Just a question, why/how would a HDT put a lot of stress on the frame?
It's a combination of things.
HDTs have a lot stiffer suspensions, even with air ride helping things out, typically rated for 17,000 - 22,000 lbs on the rear axle on a single axle to 38,000 - 44,000 lbs on a set of tandems. 3 - 4k pin weight is nothing for these trucks.
HDT suspension bushings are harder to flex than a pickup truck.
Shock absorbers are as big as the fat end of a baseball bat needing more to move them than shocks on a 3/4 or 1 ton.
tires are rated at about 6,000 - 7,000 lbs each on 22.5 - 24.5" wheels and have stiffer sidewalls running pressures of 95 - 130 psi
Truck frames do not flex nearly as much as a light duty truck frame. Yes all truck frames flex, if they didn't they would break in half.
Light duty truck frames are mild structural steel rated at 36,000 - 50,000 psi.......MDT truck frames are usually 9" or 10" x 3" x 1/4" thick structural C channel rated for 50,000 - 80,000 psi, some up to 120,000 PSI and heat treated.......... HDT truck frames are typically 10-1/2" x 3-1/2" x 3/8" hardened steel C-channel rated for 120,000 psi. There are also some trucks with double frames typically found in heavy haul and construction trucks.
Take a tandem axle road tractor as an example..... when you cross a frost heave in the road in a pickup you get a little bump twice. It's a big bump 3 times on a tandem axle class 8 truck. Air ride cab, seats and suspention hide what is really happening when you are sitting in the seat.
There are things that you can do to reduce some shock like running a single rear axle, singling out the duals if the tires weight ratings allow and adusting to an air pressure that is correct for the weight you are carrying without running pressure too low.
Thanks for the info too
