derailleur with a slack-or-slightly-slacker cable ... use the barrel adjuster(s) to dial in how slack a cable will allow the indexing indent to be engaged.

The setup won't have any trim, but it should be useable.

 

[alfeng]

is there any difference between the gaps on road and mtb chainrings?

The spacing on ROAD & MTB chainrings is the same except for the 10-and-11-speed Campagnolo chainrings (which are closer together) ...

That brings up an option that you can investigate -- that is, add a thin spacer to make the gap between the chainrings wider. Several years ago, someone once measured the thickness of an aluminum soda/beer can as being 0.2mm ... that may no longer be true.

A possible danger of increasing the distance between the chainrings is that the chain can be possibly become trapped between the chainrings (unlikely, but who knows?) if the gap is too large and your shifting action is too slow.

 

[Peter@vecchios]

Hey Peter,
good tip. Thanks. How old is an old derailleur?!
also, is there any difference between the gaps on road and mtb chainrings?
thanks for the posts guys, much appreciated.

9s rings are the same distances, road and MTB cranks. Old as in 10 years old or so but the older the better since the outer cage got tighter and tighter as the big ring got smaller.

 

[theboykidney]

Alfeng - nice idea setting it up with some slack. Ill get on it when i get home.
Failing that it looks like I'll be resorting to ebay for some old school derailleurs. Cant say I relish the idea!

Thanks again, I'll keep you posted on progress.

 

[alfeng]

Yep, road front derailleurs generally aren't compatible with MTB LH shifters. Look for an older XT front derailleur when shimano MTB cranks had a bigger(46-48)t big ring. In other words, a shimano MTB FD where the arc of the outer cage approximates the arc of your big chainring.

I don't know where the notion of the arc of the outer plate on a front derailleur being significantly different enough on a MTB front derailleur than on a ROAD front derailleur to preclude the MTB front derailleur handling a typical ROAD chainring ...

While the back half of the front plate of a MTB front derailleur is slightly different (tighter) than on a ROAD front derailleur, most contemporary Shimano MTB front derailleurs are nonetheless capable of handling a 53t chainring.

A larger chainring (e.g., 54t) would be problematic with a MTB front derailleur.

 

[Peter@vecchios]

I don't know where the notion of the arc of the outer plate on a front derailleur being significantly different enough on a MTB front derailleur than on a ROAD front derailleur to preclude the MTB front derailleur handling a typical ROAD chainring ...

While the back half of the front plate of a MTB front derailleur is slightly different (tighter) than on a ROAD front derailleur, most contemporary Shimano MTB front derailleurs are nonetheless capable of handling a 53t chainring.

A larger chainring (e.g., 54t) would be problematic with a MTB front derailleur.

Will a MTB shift the chain from a small-middle-big ring and back? Probably but the problem comes from the height you need to place the FD and the possibility that the chain will be chucked off the outer ring when trying to shift quickly or under load. If you reduce pedal pressure, but keep the cranks turning, kinda like when the bike is in the workstand, it'll work but on the road it may not.

 

[alfeng]

Will a MTB shift the chain from a small-middle-big ring and back? Probably but the problem comes from the height you need to place the FD and the possibility that the chain will be chucked off the outer ring when trying to shift quickly or under load. If you reduce pedal pressure, but keep the cranks turning, kinda like when the bike is in the workstand, it'll work but on the road it may not.

Peter, your comment is illogical ...

If the chain is being thrown off the outer ring, then the front derailleur wasn't set up correctly ... or, the chain is a serious mismatch for the front derailleur ... or, the front derailleur is one of a few vintage front derailleurs from a few decades ago ... or, the user has Shimano STI shifters!

A MTB front derailleur would be set up where the outer plate would be the same height above the largest/outer ring as you would set up a ROAD front derailleur.

 

[xenith]

Easiest fix is to use a SRAM XO mountain bike front shifter, these shifters work perfectly with road front derailleurs and the best thing is xo shifters have ALOT!!! of trim settings and are also dirt cheap.

 

[theboykidney]

Got it all hooked up and working fine on the weekend guys. The slack cable method worked a treat.
thanks for all your tips, you helped get my bike on the road after 4 months of building! but it was worth the wait, sublime ride!