So, I’m putting gears back on my Cotic Escapade. 2×10.

I’ve two front mechs. The one which is the correct band size for the seat tube is an Ultegra mech. However, there’s no real clearance behind the seat tube due to the 45mm mudguard and the 40c gravel tyres, for the mech lever arm to travel far enough over such that the cage shifts the chain over to the outer chairing.

The other mech I have is a 34.6 (or something). I think it’s an old Sora / Tiagra. The lever arm is much shorter and there would likely be enough room for the full throw without the mudguard getting in the way.

So, can I shim out the 34.6 so it fits the 28.6 seat tube?

Or, if I’m looking for a front mech with a short arm/throw, what am I looking for?

Ta

So, can I shim out the 34.6 so it fits the 28.6 seat tube?

Yes.
There are specific shims available or a bitnof old inner tube might work. Try the old tube to check clearance etc first and if it looks OK get a proper shim

First Google hit, something like this https://www.ebay.co.uk/itm/Cycle-Front-Derailleur-Clamp-Shim-Adapter-Converter-28-6mm-34-9mm-/402867093836?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&customid=CjwKCAjwoP6LBhBlEiwAvCcthOWh09adz7xY4ssVhhAeLVTU48mKU4UYimr132GlYjA4zVtYi7LgHhoCtloQAvD_BwE

Yeah, I’ve done it with inner tube a few times. No problems apart from looking a bit crap.

Which ultegra mech is it? I had an older 6800 one which didn’t work with my gravel tyres for same reason as yours. However the more recent ones have a different design which works fine Pro bike kit Ultegra r8000

The newer design is better. I have an ultegra one on my escapade with mud guards with plenty on clearance. All the models are very similar from this generation. Seems to be just difference in the amount of stamped steel Vs alloy parts as you go up the range. I have a 31.6 105 one for sale but don’t have the spacers spare sadly.

The actuation ratio differs between the old short arm and newer long arm ones, so it won’t work with your shifter (assuming your STIs are relatively recent).

As mentioned above, the newer R7000, R8000 and GRX mechs have the same actuation ratio as the long arm mechs, but with far better clearance for big tyres/short chain stays/mudgaurds, and are also more tolerant of out of spec cable routing by frame manufacturers.

and are also more tolerant of out of spec cable routing by frame manufacturers

Really? I think it’s been discussed on here before but I find the new design to be the most fickle front mech design I’ve ever had to work on, it’s almost as if Shimano want to force people on to 1x…

The Ultegra still works fine on my ‘good’ bike that never gets wet, the 105 on my day-to-day road bike is merely ‘ok’ but needs some persuasion on to the big ring sometimes and doesn’t trim, and the GRX on my gravel bike ‘worked’ but also wouldn’t trim. I got rid as soon as.

However this thread has saved me an expensive mistake as I was considering buying some old stock long arm front mechs for a new gravel build and to replace the 105 mech on the winter road bike, but that’s perhaps not such a good idea…

My 6800 was a pain in the ass on my bike as the routing didn’t comply, but the GRX one was spot on.