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.

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

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.

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.

subbed, good stuff. Thanks for posting.

Race Car Vehicle Dynamics

http://books.sae.org/r-146/;

[ame="http://www.amazon.com/Race-Vehicle-Dynamics-R146-Publisher/dp/B004XEA3E2"]Race Car Vehicle Dynamics (R146) Publisher: Society of Automotive Engineers Inc: William F. Milliken: Amazon.com: Books[/ame]


The author's page on the book with links to further information, including a separate 300-page companion workbook, software, etc.: http://www.millikenresearch.com/rcvd.html.

How do we figure out how much change in toe dude to ride height change with the numbers that shankenstine gathered for this car? I ask this because I have been measuring strange changes in rear toe dude to adding and removing weight of the factory muffler assembly and fuel levels.

Honestly, you'd need to refine the data if you wanted accurate toe curves. Especially at the top and bottom of your travel, minor errors in the "points" will give you major errors in geometry... and there are some minor errors in the data (to say the least).

The thought is with an open-source spot for the information, the Google Doc will evolve as people discover more and more accurate data. With the car being so new, there aren't many "grassroots" projects yet... but I have no doubt there will be plenty of people to over-analyze this car.

One potential twist for the thread that I've been scheming would be to use 3D scanners to generate full CAD models for each component. Assemble and constrain the system in Solidworks or Pro/E. Go as nuts with the simulations as you'd like. Design lighter/stronger/better components, 3D print your ideas, and pass your idea straight to a machine shop. :party0030:

Anybody have access to a 3D scanner? Makerbot Digitizers are only good for 8" (diameter) x 8" (height). Not sure it would get the job done.

I'm just curious about how much toe change within plus minus 1/2" from static height, so I can determine whether the toe change is designed in the suspension or due to the toe links not holding the alignment. I've gotten as much as 1/8" ~ 3/16" change in toe by just replacing the stock exhaust with a track pipe and a bit more than half tank less gas in the tank versus a full tank and stock muffler. That cant be more than 1/4" of change in rear ride height...

I installed some toe links coupled with eccentric lockout to try to eliminate possible slippage and toe change with the stock setup.

Here's the alignment specs with stock muffler replaced with a track pipe, all the stuff in the trunk removed and about 1/4 tank of gas.
http://i174.photobucket.com/albums/w...F6325D363C.jpg

Here's the alignment after I replaced the stuff in the trunk, factory muffler and filled up to about 3/4 tank of gas. (disregard the front alignment, I believe the front adjusters were not torqued down sufficiently causing it to shift)
http://i174.photobucket.com/albums/w...0ace097552.jpg

A total of 0.26 degrees of difference between the rear toe with the weight added back on. According to this calculator/converter that's more than 3/16" of change in toe with only a quesstimated 50~60lbs difference in the rear. http://robrobinette.com/ConvertToeDegreesToInches.htm

That's is a lot of bumpsteer, no? Something wrong with this picture?? @Shankenstein @Wepeel

You're going from 1/32" toe in... to 3/32" toe in. Obviously there's some variance in the data, but 1/16" (per side) is not insignificant for static settings.

For 60 lbs, that's 30 lbs/side. Rear springs are 211 lbs/in, so that's ~1/8 in. of compression.

I love extrapolating in public. If we have 2+ inches of travel, one could (wrongly) assume that the toe curve is a line... and your toe at full compression would be 1" toe in per side. Such stability, wow.

I remember from the earlier posts the rear toe change you were seeing seemed really dramatic. That seems like a HUGE change in rear toe for just a few pounds of weight... imagine if you are in the car or have a passenger or are carrying groceries, that would mean the toe would be changing. If I did the math right you are seeing a change of more than 1.5mm per wheel due to a weight delta of ~60 lbs. That just seems nuts to me...

I know you said to disregard the fronts... what did you think was loose between readings for the front?

