My HO layout has grades up to 3% and I can't pull a decent cut of cars without some sort of rubber tires on a driver wheel on my Bachmann 2-6-0 Alco steam loco. The loco wheels are all smooth with no groove to install rubber tire rings. Does anyone know of a source for driver wheelsets with axle that would have wheels with a groove that accept rubber tire rings? I have tried putting rubber rings on the smooth rear driver axle wheels but in some curve areas a wheel with a rubber ring will go off track.
Traction tires are a sign of a poorly designed locomotive. In the case of the 2-6-0 you would sacrifice the good electrical contact necessary for DCC and especially DCC with sound for the ability to pull a couple more cars up the grade. By my testing, this locomotive will pull 7 cars on 3% grades, and 5 cars on 4%. This is typical for a model steam locomotive. Adding traction tires to a locomotive like this would entail disassembly and rebuilding with the new wheels if you could find something that fits, and the result would be degraded locomotive performance. Are you ready for things like quartering drivers?
Honestly, if you want to pull longer trains with a single locomotive, you'd be better off with a diesel. The Bachmann FT will pull 20 cars on that grade, and even the tiny MDT Plymouth will pull as much as your 2-6-0.
I added weight inside the cab and on the pilot so mine would pull more.