JiminVirginia

Because I 've been there. See Sam's post.

My car handles really well now, and I don't see how I would have gotten there on the OEM springs. Simple as that.

Just trying to be helpful. I hate to see guys spend tons of money doing one mod at a time and not getting where they want to go.

Cheers, Jim.

Sam Strano

As speed climbs the car will become more free. Understeer is always worst in the slower tighter corners. 1. They are the easiest for the driver to overdrive. 2. Tighter radius but the same tires and mass and lack of grip will always show up at the front first. And the car will always push a bit if you are at the limit on those tires, and at some point will more easily transition to oversteer. The entire package effects balance, starting wtih the driver, through the suspension and down to the tires. Change one thing and 3 other could go with it. What we want is balance. I think the springs will help you there, and we can use the shocks to help settle the car transitionally. We can also play more with pressures since we wouldn't be relying so much on the tires for spring rate having more spring in the car.

And banking will always help the car turn. Add the banking to the higher speeds and it's not surprise the car is "better" balanced there.

Red06

It’s interesting that the first thing most folks go to to solve handling issues is additional hardware. But damping and tire pressure are also supposed to help. From my reading to date, understeer is corrected by (not necessarily in order of importance): 1. Adding more rear bar/stiffness which I understand, take weight off of the inside wheel and reduce traction in the rear. I’ve seen fast front wheel drive cars lift the inside tire more than 6 inches off the ground through esses. 2. Increase rear damping or softer front setting, stiffer rear seting (per the D-Spec manual). I haven’t been able to figure this one yet. It's not really the same as a stiffer rear bar because as Argonaut says a slow rear end through transitions (heavy rebound damping) means less responsiveness not more (not un-weighting the inside rear tire). Maybe it helps in wide fast corners but I don’t see it fast transitions. And 3. Higher tire pressure in the front and lower tire pressure in the rear. I don’t get this one. Making the fronts harder and the rears softer seems like you’re adding less traction to the front and more to the rear. A recipe for more understeer to me… I’ve heard some pretty fast RWD drivers say they run more pressure in the rear (one being an instructor in my track group who drives an 03 GT). However, he has an IRS from a Cobra and maybe that makes some difference… I don’t know. Thoughts anyone?

I tried higher rear pressure on a wide fast track (Grattan Raceway) and really smoked. I also tried lower rear pressure at the next event at a tight technical track (Waterford Hills Raceway) and seemed to plow more not less. However, I did figure out how to use late heavy braking to “plant” the front end just as you're turning into slower tight turns. Once you plant/stick the front end, it really stays! Much more effective than trying to power through them.

Maybe Sleeper 08 meant to say he sets his pressure to 32 lbs cold because he’s keeping them at 40 lbs hot. They’re definitely not going down in pressure when they heat up… ☺ I’ve been setting the pressures to 35 cold and the shocks from 2 to 2.5 front and the backs the same to ˝ turn softer. I was going to play with the softer front settings the last time I was at the track but it rained most of the day so I couldn’t really tell what (if any) difference it made. There was only one session with a nearly dry line so there was nothing really to compare it to.

I’m one of the small trailer guys for the tires and tools. I think Argonaut must be part contortionist and part magician to get his tires in the back of the car. I didn’t even try because I didn’t think it could be done. You are definitely a man of vision to get all that into you car. Hats off to you.

Argonaut

I agree, to me its the other way around, raise pressue in rear and lower in front to reduce understeer. Either - I don't get it at all or someone accidentally switched those in an earlier post.
LOL - it is a tight fit and a pain in the a$$ but you-do-what-you-gotta-do. I hope to get a car trailer and pull it with my Suburban within the next couple years.

Norm Peterson

During corner entry it shifts the corner weights around. If you let the inside front corner rise faster than the inside rear by playing with rebound damping the ultimate effect is to increase the difference in rear tire loading during the time that the car is rolling.

Lower inflation pressure is generally associated with requiring a greater slip angle to generate a given lateral force at a given vertical loading. More rear slip angle = a "loosening" tendency. How effective this approach is probably depends on things like how wide your rims are relative to your tires. With IRS, you're using additional tire stiffening from the higher pressure to crutch camber change (loss, actually, as in less negative/more positive) in addition to the effects of lateral tire distortion.

You can also make a car loose by running the rear pressures up into the range where you are mostly just throwing away rear grip. This way is a common FWD tuning approach. Then too, with FWD you don't need rear grip for acceleration during corner exit, so it doesn't matter once you've got the car rotated and are unwinding the steering/squeezing down on the throttle.


Late edit - I'm pretty sure that Sam Strano runs slightly lower tire pressures in the rear than up front.


Norm

Sleeper_08

After reading the comments above I remembered we took some tire temps on my third track day and would be interested in hearing your comments.

These were taken on Aug 4 with a non contact pyrometer at Dunnville on the Stewart circuit which goes through Gilles, Len's in the diagram below. The track has no elevation changes. The final curve before the pits is a third gear right hand sweeper, Curve Grande, and normally you shift to fourth about where you exit to the pits. The temps were taken immediately after we came off the track running hard through the last corner.

First run 9:30 AM my brother driving, track temp 85F and his lap times were from 1:17 to 1:20. The tires had been set to 38 lb before starting the run
LF 46 lb hot RF 44 hot
O M I I M O
156 153 140 147 140 139

LR 46 hot RR 44 hot
O M I I M O
159 155 147 154 153 141

Second run - me driving track temp 98F and my lap times were from 1:19 to 1:22. The tires had been set to 40 lb hot before starting run
LF 40.5 lb hot RF 41 hot
O M I I M O
154 151 140 153 151 148

LR 41 hot RR 41 hot
O M I I M O
158 156 150 142 148 143

Front end is set to -3/4 camber and 1/8 toe in. Mods per list below.

Sam Strano

If theories ran the world, it'd be a different place.

Let me ask this: Which end of the car is heavier? Which end is worked harder? Yes, you use pressures to balance the car. In fact I run very different pressures on my Mustang GT than we use in the Shelby GT I also autox (but only in the rear). Why? The balance of the cars is different. But I don't run less air in front of my GT than the Shelby, you still need enough to deal with the mass and tire flex appropriately.