the Tire pressure you're running...

Are you saying the tires are a Max PSI rated @ 45...
AND you're running them @ 40 PSI?

If so MUCH, MUCH TOO MUCH PSI !

See the Tire Inflation Placard on the Inside of the Fuel Fill Door.
It has a Proper Inflation Pressure for High Speed Operation.

You'd better be running At Least H rated skins at that speed.

(Also,take into account the increased heat/pressure from High Speed operation.)

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'84 300SD sold
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