I didn't do the experiment of measuring toe while adding weight to the trunk, but I know when I installed my coilovers, dropped the ride height by 1" in the rear, that the toe change was minimal enough for me not to have to reset the toe in the rear.

Can you please translate that 1.5mm per wheel into degrees?

They're in his pic. I converted the degrees in his pic to mm.

So there's got to be something weird going on. I initially measured similar change in toe myself using measuring tapes, so 'operator error' was very likely. This prompted me to have this measured at an alignment shop with proper equipment. Hawkeye machine, in this case, with frikin laser beams. Lo and behold they get the same numbers I'd measured myself using wooden blocks and measuring tapes.

The front camber was added using camber bolts. I'm quite sure they were not torqued down sufficiently by the alignment guy who did it the first time. I actually felt the front alignment shifting while driving. The car would steer more or less in the middle of a turn without additional steering input. Pretty scary. I took it back in only a few days after the first alignment to get this fixed and got the printouts on my previous post. Funny thing is I actually did a trackday before getting it fixed and put down a personal best lap that day. Lol

Holy Crap!

http://www.vsusp.com/

I'm sure the scaling is off... but that's a mighty cool tool!

Link to VSusp

This thread is awesome! Great work so far gathering information.

No one wants to measure the suspension points of the car?? :D

I used to work at OptimumG and have used OptimumK quite a bit. I've been very tempted to put the car up on jack stands and measure the points the old fashioned way so that I could have a good baseline to start with before I start doing suspension modifications. But it's a lot of time consuming work.

I contacted Bob Simmons over at Morse Measurements (http://www.morsemeasurements.com/), who has actually done some K&C testing on a BRZ, and has all of the suspension data, but he was reluctant to give any sort of deal (he wanted ~$1,600 for the data).

EDIT: Also very happy to see so many people saying "Damping" as opposed to "DampENing".... drives me crazy :bonk:

But, I doooooo need dampeners though.

Because it's hot and dry as hell in Phoenix.

Which test plan was he offering for that amount?

http://www.morsemeasurements.com/pro...t-description/

I cant believe this keeps coming up.
From a technical terminology standpoint BOTH are correct.

A damping system dampens oscillations in a suspension.
A damper(noun) dampens(verb) oscillations.
Something that performs dampening is a dampener.
Just like someone that performs gardening is a gardener.

See how that works. Grammar Bitches!!

Sombody buy this and let me know what going on with the rear toe, please. :bow:

Nope. FIFY

Had to do it. I can't stand it either. To dampen something is to make it wet - plain and simple.

Full Definition of DAMPEN
transitive verb
1
: to check or diminish the activity or vigor of : deaden <the heat dampened our spirits>

However, in the context of mathematics/physics/engineering, to prevent ambiguity, the terms damp and dampen are never mixed.

Throughout my undergraduate work, not only was the distinction reinforced by each and every one of my professors, I have yet to see the term misused in any professional or academic text. Period.

As much as linguists and grammarians may want to draw equivalence, in this context, misuse would immediately be squashed in the first pass of a peer review.

20 years aerospace engineer. I hear it all the time.
In fact, I am looking at a drawing in our configuration management system right now entitled "Dampeners, Oscillation - Test Station".

But I guess a world-class engineering facility with over 1000 engineers is wrong.
I am currently sitting in one of the best dynamics test facilities in the world. We use vibration dampeners in testing.
(Full disclosure: there are far more documents in our system labeled 'damper' than 'dampener', so the latter is the less accepted version)

There's also the part where WHO GIVES A SHIT. :lol:

I say damp and damper but I don't really care what anyone else says.

- Andy

Ah, aerospace. You're just a victim of all that watered-down curriculum. My sympathy.

It wasn't a test plan, just the data from the test that had already happened. The test is ~2x the price. And to be honest, I'm not sure exactly which test it was.. I really just wanted the x,y,z points of the suspension, although the K&C data would be helpful in determining force based roll centers.

