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Discussion Starter #1 (Edited)
OK so I'm working on a spreadsheet to help calculate ideal spring rates, sway bar dimensions, and other settings. I wanted to know if others on this forum have attempted it before and had any advice. The general idea was selecting your desired or design frequency, and then selecting springs and sway bar settings or dimensions that get you to those ride and wheel rates. You would also want to stay away from your natural frequencies and make sure that the sway bar makes up a good percentage of the total roll resistance so that it is easier to adjust while you tune. Making some assumptions about friction also have it calculate how close to an oversteer/ understeer condition you are. Or another method is just add a 5% safety factor in roll resistance to the front or rear to ensure an understeer condition.


Here is screenshoot of what I have so far, when it's done I'l post it up here. So any thoughts, comments or experience is welcome
 

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My first comment is that we have no rear bars available, so when a stiff front bar is used, stiffer springs are required at the rear than may be optimum, especially for higher powered cars. I suspect the lack of a rear bar is why so many racers are going to uber-stiff springs all around, instead of more moderate springs with a stiff front bar and a light rear bar.
 

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Discussion Starter #4
My first comment is that we have no rear bars available, so when a stiff front bar is used, stiffer springs are required at the rear than may be optimum, especially for higher powered cars. I suspect the lack of a rear bar is why so many racers are going to uber-stiff springs all around.
Yeah I agree the lack of a rear bar is a disadvantage. For this calculation it would be easy to leave it off or just put in zeros for it's dimensions and then see what the spring rates would be to get you to your ideal wheel rate in the front and rear. In this exact case just going to stiffer springs all the way around may give you totally different wheel rates in front vs rear
 

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Yeah I agree the lack of a rear bar is a disadvantage. For this calculation it would be easy to leave it off or just put in zeros for it's dimensions and then see what the spring rates would be to get you to your ideal wheel rate in the front and rear. In this exact case just going to stiffer springs all the way around may give you totally different wheel rates in front vs rear
One of these days I'll stop being lazy and figure out how to mount a rear bar of some sort. I suspect that even a very small amount of roll stiffness (maybe 25 lb/in at the wheels) would aid chassis tuning a lot.
 

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Discussion Starter #6
Looking for Elise Data

I’ve basically got my spreadsheet up and running So anyone have the following data on the Elise

Front/ Rear Motion Ratio

CG Height

Stock Front rear spring rates

Front sway bar motion ratio

Wheelbase

Front/ Rear track width
 

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I was going to try and make a worksheet like this too!

I was going to do most of it this winter(no lotus driving in the seattle winter for me). I envisioned the most difficult problem to be figuring out center of gravity. I think you could just pop the wheels off and measure everything else. I've got the front clam off right now while I install some new shocks and springs. I can probably get a few measurements for you this week. What do you want?

justin
 

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Discussion Starter #9
I was going to try and make a worksheet like this too!

I was going to do most of it this winter(no lotus driving in the seattle winter for me). I envisioned the most difficult problem to be figuring out center of gravity. I think you could just pop the wheels off and measure everything else. I've got the front clam off right now while I install some new shocks and springs. I can probably get a few measurements for you this week. What do you want?

justin
Wow that would be awesome!!!!

I really need
CG Height (May have to jack up the vehicle to get that one, with the Corner weights)
Front Sway Bar Dimensions, and Motion Ratio

Front and Rear
Spring Motion Ratio
Spring/Shock Angle from vertical
Unsprung Weight (when you do this one Don't include tires and wheels measure them separately so others can use the weight of the control arms and hubs)

I think we might have a zero roll center for front and rear but if you think the control arms project a roll center height for the front and rear that’s another variable.

My rear clam is off I'm going to try to work on the rear if you want to tackle the front that would be great. I'll take some pictures of the measurements when I take them.

Thanks again
 

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I'll help as a can, but I don't have too much time right now.

My main lotus priority is getting the car back together for fridays track day.

When I was swapping the suspension I did measure the unsprung weights. I was surprised enough that I feel like I made some sort of mistake. Jacked up car, took the wheels off, took the shocks off, unhooked the front sway bar, propped up each scale so the corner was at approximately ride height when weighed... :shrug:

Front (without shocks, and wheel, swaybar detached) = 23#
Rear (without shocks, and wheel, what swaybar) = 11#

track pack shocks
front = 6#
rear = 7#

I MIGHT get the CG when I'm setting the ride height and corner weights.
 

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Discussion Starter #11
I'll help as a can, but I don't have too much time right now.

My main lotus priority is getting the car back together for fridays track day.

When I was swapping the suspension I did measure the unsprung weights. I was surprised enough that I feel like I made some sort of mistake. Jacked up car, took the wheels off, took the shocks off, unhooked the front sway bar, propped up each scale so the corner was at approximately ride height when weighed... :shrug:

Front (without shocks, and wheel, swaybar detached) = 23#
Rear (without shocks, and wheel, what swaybar) = 11#

track pack shocks
front = 6#
rear = 7#

I MIGHT get the CG when I'm setting the ride height and corner weights.
Sweet were getting close

Here is a couple I got from the rear

Front Outside tire to outside tire 65'
Front Inside to inside 49.5'
Front track width 57.25'

Rear Outside tire to outside tire 67.75'
Rear Inside to inside 50.25'
Rear Track Width 59'

Rear Shock angle from vertical 9 deg
Rear LCA spring to pivot D1= 10.75'
Rear LCA ball joint to pivot D2= 14.25'
Rear Motion ratio .754

If we can get three items for the front I think we can finish it

1. Angle from vertical,
2. Spring Motion Ratio.
3. Sway Bar Motion Ratio
 

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Nice work. I have been looking for some of this data as well.

For the front:

Motion ratio= 0.66694444444
M1 (LCA spring to pivot) = 12.25
M2 ( LCA ball joint to pivot )= 15.0

Front shock angle = 0.78549 radians

THe motion ration of the shocks and swaybar are the same, since the sway bar bolts to the lower shock perch.

How did you calculate the front and rear roll centers? What are you units?
 
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