Hello all. I usually lurk on the vehicle-driveline forum, but came over here to ask about torsional rigidity (or lack thereof!) of vehicle frames. Here's why: I'm totally rebuilding my '59 GMC pickup and was alarmed to discover (accidentally) that the chassis (no cab or bed yet mounted) has very little torsional rigidity. Over a small range (up to two degrees twist) it measures in the ballpark of 125 lb.ft. per degree (and is fairly linear in this range). This low number is apparently by design, not from degradation- it had almost no rust, has no cracks, and rivets are complete and tight. It's admittedly not a substantial design- open C-channel rails and no X-member. But here's my problem- poking around the Internet for torsional moduli (competition cars and hotrods), I find numbers ranging from 3,400 to 7,500 lb.ft. per degree!! (the low number is from a 1954 article!)
I'll appreciate any comments which will help me "get a grasp" on this huge discrepancy...
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