Rick

For what it's worth, here's the email I just sent to the guys at Hoosier asking for their feedback; I'd welcome any comments that any of you might have.
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Mike & Jeff,

I was able to spend all day yesterday at Gingerman testing out the S04s and had someone there to help me with a pyrometer for 4 run sessions - each were approx 10 hot labs and my lap times between 1:32 and 1:35:5. It was a beautiful sunny day with air temps around 75 degrees.

As you may recall this is a race-prepped 1988 Porsche 944 Turbo S (approx 3092 pounds) and I was running 275/35/18s and 245/35/18s. I had heat cycled these tires at Mid-Ohio about a month ago.

Here are my current alignment settings:

Front Left..........Front Right
Camber: -2.5....Camber: -2
Toe .5 Out........Toe .5 Out


Rear Left...........Rear Right
Camber: -2.6.....Camber: -2
Toe 4 In............Toe 4 In

I started out with 35lbs front and 36lbs rear cold pressures. After my first session I had pressures ranging from 44.5 - 47lbs as follows:

LF 47
RF 46
LR 45
RR 44.5

I bled each of the tires down to 44.5lbs. My pressures stayed very constant between 44.5 and 45 for the remainder of the sessions.

My tire temps were a bit confusing to me because they weren't really consistent but here's what I found (we only recorded front temps):

......................Front Left..........Front Right
.....................(In/Mid/Outer)...(In/Mid/Outer)
Session 1: 179/175/168......163/160/158
Session 2: 159/177/190......159/163/164
Session 3: 186/184/195......185/171/173
Session 4: 195/188/196 187/168/173

The handling of the car was wonderful - I really couldn't have been happier. In all heat cycles there were no spins or abnormal events that would have caused unusual tire wear. We inspected the tires after each run and didn't see any issues until after session #4 (which was the 5th heat cycle overall) - it was evident that the fronts are wearing more rapidly on the outer edges and the left front was showing cords (see photos). The cording was entirely on the outer edge of the tire except for one spot on the inner (see first photo). The right front did not cord but it is evident from inspection that they would have within another session or two. The wear on the rears was very even and I've got no concerns with the rears.

Obviously I'm disappointed to have my fronts finished after only 5 heat cycles - I just can't afford that. My current thought is to raise my hot pressures to about 46lbs and to increase my negative camber by about .5 on each of the fronts based on seeing slightly lower middle temps and the wear pattern I observed on the fronts.

Rick

Edit: I just realized that I posted the wrong set of photos - my apologies. Here are the correct photos.

RedlineMan

Hey Rick;

I hope that your efforts on their behalf bear fruit.

To "whom it may concern" - official folks that may be looking on, I would not have been likely to purchase new Hoosiers before because they did not represent a good value for my usage (recreational DE).

I CERTAINLY won't be purchasing the new 04s!

Premier Motorsp

Those tires look like S03's. Don't S04's have two grooves centered on the centerline of the tire?

Why are you running toe-out on the rear?

Petevb

Hmm. Those DO like my S03s. My S04s do have 2 groves symmetric about the centerline of the tire. I just went out to the garage to look at both types... I'm on 16" wheels, but...

Rick

Premier,

First, I just realized that I posted the wrong photos - I'll post the correct photos tomorrow. The photos were in fact my old S03s that had recently corded after about 14 heat cycles.

Second, I have to admit that I don't have a good answer for why I'm running toe-out in the rear; when the car was setup by Wright Tuning in Cincinnati that's the way they aligned it and I haven't questioned it since - the car has handled very well and I haven't had any tire wear issues in the rear.

What is your suggestion?

Thanks much.

RedlineMan

Hmmm...

I don't think I've ever heard of anyone running rear toe out successfully. It certainly would not work on a 911!

Perhaps your springs are stiff enough to keep from suffering drastic toe change in the corners? Anyway, I've had toe out before and it was FRIGHTENING! Up to 70%... and SCHWIIIING goes the rear!

It seems to work for you OK... at least at this juncture. I wouldn't have it, nor would I set up a customers car that way. Maybe not even if they "knew what they were doing" and asked for it! Wouldn't want to risk it.

Greg Fishman

Rick,
Double check with Jon about the toe out in the rear, that doesn't sound right to me. You wear looks good except for the outside shoulder. I think you need some more negative camber. Gingerman is very tough on tires so any "faults" in your alignment would show up very quickly. Did you swap the tires left to right?

When you listed the toe measurements, what units are those? Degree or MM? If you had 4 mm of toe out in the rear, I congratulate you for keeping the car in one piece.

Rick

Greg,
I'll talk with Jon - we're putting on Charley arms shortly so it will be a good time for us to tweak the alignment.
I just realized that I made a HUGE typo error - the rears are Toe IN...not Out. I guess that should teach me to use 'cut & paste' so quickly. (I'll edit the original post above).
Also, we did swap the fronts between sessions 2 & 3 - other than that they were not swapped.
Thanks,
Rick

SundayDriver

Here is what I see...

Tire temps indicate not enough negative camber. Note how in session 1, the inside temps were higher than outside. This is what you want but it reverses in the later sessions. This tells us there is too much 'contact' on the outside. I assume that reflects harder running as the sessions progress - pretty usual.

2-2.5 neg camber seems low for these tires. I thought they generally liked more camber.

