This is an old post but I believe I am having the same traction issues as the original poster and want to find out if there are alternative tires for the 42x19mm wheels. I'm using the Pololu wheel encoders so I need to stick with the custom Pololu hub.
Here is a link to a journal entry showing the problem I'm having on smooth surfaces: wp.me/p493sy-ap
The encoder and PID control are working perfectly so at this point I can only attribute the problem to traction.
Any help much appreciated.
Maybe there is something I can coat the wheels with to increase friction? In the end I think they just need to be a lot softer.