Nohachi's suspension ramblings thread
07-23-2010, 06:58 PM
Post: #31
Nohachi's suspension ramblings thread
using the numbers of drako this is leading to a roll center at 182.5mm above ground... Wink


the numbers in your drawing regarding height don't add up.

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07-23-2010, 07:53 PM
Post: #32
Nohachi's suspension ramblings thread
Bean Bandit Wrote:using the numbers of drako this is leading to a roll center at 182.5mm above ground...
Thanks mate! Edit: actually, that number isn't that bad. Quite believable. Time to crunch those numbers.

Bean Bandit Wrote:the numbers in your drawing regarding height don't add up.

Its a damn bugger to come up with decent measurements. Everyone is invited to do a better job then I did Smile For now I guess we'll have to do some sensitivity analysis.

What is the biggest influence? lower controll arm or height of strut tower?

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07-23-2010, 10:21 PM
Post: #33
Nohachi's suspension ramblings thread
did a second quick drawing assuming a 40mm longer LCA but same strut hight this results in a rollcenter ~5mm lower... (drawing by hand with a ruler isn't very precise, I'll do it again on PC later)

EDIT: if a 40mm shorter strut is used with stock LCA the rollcenter is lowered by ~70mm

all data based on darko's numbers.

so in short: changes on the strut length have way more influence on rollcenter changes compared to changes in LCA length Smile

EDIT: important for all these drawing is maintaing the fixed figures.
215mm horizontal and 560mm vertical distance between strutmount and LCA pivot on chassis

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07-24-2010, 08:01 PM
Post: #34
Nohachi's suspension ramblings thread
Guys, I believe in a few months I will be able to provide accurate graphs of the 86 suspension most important geometry factors, such as RCH migration, camber change, anti-squat etc during roll and bump for my suspension setup, which can be used as a guideline for everybody. From then on it would be easy for me to try things, like RCAs of different thickness etc at your request.

I am currently working on my chassis, and before I assemble it (hopefully before October) I will take measurements and use them in my analysis during winter. I hope you are not in too much of a rush!

I had done an analysis with some rough measurements back when I studied vehicle dynamics and if I recall correctly the RCH was indeed somewhere near 200mm and it went up-down approximately between 100-300mm during a 120mm bump travel (60 bump 60 rebound) and went left-right within the engine bay (about 700mm total travel) as well as 50mm up-down during 6 degrees roll (3 degrees left and 3 right). Not too bad for an 80ties mcpherson setup! The rear RCH was always in the center of the panhard rod and didn't move around much... I hope that would help for now!

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07-25-2010, 09:47 AM
Post: #35
Nohachi's suspension ramblings thread
Thanks to everyone so far for this collaborative effort. I have some spare time this afternoon, so I'll try to crunch the numbers for the most basic AE86 setup.

@Bean and drako:
The 305mm LCA length, balljoint to ground, LCA pickup point to ground and shock tower to shock tower measurements are the ones I am most certain of (less then 5mm variation). The variation is mostly in the strut length and in the height of the shock tower (+/- 2 cm or so). Also the angle of the strut might be wrong (iPhone measurement), but the numbers seem logical enough. All in all, I don't think I did too bad for a rough model.

Kind request for CAD wizards:
Now that we have the rough basic geometry fixed. If you have time and interest, we could look at the following things:

The car I measured had no cyl head or front apron. As a result the car was light and sitting higher on its legs. The thing had +1 degrees pos. camber. 1st step is to shorten the strut length untill the strut angle is 9 degrees. That should give the stock 0.3deg neg camber of an AE86 and a good RCH baseline.

Second: Who knows how much a typical 8/6 sprung hachi is lowered? Further shorten the strut by this number and then add 33mm's of Roll centre adjusters below the hub mount location. What is the new RCH?

