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Discussion Starter #41
I need to recheck my measurements. Maybe there is problem. To get accurate measurements I had to add multiple measurements together since things are in the way that prevents direct measurements.

I have found data on another forums that states the front roll center is 40mm off the ground and the rear is 70. I don't know how accurate that info is, buts its not even close to these results.
 

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Discussion Starter #42
These meaurements in the spreadsheet were wrong. I forgot to add something.

These are correct:
Height to upper ball joint 398
Height to lower ball joint 167

However, now the calculated roll center is negative?? I still think something is wrong.

I found this data from another source (I don't know the accuracy):

Lotus Elise

Front suspension
roll centre height 30mm
travel 50mm bump / 60 mm rebound
camber gain in bump 0.31 degrees per inch
frequency 90cpm
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

Rear suspension
roll centre height 75mm
travel 50mm bump / 70 mm rebound
camber gain in bump 0.45 degrees per inch
frequency 98cpm


Using the spreadsheet, I am getting -3.9mm front an +8.4mm rear. Thats pretty far off from the data above (30/75mm).
 

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These meaurements in the spreadsheet were wrong. I forgot to add something.

These are correct:
Height to upper ball joint 398
Height to lower ball joint 167

However, now the calculated roll center is negative?? I still think something is wrong.

I found this data from another source (I don't know the accuracy):

Lotus Elise

Front suspension
roll centre height 30mm
travel 50mm bump / 60 mm rebound
camber gain in bump 0.31 degrees per inch
frequency 90cpm
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

Rear suspension
roll centre height 75mm
travel 50mm bump / 70 mm rebound
camber gain in bump 0.45 degrees per inch
frequency 98cpm


Using the spreadsheet, I am getting -3.9mm front an +8.4mm rear. Thats pretty far off from the data above (30/75mm).

Yea I don't know the answer to if the control arm lines intersect on the outside of the on the same side as them then that would automatically give you a negative or below ground roll center, Is that right?
 

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These meaurements in the spreadsheet were wrong. I forgot to add something.

These are correct:
Height to upper ball joint 398
Height to lower ball joint 167

However, now the calculated roll center is negative?? I still think something is wrong.

I found this data from another source (I don't know the accuracy):

Lotus Elise

Front suspension
roll centre height 30mm
travel 50mm bump / 60 mm rebound
camber gain in bump 0.31 degrees per inch
frequency 90cpm
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

Rear suspension
roll centre height 75mm
travel 50mm bump / 70 mm rebound
camber gain in bump 0.45 degrees per inch
frequency 98cpm


Using the spreadsheet, I am getting -3.9mm front an +8.4mm rear. Thats pretty far off from the data above (30/75mm).
Sure that's not S1 data?
 

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Discussion Starter #45
It could be S1 data.

However, it appears that many preformance cars have roll centers in the 30 to 70mm range.

Based on my data from the control arm positions, even at stock ride height of 130mm, the formula is giving me a roll center below the ground. I still think there is either a problem with some of my measurements, or the forumula is in error.

I do find it odd that the lower control arms are pointed up, even at stock ride heights. That typically is not good geometry, but thats what my ruler said when I took the measurements. :shrug:
 

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It could be S1 data.

However, it appears that many preformance cars have roll centers in the 30 to 70mm range.

Based on my data from the control arm positions, even at stock ride height of 130mm, the formula is giving me a roll center below the ground. I still think there is either a problem with some of my measurements, or the forumula is in error.

I do find it odd that the lower control arms are pointed up, even at stock ride heights. That typically is not good geometry, but thats what my ruler said when I took the measurements. :shrug:
I remember reading an article somewhere about Lotus having trouble with the Elise oversteering in the design phase, and their solution was to put the instantaneous centers outside the front wheels. That was a while ago I saw that (years) and I wondered if it was true, but it's sounding like it is.

Edit: It would be a relatively easy thing to modify, by making a redesigned steering arm (piece 4) that moves the upper ball joint and outer tie-rod upwards.

 

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Here we go latest and greatest, let me know how it works.
Don't know if you still need it :) Buy I have tried to get the front roll centre from solidworks with the geometry data I have and I think your problem is the upright pickup points position!!..I have estimated them from a CAD file of the upright found in grabCAD, and I get around 30 mm..
 
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