[Ron Sutton]

Rob,

What I have outlined below is a soft spring/big bar … high travel, low roll suspension setup that you & I discussed … to optimize the handling of your long wheelbase car with tires 21% larger in the rear.

It is just a baseline to start from ... and it assumes a lot of things for us to discuss & get clear on. Most of these assumptions can be tuned around, if my assumption is wrong. Some can not.

Assumptions:
3500# car
116" Wheelbase
51.5% front weight
19” CG height
2.5”-3” front shock travel in dive
Front track width 56” & rear 58” / 2” wider in rear
285 front tires & 345 rear tires / Same compound front & rear

Readers … do not run with this set-up for your car. That would be like taking someone else’s medicine when you have no idea what health issues they have. I can not say this strongly enough. This is not a universal set-up or even a universal concept. I have outlined this for Rob’s long wheelbase Torino with tires 21% larger in the rear & a 2” wider rear track width.

Baseline Starting Point to Tune From:

Springs & ARB's:
Front Wheel Rate: 275#
Front Spring Motion Ratio: _________?
Front Spring Rate: _________?
Front ARB Effective Rate: 1050#
Rear Wheel Rate: 350#
Rear Spring Motion Ratio: _________?
Rear Spring Rate: _________?
Rear ARB Effective Rate: 400#

ARB (Anti Roll Bar) Arms:
Front: Short, strong (4130 chromoly)
Rear: Steel, no aluminum

Front Roll Center: 4" at ride height & 1.25"-1.5" in dive
Rear Roll Center: 11” with level Panhard Bar at ride height

4-link Specs:
Lower Bars: 0.0 degrees / Level at ride height
Upper Bars: 9-10 degrees down in front
Instant Center: Same height as lower bars … 50-60” ahead of rear axle CL
Pinion angle: 2-3 degrees negative from the driveshaft*

Front Shocks:
I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the front, to slow the rate of compression on braking & corner entry & substantial rebound valving to hold the front end down through the corner.

Rear Shocks:
Again, I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the rear, to slow the rate of compression on & corner entry & moderate rebound valving to keep the rear tires planted on corner exit.

Adjustable Shocks:
Triple adjustable shocks ... low-speed rebound, hi-speed rebound & hi-speed compression ... are a key to dialing in a bad ass race car on track day ... and dialing it back to a drivable Pro Touring car at the end of the day. There are poor shocks, good shocks & great shocks available. I choose not to talk brands on a forum.

Wheel width:
Your 285’s need to be on wheels 1” wider than the tread width & put the rear tires on wheels with the same width at the tread width. You want the front tires “stable” and you want the rear tires to “move around” a little.

Tire pressures:
Optimized for full contact patch & even temps.

Rob, as with all cars that get pushed to their limits ... when you find the limits, you WILL NEED TO TUNE on this set-up. I’ve got you close … except for shock valving … which we’ll need to discuss.

In my next post, I’ll outline some tuning strategies after you run it on a road course. And if you want, we can discuss some changes for better AutoX performance.