Dissappointing autox with the LS Z

[carusoracer]

Great answers from the forum. What region are you in? If te SS guys are fast then take one SS driver and have him take a fun run ride with you or better yet if you trust let a very experienced driver take a run.

I have taught many drivers schools for AutoX and the first thing I usually notice when I ride with someone is there line and throttle inputs.

 

After a few runs we would swap, most drivers can figure out your car after 3 manuevers. It is up to you to fine tune after that for driver likes and dislikes.

Also if you are running short 22" tires with all that power you need to try the 23.5" Slick on 10-12 inch rims with around one degree or less camber in the rear. Bias Ply tires do not need that much camber and are more forgiving than the radials.

Good luck!

Good rule of them is to check your control arms especially in the rear static to make sure they are level.

[heavy85]

So this is what I did:

 

Front left camber 2.75 deg, front right camber 2 deg (needs more work)

Rear camber 1.5 deg, Front toe 1/4" out, rear toe 1/8" in. Front height 5 3/4" just in front of the fender bolts (w/ 24" street tires ... race tires are 22.5"), rear height 6 1/8" at the rear quarter to rocker seam. Added back rear bar. Lowered air pressure a couple pounds. Concentrated on throttle modulation. Learned that camber is very sensitive to ride height. Also set everything with me in the car thinking since it's stiffer it'll be more sensitive to cross weight.

 

And the results ......... I froze my a$$ off today but was within 0.1 sec of FTD ... and I corded a tire (the inside edge which the only thing that wears on them). So now I am much happier and need new tires. Part of this was the super fast guy was not there and the track layout was very well suited to my driving style but all things considered I've gained seconds over last race. It now feels like I remember it running before just with more power.

 

So now I have two questions:

1) What tires should I get for 15x10 rims? I'm using 35 compound hoosier 22.5x9.5x15 slicks and they seem a little hard. Good on HOT days but otherwise dont really heat-up. Lasted maybe 13 races.

2) Should the front springs be stiffer or softer than the rear? I'm currently running 225F/250R but am considering maybe going up a little.

 

I think I need some way to adjust caster (I have EMI plates but that doesn't seem to get you much) and maybe add wheel spacers on the front.

 

Cameron

[johnc]

The 275/35-15 Hoosier A6s are working well for a lot of the SP guys. A customer who has moved his DSP E36 BMW to FP is staying with the A6s because, at 2,100 lbs, his BMW is quicker on those tires then the Goodyear and Hoosier slicks he's tested. The guys at Hoosier confirmed this in a couple phone conversations.

[johnc]

Regarding caster, the TC rod and the LCA bushing has more to do with caster then the camber plate. The EMI plates let you get 1 to 2 degrees more caster by themselves but you have to watch out for bind in the LCA bushings and a stock length TC rod will negate some of the additional caster the EMI plate allows.

 

I typically lengthen the stock TC rod about 1/2" to work with the EMI racing camber plate. Just that combination alone, along with custom Hydlar LCA bushings, got me 7 degrees of positive caster on my old 240Z with very little friction. If you're running a monoball for the LCA pivot you can get up to 9 degrees of positive caster, but you'll have to cut the front valance and air dam.

[JMortensen]

So now I have two questions:

1) What tires should I get for 15x10 rims? I'm using 35 compound hoosier 22.5x9.5x15 slicks and they seem a little hard. Good on HOT days but otherwise dont really heat-up. Lasted maybe 13 races.

People have said that the R35 compound is about the same as the Yokohama slicks that I ran when checked with a durometer. If that is the case, I agree with you. Those Yokohamas really were too hard for autox. I think the simplest answer is try an R25 compound. Or an R15. For other options I'd try the Goodyear FA front slicks. They're just a hair taller than what you have now, and they come in an R160 and an R100, I think they used to have an R080. All should be softer than what you're currently using.

 

If you ran the A6's John recommends you could be re-classed in O/SP, which might be cool. I ran that class for a couple years and loved it, just because I got to race against all kinds of weird cars. I thought there was some issue with those tires not holding up on heavier cars though. I thought it was even John who posted about it.

 

I think the rod end front control arm is the best solution when you're adding caster, because a poly or other LCA bushing will tend to want to bind. I'd do a rod end TC rod too. You'll end up with a shorter TC rod, but you can dial in a lot more caster. Unless you start modifying the frame, that is...

