unlikely it makes much difference. You radar signature is most affected by the shape of your car. IF you look at stealth airplanes, there are 2 technologies.
1) multifaceted surfaces. This scatters radar such that it cannot reflect directly back to the source. Thsi is the older technology used on the F-117
2) Continous curved surfaces. If there are no edges or corners, radar will essentially flow aroudn the object and not reflect back ot the source. THis newer technology is used on the B1 bomber and F-22 I think.
THe ability of a surface coatign to absorb or refract radar, would be highly limited. You might be able ot reduce the reflectance by 5-10% but that's not going to help much.
Laser OTOH tends ot be easier ot defeat. Infrared interference can confuse msot systems. Simply using you high beams and not havign any chroem on the front of your car will work. But unfortunately we have front plates in IL, so you're pretty limited.
On a biek, no wax ro special device is goign to help. Although they are small, they are realatively blunt compared ot a car and have lots of nice edges to reflect radar off of. You're best hope is to always let 1 faster car stay ahead of you liek a lead blocker.