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I seem to chew up my tires more rapidly than many of the guys I run with. However, that is an apples to oranges comparison as they mostly drive 911/Caymans. So I need some 928 specific input.
I certainly understand that tracking a car is going to eat tires, but I want maximize where possible.
This is how my tires die; Cording on the OUTSIDE Edge, fronts first, but rears also affected:
Related data:
1. I have run pressures from the low 30’s up to low 40’s (HOT). I have settled on 39 -41 (Hot) depending on track for best feel. Less than that does add very moderate improvement in performance, but dramatic increase in wear.
2. Tires are Nitto NT01.
a. Front: 225/40ZR18 (I have also run 235/40ZR18)
b. Rear: 275/35ZR18
3. Rims are Carrera III
a. Front 18/8/57
b. Rear 18/11/51
4. Most recent alignment as below:
5. Koni Adjustable Reds, set about medium.
6. Eibach Springs, Rates are as follows:
a. Front 399-559
b. Rear 285-372
7. Car is driven 2 or 3 times a week on street tires, wear is ~normal
8. Car is tracked ~1 a month spring/summer/fall
9. I have always swapped tires left to right ( as the track I drive are much harder on left side) and have started swapping inside to outside on the tires when possible ( my tire guys hates this, and it does add up $$))
10. Ride height
a. 160 Front
b. 163 Rear
Questions:1. Am I overdriving the car/tire? If so, I can dial back and keep stroking checks.
2. Is it essentially my “Street” alignment that is causing the poor track life? If so, am I at the best compromise for:
a. Camber?
b. Toe?
c. Height?
d. Etc.?
e. I understand that a combination track/street car is always going to be a compromise, but it make sense to maximize that compromise.
3. Other suspension issues?
4. Adding “more” tire up front? 235/40’s fit . 245/40 may need a touch of fender roll.
5. Driving style? I work hard on smoothness and proper corner entry, but can always improve/change.
6. Other?
More camber front and rear. This eats street tires but it's a compromise. Go with -2 in front and -1.5 in rear.
After each event have the fronts "flipped" on the rims and re-balanced and then swap sides. This keeps the tires turning in the same direction while making the outside edges inside edges.
Right more negative camber is needed....I have 3 1/2 or so on the old very brown 1980 and even tire wear on the track but street driving it wears the inside edges over time.
Most modern performance street tires actually enjoy a little more negative camber than the factory street recommendation. Many folks get nervous about big numbers because they are worried about increasing inner-rib scrubbing, but that is much more a function of toe-out scrub than negative camber. Your toe numbers look good for street driving, OK for track. Most track drivers like the quicker turn-in that comes from a zero toe setting. So don't be too worried about getting another alignment with more negative camber.
What anti-roll bars are you using? And what are your ride-height numbers?
Flipping tires inside/outside ( along with left/right swap) is already part of the plan, but this does add cost to each event.
Dr. Bob:
Swaybar Stock in front, 928 Specialist adj in back, set to mildest setting ( slightly stiffer than stock IIRC)
10. Ride height
a. 160 Front
b. 163 Rear
Nitto specs recommend negative 2.5- 5 degrees based on the information I found. And 5 is a huge amount of tilt But they made the tires they should know.
For a data point, I'm running close to 3* camber - pretty much maxed out on the 86.5. So far, my tire wear has been pretty even. Depending on the year of your track car, you might get more or slightly less camber. Just be sure they are even on each side.
The other thing to note is that when you adjust camber it will throw your toe off. It looks like you have a little toe in right now. I think when you increase camber, it tends to give you toe out... but it's been a while. If you go somewhere to adjust it, I would have the guy set the toe to dead nuts 0 if possible. With these adjustments, you'll find turn-in will improve.
Finally, what kind of pressures are you running? I usually shoot for about 34-35 psi in front - hot. THat means I usually start at about 29-30 cold (depending on the day).
