Developing a Proper Suspension Model

[7thgear]

is this the only source of an OEM damper dyno?

Originally Posted by u/Josh

[7thgear]

@Racecomp Engineering
@Shankenstein

Can you guys confirm that the information in the 1st post has been peer reviewed and can be taken as absolute fact, particularly the OEM weight distributions and motion ratios and damper travels.

[Racecomp Engineering]

Originally Posted by 7thgear

is this the only source of an OEM damper dyno?

We posted one very early on, not in this thread but somewhere. It looks similar.

EDIT: it's in post one here.

I looked through everything on page 1 the other day (see when I caught a typo) and everything looks pretty good.

- Andy

[7thgear]

Originally Posted by Racecomp Engineering

We posted one very early on, not in this thread but somewhere. It looks similar.

EDIT: it's in post one here.

- Andy

thank you

if possible, can it be posted in its original medium (so that it could easily be overlayed over another graph)

[Racecomp Engineering]

I'll see what I can do later today.

- Andy

[dezmoondo]

Originally Posted by pseudo

Great looking thread, guys. Kudos to @Shankenstein for starting this and adding a lot of useful information.


I stumbled upon this while looking for a computational model of the BRZ suspension. I am a mathematician with a slight theoretical physics background and strong computer science skills. So not much engineering experience.

Does anyone have suggestions on a resource for rapidly learning the ME side of a good suspension setup? Specifically what the ultimate, theoretical goals of an ideal setup are, and the fundamental theory that drives suspension design. Books, technical papers, online articles, forum posts, etc would all be appreciated.


I would be happy to help out with this project once I get up to speed, looks like it's off to a great start!

You can read Tune to Win by Carroll Smith. There's a section for suspension geometry.


Sent from my iPhone using Tapatalk

[Shankenstein]

Originally Posted by 7thgear

@Racecomp Engineering
@Shankenstein

Can you guys confirm that the information in the 1st post has been peer reviewed and can be taken as absolute fact, particularly the OEM weight distributions and motion ratios and damper travels.

The usual legal mumbo jumbo.

Shankenstein shall not be held liable for any personal or business decisions made using information supplied to this or any other website. Although Shankenstein may be a licensed engineer, Shankenstein has never been contracted by FT86Club or any other entity (private or public) to disseminate accurate information in this thread or others on this site. Any confidence in Shankenstein's posts should be tempered by the fact that Shankenstein is probably tired, daydreaming, at work, and/or drooling over build logs while posting.

That being said, the vast majority of the information has been read over numerous times by people smarter than me. It should be more accurate than most forum posts, if that counts for diddly squat.

[7thgear]

Well, i was simply hoping for more peer-editing

particularly when it comes to motion ratios. I've yet to find anyone diagraming the suspension piecemetal.


Two weeks ago i took apart the rear coilover and attached the damper back to the car without the spring.

I then took measurements of how much the wheel travelled vs how much the damper shaft travelled and got some wild results.

even accounting for measurement error, i could not get close to the 0.75 figure ( was averaging around 0.85 ish).

Furthermore i would get different results depending on where along the path i measured. Full droop to oem height i averaged around 0.9.. from OEM height along about 1.5" of compression i averaged 0.80ish (need to check my notes, its been two weeks)

now i'm curious...

[Wepeel]

Originally Posted by 7thgear

Well, i was simply hoping for more peer-editing

particularly when it comes to motion ratios. I've yet to find anyone diagraming the suspension piecemetal.


Two weeks ago i took apart the rear coilover and attached the damper back to the car without the spring.

I then took measurements of how much the wheel travelled vs how much the damper shaft travelled and got some wild results.

even accounting for measurement error, i could not get close to the 0.75 figure ( was averaging around 0.85 ish).

Furthermore i would get different results depending on where along the path i measured. Full droop to oem height i averaged around 0.9.. from OEM height along about 1.5" of compression i averaged 0.80ish (need to check my notes, its been two weeks)

now i'm curious...

This is the best way to do it. And yes, it will change throughout the range - it's mostly relevant at ride height +/-[however much travel you expect to see]. So maybe +/- 1". The motion ratio will be greatest (i.e. greatest difference between wheel travel and shock travel) when the lower arm is near horizontal, which is near reasonable ranges of ride heights, so your numbers make sense, should be close to the "analytical" MR of 0.78 that I measured (you said 0.80ish, I'd be interested to see your exact numbers, but I'd say that's pretty close).

Did you do the same thing for the fronts?

[7thgear]

Originally Posted by Wepeel

This is the best way to do it. And yes, it will change throughout the range - it's mostly relevant at ride height +/-[however much travel you expect to see]. So maybe +/- 1". The motion ratio will be greatest (i.e. greatest difference between wheel travel and shock travel) when the lower arm is near horizontal, which is near reasonable ranges of ride heights, so your numbers make sense, should be close to the "analytical" MR of 0.78 that I measured (you said 0.80ish, I'd be interested to see your exact numbers, but I'd say that's pretty close).

Did you do the same thing for the fronts?

hoping will have time to do the fronts next week. I can only work at my parents place because i am forbidden to do car work at my apartament.

This was my first time taking apart the FRS suspension components so it took longer than anticipated. The Strutted impreza and also my old VW were much, much easier.

[Racecomp Engineering]

As Wepeel said it does change throughout the range.

0.8 is very close at ride height. 0.75 in that thread is not exact, I meant it to be a simplified example. I should have mentioned it was not exactly 0.75 in retrospect.

- Andy

[Shankenstein]

Originally Posted by 7thgear

Well, i was simply hoping for more peer-editing

particularly when it comes to motion ratios. I've yet to find anyone diagraming the suspension piecemetal.


Two weeks ago i took apart the rear coilover and attached the damper back to the car without the spring.

I then took measurements of how much the wheel travelled vs how much the damper shaft travelled and got some wild results.

even accounting for measurement error, i could not get close to the 0.75 figure ( was averaging around 0.85 ish).

Furthermore i would get different results depending on where along the path i measured. Full droop to oem height i averaged around 0.9.. from OEM height along about 1.5" of compression i averaged 0.80ish (need to check my notes, its been two weeks)

now i'm curious...

The feedback is much appreciated. I've added the following:

Rear = 0.85 (at full droop) to 0.83 (at stock height) to 0.80 (compressed to bumpstops)

Since I can't vouch for the accuracy of either you or RCE, I split the difference and tried to make it clear that the value changes. Constants are for suckers anyways.

[7thgear]

Originally Posted by Wepeel

(you said 0.80ish, I'd be interested to see your exact numbers, but I'd say that's pretty close).

Did you do the same thing for the fronts?

accordinging to my notes, 0.8~0.82 motion ratio from OEM heigh through ~31 mm of damper shaft compression in the rear

also if i was to eyeball it i would say the rear bumpstops are engaged after about 8-9mm of compression... yikes.

[jeepmor]

subbed, good stuff. Thanks for posting.