Maximum teeth from shimano derailleur?

I've got a 9 speed training bike with a short cage rear derailleur - either 9 speed or 10 spee.
It has a cassette with 12-28. The upper pulley looks pretty close to the 28 now.

I wouldn't mind putting say a 30 or 32 on it as its coming on to Winter and I still want to climb the hills here.

What is the max. teeth count it can cope with?

Thanks, Paul

 

Exactly which derailer is it?

 

Most of the shimaNO short cage road derailleurs that are spec'd to run a 28-tooth maximum gear can be 'forced' to shift a 30 or 32 by cranking the 'B' screw to reduce the chain wrap. Some guys reverse the 'B' screw and some guys replace the OEM one with a longer one.

Another option is to go buy a cheap mountain bike derailleur that's compatible with your shifters. Lastly, it may be possible to fit a longer hanger if your frame has a replaceable one. That would be beyond my patience to track down, but they do exist for some frames.

 

Your CampagNOlo blood run deep. I have my Record 10 speed 'rello so I'm not all bad.

Thanks for the advice.
I wound the B screw all the way in because of the 34.
I'll never find a longer hanger for this frame - a Genius (like me?!) so might have to look at another derailleur.

 

The thing about Shimano rear derailleurs is that MTB 8- and 9- speed derailleurs are compatible with road 8-, 9-, and 10-speed. The pull rates are the same. Road 11 and MTB 10 and 11 are different animals, as are front derailleurs.

 

This is 9 spud so if I find a secondhand one I might grab it.