Developing a Proper Suspension Model

[RBbugBITme]

I think only a few hundred a year plus the computer/RAM/GPU to handle some of the file sizes, and CAD software.

[7thgear]

Originally Posted by fika84

I also wonder what sort of adjustments (for better or worse) the roll center correction kits for this car do.

for all mass production macstrut vehicles roll adjustment kits are, imo, a universal good to a balanced degree


and more so for lowered cars (usually returning the geometry to OEM levels)




ideally you want a custom made tubular crossmember, front and rear, for ultimate customization (what those rally cars have).

Funny thing is, making a production car like this is easy peazy, but they will be so capable that they'll offer no fear for average drivers and they'd just crash in the canyons.

[Thorpedo]

Does anyone have any information in regards to the actual amount of roll we see? (yes, I know it is car specific dependent on modifications and conditions) I have a fender video from last year's autocross season that shows what looks like 3-4" of roll total if turning left to right. This was with 245-40 200TW tires and the strano front bar.

Now that I have my coilovers and I'm lowered it would presumably be much less, I'm guessing in the range of 2.5" based on watching others run my car around the track. This may be a HUGE oversimplification, but are we aiming to have the outside tire flat on the ground while cornering?

Edit: after doing some reading it seems the increased spring rate is probably offset by the by the leverage of the center of gravity over the roll center. I'll shut up until i have a deeper understanding.

[Amaya]

I have a question about suspension design and it probably requires too large of an answer but here goes. What values of caster, camber, etc are optimal throughout the range of motion of the suspension? I'm guessing this is determined by tires, body roll and forces expected at given angles.

[7thgear]

Originally Posted by Amaya

I have a question about suspension design and it probably requires too large of an answer but here goes. What values of caster, camber, etc are optimal throughout the range of motion of the suspension? I'm guessing this is determined by tires, body roll and forces expected at given angles.

optimal dynamic camber (ie, the instantaneous camber the tire has with the road) is determined by the tire manufacturer, but it is generally in the ever so slightly negative value.

in cars where dynamic camber cannot be maintained optimally, static camber is setup so that the average is optimal for the situation (tire)


castor plays into handling characteristics, a car driven on 0 castor and 10 castor are going to feel noticeably different

and also plays into the dynamic camber change during steering.

"optimal" is a matter of setting the car up to give you confidence and control while maximizing grip.. so the answer is "it depends" :p

[fika84]

Right on! I cant read your text without doing it in Sheldon's voice btw.

It would be nice if Ryan could rerun the sims with the roll center correction kit locations adjusted to see how it affects things and see if the roll center is still jumping above and below ground.

Originally Posted by 7thgear

for all mass production macstrut vehicles roll adjustment kits are, imo, a universal good to a balanced degree


and more so for lowered cars (usually returning the geometry to OEM levels)




ideally you want a custom made tubular crossmember, front and rear, for ultimate customization (what those rally cars have).

Funny thing is, making a production car like this is easy peazy, but they will be so capable that they'll offer no fear for average drivers and they'd just crash in the canyons.

[fika84]

Originally Posted by Amaya

I have a question about suspension design and it probably requires too large of an answer but here goes. What values of caster, camber, etc are optimal throughout the range of motion of the suspension? I'm guessing this is determined by tires, body roll and forces expected at given angles.

Your guesses are right. Typically you want to adjust a car around the tires to have maximum lateral forces capable for a given track. Everything is a compromise. You might benefit a lot by having a lot of camber in the corners, but you will lose under braking and acceleration for example. Its best to setup the car depending on the track and do lots of simulations beforehand if possible because track time and tires are expensive!

[fika84]

Castor changes the force required to steer as well

Originally Posted by 7thgear

optimal dynamic camber (ie, the instantaneous camber the tire has with the road) is determined by the tire manufacturer, but it is generally in the ever so slightly negative value.

in cars where dynamic camber cannot be maintained optimally, static camber is setup so that the average is optimal for the situation (tire)


castor plays into handling characteristics, a car driven on 0 castor and 10 castor are going to feel noticeably different

and also plays into the dynamic camber change during steering.

"optimal" is a matter of setting the car up to give you confidence and control while maximizing grip.. so the answer is "it depends" :p

[Amaya]

Originally Posted by 7thgear

optimal dynamic camber (ie, the instantaneous camber the tire has with the road) is determined by the tire manufacturer, but it is generally in the ever so slightly negative value.

in cars where dynamic camber cannot be maintained optimally, static camber is setup so that the average is optimal for the situation (tire)


castor plays into handling characteristics, a car driven on 0 castor and 10 castor are going to feel noticeably different

and also plays into the dynamic camber change during steering.

"optimal" is a matter of setting the car up to give you confidence and control while maximizing grip.. so the answer is "it depends" :p

Thanks for the quick reply and ya I figured "it depends" would figure into the answer :p there's just so many variables that have to be accounted for.
Where do you find manufacturers recommended camber values?

[RBbugBITme]

Originally Posted by Racecomp Engineering

Ryan, can you post the front view of the car at a 1 inch drop? It might clarify what you mean about roll center location at that height...

- Andy

Here is what I was talking about with the instant centers flipping the side of the car its on. 1" drop with one image at -.983 deg of roll and the other at -.984 deg of roll. May not be a huge deal but its weird.




I'll get to some other stuff later.

[fika84]

Originally Posted by Amaya

Thanks for the quick reply and ya I figured "it depends" would figure into the answer :p there's just so many variables that have to be accounted for.
Where do you find manufacturers recommended camber values?

I doubt a manufacturer is going to give you a recommended camber value. It's going to change depending on what goals you have. When I was working as a vehicle dynamics engineer we would go to Calspan and test the tires we wanted to model on a tire testing machine, fit a Pacejka model and use it in simulations to determine optimum setups per track. Tire manufacturers do this testing in house typically keep it hush hush.

[RBbugBITme]

Yeah, tire data is as rare as a unicorn. You literally have to buy tons of sets yourself and run the same track over and over at different settings with shock pots and g-meters to get any real understanding of whats going on. That's on top of having the suspension modeled accurately.

[Amaya]

Originally Posted by fika84

I doubt a manufacturer is going to give you a recommended camber value. It's going to change depending on what goals you have. When I was working as a vehicle dynamics engineer we would go to Calspan and test the tires we wanted to model on a tire testing machine, fit a Pacejka model and use it in simulations to determine optimum setups per track. Tire manufacturers do this testing in house typically keep it hush hush.

I figured that would be the case

[RBbugBITme]

Originally Posted by Thorpedo

Does anyone have any information in regards to the actual amount of roll we see?

This can be calculated... Its very basic math, you just need to gather all the required information.