6 Attachment(s)
Suspension Optimization and Tuning Help
After seeing several of Rons very educational threads I decided that it was time to put in some extra work and go to the next level and try to optimize my less than ideal budget setup. Here is a basic breakdown of my vehicle.
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1972 International Scout II
T: 2,805 lbs (F: 1,460 lbs & R: 1,345 lbs)
F: 52%
R: 48%
(These are close estimates based on less than ideal four corner scales, which were downhill and showed 53% & 47%. I am in the process of getting more accurate up-to-date weights)
Wheelbase: 99.75
FT: 57.8375
RT: 57.25
Ride Height Behind Front Tire: 4
Ride Height Center of Crossmember: 4.25
Estimated CG Height: 12 (That's the height to the center of the harmonic balancer, but I am not sure that is entirely accurate for my vehicle)
Front Tires: 315/35/17 Nitto NT05 on 17x11 (11.5 tread width)
Rear Tires: 335/35/17 Michelin Pilot Sport 2 on 17x12.5 (12.5 tread width)
Front Suspension:
The front suspension is S10 based with a combination of aftermarket and stock style parts. Its a basic stock style 2 drop spindle, with a larger stock style 33mm sway bar from a newer model and RideTech PosiLinks.
The tubular upper control arms are from a swap meet and apparently were designed for a metric dirt car, but have been modified. The upper arms use Allstar Adjustable ball joints adjusted approximately 1 from the tallest setting.
The lower control arms are RideTech StrongArms with the standard Moog ball joint.
The upper spring pocket has been removed to fit a 4.1 stroke RideTech Triple Adjustable Coilover with 4.1 stroke (10.125 compressed & 14.225 extended) running a 10 tall 2.5 ID 450 lbs/in spring.
I believe that my front suspension might possibly be considered a Tweener set up or at least it might be possible to set it up as a Tweener. Taking actual shock travel measurements at an event or by simulating event conditions is a priority once the weather is better. But for now I can only estimate based on videos and jouncing the front end that my front shocks can compress about 2.5-2.75 under heavy braking and are nearly bottomed out when the front cross member scrapes.
I typically shoot for about -1 degree of static camber, 0 toe in/out, and according to the FasTrax Adjustable Caster Camber Gauge I can currently register about 8.5-8.6 degrees of caster.
I am also battling a relatively high scrub radius due to my 17x11 wheels with just 4.25 backspacing. Using the method in Lances thread, I measured the scrub radius at 4 13/32
A few videos for reference:
http://www.youtube.com/watch?v=R9o9U...urp7H6zsMZlgX7
http://www.youtube.com/watch?v=ISMsvaYOpuE
An older video with the 47 truck body, but same basic setup with similar front weight. In this video the fender drag quite a bit because I had a tall passenger riding shotgun.
http://www.youtube.com/watch?v=t3Jg_RBur7Q
Heres a really tight GG course where I struggled with tons of push in the middle of the corner.
http://youtu.be/2RlgucBBqO4?t=1m8s
Steering:
The S10 spindle steering arm geometry has always annoyed me because its front steer and the arm is actually angled forward toward the centerline of the front of the frame because the tie rod must clear a tire (for small diameter stock style wheels) or in my case the wheel itself. Moving the tie rod end outward any further will require shortening the steering arm at least an inch or two so that it can clear the rim lip and barrel, but I have not quite been able to determine whether this is feasible or not. I have a 12.7:1 Grand Cherokee steering box. The stock spindle steering arm has a flat base at the end where the tie rod end mounts, but there was room for moving the mount back slightly, which effectively shortened the arm with good results.
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Rear Suspension:
Homemade truck arms with a single front pivot point (spherical bearing). The truck arms are mounted solid to the axle pad underneath the axle tube with RideTech Triple Adjustable Coilovers mounted behind the axle. It has an adjustable pahhard bar.
After reading the mapping instructions, and then rereading them again, my dad and I spent the better part of two days developing creative ways to map out the front suspension. There were small, but mostly consistent variations side-to-side, but we double checked each measurement and/or checked against a different measuring method in some cases. I have those measurements in a spreadsheet. Thus, if possible, I would like to set and tune the front roll center height.
I primarily want to excel at autoX and tighter corners. I drive to events, but comfort is largely not an issue as long as the setup is not so harsh on wear parts that a 200 mile trip is out of the question. I also occasionally run track days, where I think the Scout feels much easier to drive than on a tight autoX course, but I do these mostly just for fun. At Mid-America Motorplex I was not running 10/10ths by any means as it was only my 2nd time on course, I have very little formal training, and I do not have anything near a racecar level of safety gear. Anyway, once I was a bit braver at the end of the day my quickest timed and recorded lap with Harrys Lap Timer was 1:47. One of the quickest times I logged without a video was nearly a 1:46 flat with a gear limited top speed of 128 mph on the main straight. I am told that a good driver with a stock C6 Z06 should run in the realm of 1:45.
I favor running a modern high travel/low roll setup if possible, but I think I would currently fall into a tweener setup.
As I was reading through some of the helpful threads I came up with a few general goals based on what I have read so far:
1) Map the roll center and correct problems shifting towards a high travel/low roll setup if feasible
2) Correct and potentially improve LCA geometry
3) Correct and potentially improve UCA geometry
4) Build in Ackerman steering (I think but am not certain that my steering geometry is a huge hinderance on tight autoX courses)
5) Dial in caster and caster gain
6) Determine if more sway bar is necessary
7) Determine if spring rate changes are necessary
8) Possibly revalve my Ridetech coilovers if appropriate
9) Properly dial in and adjust my coilovers
10) Learn as much as possible