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Discussion Starter #1 (Edited)
Recap: Dinan/JRZ Stage III suspension, -1.5 front camber. The picture below is a Dunlop Super Sport Race (265/35/18) which has four days at Lime Rock on it so far. I rotate my tires, so it's only been my left front (which takes most of the abuse) for one day (I think). But this tire is the worst of the four.

Cold presssure of 32psi. After the first session, tires feel greasy and car is loose. Instructor says tires have lost grip. Check pressures when done, left front is 44-45 psi. Bleed some air, shoot for ~41psi hot, and tires feel good for the rest of the day. This has been my experience at a couple of events. Tires are not shaved.

I'm driving the car pretty hard, but I promise on a stack of Roundels that I'm not overdriving it to the apex. Car feels like it has a touch of understeer, but I'm not grinding my way around the turns. I'm in B run groups, albeit usually the fastest car in that group, even on a tight track like Lime Rock. I took some pleasure at my last event getting around a well driven e36M3 that was lifting its inside front wheel around turns. I am trail braking where I can, but I'm sure there's plenty of room for improvement. I'm not left foot braking. Basically, I'm a high-intermediate driver.

Track gurus - is it the tire, pressures, the suspension, the driver, or a combination of all of the above? Obviously, this kind of tire wear is pretty poor. There's plenty of tread left in the middle and inside of the tire, but I may burn through the sidewall after just a couple of more events.

Thanks in advance for your feedback. I'm trying to decide whether to upgrade my suspension (again) and track this car for several more years, or plan on putting the money towards another car, maybe an e30 M3. I guess I'm leaning towards the two-car strategy for the usual reasons, but if I can't make that happen, should I get the GC suspension or tweak what I already have?



 

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Ed,

My take is that the only real cure is more negative camber. I've been meaning to call GC about their adjustable camber plates for the stock spring design that they have available now since I want to know what they feel is the max negative camber it will allow. I know on Redshift's car (regular GC setup with plates and 350/315 springs), he can only get around -2.2 degrees with the adjustment max'd out. He would like more negative camber for the track, but his wear is a bit better than yours (instructor level driving).

Bushing deflection could play a role in the camber control up front. Perhaps with your current setup going to the GC adjustable plates along with poly bushings up front would suffice (if you can stand the road noise). RRoberts is running the poly bushings I think.

Even though it transfers more load to the outer tire, a stiffer sway bar will reduce the body roll angle and hence the true camber angle the tire sees with the pavement...just a thought.

Chuck
 

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It looks to me like your tire is rolling way too far over onto the sidewall which would indicate a tire pressure which is too low. I have never seen that much sidewall wear on my track tires although I track my E36 M3 which has completely neutral handling without even a hint of understeer.

On my E36, I usually start at 36psi F&R and adjust down so that the tires are at ~40psi hot (Bridgestone S-03 and Kumho Ecsta MX). I just bought some Kumho Ecsta V700s and was planning on the same strategy. Start at 36 PSI and then adjust so that the tire rolls over to use the entire tread but none of the sidewall.

IMO with as much as you are scuffing the sidewalls, the tires aren't going to last you long.

Regards
 

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the outside tread wear looks pretty normal for the outside front tire, although the sidewall shows all lot more wear than i've seen on Michelin Cups or RA1s, even when i was running 1 degree in front - i run the RA1s between 42 and 44 hot

going front 1 1/2 to 2 1/4 or so is not going to make a very large difference

if the Dunlops are directional you can flip them on the rims for more wear as i have done with the RA1s

shaving new tires to 4/32 new will help them run cooler, but i doubt this is your problem

it's expensive, but i'd suggest RA1s when the Dunlops go away
 

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starting out with 32PSI is going to take some time to come up to pressure -- you may be going to hard (or have done so in the past) before the tires get up to pressure -- you're seeing a pretty extreme temperature rise with these tires and you may need 3 warmup laps before you get up to temp and pressure

what is the difference in pressure rise between the inside and outside front tires?

you might try putting some chalk marks on the sidewall to explore when the front tire is rolling over on the sidewall
 

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Discussion Starter #6
the outside tread wear looks pretty normal for the outside front tire, although the sidewall shows all lot more wear than i've seen on Michelin Cups or RA1s...

