Developing a Proper Suspension Model

[AlexTheGreek]

Originally Posted by neurokinetik

If I am thinking correctly here, I think the R variable is supposed to be the axial distance from the center of the swaybar to the center of whichever mounting hole you are using (in case of an adjustable bar). Think of it like attaching a lever to the end of a pipe, and the measurement would be as if you are looking straight down that pipe and taking the measurement of the length of the lever that way. So that means that using the Miata figures will not be accurate.

The motion ratio should be calculated by measuring the distance from the inner control arm pivot point to the swaybar endlink mounting point, and comparing that to the length of the entire control arm. It probably also won't be 0.6, as it is on a Miata.

Also keep in mind that the motion ratio is not a constant value. It will vary with wheel travel. This is one of the benefits of kinematic solvers because they will plot the motion ratio vs. wheel travel/shock travel curve.

To clarify what I'm talking about think of a piston vs. a crank shaft. the piston position is not a direct ratio of the crank postiion. Similarly, the rotation of the anti-roll bar won't be a direct linear relationship of the wheel travel (or wheel travel deltas).

[Shankenstein]

u/Josh and @mad_sb, Thanks for all the contributions guys! I'll update the original post.

@AlexTheGreek, I appreciate the kind words. I am indeed a "he".

@plucas, As much as I love open source... MATLAB is just a superior program in terms of functionality (toolboxes) and coding efficiency (multi-core utility). If it's a commercial project, and buying a $2k license is overkill... Octave is the way to go.

@MrH, would you be willing to share the m-file with the group? I'll dig through it and maybe someone can get it running in Octave

Lonely Sushi , I've always been taught that sway bars are a band-aid... albeit a very useful bandaid. If you can get the proper wheel rate without sway bars, the car can articulate across bumps more effectively.

Using soft springs and thicker sway bars (as modern vehicles do) gives you a sporty roll rate without the NVH of stiff springs. The other benefit is that (with certain geometries) the vehicle feels like it's "biting in" during turns which modern manufacturers seem to value highly. For me, I'd prefer the wheel dynamics to be as uncoupled as possible (so minimal sway bars).

Certain racing leagues (ex: SCCA) may not let you change springs for certain classes, but sway bars can be upsized. This does boost the wheel rate, but these cars have trouble staying at their performance limit in cambered turns or rough pavement.

[Lonely Sushi]

Thanks for the explanation. When I say softer springs I do mean having the proper wheel rate before all else, just not too crazy with it (a lot of locals here go by "it feels stiff" = "it handles" and go way too crazy with their spring rates). But having the roll bar (adjustable one at that) to tune the characteristic of the vehicle is quite major to me rather than view it as a band aid.

Anyways, back to the topic of building a model I just realize you said the dimensions you posted are estimates from pictures? maybe I should find another time to try and use pumb bobs to measure the pick up points to compare the result with yours

[robispec]

A little note on the "band aids". Because a car with a strut suspension has so much trouble finding enough camber gain in roll, and a high spring rate on the inside tire not resisted by a swaybar tends to jack the inside tire down in droop (making this even worse). I use sways to combat the overall lean angle. This is especially so with cars that use strut suspension front and rear...just experiance with the real world talking here.. lol

[zohare]

Updates anyone?

I'm looking forward to this. A miata vet gave me some numbers for how to set my coilovers when I install them, and some alignment numbers to hit. I haven't had the time to get them in yet, but I own a 94, which I replicated in Forza (don't laugh, it's a *decent* simulator) and drove with what I THOUGHT were good settings, then his, and shaved nearly a second or more off of laps, and at the limit, the exits were SO much better. For the NA miata, he recommended running NO or stock rear sway bar, which sounded weird, but he stands by it for lower powered miatas and claims that if springs and dampers are adjusted correctly, all will be well, and Forza said he was right. Anyhow, I'm trying to read this, but to even understand this thread, will take me months of research and learning. Regardless-
I am curious what the "ideal" setup will be. I'm not going to be buying suspension till I get the advice here that I've had in the Miata community. People smarter than me helping me out haha. Thanks a ton everyone. I'll learn what I can and try and contribute eventually....

[EarlQHan]

Originally Posted by zohare

Updates anyone?

I'm looking forward to this. A miata vet gave me some numbers for how to set my coilovers when I install them, and some alignment numbers to hit. I haven't had the time to get them in yet, but I own a 94, which I replicated in Forza (don't laugh, it's a *decent* simulator) and drove with what I THOUGHT were good settings, then his, and shaved nearly a second or more off of laps, and at the limit, the exits were SO much better. For the NA miata, he recommended running NO or stock rear sway bar, which sounded weird, but he stands by it for lower powered miatas and claims that if springs and dampers are adjusted correctly, all will be well, and Forza said he was right. Anyhow, I'm trying to read this, but to even understand this thread, will take me months of research and learning. Regardless-
I am curious what the "ideal" setup will be. I'm not going to be buying suspension till I get the advice here that I've had in the Miata community. People smarter than me helping me out haha. Thanks a ton everyone. I'll learn what I can and try and contribute eventually....

Forza is a good simulation for getting setup ideas.

This may not be the answer you were expecting, but I believe it largely depends on the track. The tuning of your parts will also have to be based on driver preference. While a specific setup may not be the fastest one possible, if you are more comfortable with it, you will be faster around the track.

