Nohachi's suspension ramblings thread

[NoHachi]

To whomever still felt compelled to open this thread after reading the title :
I needed a place to store some of the information and links that I found whilst searching for a suspension setup that will actually work. Don't expect much coherence or explanations. Just a braindump/link collection to hopefully some interesting stuff for those searching for a decent suspension setup.

[edit - I'm more or less editing each post as interesting stuff comes up, so say bye bye to coherence or readability]

[boo50]

it's really interesting.
and as I read from your posts, you've choosed softer spring rates finally.
but all japan brand, who make suspension for ae86 are go with 8kg front, 6kg rear.
what you can told about this setup ? why it's chossen by japanese manufacturers.
is this only drift purpose specs (I think most tuners in Japan are drift on ae's but those who go on the tracks have their personal setup).

[Ozone]

My image is that some big brand chose this setup and everyone else has copied it! Also most Japanese roads are quit smooth with the occasional step input like a bridge joint ie. for short time. European roads on the whole have more undulation and can be more rough ie. continuous inputs. Therefore stiff suspension does not work so well. Also although stiff suspension can make a car feel more responsive and quick it can actually be slower as grip can be reduced.
I'm with nohachi, big spring rates does not equal big handling. Once I've got other bits of the car sorted I'll be looking to see how much I can reduce the spring rates on my Greddy suspension (no much i fear...).

[NoHachi]

And exhibit no.1: a K-sport dynograph!
These things are pretty rare since K-sports don't usually end up in the hands of people with shock-dyno's. The shocks are for a Nissan S-body. No problem since the AE86 stuff has a 90% chance of being the exact same shock adapted to our setup. The springrates are 100% the same.

source: http://www.mazdas247.com/forum/showthrea...=123666252

Fronts:


Rears:


What do we see:
Only rebound adjustment
Not ideal but common. Koni sports are similar.

Ratio Bump/Rebound = 1/3.6 to 1/5.6 (not ok)
You do need more rebound then bump..as the spring compresses during the compression stroke it stores energy. During rebound energy is released. Shocks dissipate energy so you need more rebound damping then compression. Current wisdom is to have a ratio of 2:1 rebound:compression.
The K-sport range covers the range from too much rebound to way too much rebound. What happens when the damper is much stronger in one direction? The suspension will resist moving in one direction more then moving in another. In this case moving in compression is easier then rebound. If the car runs over bumps it moves downwards more then it moves upwards. This in effect lowers the car and the car "packs down" onto the bump stops or into coil bind. Not good for grip, comfort or anything really. It feels sporty but it isn't.

Rear shock damping ranges do not overlap.
That means that even with the left set to full stiff and the right to full soft the shocks still don't produce the same forces. Try and imagine what that does to your handling. Not pretty.

Front shock damping ranges overlap only above 550lbs
So to get the front left and right equal you have to have a minimum ratio of 4:1 and there is no room for adjustment afterwards.

At least the adjusters seem to be actually working and stiffer settings lead to stiffer shocks.

Difficult to say much more about them without a force-velocity graph.

Conclusion ->
Plus sides: suited to give a stiffer ride so you can slam your ride height to the ultra-cool setting. Better handling at slow speeds due to stiffer springs and less camber change from the suspension. Probably easier to drift.

Downsides: control at the limit likely to be very tricky (mind you, less then 5% of people actually use that limit). Grip and comfort over rough surfaces compromised. Difficult to adjust since there really is only one setting of the adjusters that you can't really use (and you have to find this setting for each shock individually by feel).[/b]

[edit: just for reference, its possible to become a pro-drifter on these things. Vernon's has proven that adequately with his successful Trueno. Just goes to show that drifting is not a comparable to timed-events.

[NoHachi]

Sorry no info yet..Just collecting and dumping information. [selfish old me]

HTS dyno (single shock - possible marketing influence)


[edit: notice boys and girls that the bump:rebound ratio for the HTS is pretty damn close to 1:2
This holds for each setting]
Are they perfect? For racing they are actually quite nice! But there is room to improve comfort on the street and grip in bumpy tracks. More to come later on that subject.

