Droop Limiting and Bumps.

[7uptruckracer]

here is something to try that might help some one understand what im doing a little better, put car on scales with ride heights close, now remove rt frt spring and let it down on bump , now set your rear neutral (no bite) , now put spring back in and look at how much your bite is now, you would be surprised. mine is way more than i ever ran on conventional rt frt spring. im not gone tell every thing im doing on here , but i think around 50 lbs of bite on the bump is a good starting point and work on that mid turn throttle push by adjusting bars. JMO

We all know dynamic ride height changes changes bite. I try to set it at dynamic heights and see where the cross is migrating. Things to keep in mind. Are my bump or stack setup for wheel loading or travel limitation. Its good to know where dynamic bite is going and with some of the new tools you can simulate rear end loading into the equation as well with pull down rigs and actuators on the lift arm etc On asphalt we get the static loads then depending on the bump setup set the car on the bumps, account for tire sqrunch and check valance clearance and you can add or subtract shims ot change dynamic bite on the bumps or total clearance if you are too high or low. In short its all about shop work and the more you know and try to more things you can rule out or go into deeper

[Matt49]

I'm seeing the word "dynamic" a lot but none of what is being described actually simulates the "dynamics" that happen on the race track. Ride height changes on the race track because of induced forces (deceleration, engine torque, centrifugal, etc.) not because a spring got pulled out or an arm got moved. These induced forces have a very real impact on the loading of each tire and that can't be simulated sitting in the shop regardless of how many pull downs and jacks you have. I'm not saying there isn't something to be learned by doing this stuff but to think that it simulates some on-track situation seems like nonsense to me.

[7uptruckracer]

I'm seeing the word "dynamic" a lot but none of what is being described actually simulates the "dynamics" that happen on the race track. Ride height changes on the race track because of induced forces (deceleration, engine torque, centrifugal, etc.) not because a spring got pulled out or an arm got moved. These induced forces have a very real impact on the loading of each tire and that can't be simulated sitting in the shop regardless of how many pull downs and jacks you have. I'm not saying there isn't something to be learned by doing this stuff but to think that it simulates some on-track situation seems like nonsense to me.

Some guys are using actuators on the lift arms and pullbars to simulate engine torque that is supposed to load the rear tires like engine torque would I think I mentioned it in my post but Ive seen it on the pull down Rig you also have to account for lateral forces that are hard to simulate and aero

[Mr.Kennedy777]

Matt49, you can actually simulate lateral loading on a pull down rig. I think. Here is my idea. Lol. You need an accelerometer or a g force meter and a TPS and BPS in your car on a test day, maybe put a go pro in the thing and have it watch the meter so you can pay attention and drive the car hard. You will need to figure out what your baseline for banking will be. You will also need to figure out the exact centre of gravity on your car. You can determine lateral and longitudinal location by static scale numbers and you can figure out the height if you replace all your coils and shocks (including the 5th coil and 6th coil) with solid bars, place the car on scales and lift each end. There's some formulas that you can run that give you CG height based on the scale number changes. The higher each end can get lifted the better. From that point you'll need to mount a clevice of some kind so that you can attach a cable and a winch. Your cornering force is almost never at 90 degrees so the rig will have to tilt to simulate banking. Put a pull scale on the winch and cable on the car and apply the force you need to the center of gravity. You might need to make a better surface to keep the car from sliding off (this can be done). if you really wanna get carried away you could install wheel dyno on pads on the rear with a track so the LR and RR tires could move while you rev the crap out of the car. it would be quite the endeavour and while technically what I am talking about isnt really a pull down rig, you could probably just run a tilt on a pull down rig and use the pull scale and cable at CG to get somewhat close. The other thing is the torque from the rear end always tries to push the LR down and unload the RR, due to its rotation, while at the front trying to lift the LF and load the RF. so to get real dynamics you need the car on scales while it's running under load as well as applying force to CG AND aero, so you would need to simulate a surface under the car as well. THEN you would need to have this entire setup on a four post shaker as well as the rest so you could simulate wheel loads not just on a smooth surface but to see what happens over imperfections.

[Mr.Kennedy777]

Oh and instead of a cable/winch pull scale you could use a pendulum style hydraulic arm that could apply not only lateral force but forward and rearward force to, to simulate braking and acceleration.