daroemer

I am converting a Trek 7.5 Fx to run cyclocross, because I happened to have the bike available to play with and transform for nothing. I put the tires on it, and ran it a couple of races with the straight bars, but then got the itch to convert further.

I purchased Shimano 105 STI shifters and drop handlebars for the bike and took them to a friend and fellow racer at the LBS I frequent to have them installed. I switched the v-brakes for new cantis, and we put the bars and shifters on -- and ran into a problem.

The STI shifters appear not to work well with the top pull front (mtb?) derailleur (top pull cables, too). The rear derailleur works fine, but the top is REALLY touchy, and we could only get it to work with two of the front chainrings, even though the shifter is definitely a triple compatable.

Is there ANY way to get the STI shifters to work with this current mtb derailleur setup?

If not (it might just not work), what can I do? I think I can switch the front derailleur out for a bottom pull, road derailleur (we've got all kinds of parts like this at the LBS), and then purchase a specialty clamp/pulley (found something that seems to be what I'm looking for at cyclocrossworld.com) to get the top pull cable to run into the bottom pull road derailleur. Is this my best option? Best? Will this fix the issue completely?

Thanks.

tellyho

I've heard that road shifters don't work well with mtb derailleurs. From Sheldon:

That said, I'm positive that this has been done effectively. Hopefully someone else will tell you how.

HillRider

The most effective change would be to use a road fd and go through whatever is needed to get the cable run to match.

BTW, I believe most CX bikes run wide range double cranks so you may need to use only the two larger chainrings anyway.

DieselDan

A bar end shifter is another option.

maddmaxx 

You will need a real road front D.

There are pulley's to attach to the seat tube so that a top pull cable setup can become a down pull cable for use on the front D. Perhaps someone here can advise you on where to get one. They are used on some cyclocross frames.

cyccommute 

Get a new front derailer for a road bike. The best one for a triple is the Tiagra. It works better with a triple then it's more expensive brethren.

Al1943

And road front derailleurs don't work well with mtn. cranksets. You may want to go with a 110 BCD touring size triple crankset or compact double.

cyccommute 

You're wrong on that one. I have a Tiagra shifting a 46/34/22 Race Face Turbine (it was 44/34/22 before I swapped the outer ring) and an Ultegra shifting a 48/36/26 Shimano XT Trekking crank which is an XT mountain crank with bigger rings (104/64 BCD). Both bike shift nice and smooth.

saturnhr

Due to the different cable pull requirements for Rd and MTN front derailleurs you can make it work by using a straight cable pull adapter from shiftmate. https://jtekengineering.com/shiftmate.htm which will increase the cable pull from your road shifters. I have done so and it works. (the adaptor costs app. $30 plus shipping, so it is not so much the question of technical do-ability but cost)
If you use a road front derailleur on your setup the curvature of the front derailleur might need modification (can be filed or grinded) to a fit the smaller front chainwheel. Rd font derailleurs are most fo fit 52 (plus minus 1) chainrings.
Good luck

cyccommute 

Considering the cost of a new front derailer, $30 for an adapter is steep. Better to just get a new derailer.

I've never found the need to modify the front derailer on my road bikes. The Ultegra front I currently use was first used on a 105 52/42/30 road crank and then on a 48/36/26 trekking crank. The only think I had to do was move the derailer down on the seat tube. The Tiagra I have on my touring bike was on a 48/38/24 crank then a 44/34/22 mountain bike crank and then a 46/34/22 crank. Never had any issues with any of the cranks nor did anything to the derailers outside of adjustment. It's not really an issue.

saturnhr

The cable pull requirement for indexed shifting are a factor 1.2 higher for Mtn front derailleurs compared to Rd front derailleurs (Shimano). Shifting might work even without modifications, otherwise can be optimized by pull-adaptors (shiftmate) as mentioned above and in the case of Rd shifters to front MTN derailleurs can also be accompliswhed by modification of the cable attachment at the front derailleur. With most Mtn front derailleur cable attachment can be modified so that cable attachment comes a factor 1.2 closer to the rotational axis of the lever. By that, a defined cable pull moves the front derailleur more.
It has been my experience that the modifcation of cable attachment works best for the road shifter MTn front derailleur scenario, because ist minimizes the increase in forces required for shifting (which naturally comes with this setting (and which adapter due to internal friction loss would slightly further increase), the adapter works best in the reverse setting (Mtn shifters road front derailleur) and often is the only option, since elongation of the leverarm at the derailleur is difficult to achieve.
I hope this helps,
Good luck

daroemer

In case someone comes across this in a search and wants to know what works or doesn't...I actually just ran well in a messy race here this weekend with the makeshift system on there (tweaked to work on the biggest two rings up front, which is all that was needed anyway). Wanting to have it "right", so to speak, however, I ordered a clamp/pully from Cyclocross World (misc parts) last week, and am taking it into the LBS today where they have a used Ultegra F.D. we're going to use. He had to buy another small part (a rear cable hanger of some sort, I think), to make the whole adaptation work, but that was our decision -- to go with the road F.D., and reroute the cable (upward) using the aftermarket clamp/pulley. I'll post results once it's done.

Thanks for all the input!!

DR