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PostPosted: Thu May 31, 2018 10:29 am 
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Location: Oregon City, Or.
Just because I am curious, How much does your EP BMW weigh? What camber settings are you running?

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PostPosted: Thu May 31, 2018 11:43 am 
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Location: Dubuque, Iowa
We're hunting for the last 90lbs.

Its likely me. :roll:

We're at 2290.

I'd have to look at my notes from my last alignment, but Its somewhere around -3.5F/-2.5R We haven't played much with camber from the DOT/IT setup.

We have about a 20-25 degree gradient across the tire. I am guessing we are sprung too stiff and running way too much pressure if we're saying the Radial slicks are already stiffer than their DOT equivalents. We uprated springs due to widening the track considerably when we went to the wider prod suspension arms. My guess is it was a wash in spring rate when we added the leverage from the wider arms, but went to the supposedly stiffer tire.

Hopefully dialing back tire pressures gets the right feel back, and if not we can go back to the old spring package for a bigger shift.

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PostPosted: Thu May 31, 2018 11:53 am 
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tschreyer wrote:
We're hunting for the last 90lbs.

Its likely me. :roll:

We're at 2290.

I'd have to look at my notes from my last alignment, but Its somewhere around -3.5F/-2.5R We haven't played much with camber from the DOT/IT setup.

We have about a 20-25 degree gradient across the tire. I am guessing we are sprung too stiff and running way too much pressure if we're saying the Radial slicks are already stiffer than their DOT equivalents.


2290 is that impound weight?
If yes thats pretty awesome for an E30.
Good on ya for getting it that low.

Mine is at 2450, thats with me at 218 and a few gallons in the cell.
I do still have a shell of a dash and of course Im a fat basterd and could stand to lose 20-ish lbs, but getting an E30 to 2290 is no easy feat.

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PostPosted: Thu May 31, 2018 12:13 pm 
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Anytime you guys want to come off the track at 2739, just let me know...


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PostPosted: Thu May 31, 2018 12:17 pm 
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Location: Cbus, OH
There's no absolutely golden answer to this question, which is why a multiple page long thread occurs every few months about it. It's also why when I talk about my experiences, I always very explicitly say "This is what works for me and my driving style on my 2300lbs FWD car. It may not work for you." But yes, a radial tire is going to be way less sensitive to tire pressure than the old bias tires. I personally run 32f/28r hot, again, on my 2300lbs FWD car. Even then, after nine years now of running on these things, I continue to play with pressure, spring, bar, and camber settings, because there's no such thing as "perfect". Relative to the bias tires though, I personally had to drop both spring and bar rates, or else the car was an evil bitch to drive. And relative to the Hoosier DOT's, I'm pretty similar on springs and bars, but run 8-10psi lower and actually more camber. I set camber so that when I come in hot off the track, and checked with an actual probe pyrometer, I'm about 15-20 degrees warmer on the inside edge than the outside edge. I also look very closely at wear across the tire, don't want any build up or excessive wear on either shoulder (camber), and no graining that's worse in the middle or on the edges (pressure).

Test, test, test. Try stuff. Every lap of every session should be a test. And keep records!!!

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PostPosted: Thu May 31, 2018 12:18 pm 
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Location: Oregon City, Or.
tschreyer wrote:
We're hunting for the last 90lbs.

Its likely me. :roll:

We're at 2290.

I'd have to look at my notes from my last alignment, but Its somewhere around -3.5F/-2.5R We haven't played much with camber from the DOT/IT setup.

We have about a 20-25 degree gradient across the tire. I am guessing we are sprung too stiff and running way too much pressure if we're saying the Radial slicks are already stiffer than their DOT equivalents. We uprated springs due to widening the track considerably when we went to the wider prod suspension arms. My guess is it was a wash in spring rate when we added the leverage from the wider arms, but went to the supposedly stiffer tire.

Hopefully dialing back tire pressures gets the right feel back, and if not we can go back to the old spring package for a bigger shift.

