Nohachi's suspension ramblings thread

[SekiguchiUeno]

Good thread Nohachi you speak out of my mind mostly, although i have much to learn.

I am not sure about the data i provided, not sure about speeds, need to meet Reinhard and get the graphs in my hands.

That pickup pic is nice, thats what i always try to explain to some jdm fanboys around, springrates found mostly on ready to mount coilovers are unrideable the body starts to act like spring itself and can disturb the shocks.
But thats logical, the 8/6 coilovers setups from Japan started as some racing oriented setups for caged cars with slicks on smooth tracks.By mistake some guys explored that they are very good for drifting and gymkhana with their lack of grip and almost no travel, the rest is history, we all know the crazynnes of jdm petrolheads, they are able to run high modified cars without shaken on public roads.
None of the sets availlable is approved for road use as i know, only for offroad say track use(so was the greddy i god with my last car), that most guys mount it and use on the road is another thing. So you cannot blame the factories for very high springrates that are made for different conditions that the setups are really used. You can blame them for using the hype for better sales without to explain or trying to redesign.
I was trying to use 6/4kg spring on the greddy and was constantly on bumpstops but not only at cornering but also on every bigger bump. Ended up with preload that gave me exact the same negative travel like 8/6 springs. Some little hard to noticeable improvement of comfort was seen on good roads, not worth the change as the other things in my opinion worsened.Problem of the fancy coilover setups in general is lack of the stroke. You can get stiffer springs on them but not softer ones to make compromise.

Last year i let me made some custom springs with 3,6f and 3,2r springrates to match the stock bilstein shocks as some locost perfect road setup. They still are lying in the garage as they made them shorter as i wanted. As more as i read your threads i want give them a chance again, probably let me made some spacers(Jondees idea but need to design it right to trust them) to try them out. I also bought some Apex springs which are around 2,5-2,7kg to have some direct fit stiffer springs. Bilsteins seem to be overdamped on stock springs and from some calculations i figured out that 3,8/3,3 would be the perfect choice, but 3,8 probably too much for front stock B6. Frequencies i had calculated for 3.8/3.3 are around 1.9hz(F1.924/R1.866) which i found to high from your explaining and the optimung site.

Btw: Miata seems to have stiffer body than ae86 hatch to me.(miata on HKS6/4, ae86 on Greddy 8/6) You really hear the metall twisting and also some rubing from doors and hatch as the body is moving(mostly on uneven roads where the lack of negative travel cannot match the axle crossing.If the road surface bumps not exceed some point, the suspension feels quite comfortable. I can imagine to have tons of fun with them on some small cart track. But i am not the driver that can handle it on roads (massive understeer or oversteer).

My English explanation sucks so i hope all is understandable.

[NoHachi]

Hi, don't have much time but a few pointers:
Suspension frequencies don't tell the whole story.. you need more roll resistance then a miata, S2000s or Elises, so somewhat high springrates are needed.. Just not a whole lot higher. 1.9Hz is very liveable. More on that topic once I figure out a way to fill in some variables I'm missing..(cog and rc height).

Also, you are forgetting about the suspension motion ratio in your comparo between the miata and AE86. At 6/4 the miata is at 1.9Hz, while the greddy AE86 is near 2.8-2.5Hz. You should really compare that miata to an AE86 with similar wheelrates (e.g. 3.8/3.3).

[SekiguchiUeno]

I know this comparing is not very accurate but never riden in some other miata, and then you are right ae86 with stock springs you dont feel the movement of the body that much.How much is the weight of the miata i though pretty same as ae86 or max 1060kg.

