Houston we have a problem! (the bent frame thread)

[Bad company]

Bad company, when you compare the kickers to jumps, is that comparing the suspension compressed cycle speed? Are the forces also equal at that point?

What I was trying to quantify is the energy in the impulse when the axle bottoms out against the frame rails.

There is a ton going on here, and you have to make some assumptions. However at high speed, when you hit a kicker AND it is big enough to bottom out the suspension, you create an impact between the axle (moving up) and the frame (holding steady more or less due to its own inertia).

What is equal in the two cases is the relative velocity between the frame and the axle. The reason why you can compare forces is because in both cases the axle is accelerating the frame upwards, and acting on the same mass (the truck itself) with the SAME relative motion forced by the ground moving upwards relative to the truck. In one case the truck's relative motion is caused by a fall (acceleration due to gravity), in the other the relative motion is caused by the tires being forced upwards by a bump.

Where the two comparisons begin to differ is that after the kicker is cleared, the suspension recovers, however, on a 56' drop it does not. So the comparison is valid only in this case for the first 12" (or height of compacted kicker) of relative displacement, which is plenty to deform the frame. In other words, the forces are equal for the first 12" of displacement. The mass being accelerated is the same (the truck minus the suspension and tires), the acceleration is the same (defined by the suspension geometry and materials), therefore the forces are equal.

Make sense?

I calculated the speed at which the suspension is being compressed, and determined from what height the truck would have to fall to generate that relative velocity.

 

[BlueSVT]

Although that is the same "Velocity" as you say... there would be MUCH more actual "load" on the frame at that same point if it were dropped, as oppose to this scenario which is instant shock, followed by no additional force by the weight of the truck, etc... It's definitely not comparably to "Actually" dropping a truck 56 feet, as we all know the outcome of that! haha

I can forsee more than just a slightly tweaked frame with an additional 6000lbs of force in play!

 

[pirate air]

What I was trying to quantify is the energy in the impulse when the axle bottoms out against the frame rails.

There is a ton going on here, and you have to make some assumptions. However at high speed, when you hit a kicker AND it is big enough to bottom out the suspension, you create an impact between the axle (moving up) and the frame (holding steady more or less due to its own inertia).

What is equal in the two cases is the relative velocity between the frame and the axle. The reason why you can compare forces is because in both cases the axle is accelerating the frame upwards, and acting on the same mass (the truck itself) with the SAME relative motion forced by the ground moving upwards relative to the truck. In one case the truck's relative motion is caused by a fall (acceleration due to gravity), in the other the relative motion is caused by the tires being forced upwards by a bump.

Where the two comparisons begin to differ is that after the kicker is cleared, the suspension recovers, however, on a 56' drop it does not. So the comparison is valid only in this case for the first 12" (or height of compacted kicker) of relative displacement, which is plenty to deform the frame. In other words, the forces are equal for the first 12" of displacement. The mass being accelerated is the same (the truck minus the suspension and tires), the acceleration is the same (defined by the suspension geometry and materials), therefore the forces are equal.

Make sense?

I calculated the speed at which the suspension is being compressed, and determined from what height the truck would have to fall to generate that relative velocity.

Makes sense. In both cases, mass, acceleration, and time are roughly the same. I had to re think a few times doh2. Thanks

 

[pirate air]

Just sayin...

I think someone is being facetious........ Traitor!!

 

[Madcowranch]

I think someone is being facetious........ Traitor!!

Clever, witty, humorous, or jocular maybe. But never facetious.

 

[relicdog]

recall issue

I have a supercab built 4-7-2011 it has old driveshaft part # ending in
AB which should be replaced according to man at SVT, although there
was a fix implemented some time mid March. My question is could I have
updated driveshaft with old part #, any info would be great.

 

[gotSVT]

Just be glad we have fully boxed frames instead of those inferior Toyota C-channel frames that FLEX.

Yeah that's the problem. No box where it "flexed".

 

[Bad company]

Given the loads, it will flex, period. Maybe if the cross section was 3/8" it wouldn't flex, but then your axle would break.

The load conditions are extreme!

 

[Dr Tone]

If you truck is built after the TSB date you are fine.

I have the old model numbers as well built after the date and no clunk.

 

[Bad company]

Although that is the same "Velocity" as you say... there would be MUCH more actual "load" on the frame at that same point if it were dropped, as oppose to this scenario which is instant shock, followed by no additional force by the weight of the truck, etc... It's definitely not comparably to "Actually" dropping a truck 56 feet, as we all know the outcome of that! haha

I can forsee more than just a slightly tweaked frame with an additional 6000lbs of force in play!

The 6,000 pounds (maybe less than half on the rear axle) is in play for both cases. In one case (the drop) the suspension is trying to act on the truck's mass by decelerating it from ~60 ft/s downward to zero (at rest).

In the other case (the kicker), the suspension is trying to accelerate the truck frame from 0 to 60 ft/s upward.

The masses are equivalent, the accelerations are equivalent, therfore the forces are equal. This is valid for the entire height of the bump.