Maybe the sidewall is a little soft on the Dunlops versus PSCs or RA1s?

It looks to me like your tire is rolling way too far over onto the sidewall which would indicate a tire pressure which is too low.

That's what I would think too, except that on at least two occasions, I've run sessions at higher pressures (44-45) and felt the grip go away. The instructors with me at the time also thought the tires had lost their grip.

going front 1 1/2 to 2 1/4 or so is not going to make a very large difference...

That's critical and will help me and maybe others make an informed decision. Anything else you can add on that score would be appreciated. Thanks.
 

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Discussion Starter #7
stever said:
starting out with 32PSI is going to take some time to come up to pressure -- you may be going to hard (or have done so in the past) before the tires get up to pressure -- you're seeing a pretty extreme temperature rise with these tires and you may need 3 warmup laps before you get up to temp and pressure...
You may be right.
 

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i'd also say the tires are rolling onto the sidewall, which would indicate pressures are too low. However, i use the same tire on my m5, also with dinan stage 3 suspension ( iirc, i ended up with -1.7 camber though) and also start off with 33psi cold. Different tracks will require different pressures, i mostly have driven at sears point lately. My tire wear is quite uniform. I trail brake A LOT and feel that my car is pretty well ballanced on the track. I instruct myself, and other instructors have been impressed with the way the car handles. I wonder if stiffening up your front shocks a touch (like 1/8 a turn) for the track might help. Looks like too much weight going to that outside tire too quickly.
Mike
 

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Ed
41-44 psi hot is OK, subject to how they are working. I think Mike is right about the shocks. To me, the outer edge of the tire does not look uniform, indicating shocks are not completely doing their job.
Also, remember tire pressures work on both ends of the car, so if you lower the rears a little, you will be better able to rotate the car, (trailbraking) taking some pressure off the left front. TB is important going through the second half of Big Bend, which is the only place I think you need to TB. The left hander would be a place to trail brake, but most cars aren't fast enough from BB to the left hander ( although a VERY late turn in works well).
Enjoy your track time!!
Regards,
Jerry
 

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EdP said:
It looks to me like your tire is rolling way too far over onto the sidewall which would indicate a tire pressure which is too low.

That's what I would think too, except that on at least two occasions, I've run sessions at higher pressures (44-45) and felt the grip go away. The instructors with me at the time also thought the tires had lost their grip.
Ed,

There are conflicting issues with tire pressure changes. Tire pressure is a balance between proper contact patch versus sidewall spring rate. When pressures are increased to raise the sidewall spring rate and prevent sidewall rollover, what can result is a far from optimal contact patch. As you know, increasing the pressure results in a smaller contact patch; however, at the same time that smaller contact patch is carrying a higher pressure at the tread/road interface (load per unit area). Now take a curve and force a less than optimal camber angle on the tread/road interface, and you end up with a situation where the max operating temp of the tread compound is exceeded in the local region (perhaps outside 2" of the tire). This is what you experience when you feel the tires "go away" after a few hot laps.

So it is kind of a double edged sword in a way. Higher pressures to counter sidewall rollover (increase sidewall spring rate) yield smaller contact patches that have to carry the same cornering load and therefore are more easily overheated.

The only real solution is proper camber control.

Chuck
 

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i agree with setting the front shocks at 75% stiff or so -- Dinan usually sets them toward the soft end claiming better weight transfer coming out of corners, but it doesn't seem to work that way for me

similarly i'd try the rear bar in the middle position
 

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stever said:
similarly i'd try the rear bar in the middle position
I'd definatley agree with that!
 

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I see a camber issue for sure. Rolling onto the side wall like that is not good. Tire pressure could be the culprit due to the lack of camber. You will need more air the stiffen the sidewall. I would also have a look at rebound on the shock this will help push the wheel down. But I doubt it will totally solve this condition. Remember that shocks control bump/shock to the wheel.