AE86 cornerweights from an actual measurement (coupe with full interior and some mods)


Some datapoints from SekiguchiUeno

Quote:Old stock springs taken from old corolla:
F 19N/mm
R 20N/mm

Old, used KONI lowering springs
F 20N/mm
R 20N/mm

Older used Koni oil dampers
REAR:
Comp: 51N
Rebound open: 125N
Rebound Half open: 160N
Rebound 3/4 close: 260N
FRONT
Comp: 20-50? not measured,only comparing to the bilsteins with hand. Rebound open: 80-100? same as above
Rebound: 3/4 close: 160N

2year Amateur rally driven Bilsteins B6, stock settings.
REAR:
Compression: 100N
Rebound: 220N
FRONT:
Compression: 72N
Rebound: 140N

Stock abused shocks
REAR only:
Compression: 35N
Rebound: 120N

[NoHachi]

Spring stiffness: What works best stiff setups or softer ones.
Answer -> it depends

For starters..if you know your car, spring stiffness, suspension geometry, weights etc, you can calculate a "stiffness number" for your car (in actuallity it is the resonant frequency of an end of a car). This number is comparable between cars while springrates aren't even comparable between the front and rear of the same car.

Guidelines:
0.5 - 1.5 Hz for passenger cars
1.5 - 2.0 Hz for sedan racecars and moderate downforce formula cars
3.0 - 5.0+ Hz for high downforce racecars
from: http://www.optimumg.com/OptimumGWebSite/..._Tip_1.pdf

Examples in practice:

* 1990 Mazda Miata ~ 1.15hz front, 1.01hz rear
* Mitsubishi Evo VIII ~ 1.3hz front, 1.2hz rear
* Honda S2000 ~ 1.3hz front, 1.4hz rear
* GD Subaru WRX STI ~ 1.6hz front, 1.8hz rear
* Lotus Elise ~ 1.8hz front and rear
* C4 Corvette ~ 2.0hz front and rear
* Mazda RX-7 ~ 1.22hz front, 1.16hz rear
* Acura NSX ~ 1.6hz front, 1.5hz rear

AE86 values according to my model (disclaimer ->this model is NOT perfect, I'm just a hobbyist and make mistakes here and there. So maybe +/- 0.2 Hz):
Car - Spring rates F/R - susp.frequency F/R (description)
* Toyota AE86 1.8/2.2 ~ 1.3hz front, 1.5hz rear (stock)
* Toyota AE86 8/6 ~ 2.7hz front, 2.4hz rear (JDM-land)
* Toyota AE86 6/4 ~ 2.3hz front, 2.0hz rear (oldskull?)
* Toyota AE86 5.8/4.5 ~ 2.3hz front, 2.1hz rear (me and Ivan)
* Toyota AE86 3.5/3 ~ 1.8hz front, 1.7hz rear (best street setup?)

Possibly interesting setup values that I know off:
* 1990 Mazda Miata (1.6) ~ setup for stock class club racing on smooth tarmac tracks. Broke the class lap record during first training session.
2.28hz front, 2.09hz rear

*1993 Mazda Miata (1.9 turbo). Setup for Time Attack on Nurburgring Nordschleiffe (which is a very bumpy track, comparable to smooth streets).
Current best time 8min03 bridge to gantry. This years goal ~7.45 BTG and sub 8min full lap.
1.8Hz front, 1.8Hz rear

(note -> miata's, elises and other cars with double A-arms or other decent suspensions have good camber controll and can get away with softer springs)

If this interests you -> simple explanations here: http://buildafastercar.com/tech/Spring-Rates

[edit: some disclaimers have to be made:
(note -> miata's, elises and other cars with double A-arms or other decent suspensions have good camber controll and can get away with softer springs)
(note-> stock miata's are designed to corner on their bumpstops. New Mini's are similar in that respect. The bumpstops on a miata have increasing stiffness (up to 12kg/mm). Stock MX5 suspension frequencies therefor do not reflect their handling setup. They are far stiffer in handling then the freqs suggest.)
(note -> note that a stock AE86 seems backwards in regards to F/R springrate, this is compensated in roll (handling) by the swaybars (ARB's) ) This post has little to do with the "balance" of a car. It gets more complicated when you look at balance.

[Jan Pedersen]

Really interesting reading, Nohachi Keep it comming :!:

[XJS]

Subscribed. Keep it comin'

[NoHachi]

How much is too much?
So after looking at all these frequencies etc you kinda start to wonder..who to believe: the JDM companies with years of experience or some simple number that corresponds to some frequency..what's up with that? You would be wise to be more then a little sceptical.. So I started thinking, how much really is too much? Yeah AE86 spring rates tend to be high..but their suspension is pretty archaic so you need plenty of roll resistance to compensate. Maybe that's what's going on? Then something popped into my head. What exactly is doing the suspending here?