Again I think it car dependent my last GTL car we went from 55o to 600 front spring rate on bias to 800 to 1100 (track dependent) front and 250 rear to has high as 400 rear on the 13 inch radial. That car liked to come in at 34 to 36 hot on the 80 compound. I don't have enough time on the 15 inch but I can tell you we are up 200 spring rate over the bias.. this car is 2116

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PostPosted: Thu May 31, 2018 12:20 pm 
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Location: Dubuque, Iowa
I'm 250 btw...

I'm guessing that the last 90lbs is going to cost me in the neighborhood of $50-100 per pound, you know, or a diet.

But I've really run out of stuff to do, we're at the Colin Chapman phase of cutting bolts.

Hell, I'd be cool with a sub 2k lbs raw car.

2290 is with basically no fuel and me in the seat - so figure 2295 cross the checker

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PostPosted: Thu May 31, 2018 12:26 pm 
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kruck wrote:
There's no absolutely golden answer to this question, which is why a multiple page long thread occurs every few months about it. It's also why when I talk about my experiences, I always very explicitly say "This is what works for me and my driving style on my 2300lbs FWD car. It may not work for you." But yes, a radial tire is going to be way less sensitive to tire pressure than the old bias tires. I personally run 32f/28r hot, again, on my 2300lbs FWD car. Even then, after nine years now of running on these things, I continue to play with pressure, spring, bar, and camber settings, because there's no such thing as "perfect". Relative to the bias tires though, I personally had to drop both spring and bar rates, or else the car was an evil bitch to drive. And relative to the Hoosier DOT's, I'm pretty similar on springs and bars, but run 8-10psi lower and actually more camber. I set camber so that when I come in hot off the track, and checked with an actual probe pyrometer, I'm about 15-20 degrees warmer on the inside edge than the outside edge. I also look very closely at wear across the tire, don't want any build up or excessive wear on either shoulder (camber), and no graining that's worse in the middle or on the edges (pressure).

Test, test, test. Try stuff. Every lap of every session should be a test. And keep records!!!


I agree - my beef was with being told we were shooting for a narrow safe operating range, only to find out others are running something 25-33% different! I would have never came to the conclusion myself to take the car out with 10PSI less pressure than what Hoosier had told me initially. Knowing that the window is 20-40 then would tell me to explore that first. But telling me the window is 28-30, if that wasn't working I would think well my tire is good - time to move onto something else to get it to work. I just wanted the appropriate parameters - I have no issue developing from there.

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PostPosted: Thu May 31, 2018 12:30 pm 
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im with ron - you keep adding air until they are too squarely for your driving style then back it off a lb or 2 until its where you like it. Basically run them as high as you can tolerate it (with temps across still within 20 deg of each other). The higher the pressure the lower rolling resistance and thus more speed. I have been running radials since radical brought the first pro sport dsr cars to the states (like late 90's). had to import the avon radials as no radial slicks were really available back then.


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PostPosted: Thu May 31, 2018 12:36 pm 
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Location: Atlanta, Ga
It is super important to remember that a car must be set up for your driving style. Just listen to the vast variation the Cup drivers talk about within team cars and those cars as close alike as is physically possible. What is very comfortable for one driver maybe absolutely a terror for another.

As a team owner, I often tested other drivers cars and was astounded at what some drivers felt was right for them. I soon found that a change that felt great to me could be horrible for another. Note, always know exactly what you changed and exactly how to put it back before the change. Never change something without making notes. I have note books full of notes on cars we had.

So, the real message is to make the car feel right for you. And you have to keep changing things until it feels right for you. If it is absolutely terrible, throw a big change at it and see what happens. Keep doing that until you are down to small changes and then even smaller ones. And always keep in mind that air temperature, track temperature and tire wear need to be considered when making these changes. If the track temperature in 150 degrees one day and 90 degrees the next, you must take that into consideration.

And finally, if your having stupid driving day, don't change anything. Set up can't fix stupid.

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