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Tuscany wrote: Mon Jul 29, 2024 11:32 am As the steel torsion bar twists and turns millions of times, it will stiffen.

My mechanical engineer friend says the opposite happens.

I've had three of them as winter trucks in the last 15 years. You can make your own judgement. The ride gets ugly.
I will say that all of them have been extremely reliable, as well as my string of Fords.. Probably because I maintain them to a grade A level myself.

bruceb58 wrote: Mon Jul 29, 2024 7:09 pm My mechanical engineer friend says the opposite happens.

Steel generally tends to get very gradually more brittle but less stiff as it flexes over time as long as you stay within its elastic deformation range or well shy of its yield strength. Some metals like aluminum don't fatigue the same way as steel, but tend to fail much more suddenly and dramatically. It's been over a quarter decade (edit - century) since I took Strengths of Materials or Mechanics of Materials in engineering school, but that's my recollection.

For something held under constant load, it can also permanently deform or creep, which you would see as a sag in the spring or a reduction in ride height along with an apparent reduction in spring rate. Combine these two, and I can see how the ride would go downhill after years of use, especially for a relatively compact torsion bar. I'm surprised more trucks don't use coil springs where you can distribute the load across many more feet of spring steel, but I suppose there are other considerations like cost and packing it all in there somewhere to consider too.

If the ride actually stiffened, which my mechanical engineer friend highly doubts...he also used to have a GM 3/4T with torsion bars...you would never feel the difference from "work hardening". If anything, he said the torsion bar would actually get less stiff over time.

The good thing...a torsion bar is $200 per side and takes about an hour to replace.

jhnmdahl wrote: Tue Jul 30, 2024 9:20 amI'm surprised more trucks don't use coil springs where you can distribute the load across many more feet of spring steel,

The GM torsion bars are 56" long...that's a lot of steel.

jhnmdahl wrote: Tue Jul 30, 2024 9:20 am It's been over a quarter decade

Did you mean a quarter century?

Good point, Bruce. Measured some sedan springs in my garage out of curiosity, and 5.5 turns of 5" diameter coil is only about 86" - less of a difference than I thought. Biggest difference is that the coil spring is effectively being bent instead of twisted to provide spring resistance.

Titaniumboy wrote: Tue Jul 30, 2024 3:52 pm

jhnmdahl wrote: Tue Jul 30, 2024 9:20 am It's been over a quarter decade

Did you mean a quarter century?

Yeah, I'm old. And, because I'm old.

I guess one can look for a reason. For me it’s experience. There are big reasons Ford and Ram prefer the live axle instead of torsion.

Love it when old threads pop up!
Actually in an odd way our torsion GM trucks “do get stiffer in time”.

What you say??

It was explained years ago by a GM engineer on trucks settled on one side with torsion load suspension.

it’s actually fatigue over cycles that allows the metal to yeld at its extension points.

Thus the vehicle is actually becoming less supported at ride height and slowlllyyyy lowering itself.
It’s the compression and rebound characteristics that go flat and then.
Even more on the snubber than usual.
Stiff ride.

Just my .03 cents

cmattj wrote: Thu Aug 01, 2024 3:13 pmThus the vehicle is actually becoming less supported at ride height and slowlllyyyy lowering itself.
It’s the compression and rebound characteristics that go flat and then.
Even more on the snubber than usual.
Stiff ride.

Just my .03 cents

That makes WAY more sense that the torsion bar getting stiffer.

Talked to a guy that works for GM the other day. He said torsion bars sag over time...they do not harden. He also says the main reason Ford and RAM use a solid front axle is because it's cheaper!

Man if I was towing big toys diesel is the only way to go. T5billion just towed 26 hrs with a 3500 chevy durtymax! What a rig cameras all over the place to help you turn and watching your trailer while turning. Only way to go. They are so smooth and so quiet. After working at Gm and Ram I would go with Ram all day long. FORD sorry. Don't like but thats me and a chime thing! The extra torque towing up a mountain is easy better then any gasser.

So I have towed 11hrs to TRL 5 times and never a issue for my hemi in the Durango I love the power. To me it out pulls the 6.2 in the GM vehicles.
But what the small SUV lacks is a frame which Dodge is addressing in the next generation models. When a truck passes you or you pass a truck the vehicle moves around. I really am not fond of that.
The brakes are fine they are large and can stop on a dime. I have a 7200lbs tow rating and I'm at around 6000 and it handles it just fine. Here's a picture on the day that I just went to TRL

bruceb58 wrote: Thu Aug 01, 2024 6:18 pm

cmattj wrote: Thu Aug 01, 2024 3:13 pmThus the vehicle is actually becoming less supported at ride height and slowlllyyyy lowering itself.
It’s the compression and rebound characteristics that go flat and then.
Even more on the snubber than usual.
Stiff ride.

Just my .03 cents

That makes WAY more sense that the torsion bar getting stiffer.

Talked to a guy that works for GM the other day. He said torsion bars sag over time...they do not harden. He also says the main reason Ford and RAM use a solid front axle is because it's cheaper!

Yes. You got it Bruce.
As I just shared with you that GM engineers have explained the settling or sag as well.
It’s actually sag to stiff.

Like a bolt that’s is measured for stretch upon torquing it down. , it’s twist.
Then snap at its brittle or stiffest point.
As the torsion bar twists over time it is actually on the verge of breaking as it’s settled to max yield and can’t rebound anymore.
Cranking up the torsion bars give a hard ride for the same reason.
So yes metal will get stiff before it’s breaking point can’t be extended.

I really don’t know much about Ford and Ram costs .
I feel the ride quality is better in there HD truck as a coil over using a standard shock to rebound and compress is always a car ride.

Tomorrow we will discuss pinion angle change when overloading and driveshaft harmonics causing issues when towing .$$

cmattj wrote: Thu Aug 01, 2024 8:11 pm

bruceb58 wrote: Thu Aug 01, 2024 6:18 pm

cmattj wrote: Thu Aug 01, 2024 3:13 pmThus the vehicle is actually becoming less supported at ride height and slowlllyyyy lowering itself.
It’s the compression and rebound characteristics that go flat and then.
Even more on the snubber than usual.
Stiff ride.

Just my .03 cents

That makes WAY more sense that the torsion bar getting stiffer.

Talked to a guy that works for GM the other day. He said torsion bars sag over time...they do not harden. He also says the main reason Ford and RAM use a solid front axle is because it's cheaper!

Tomorrow we will discuss pinion angle change when overloading and driveshaft harmonics causing issues when towing .$$

As someone who has overloaded their F150 towing I am here for this!

Let me know when class starts.

As always Matt you have demonstrated you have forgotten more about many items that I could ever hope to know.

Unless we are talking Computers / IT / Bourbon or Turtles, then I may win? Maybe?