OR, the differing road surface really causes varying amounts of static, as
the OP observed. The act of a tire rolling on an asphalt surface involves a
certain amount of deformation or "squirm" of the tire body. This scrubbing
action will allow triboelectric charging; the same effect you get by rubbing
the faceplate of a plastic meter or shuffling your shoes across a carpet.
Different mating surfaces yield differing amounts of triboelectric
generation.

I have experienced static conditions, during a Wyoming snow-storm, so bad
that it blanked out broadcast AM radio in my car. So just driving through
the air can cause vehicle charging. Even if you discount the road surface
triboelectric effect, it's also quite possible that different road surfaces
might have widely varying conductivity (perhaps due to contaminates and
moisture trapped in the road surface texture).
--
Ed
WB6WSN



Bingo!
Install little wire brushes on the bumper, like seen on the wings of airplanes,
for the static dissipation and your troubles will vanish.

Yuri, K3BU/m