Didn't mean to start an argument over the terminology. :) It's just how I was taught going through school.. As engineers I don't think we really have any say on how things are said, I'm lucky I can speak at all!

I like you, we can be friends.

:threadjacked:Degree is EE.
Feel free to offend, but try reading (or I guess 'the Grammarist' is full of shit too):

A dampener is someone or something that dampens.3So damper and dampener can both refer to one that deadens sound vibrations. But damper does not work for something that makes something slightly wet.

http://grammarist.com/usage/dampen-damper-dampener/

Using your twisted logic, since damp means slightly wet, then 'damper' means "a little more than slightly wet".

/:threadjacked:

.. back to suspension talk!

Does anyone know at what point of lowering (0.5", 1", 1.5", etc) our cars it's advisable to get the roll center correction kit? Or is it advisable anyway to be able to run softer springs and increase mechanical grip?

Awww, c'mon, Stu. Dampen? watered-down? Just having a little interdisciplinary fun. Truly didn't mean to offend.

One last comment and I promise no more thread-jacking. The grammarist is correct until one considers the context in which the terms are used. There is no such thing as a dampening coefficent.

Here is a link to the suspension points on the car. They were posted on this forum somewhere. Not sure how accurate they are either but it is a start.
https://docs.google.com/spreadsheet/...rive_web#gid=0

I've been thinking about applying to Optimum G (FSAE alumni here). Can't make up my mind

Yep! That's my spreadsheet.

It's not accurate. I started with the track width, then looked at alot of pictures of the geometry to get a rough estimate. Things like wheel/tire size and offset helped a bit for scaling.

Using the rough estimates, I ran the kinematic model and made some minor tweaks to get the curves to look halfway normal.

If anyone has better data, I've left the read/write access on that spreadsheet wide open for anyone to contribute.

Yeah, I saw that and then read the rest of the post. :)

One of these days when I'm bored I'll jack the car up and measure points with string, chalk and the concrete floor with reference points for front and rear so that people can adjust for different ride heights, wheels and tires.

I just wanted to offer a word of caution with the suspension coordinates in the google document on the first page. It would be wise to double check the work :).

Great ideas, a ton of excellent information and work in here!

ahhh cant wait until I can finally start using SolidWorks in class. Ill actually be able to participate in this discussion and know what Im talking about lol

Unfortunately SolidWorks won't really teach you anything about a proper suspension model. You need to read books like

[ame="http://www.amazon.com/Race-Car-Vehicle-Dynamics-Experiments/dp/0768011272"]http://www.amazon.com/Race-Car-Vehicle-Dynamics-Experiments/dp/0768011272[/ame]

and

[ame="http://www.amazon.com/Fundamentals-Vehicle-Dynamics-Thomas-Gillespie/dp/1560911999/ref=sr_1_1?s=books&ie=UTF8&qid=1415724849&sr=1-1&keywords=vehicle+dynamics"]http://www.amazon.com/Fundamentals-Vehicle-Dynamics-Thomas-Gillespie/dp/1560911999/ref=sr_1_1?s=books&ie=UTF8&qid=1415724849&sr=1-1&keywords=vehicle+dynamics[/ame]

and

[ame="http://www.amazon.com/Vehicle-Dynamics-Application-Reza-Jazar/dp/0387742433/ref=sr_1_3?s=books&ie=UTF8&qid=1415724849&sr=1-3&keywords=vehicle+dynamics"]http://www.amazon.com/Vehicle-Dynamics-Application-Reza-Jazar/dp/0387742433/ref=sr_1_3?s=books&ie=UTF8&qid=1415724849&sr=1-3&keywords=vehicle+dynamics[/ame]


These books teach you what equations and theory is needed to understand and implement a suspension model. SolidWorks can help you visualize the system, but without understanding of why points are where and what moving them does to your system, SolidWorks is useless.