Ok, I'm curious, why do you care so much about traction on an airplane?

After all, the wheels are unpowered, it's not like a car where the power to move the car is transmitted though the wheels. Heck, the vast majority of RC planes don't even have brakes, so you can't be worried about getting better breaking.

If you're having problems with ground traking during a takeoff roll, there are piles of other things that are far more important than wheel traction, things like toe-in/out, caster/camber, how you use the rudder, wheel location vs CG, and so on.

In my experience, in the real world, you'll never notice the differnece on most RC aircraft between smooth and treaded wheels. Heck, I've even flown planes with mixed wheels, some smooth, some treaded. I've also flown with oddly bent gear, and all kinds of goofy setups at various times, and wheel tread is just a non-issue.

Foam vs rubber wheels, on the other hand, is a more useful topic. I didn't see anyone mention this: foam wheels can absorb water, and get a lot heavier than they started out. If you fly from a swampy field like I do, this can acutally be noticeable. (It's especially noticeable by the wife when she sees the muddy-wet splotches in the car that match the airplane's gear setup).

Foam wheels also sometimes don't cope with pavement well, but in general foam wheels are lighter, and lighter is always better. I did see someone manage to pull a foam tire off the hub making a tight turn on pavement while going rather fast. There are some light rubber-over-foam wheels out there, but I haven't sat around and weighed all the wheels that are out now, so I honestly don't know what is the lightest available. I did make a plane fly better by replacing some old Dubro rubber wheels that weighed a ton with some light foamies a while back. So, if you are flying off of grass, the lightest wheels you can find is a good thing. On pavement, light is still good, but replacing wheels is annoying.