You can effectively stiffen the front sway bar by using polyurethane bushing and solid drop-links. That'll help keep the car flatter.
What's the year/model of the car?
I didn't think the Eibach springs were that stiff. Are those numbers official in some way?
And let me bump my camber recommendation up to -2.5 front and -1.75 rear. That's what I run and it seems a good compromise for street/track. My '80 needed S4 upper A-arms in front to get that.
The answer lies in the photos of your front tires- you are scrubbing the shoulders- no great surprises there. More front camber will help but the simple fact is a 225 is just not enough front rubber and the car will invariably understeer as you try to force it- end of discussion. Once you start "bunny hopping" the front tires will go in no time.
I did not notice front wheel size/offset so cannot comment on that. A 245 front section would probably work well with a 275 rear section. Ideally you really need is some serious wheels with 265 rubber up front and 295 on the rear and appropriate offsets [ET68 9.5 inch fronts and ET60 10 inch rears]- then it is a different ball game.
You should try a front camber of two degrees and rear camber of 1.5 degrees and set the front toe at the low end of the range but do leave some toe-in. Another thing you can try is Carl's [928 Motorsports] lower front brace to help stiffen the lower geometry and reduce the need for excessive front camber that does nothing for braking.
Two degrees front camber is no problem for street use and will not cause excessive differential wear on the inner tread but may make a lot of difference to shoulder scrub.
Nitto specs recommend negative 2.5- 5 degrees based on the information I found. And 5 is a huge amount of tilt But they made the tires they should know.
"According to Nitto they suggest the following:
•Camber: -2.5 to -5.0
•Hot inflation pressures: high 30's to low 40's
•Operating temperatures: 140F - 220F
•Optimum tire temperature: 200F
•Caster: as much positive as possible"
....
Finally, what kind of pressures are you running? I usually shoot for about 34-35 psi in front - hot. That means I usually start at about 29-30 cold (depending on the day).
40 to 41 depending on track. Seems to work well. Have tried everything from low 30's up.
From what I can see Nitto's like ( see quotes above):
"•Hot inflation pressures: high 30's to low 40's"
The answer lies in the photos of your front tires- you are scrubbing the shoulders- no great surprises there. More front camber will help but the simple fact is a 225 is just not enough front rubber and the car will invariably understeer as you try to force it- end of discussion. Once you start "bunny hopping" the front tires will go in no time.
I did not notice front wheel size/offset so cannot comment on that. A 245 front section would probably work well with a 275 rear section. Ideally you really need is some serious wheels with 265 rubber up front and 295 on the rear and appropriate offsets [ET68 9.5 inch fronts and ET60 10 inch rears]- then it is a different ball game.
You should try a front camber of two degrees and rear camber of 1.5 degrees and set the front toe at the low end of the range but do leave some toe-in. Another thing you can try is Carl's [928 Motorsports] lower front brace to help stiffen the lower geometry and reduce the need for excessive front camber that does nothing for braking.
Two degrees front camber is no problem for street use and will not cause excessive differential wear on the inner tread but may make a lot of difference to shoulder scrub.
Rgds
Fred
Fronts are 8" width / ET57. 235's fit fine, 245 rub.
I could certainly install Carl's brace if it helps.
You can effectively stiffen the front sway bar by using polyurethane bushing and solid drop-links. That'll help keep the car flatter.
What's the year/model of the car?
I didn't think the Eibach springs were that stiff. Are those numbers official in some way?
And let me bump my camber recommendation up to -2.5 front and -1.75 rear. That's what I run and it seems a good compromise for street/track. My '80 needed S4 upper A-arms in front to get that.
I could stiffen up the front bar, however, I would do that as a Phase 2 approach. I am wary of trying to solve one issue, while creating other setup complexities. I only have limited track days, so the less set-up I have to futz with, the better.
09-14-2015, 12:59 PM
Maximizing Track Tire Life
