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Suspension analysis

 
Old 10-08-2016, 11:08 AM
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Default Suspension analysis

Finally I have had time to measure all the values, pick-up points, arms, length, etc. of my S2000.
I have installed front ASM and rear Spoon wider fenders (+35mm each side = +70mm track width) and now I am playing wiht the suspension analysis, including new ARBs, coilovers, etc. I am also running 255/40 R17 in both axis.

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I need now to know the coordinates or dimensions of the Centre of Gravity (CoG or CG) and the unsprung weight per axle (or per each wheel).

Do someone know, have measured or have got a link to where to find those please? I´ll happily share the analysis results here.

At a first glance, we can tell that the front suspension geometry can be improved by a good margin but rear is very good indeed. Standard geometry on the S2000 is one of the best we have seen in a street car.
However, rear and front are not compensated, specially if you start playing with new wheels, new offsets, wider front tyres, etc.

I can also see why the front bump steer kit is quite famous and certainly improve bump steer just by spacing up the steering rack if you drop the car just a tiny bit.


I can also see why the roll centres kit were developed, but you need to drop the car quite a lot to get the roll centre below the ground level. And probably if car has only been drop by 15mm like mine at the moment (TEIN Springs only) you won´t need to modify the roll centre and will be actually very well located geometrically.



In summary, do you know where can I find out location of the Centre of Gravity and unsprung weight?

Thanks
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Old 10-08-2016, 11:20 AM
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Old 10-08-2016, 11:40 AM
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Originally Posted by Daytona-Dave View Post
i find this book very helpful,,,,https://www.google.c...LR71P57r0YkK_6Q
oh yeah! one of the suspension bibles along with the Milliken, Carrol Smith, etc.
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Old 10-08-2016, 11:54 AM
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some useful links that I´m finding:

Unsprung weight estimate:
https://www.s2ki.com/s2000/topic/719...sprung-weight/

CG and unsprung conversation:
https://www.s2ki.com/s2000/topic/912...er-of-gravity/

I just keep finding posts about the garage Centre of Gravity manged by Chris, who apparently knows well what he´s doing...
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Old 10-08-2016, 01:01 PM
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Some number that I have gathering, in case you find them useful. Even though you might know about them already, like OEM wheel sizes, etc.

Stock CG height around 19-19.5" = 483-495 mm
Total unsprung weight around 315 lbs = 143 kg. Assuming 71.5 kg per axle.
Unsprung CG height around 12" = 305 mm
Sprung CG height around 20" = 508 mm
Total CG height around 19" = 483 mm

With driver + 1/2 tank, etc. by CG:
Total weight around 1360kg
Weight distribution with driver + full tank = 50.22% front 49.8% rear.
Front: 685 kg
Rear: 675 kg

Wheel base = 2400mm
Stock front track width = 1470 mm
Stock rear track width = 1510 mm

Front OEM wheels. 16 x 6.5" et55 205 tyre
Rear OEM wheels. 16 x 7.5" et65 225 tyre
You can use this offset calculator if you are changing wheels or using spacers, etc.
http://www.1010tires.com/Tools/Wheel-Offset-Calculator
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Old 10-08-2016, 02:29 PM
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This is really interesting. Keep the posts coming.

Unsprung weight is going to depend on your choice of wheels as much as anything I would have thought. Otherwise it's all the suspension outboard of the pick-ups for the dampers, isn't it? How do you calculate the unsprung weight of the upper arms? Or is it all calculated from the inner pivots of the wishbones as they all move? What about ARBs?
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Old 10-08-2016, 03:02 PM
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Originally Posted by Tim S View Post
This is really interesting. Keep the posts coming.

Unsprung weight is going to depend on your choice of wheels as much as anything I would have thought. Otherwise it's all the suspension outboard of the pick-ups for the dampers, isn't it? How do you calculate the unsprung weight of the upper arms? Or is it all calculated from the inner pivots of the wishbones as they all move? What about ARBs?
Definitely, wheels and don´t forget tyres as their weight is pretty important too. Upright, brake discs, caliper, etc. I did read in a book that you can estimate by a factor the total weight of the arms, etc. However, there is a way to measure it analitically by using a balance and undoing the bolts of the dampers a bit on the strut tower so all of the unsprung weight can lean on top of the balance.
I have not done it, but I found a couple of posts guessing around 300-315 lbs and it seems quite reasonable.
https://www.s2ki.com/s2000/topic/719...sprung-weight/

ARBs are not unsprung, only the small droplinks.

In this case it is just a matter to see what is the right direction for the modifications and I´m not looking for 0.5mm accuracy on measurements or 1kg on weight... We used a spirit level, a metric tape and a plumb bob. That is good enough and used extensively in Motorsport for GT Cup cars, etc.



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Old 10-09-2016, 12:40 AM
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Interesting stuff, subscribing to this.
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Old 10-09-2016, 10:11 AM
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Subscribed...vanity wants me to lower the car but I don't want to fook with the way it drives so that first post is very helpful, cheers
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Old 10-09-2016, 12:10 PM
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Interesting the front bump steer kit come in 12 & 20 mm
and at a silly $ for what they are
would like to fit some though as lowered 20 or 25mm on Ohlins DFV R&T and read needed for a lowered car.

Interesting stuff
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