slippery surfaces

my problem is probably a simple one when you think about it really, i have a wheel with weight on top of it and is controlled by velocity. however when i hit a slope the objects tyre seems to slip a lot i have applied surfaces to the objects but nothing doesnt even help.

my tyre however is smooth as i had to use a sphere collider instead would this be the cause do i need to add some tread to this. i would jst use a mesh on my wheel but it causes jumping and other stuff when reaching a high speed.

so anyone any ideas i did have a script that changes the max angular velocity on the wheel but still doesnt help much