The graining pattern supports the above. The grain coarseness looks good inthe center/inside. The outer edge is coarser, indicated higher temps AND we see a diagonal pattern in the grain on the shoulder. This tells me the loading and slip angle are too high out there, but since it is only the shoulder, it is not overall slip angle - only the slip when very heaviuly loaded.

From the looks of everything else, I would think the tires should do well and will last a decent amount of time with more negative camber. Try to go for about 10 degree delta as you move across the tire with inside being higher. Absolute temps won't mean much as that very much depends on how quickly you measure temps after hard loading.

Pressures sound high to me (heck, I run 11 psi cold so everything seems high to me), but that may be what those tires like on your car. What does Hoosier say about pressures.

Petevb

This might be obvious, but there is an alternative you could consider to increasing camber. That would be making the car roll over less...

Lowering the car and/ or stiffening the springs/ swaybars will improve all of your contact patches in both the corners and the straights. I bring it up because I’m able to run about 2.75 degrees on my 911 with ‘04s, and I’m not having your issues. The stickier the tires, the stiffer the springs you want to run. Something to consider. I’d probably try to do a little of all of the above in addition to a little more camber if I was you. What springs are you running now?
I’m also running about 5 psi less than you are at the moment, but then my car is 800 lbs lighter…

Greg Fishman

Rick,
My guess is that he is measuring in mm. That is how we did my car last time. .5mm toe out in front, 4mm toe in for the rear.

My relatively short time with the new Hoosiers points to them liking a bit higher pressures than the So-3's. 44lbs hot seemed to work good on my car (2800lb 993). Also I am running slightly less than 3.0 degrees of negative camber and I am not getting the wear you are seeing on the outside edge.

Good point about the spring rates you may want to consider increasing them if while you are doing work on the car.

RedlineMan

Spring rates to mitigate body roll... indeed, BUT;

Like everything, you reach a break point. If the car gets so stiff you can't keep the tires on the road, you'll certainly save those expensive Hoosiers!

We have seen that with the various vintages of 996 Cup Cars. The pre '04 cars have a lot of trouble under braking compared to their '04 brethren. '04 cars got the discrete adjust shocks, and while they stop on a dime, the '01-'03 cars are ABS-ing their brains out! Big Advantage. These Cuppies are running 1200-1500lb rates!!!

You do have Motons, which I assume are discrete double adjust. This allows you to run higher spring rates because you can back the rebound down accordingly to help keep the tires on the road, but there is still a break point in rate effectiveness. If you hit a bumpy place like Mid Ohio or Lime Rock, softer is the rule.

There's a lot to this stuff! I myself am going to have to start running differential camber settings for the first time because I am dragging the rubber off the inside of my right side tires.

It never ends!!

Rick

Mark, Greg & John,

First - thanks much for the help; I really appreciate it.

The tire pressures are right where Hoosier is specifying for this weight of a car in their documentation - it's my understanding that they've verbally recommended as high as 50 but I can't buy into that.

Any sense of how much additional neg camber I should add? 1/4 degree, 1/2 degree, 1 degree?

Re: springs, I'll talk to John Wright to see what his thoughts are re: going to a higher spring weight. I'm currently at 700# in the front. I kind of hesitate to go much higher because I really like the way the car feels and my lap times at Gingerman, Putnam & Mid-Ohio are within 1-2 seconds of E stock qualifying speeds - I hope that means that I'm not too far away from a good setup.

On a side note...any recommendations on books that will educate me on this subject (alighment, suspension, spring rates, adjustments, etc...)?

Greg - see you at Holiday World; should be fun.

Mark - let me know the next time you're passing through Indy; I've got plenty of room for friends and the beer is always cold.

Thanks again.

SundayDriver

I'll start with some book comments. There aren't any that I have found that provide a good, understandable source of suspension info. Most are heavy into design and can make my head spin. Others offer bits and pieces, but no really great single source. That said, however, the Caroll Smith books are all good resources. Tune to Win, Drive to Win, Engineer to Win, Nuts bolts & Fasteners (Screw to Win). One of the most valuable is a pocket guide called 'Engineer in Your Pocket' or something similar. It lets you look up a problem like corner entry understeer, and it offers solutions. You can also look up changes like stiffen rear bar, and it gives effects of that change. No theory, but a great thing to have at the track. Unfortunatley, to learn more about this stuff seems to require a lot of different books and stumbling into information, plus lots of questions.

If I were making the camber change, unless you can find someone who knows your car and those tires, I would go for ~3/4 degree - just thinking that 1/2 may be too little and a full 1 degree sounds like a lot. I have no real basis, just a guess.

Realize that the job of the springs and shocks is to keep the tire on the pavement, and to try to maintain the weight balance. That is, to manage the footprint. Many designers feel that sway bars are not needed, but when used, they are also part of that equation. You can hide all sorts of other issues by tuning these things, but that is not the best way. Yes, you can reduce body roll with stiffer springs and then you won't need as much camber, but why do you want to stiffen the springs? Unless you are solving a problem that should be addressed with stiffer springs, then you are hiding one problem with springs, and may well be creating more problems. Personally, I would not try to address the problem with springs or ride height or shocks or sway bars. Get those things set right to make the car handle and behave on track. Let the camber then manage the tire angle (all within reasonable limits, etc).

Thanks for the offer in Indy. See ya soon.