[tube80z]

The 275/35-15 Hoosier A6s are working well for a lot of the SP guys. A customer who has moved his DSP E36 BMW to FP is staying with the A6s because, at 2,100 lbs, his BMW is quicker on those tires then the Goodyear and Hoosier slicks he's tested. The guys at Hoosier confirmed this in a couple phone conversations.

 

The new B compound is supposed to be the same as the what the A6 uses and I've been told negates this advantage. You still have the radial versus bias ply thing and so far I've found radials quicker. How long it will take Hoosier to get radials into all the slick sizes has yet to be seen.

 

Given your soft spring rates you will probably be better with A6 hoosiers or using the kumho 710s. The slicks need to be worked pretty hard to get heat into them and make them function. The Atlantic tires even more so. So keep that in mind when you read "our" tire advice.

[johnc]

I thought there was some issue with those tires not holding up on heavier cars though. I thought it was even John who posted about it.

 

Oops. Forgot about that. How heavy is the "heavy85"?

[heavy85]

Oops. Forgot about that. How heavy is the "heavy85"?

 

Heavy85 is actually leftover from gokart days when I ran the heavy class due to my personal trim 220 lb curb weight (cough cough).

 

Car is a '72 240 with a LS1, T56, R200, stock brakes, SFC, no rollbar (yet), stripped interior (dash, one seat, door panels and that's about it), no wipers or heater. It's pretty basic to say the least and right now I dont even have a passenger seat because then I couldn't fit the race tires inside. I'm guessing somewhere between 2300 and 2400 lb but that's just speculation based on what other cars have weighed.

 

I would like for whatever I get to last the rest of this season which is maybe 8 or 9 autocrosses and hopefully one track day. Would the A6 do this? Also like the cost of the used slicks like I got before but that's just because I'm cheap. I could be swayed to spend more. My current hoosiers were like $75 per with only one heat cycle on them and literally 100% tread. I'm also tossing around the thought that I add a passenger seat back in so I can give rides and just get some ultra high performance (or whatever they are called these days) street tires. Not sure I could stand losing a second or two over the race tires though ...

 

Cameron

[tube80z]

The slicks will last a lot longer if you flip them on the wheels and rotate often. I do two events (Fri, Sat, Sun) on a set before flipping. I use two sets of wheels to do this. Friday I will run in the Sunday tires. Saturday I will run the practice set. If done right I get a new set of used tires that are added to this each year and the 4 worst tires are removed. For the bias ply slicks I match them by diameter. Tires are bagged after each event and treated with formula V following the directions.

[heavy85]

Looks like I will be getting the new (actually will get them used w/ 100% tread) Hoosier radials 23x9.5x15 in the R25 compound. Any recommendations on setting changes to work with the radials vs the bias plies? Also unanswered is question which end should have higher springrates - the front or the rear if anyone wants to bite.

 

Cameron

[260DET]

I think that F/R spring rates have already been suggested. Anyway, if you have a persistent straight line traction problem it may be worthwhile trying heavier in the front, which is opposite to the usual with the S30. Say 325F 275R, 350F 300R...........

[JMortensen]

Looks like I will be getting the new (actually will get them used w/ 100% tread) Hoosier radials 23x9.5x15 in the R25 compound. Any recommendations on setting changes to work with the radials vs the bias plies? Also unanswered is question which end should have higher springrates - the front or the rear if anyone wants to bite.

You'll need quite a bit more camber for the radials.

 

As far as the spring rate thing goes, I think you're chasing your tail asking the crowd. What you need is to figure out the front to rear balance. Things like having a rear sway bar and the diameter of the front bar, the ride height front and rear can really vary the spring rate needed to balance things out. Try the Weight Transfer Worksheet. Play with the spring rates, and play with the roll centers. You'll see that there are so many variables that affect the car so much that its really not easy to make a very accurate recommendation.

[heavy85]

Quick update so others who've swapped dont get discouraged.

 

I actually now have MORE rear grip than front on corner exit. When I first started after the swap the rear was always stepping out as mentioned above. It got a lot better after the few tweaks. However, since it's gotten hot and the slicks get much stickier combined with now softer tires in the rear (35 compound front, 25 rear) when I hit the throttle at corner exit the front end tends to wash out instead of the back snapping around. Hope to help fix this with the 25 compound radials all around. They should be going on this week in preparation for a high speed autocross this weekend.

 

Cameron