The other problem you run into with the small diameter Telair style wheel is that if the board is bent or damaged the wheel doesn't grip. Not a big problem is you're lucky enough to work with an airline that looks after its gear. Likewise if the wheel is wet, the solid tyre has a hard time gripping, although I thought they changed their compound to improve that. For the main deck posn 1-5( I think ) and 17-19, Aero-Union out of California used to make a drop in replacement that had a better wheel drive system ( ramp up torque v on-off ) and self contained cables and limit switches so you didn't have to adjust the damn things on the ramp. The Aero-Unions in positions 19 alone, gave NWA virtually delay free performance when compared to the Boeing PDU's.