[Huehuecoyotl]

Models are one thing and provide a 'departure point' but this can be way the heck off too...

adapting to your tires, track, climate etc are another can or worms

[zohare]

Originally Posted by EarlQHan

Forza is a good simulation for getting setup ideas.

This may not be the answer you were expecting, but I believe it largely depends on the track. The tuning of your parts will also have to be based on driver preference. While a specific setup may not be the fastest one possible, if you are more comfortable with it, you will be faster around the track.

Originally Posted by Huehuecoyotl

Models are one thing and provide a 'departure point' but this can be way the heck off too...

adapting to your tires, track, climate etc are another can or worms

Ok. Figured. More looking for a good baseline to start at. Looking at going with Ceika Coilovers, which are made to order. Check em out. Might bite a bullet and try one of their BBKs too. The IS300 and supra guys seem familiar and haven't had any issues. Biggest downside is the cost of pads and rotors compared to a Wilwood kit. But at least for the coilovers, I could choose what damping rates and such I want, which might be better than some or worse. As it is always said, am I really going to be able to make a better choice than a company that has thousands in R&D and hours on a track? Probably not. The idea is still tempting...

[Huehuecoyotl]

I've got a setup I'm proving each time I track, and pretty happy with where its at. Soon i will try and get out to play with some other properly built cars I see floating around in SoCal to see what fine tuning is needed. I am of the opinion there are two slightly different schools of setup thought, drift and grip, and everything in between so be careful who you listen to as it can be good or bad advice depending on what you want.

[Gunman]

Originally Posted by andrew20195

Of course, with soft springs and stiff sway bars, you might end up with more dive and possibly more squat than you want for ideal handling on a track, especially with sticky tires.

Then you can go more exotic with a third spring on the bar, to resist dive. I wouldn't suggest this for the at home tuner.

[robispec]

Originally Posted by Gunman

Then you can go more exotic with a third spring on the bar, to resist dive. I wouldn't suggest this for the at home tuner.

or go with a front lower control arm solution that resists dive (and is adjustable so you get the anti dive that you want..).

but that is just one more thing to tune i guess...lol

[Gunman]

Originally Posted by robispec

or go with a front lower control arm solution that resists dive (and is adjustable so you get the anti dive that you want..).

but that is just one more thing to tune i guess...lol

Suspension tuning is much like a can of worms

[EarlQHan]

Originally Posted by Huehuecoyotl

Models are one thing and provide a 'departure point' but this can be way the heck off too...

adapting to your tires, track, climate etc are another can or worms

Valid points, but a good model will take all those in to consideration. With Forza, you cannot change those aspects, but it's still useful to get ideas. It's not meant to give you the exact setup sheet.

Originally Posted by Huehuecoyotl

I've got a setup I'm proving each time I track, and pretty happy with where its at. Soon i will try and get out to play with some other properly built cars I see floating around in SoCal to see what fine tuning is needed. I am of the opinion there are two slightly different schools of setup thought, drift and grip, and everything in between so be careful who you listen to as it can be good or bad advice depending on what you want.

Good drift setups aren't that different from grip setups at the suspension level. It's not all stiff rear oversteer like people believe it to be. They will actually tend to understeer at corner entry. High powered drift cars will actually be quite soft in the rear to get traction under throttle application. Where they largely diverge is in the drivetrain. They use a much more aggressive differential setting to get the rear wheels to lock.

Originally Posted by zohare

Ok. Figured. More looking for a good baseline to start at. Looking at going with Ceika Coilovers, which are made to order. Check em out. Might bite a bullet and try one of their BBKs too. The IS300 and supra guys seem familiar and haven't had any issues. Biggest downside is the cost of pads and rotors compared to a Wilwood kit. But at least for the coilovers, I could choose what damping rates and such I want, which might be better than some or worse. As it is always said, am I really going to be able to make a better choice than a company that has thousands in R&D and hours on a track? Probably not. The idea is still tempting...

You may want to ask in the general suspension section about specific brands; this thread is for the nerds who want to theorize, analyze, and bounce ideas off each other.

Originally Posted by Gunman

Then you can go more exotic with a third spring on the bar, to resist dive. I wouldn't suggest this for the at home tuner.

That would be extremely challenging to package on the front, you'd probably have to ditch the MacP system altogether lol. The rear wouldn't be as bad.

Originally Posted by robispec

or go with a front lower control arm solution that resists dive (and is adjustable so you get the anti dive that you want..).

but that is just one more thing to tune i guess...lol

Antis are very appealing from an engineering point if you can get it right. I've heard a few driver complaints though, saying they lose feel if the anti is too aggressive, due to forces being transmitted through the arms rather than the dampers. However, I cannot verify since I've not aggressively changed the anti on my personal car. Did you notice a change in feel?

Originally Posted by Gunman

Suspension tuning is much like a can of worms

lol, can of worms is easy. Finding the right setup is more like finding a needle in a stack of needles.

[robispec]

Originally Posted by EarlQHan

Antis are very appealing from an engineering point if you can get it right. I've heard a few driver complaints though, saying they lose feel if the anti is too aggressive, due to forces being transmitted through the arms rather than the dampers. However, I cannot verify since I've not aggressively changed the anti on my personal car. Did you notice a change in feel?

Yes the front tire planted better without the front end nosing down so hard.