Ok my questions:
In need more roll resistance/springrates because of bigger unsprung weight? or because of another spring/axle ratio? For mee it seem that i need les then the miata becuase the springs on ae86 take almost the same load as the wheel.
Bilsteins. I use stock longstroke B6, they are pretty good with apex springs. But i think of some better setup in the future with the 3,6/3,2 springs mentioned above, i believe in your words that the hachi has at least 10000k/kg torsion stiffnes(but i believe is in the region of older miata 6000 at max), i want use street tyres and stock body without cage(only some mount 4 point halfcage posible). You say you want use 200sx shocks, so you change completely to 200sx spindles and control arms(thats at least my idea for some time, big brakes for free)?

http://rs-power-shop.com/product_info.ph...1f48e4e939

[NoHachi]

No, the miata has a different leverage ratio between the wheel and the springs & dampers.
http://autospeed.co.nz/cms/title_Spring-...ticle.html

When using the 200SX stuff, everything changes. I'm not sure how you would get the geometry right again after those kinds of changes and I'm not willing to do the necessary homework. My idea is to only use S13 or BMW 325ix inserts. I would not recommend doing that kind of thing to anyone..but hey, I'm stubborn.

[SekiguchiUeno]

Yes that what i mean, miata has bigger leverage ratio, on ae86 its almost 1:1. I will read this link, thanks.

[Ozone]

Hi guys,
I've wanted to add to this thread but nohachi is doing a good job on his own!
Today I found some info that may be of interest:
http://www.not2fast.com/chassis/sae1999-01-1336.pdf
Page 24

This is a NHTSA report about vehicle stability.
It included info on a 1976 Toyota Corolla which although not an AE86 is similar platform - AE51?

Key info if you are doing some calculations is Centre of Gravity height = 514mm.
You can also compare with other vehicles such as E30 BMW or 190E Merc.

Nohachi - keep up the good work!

[Ozone]

Got some more info for the suspension geeks out there - not rude, I consider myself one!

Taken from 86 Bible.

[NoHachi]

Hi all,

I'm working on a simple suspension dynamics model that will allow a very rough comparison between theoretical damping curve for various 86 setups and some of the damping curves that people here have posted.
The theoretical model isn't perfect by a long shot..but its the basic stuff that engineers go through to get an idea of where they should start looking.

Here's my problem. I have some rough suspension measurements from a stock AE86 chassis (thanks raceminded!). Because the car still has most of its components on, its impossible to measure every little bit perfectly. So I had to settle for a subset of easily measureable things. In theory they are enough to calculate a rough approximation of the stock hachi roll centre height.

My question to the forums:
Is there anyone here who is handy with autocad and who is willing to transfer these measurements to a coherent technical drawing. You'll probably have to use a cosine or two to calculate some of the measurements from the bunch that I made. Shouldn't be to much work though.

Anyone who can/want's to help? I'd do it myself. But I haven't touched autocad in 5 years and also don't have a version at the moment.

[img name=]http://www.aeu86.org/files/me/measures_565.jpg[/img]

[drako323]

Would that do?

<a href="http://s429.photobucket.com/albums/qq17/sdrako323/?action=view&current=86frontstrut.jpg" target="_blank"><img src="http://i429.photobucket.com/albums/qq17/sdrako323/86frontstrut.jpg" border="0" alt="86 front strut"></a>

I chose a common tyre (185/60/14) and corrected the top mount height from 815 to 785 (overconstraint anyway)

[NoHachi]

Drako!

Now for the interesting stuff and a bit more background.
The 135mm value is the offset of the hub-face to the ball joint. So at the moment the drawing is correct for ET-0 rims. We can easily change the value to reflect different rims, but I thought most of us have something in the neighbourhood of ET-0. We can easily change the strut length in the future too.

The difficult stuff:
This is why I needed the drawing in the first place: determining the roll centre height.

These are the steps:

copy and mirror the suspension image. The distance between the centres of the topmounts is exactly 1000mm.

Draw a construction line that is tangential to the strut and passes through the upper strut mount.

Draw a construction line that passes through the lower balljoint and the LCA pivot at the chassis.

find the intersection of these two construction lines.

Draw a construction line that passes through the intersection above and the centre of tire contact patch

The roll centre is at the intersection of these two lines. Easy!

A picture for reference:
[img] http://www.roversd1.nl/sd1web/techtalk/m...center.gif [/img]

This site explains it as well:
http://www.roversd1.nl/sd1web/mcpherson.html