Twister: a tale of chassis flex


Years ago, in my younger years I took my chariot of that time, a little civic, to the nurburgring. I threw the poor old thing into a particular corner hard, desperately trying to stay ahead of a friend in his M3 (I cheated by learning the track layout in GPL). My passenger made a comment that the view was really quite beautifull. Especially since he could see so much of it through the gap between the passenger door and the roof. Que!? Well, the little civic's chassis was twisting quite severely you see. Enough to open a gap of 2 to 3 cm's in high G corners.

So what influence does the 80's econobox chassis have on our choice of springrates?

Simple
If you think about it its quite simple. Let the tire push one corner of the car up and either the spring or the chassis will flex. Exactly how much each of them flexes depends on their relative stiffnesses. An infinately stiff spring in a weak chassis will see the chassis do most of the flexing. A stiff chassis with weaker springs will have the springs do most of the work.

What about the *86?
So what about the old 86? There are some simple calculations we could do. With a bit of math you can translate the chassis stiffness to an equivalent stiffness at the wheel. Its a simple case of calculating how much a twist of a degree at the chassis ends up being at a suspension pickup point. If you want to know more on how to model this yourself, take a look here:
http://www.theoryinpracticeengineering.c...20fsae.pdf

You can do a full car model if you want, but I'll stick to a simple and indicative single corner model for now. There is a problem: what is the torsional stiffness of a hachiroku? I have never seen a number, so if anyone has found some somewhere please post it up! Without a definate number all we can do is guestimate a range for the number. Here are some references:

Mazda NA MX5 (1990): 6000Nm/deg
Lotus Elise S2 Exige (2004): 10,500 Nm/deg
BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg
BMW E46 Sedan (w/folding seats) 13,000 Nm/deg
BMW E46 Wagon (w/folding seats) 14,000 Nm/deg
BMW E46 Coupe (w/folding seats) 12,500 Nm/deg
BMW E46 Convertible 10,500 Nm/deg
(find a small list here: http://www.germancarforum.com/test-data/...idity.html
Note that chassis rigidity has really improved in recent years. Part of the reason why modern cars hold the road quite well).

So where do we estimate the AE86? It must be stiffer then an old MX5..but stiffer then an Elise? Hmz..they are convertibles no? Looking at the BMW 3 series we see that sedans are quite stiff, but isn't the E46 a more modern design? (answer: it is).
At the very least we have a range to work with: The 86 has a torsional stiffness that is probably better then a miata's, but less then a E46 sedan's. So roughly between 6000Nm/deg and 14000Nm/deg.

What to aim for?
At first I though that maybe we would get chassis springrates less then those of the actual springs.. I'm glad to say that isn't the case. I remember from my old FSAE days that we used to aim for a chassis that's about 10 times stiffer then the spring. So for each 10cm's of spring movement we would get 1 cm of chassis flex. I searched around for references but didn't spend to much time. One I found was the following:

Quote:To keep the chassis from doing the suspension's job, Mazdaspeed's engineers designed the wheel rate to be six to eight times softer than the chassis stiffness. In other words, the chassis deflects one inch for every six to eight inches of wheel travel. To calculate wheel rate, divide the chassis' torsional stiffness by the target ratio-7.5 in this case. Finding the appropriate spring rate is then a matter of knowing the suspension's motion ratio and doing the math.

From: http://www.modified.com/features/0601_sc...cross.html

Pretty simple eh! We can do that!

The results
Included (hopefully) in the attachment is an overview of the results. I did the calcs for the front since the front carries the highest wheelrates. Entries in green are combinations of springs and chassis where the chassis is more then 7.5 times as stiff. Red entries depict combinations where the ratio is less then 7.5. Pick your own estimate of the chassis' stiffness, plug in your springrates and away you go!



My car carries ~6kg/mm front springs..hmz guess if I want to have the chassis work optimally I will have to start thinking about some serious bracing. Some spotwelding or a cage definately seems in order! Maybe thats why those modifications are so popular in Japan!

To summarize:
*To run 5kg/mm springs on an AE86 you need ideally to stiffen your chassis through seem welding.
*To run 6kg/mm or more you really need a cage.

[boo50]

Great info, so caged car need stiffer springs.
but how estimate caged car stiffness to choose propper springs ?
is any figures for ae86
or cage added so much stiffness, what this rule not makes huge difference and almost any springs can be used ?