Alignment Specs for Autocross

[musicsurf]

Sounds like "slow in---fast out" to me!

Exactly! I got to see that in play in a very drawn out, but good example. Darren came way too hot into a turnaround in my car, but instead of cranking the wheel and pushing through the turn (which would kill the exit speed) he kept braking in that straight line deeper into the turn and used that extra distance and new found grip to carry more speed into the straight. Doing that he salvaged quite a bit of time that would have been lost otherwise.

[nilfinite]

The slow in fast out concept was really hard for me to appreciate until I saw the data proving it. Going slower into a corner not only lets you set up better for the straight in the fast bits, but also lets you take a shorter line in the slow bits.

The instructors were faster in the slow parts and I was faster in the fast parts initially (because they weren't going all out). By the end of the day I was fully appreciating slow in, fast out among other things!

But at that event, that's where I was starting to see the inside edge wear a lot more than the outside edge. Makes me think I should try less static camber and more caster.

[musicsurf]

Inside tire wear isn't going to get worse at autocross unless toe out is the problem. The constant turning means the loaded inside tire is getting closer to 0 or even getting into positive camber. I'm running -1.8 and drive a ton and haven't noticed any abnormal tire wear either on my autocross or street tires. That includes having 1/32" toe out in the front. You may just want to make sure things are still aligned properly. Try getting to a race shop to have it done. I'm sure that being in San Francisco there should be plenty of options and they will not only be able to set you up, but they are a wealth of knowledge.

[nilfinite]

There are some shops but certainly not as much as areas like SoCal. I haven't found a shop yet that could make me shims to fix the rear alignment as well.

Cost of corner balancing + front-only alignment: $600...

[nilfinite]

Another idea for consideration. Has anybody tried disconnecting their front sway bar for AX?

[jguerdat]

Guess the answer is no. Depends on the class rules and what you've modded already - I have the Neu-F rear bar in stock class so disconnecting the front would be illegal. I'm also running camber bolts in stock class so it's not like I couldn't do it as an experiment (unless I finally beat that pesky HS Mini)...

[nilfinite]

I'm running in STC which allows any change to sway bars. I'll try disconnecting the front sway bar one of these days at a test n tune and see if it makes a difference. Just need to figure out how to keep the front tires happy.

[nilfinite]

I think I've finally figured out the reason: Not enough weight on the front + different sized tires.

Since the Abarth is FWD and I'm slowly building up the AX mods, for AX I use just two wheels with ZII tires. That wheel set is mounted from the front when I'm AXing. The car being FWD, all of the action is in the front and the rear rarely sees any wear when I autocross so I just leave my DD set on there.

Anyway, the point is, the only ZII size that would fit the Abarth was the 17" 215/40/17 size. So I have 17" ZII tires in the front and 16" RE-11 tires on the back.

The 17" tires have a diameter of 23.8" and the 16" tires have a diameter of 23.2". Leading to a difference of .6" in diameter (.3" radius difference).

I set the Bilstein's height based on Axle to Fender distance (F: 12.5" R: 12.9"). Technically the Axle to Fender distance should be close regardless of wheel/tire diameter. But I think I can safely guess that the tires behave differently with different diameters.

So I when set the bilsteins with the 16" tires, the front of the car is .8" below the rear of the car (radius difference x 2 = diameter difference). With the mixed tires, the front of the car is .2" below the rear of the car.

Mentally picturing the front of the car being higher than the rear of the car, I can see how that would wear the inside edge more. Granted the weight distribution is 64/36 stock, stock Axle to Fender settings are also 1" different front to back.

So the combination of the coilovers being set closer front to back and higher tires on the front, means the weight distribution is more on the rear, leading to less grip on the front tires and wheel spin.

[nilfinite]

Just a follow up to this thread. I started autocrossing with the same 17" ZII tires on the front and back. Now I'm starting to see just tire wear on the outside portion of the thread as well as the shoulder. So the mixed tire answer solved the inside tire wear question.

Now I just need to figure out how to fix the outside edge tire question, which is a lot easier to explain: Wheel spin when coming out of corners (need to be easier on the throttle & slip angle coming out of a turn) and not enough dynamic camber.

[BigDaddySRT]

So the combination of the coilovers being set closer front to back and higher tires on the front, means the weight distribution is more on the rear, leading to less grip on the front tires and wheel spin.

With Coilovers:

On a FWD Car... you Balance the Front to Rear in an X Pattern. Put the car on a set of four scales. Balance the Driver Front to Passenger Rear, Passenger Front to Driver Rear.

You will need to sit in the car, and set your Gas Level to what you plan on racing with. Let the Balancing Begin.

[doverosx]

I haven't seen a thread yet with the different alignment specs people are using for Autocross.

Here is the best info that I've seen so far: http://www.fiat500usaforum.com/showt...l=1#post630581

After almost 60 AX runs, my Direzzas are starting to see a lot more wear on the inside edge.

Measuring tire temps, it looks like the inside edge is the warmest with temps gradually dropping as I move across the tire. Then there'll be a temp spike where I've rolled over onto the sidewall. My guess is, too much negative camber? I'm currently running -1.8 camber, 0 toe & stock caster in the front.

The rear specs aren't adjustable until we find shims that work for our car. I currently have the toe correction kit which worked well to stabilize the car on the freeway. I'm not too worried about the rear because the difference in tire temps and tire wear across the tire is very minor.

What do the suspension experts think?

That sounds like you need more tire pressure. Be very careful not to get the tire too hot and dump/spray some water on them if you get them hitting the 60's.

[nilfinite]

Ran an AX event yesterday with the RE-11 tires vs the ZII Star Specs. Car felt great almost exactly how I like it. Nicely balanced with a definite preference for oversteer.

Three things may have been the cause for the improvement. The tank was close to empty, causing more weight distribution in the front? Second may have been the tires. The RE-11s are skinnier and less grippy so it might have been easier to make the car oversteer at lower speeds. Third, I tried 46 cold psi in the front and 34 cold psi in the rear when using the RE-11s. I think I need to decrease tire pressure more in the rear when using the ZIIs.

[nilfinite]

I'm very happy with my current specs. This setup includes: Neu-F Front Sway, Bilstein Coilovers, Whiteline Caster-Adding Bushings, CPR 30mm Torsion Bar, Wavetrac LSD, 17x7" Wheels + 215-45-17 ZII Star Specs

Left Front
Camber: -3.4
Caster: 3.5
Toe: -0.07

Right Front
Camber: -3.4
Caster: 3.5
Toe: -0.07

Left Rear:
Camber: -0.7
Toe: 0.14

Right Rear:
Camber: -0.8
Toe: 0.23

Rear specs aren't adjustable without shims. Will one day finalize my suspension setup and order the shims to set the rear how I like them as well.

[doverosx]

This is what I have found with the SpecV and my friend's Civic Si. Rear tires needed less pressure than daily driving usually, just so that we could get the rears rolling and contributing to overall grip. Lower it too much and you snap oversteer, increase it too much and you snap oversteer.

I have found that the Abarth rewards two things big time; trail breaking and patience (getting on the throttle nice and smooth...and waiting the hard part in any car).