I wouldn't worry about thermal expansion effects - these effects would be so small that they are effectively negligible over a small temperature range. Any thermal expansion present would most probably be a few orders of magnitude smaller than the chassis flex you'd get under cornering loads.
Besides, steel, which the car body is made out of, expands with heat too, just not to the same degree as aluminium. :P
Yep, I definitely agree with you on that one! Sounds like the $70 eBay cheapy is the way to go! Just gotta wait for my tax return to come in...
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