Tire tuning, Not getting full tread to the ground Options

[Joe Ricard]

So I just completed my 2nd Autocross of the season. Getting much closer to the front guys compared to last year.
It seems i am not getting all the rubber to the road. More wear on outer edges than inside.
1st event I set tires at 35 PSI all around Tires rolled a bit and scuffed the outers edges more.
2nd event I set pressure at 38 psi Much faster and seemed to have more grip. Still not scuffing inner edges at all. 1.5 inches from side wall shoulder.

Car is a 70 914 2.0L carbed motor, cars Weighs 1979 pounds, Stock torsion bars infront 150lb coil overs in rear. Poly suspension bushings in rear. (fronts get it this weekend) Koni externally adjustable shock all around. Weltmiester 21mm front sway bar set at 1" from end and stock 2.0L bar in back Poly bushings both bars. Running 205/50-15 Kumho Ecsta V700 tires at full tread. 2 degrees camber all around 1/16" toe out front and slight toe in at rear 1/32" maybe.

Which way should I adjust the car? More camber? or stiffen the front bar. Currently the car seems pretty nuetral with the bar as they are and shocks set at 1/2 the range.

[r_towle]

I think that given the stock torsion bars and the stock rubber bushings, you might have to much flex on the front end for the tires to behave as you would like under heavy autox turning..

What type of tire do you have?

Rich

[TimT]

More camber, less toe

crank as as much camber into the car as you can get.. set toe for 0 deg

Tire pressure is fine tuning..

You need to get the whole tire working for you

[Joe Ricard]

QUOTE (TimT @ Feb 2 2005, 08:08 PM)

More camber, less toe crank as as much camber into the car as you can get.. set toe for 0 deg Tire pressure is fine tuning.. You need to get the whole tire working for you

Less toe ??? front or back???
I agree with more camber.... Not sure how much more I can get with out camber plates $$$
Kumho Ecsta V700 R compound. Full tread not heat cycled. As recommended from successful racers here. (I like them).
Another board had some recommedations were to increase the spring rates nearly 3 times what I got???? Maybe I should have mentioned I drive the car on the street to and from the event.

[SirAndy]

QUOTE (TimT @ Feb 2 2005, 08:08 PM)

More camber

when you say more camber, you mean more NEGATIVE camber, right ????
because technically, that would be *less* camber. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

if the outside wears more than the inside, you need more *negative* camber ...
(IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif) Andy

[Joe Ricard]

QUOTE (SirAndy @ Feb 3 2005, 09:10 AM)

QUOTE (TimT @ Feb 2 2005, 08:08 PM) More camber when you say more camber, you mean more NEGATIVE camber, right ???? because technically, that would be *less* camber. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) if the outside wears more than the inside, you need more *negative* camber ... (IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif) Andy

Damn, I guess you are right. But then again Duh...... How about less Positive camber or more negative camber . For some of us lean the top of the tire inwards.

I was also thinking about stiffening the sway bar in front .... In an effort reduce body roll. However this will increase understeer unless I can increase the rear bar proportionally. Currently the rear bar is a stock unit from a 2.0L with poly bushings.
928gt.com has a end link that can mount the attachment point further from the end. Hence stiffening the bar.

[TimT]

QUOTE

when you say more camber, you mean more NEGATIVE camber, right ????

yes, I take it for granted sometimes. try to get more negative camber.
You may have to clean up the undercoating etc from the shock towers, and oval the bolt holes to get more ( negative) camber Im alwasy in a quest to get "more camber" On my car I have got near -3 deg, but I have those camber platess with the offset holes.

[Joe Ricard]

I'm going to keep this going. Because:
1. it has 914 content
2. Someone needs advice to set up car (me)
3. no porn (yet)
4. Going to work on car extensively all this weekend to get ready for 3RD event of the year (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)


SOOO (IMG:http://www.914world.com/bbs2/html/emoticons/icon_bump.gif)

[SteveSr]

3rd event of the year.....?????? (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) the SNOW ain't even off the ground here yet (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif)

SteveSr

[Joe Ricard]

QUOTE (SteveSr @ Feb 3 2005, 12:44 PM)

3rd event of the year.....?????? (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) the SNOW ain't even off the ground here yet (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) SteveSr

na na na na!!!!!!!!!!!!!! (IMG:http://www.914world.com/bbs2/html/emoticons/mueba.gif)
On the other hand we also have Night events June July and August. Because if you ever sat in grid with a full face helmet in a teener at high noon. You would be ready to give your left nut for A/C.
So who has a CHEAP bigger rear bar?