Adjusting the rear bar may make the car handle better but it may do this by slowing you down. If the car oversteers earlier then, you are going slower.

Also, not being shaved can be a cause as well. You will have much more squirm in the tread at full depth. Try getting on the power latter this will help to keep the weight on the front tires longer. This is what you want. Weight=grip. Wherever the weight is is where the grip is going to be. Try a little left foot braking to set the front end if you feel a push. This will tell you about you weight transfer.

And as I said in an earlier post, get a tire pyrometer. This is the tool needed to diagnose the problem.

Jordan
 

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Guys,

Very interesting thread thanks.

A few questions from a keen track day driver in the beast, but a novice when it comes to 'setup' talk.

-I understand what camber is, and the effects of it, but how does one measure it?

-Also, what are the best wheels for track use, the lightest i guess right?

- How do the stock wheels type and sizes rate for track day use? ( i may buy another set of wheels for this purpose)

cheers
foxy
 

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A camber gauge is used to measure static camber (on the home user level). Basically it measures degrees of lean from vertical. The one I have you rotate the wheels 20 degrees to the left, measure camber, rotate 20 degrees to the right, measure camber again and average the readings. Professional alignment equipment uses lasers mounted to the wheels to determine camber, caster and toe.

The lightest and strongest wheels po$$ible are "best" for the track in a non-stagered sizing. The problem with the stock M5 wheels is that they are relatively heavy and they are narrower in the front than in the rear. This results in an understeering condition which is not optimal by any means for track use.
 

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although i think your main issue tire/tire pressure there is one more thing that should help given your soft suspension

using Dinan's stiffer front bar (probably requires the rear set to the inside) would reduce roll somewhat (whether it's enough to notice i don't know)

keep in mind that there's no attainable camber setting that can compensate for the roll-induced camber change with soft springs - the Dinan springs are maybe 20% stiffer than stock which is hardly noticeable
 

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Discussion Starter #17
stever said:
i agree with setting the front shocks at 75% stiff or so -- Dinan usually sets them toward the soft end claiming better weight transfer coming out of corners, but it doesn't seem to work that way for me
similarly i'd try the rear bar in the middle position
I had them at 10/12 (12 being stiffest), and my rear bar is set in the middle.
 

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jhowton said:
A camber gauge is used to measure static camber (on the home user level). Basically it measures degrees of lean from vertical. The one I have you rotate the wheels 20 degrees to the left, measure camber, rotate 20 degrees to the right, measure camber again and average the readings. Professional alignment equipment uses lasers mounted to the wheels to determine camber, caster and toe.

The lightest and strongest wheels po$$ible are "best" for the track in a non-stagered sizing. The problem with the stock M5 wheels is that they are relatively heavy and they are narrower in the front than in the rear. This results in an understeering condition which is not optimal by any means for track use.
Thanks for the info :biggrin:
 

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Discussion Starter #19
gsfent said:
... TB is important going through the second half of Big Bend, which is the only place I think you need to TB. The left hander would be a place to trail brake, but most cars aren't fast enough from BB to the left hander ( although a VERY late turn in works well) ....
On BB, I am trail braking to the first apex, but not before the second, which I know would help. I usually try to TB a touch as I turn into the left hander too, as it really helps the car turn in there. The car really squirts between BB and the left hander, it's one of my favorite places on the track.
:M5thumbs:
 

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EdP said:
I had them at 10/12 (12 being stiffest), and my rear bar is set in the middle.
Ed
One other thought. Hard to diagnose from far away, but driving style plays a role. A lot of drivers come charging up to a corner too hot, use tons of brakes and then motor out. Wears equipment and not fast. Most faster drivers brake sooner, and then accelrate sooner. Conventional wisdom is slow in, fast out (at least when no one is on your bumper trying to pass!! :1: ). Don't know if that is applicable, but if you have an instructor (or access to one if you are signed off), might be worth his/her opinion.
Regards,
Jerry
 
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