Last: Once we have the shortening/lengthening of the strut down. It should be easy to measure the strut angle in the drawing for each position. Subtract 9 degrees from this number and multiply with minus one. Now you have the theoretical geometric camber. Could someone try and plot a basic AE86 cambercurve? Starting at a 10cm longer strut and finishing at a 15cm shorter strut? This one measurement has serious implications for our choice of spring, so I'll try to confirm everything with on-car measurements later.

@Drako: What did you study? Do you happen to remember what the slope of the line between the roll centres was?
The numbers aren't too shabby..but I still don't understand the design choices entirely. The ford focus has a terrible rch (around 100mm) and a very high cog (600mm or more). Still, they seem to handle pretty decently.

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07-25-2010, 07:09 PM
Post: #36
Nohachi's suspension ramblings thread
I am a mechanical engineer (Patras uni) and did an MSc in motorsport vehicle dynamics in England (Kingston uni and Lotus).

Well if you take the midpoint between the panhard mounting points at around 300mm the slope is 100*(Rear RCH-Front RCH)/Wheelbase= 100*(300-180)/2400=5% (drops towards the front), which is at ride height let's say. during bump however you get an opposite slope and with it UNDERSTEER!! It should be very noticeable in stock suspension (for instance when you go over a crosswise bump in a corner), but can be dealt with if you soften fast rebound damping and shorten the stroke while maintaining static RCH (in other words lower it and put on RCAs).

A today's passenger car like the focus cannot compare easily to the hachi. There are so many parameters affecting ride and handling that are so much different. Wider tracks, bigger wheels, more weight and higher, longer wheelbase to name the most apparent, but also more difficult to analyse things like damper settings and silent block spring coefficients. And don't let me start with things like higher driver position, different seat cushions, or even soundproofing! Many of you may laugh, but if you think about it they do affect handling...

Ride and handling is sooooo lovely! We can keep discussing it forever... Big Grin Big Grin Big Grin

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07-25-2010, 09:49 PM
Post: #37
Nohachi's suspension ramblings thread
Ghe ghe, nice to know that there are people that won't run away immediately.

Anyone happen to know what the distance is between the rear hub surface and:
a: the rear damper pickup point ( for rear coilover setups)
b: the rear spring platform (for normal setups)

Or if you already have a calculated rear motion ratio in roll that would also do Smile

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07-26-2010, 08:04 PM
Post: #38
Nohachi's suspension ramblings thread
Nevermind Smile Found it in my old notes..

Bad news-> the rear axle is ~1345mm wide and the rear damper mounts are offset 200mm from the axle ends. That translates to a damper and spring motion ratios off:

1.00 in one wheel bump
0.75 in roll

..bugger. The situation with the original axle is different. The springs have a better motion ratio (around 0.Cool, but the shocks are still at 0.75.

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07-26-2010, 08:23 PM
Post: #39
Nohachi's suspension ramblings thread
Not sure about what you talking now about the rear setup (maybe the leverage ratio from wheel to spring-shock?).

But i made quick kinematic drawing from your first drawing corrected with the LCA-strut top distances provided by bean bandit but i am not sure if the measurement are right.

I got 182mm RCH at your measured position, if i get the LCA in horizontal position and the wheel camber to -0,3 i have only 23mm RCH(strut lengh 565mm)!! and thats bad, maybe the coicidences between wheel placement/camber and the strut are not accurate in our drawings and that may the biggest diference.

Can you measure exact wheel camber for this fisrt image? Can you measure wheel center to edge of the fenderlip so i can see how high it sits.

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07-27-2010, 08:31 AM
Post: #40
Nohachi's suspension ramblings thread
Nopes can't do that (cars sitting 100km away).
But these measurements should be roughly ok:

Strut angle as measured: 7~7.7 degrees on car
Camber angle as measured: +0.3 degrees on car
Angle between hub and strut (included angle) = 9degrees.

So something is going wrong in your drawing I think Dumb question At 0.3 degrees negative wheel camber, the strut angle should be less horizontal...It should be sitting at around 8.3 degrees in the drawing.

Does that make sense?

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