Developing a Proper Suspension Model

[dradernh]

Originally Posted by pseudo

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.

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.

[solidONE]

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.

[Shankenstein]

Originally Posted by solidONE

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.

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.

[solidONE]

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...

[solidONE]

Originally Posted by solidONE

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.


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)


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

[Shankenstein]

Originally Posted by solidONE

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.

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)

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.

[Wepeel]

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.

[plucas]

Originally Posted by Wepeel

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?

[Wepeel]

Originally Posted by plucas

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.

[solidONE]

Originally Posted by Shankenstein

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.

Originally Posted by Wepeel

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.

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

[Wepeel]

Holy Crap!

http://www.vsusp.com/

[Shankenstein]

Originally Posted by Wepeel

Holy Crap!

http://www.vsusp.com/

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

Link to VSusp

[fika84]

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

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

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

[kavanagh]

But, I doooooo need dampeners though.

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