Peter you could sacrifice a couple of tires and try it for a little while. I know nothing about Buco track. It's possible that the railhead will "stick" in the groove, causing derailments or worse operation than you have now. For certain the loco will not sit level on the track. If the rail is harder than the wheel, running it this way could eventually mess up the groove, making it difficult to install a tire in the future.
Your loco struggles because the rigid wheelbase of four driving axles is long relative to the diameter of the curve. This causes some binding and a lot of skidding. Rubber tires inhibit skidding. The torque of that tiny motor at typical RPMs isn't sufficient to overcome the added drag, so it struggles. On O31, I would stick to an 0-6-0 or 0-4-0. The new LionChief Plus A5 is geared pretty well. With its shorter wheelbase, it might negotiate O31 smoothly without slowing or lurching. An MTH Docksider (with NO rubber tires) should run great up there!