Come on man I gotta fix something. (IMG:http://www.914world.com/bbs2/html/emoticons/chowtime.gif)

[Demick]

The outside edges of your tires will always scuff more than the inside. That's because the tire is heavily loaded when the tire rolls over to the outside edge, and unloaded when the tire rolls over to the inside edge. So comparing the amount of scuffing is not a useful measurement.

Your tires should have little triangles molded into the sidewall near where the 'tread' ends. These are a visual indication of approx how much scuffing you should expect. Your tires are already scuffed, so the easiest way to know how far your tires are rolling over is to use some white shoe polish and paint some marks on the sidewalls of the tires. After an autox run you can look at the shoe polish and see how far the tires are scuffing by looking at where the shoe polish has worn.

Only then can you start to make meaningful changes.

Demick

[Joe Ricard]

I see your point and this is exactly what I have been doing. So now that I have a somewhat idea of what it is I want more negative camber is whare I need to go..
as a course adjustment. So far 2 degrees hasn't had any adverse affect on my street tires (yoko AVS 100) with over 600 miles of driving to events.

[Don Wohlfarth]

Car set up looks OK. You may want to try for more negative camber all around. For ax you usually set front toe zero or out a little as it aids in turn in. Can also make car twitchy at speed. You also want a little toe in at rear, 1/16 should be fine.
Your problem may be tire squirm because of the full tred or low air pressure. The white shoe polish will give you an idea how much the tire is rolling over. Find the little triangle. If you go past it add air, if you don't barely touch it let air out.
You want to find the correct air pressure so you can maximize the tire foot print. Check the triangles and pressure after every run. A pyrometer would give you a better idea how the tire is working but in ax the runs are so short you'll never get any real temperature in the tires.
Since the car handles OK and seems to be neutral I would not adjust the sways.

[Joe Ricard]

Thanks Dan, I got the front up on jackstands last night pulled the wheels and jumped into removing old tired suspension.
The camber is ner maxed out. as the stamped steel plate is snug up to the shock tower. Also seems that the shock is also touching the inner side of the fender well lip.
Guess I will clean up the under coating as Tim mentioned. maybe I can get a little more.

[SirAndy]

QUOTE (Joe Ricard @ Feb 4 2005, 04:56 AM)

maybe I can get a little more.

that doesn't sound right ...

with that much neg. camber already, you should *not* have a 1 1/2" patch on the inside of the tire that doesn't get used at all!

are you sure your suspension (A-Arm) is not bend?
(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) Andy

[Revolution Wheels]

Unless I missed it you did not mention the width of the wheel you are using. Having been a race tire dealer in a past life, we know that wheel width will certainly have an impact on how "flat" the tire contact patch will be. Ideally the wheel width should be close to the actual tread width which will allow the sidewall to stand up straighter and work the way it is designed to. If the wheel is too narrow, the bead is "pinched" and the tread will balloon and not be as flat as desired.
As an example, a couple of years ago the Acuras running in the World Challange series were allowed to move up from 7" to 8" wheels with the same 225 tire that they were restricted to. We found that tire wear, handling and braking were all greatly improved with this match.
Just food for thought!

[Joe Ricard]

Factory 4 lug Fuchs.. And I think you are on to something. I would be happier with some 15 x 7 Panasports. Who wants to trade?

[john rogers]

You didn't say if this is on all four wheels or just the front? I would think the negative 2 degrees in front should be plenty? That is what we run on our nearly stock 74 car. We do have V700 tires, 205 size on 6 inch rims and run a very stiff front sway bar setting with stock front torsion bars. The tires wear evenly across the tread. we also run only 26# of air pressure front and back hot. Can you get someone to video tape an autocross session, especially the corners where you are putting a heavy load on the tires such as a 180 degree turn as I am thinking the front is getting too much load which means it has to push back harder, meaning stiffer front torsion bars. If you are lifting the inside front wheel then you need stiffer springs in the rear as you want the car to corner as flat as you can make it. The flat cornering will help prevent the tire roll over.

[Joe Ricard]

Thanks John. I am gaining tons of knowledge form you guys. I have been trying to get someone to go with me. However that means baby sitting the wife to keep her happy. Totally takes my mind off of the task at hand. GOING FAST IN THE SEA OF CONES.
Maybe if I bring the camera I can get one of the STS hotties to film my runs (IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif) About the only reason I tolerate the street racers They got hot girl friends. (IMG:http://www.914world.com/bbs2/html/emoticons/lol2.gif)

[mskala]

Back when I first had the kumhos, I went with 36psi and got wear all
on the outside edge, too. I use 30 now and it's better. This season
maybe I'll try lower like John uses.