Answer :
they would wear out and cause less friction with the ground and tend to slip
Soles of shoes and tyres are to be treated chemically to
make the surface strong to
withstand the pressure/stress
and force.
The material is treated to have proper and suitable friction coefficient
between the ground/road and the surface.
They are treated to be hard enough to last longer,
as they get worn out due to frictional heat melting
them.
The tyres have to be hard to withstand pressure, but should be soft enough to
be elastic enough as required. They must be resistant enough to sharp objects
like sharp stones or edges of pits on roads. The tyres need to last
at high temperatures also.
The material of tyres should be such that at high temperatures, the
physical properties do not get affected too much.