# A REALLY technical question



## bahearn (Jul 15, 2002)

What kind of steel is used in a typical unit body car?

I'm just curious as to difference in thermal coefficient of expansion between autobody steel (A36?) and 1020 (A29) used in roll cages. There can be an 80 °F temperature swing in Texas racing and wondered if the car is being tweaked on the coldest and hottest days.

If there IS a significant difference, one should have the cage built on a median (not mean) temperature day.


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## Matt93SE (Sep 17, 2003)

I woudln't worry about it.
you're looking at numbers in the fraction of a mm range.

coefficient of expansion for A36 steel is .0000117 m/m*C
that means on a temp swing of 80F, a 5meter (15ft) steel bar will lengthen by 2.57mm


unless the numbers for A29 steel (which I just spent 45 minutes searching and couldn't find, btw) are DRAMATICALLY different than A36, then you are going to be looking at differences in size of less than 1mm.

1mm of chassis flex is absolutely nothing when you're talking about a noodle frame Nissan car!


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