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PostPosted: Wed May 30, 2018 7:04 am 
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kfreiheit wrote:
Great info Joe. I am enjoying the incognito look for now! I will be at PIR June 10 for the Sunday portion of the regional. If you are there, let’s talk.

Cool, If I am in town ill stop by..

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PostPosted: Wed May 30, 2018 5:58 pm 
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As I said, I didn't get a pyrometer on my tires after the race, but the air pressure said they were just a little high.

Looking at the sidewalls, they look about perfect, which is kind of surprising to me.

Know I'm not sure about pulling camber/caster out of the car.

Guess I'll find out at a test day.


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PostPosted: Wed May 30, 2018 7:32 pm 
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Based on this thread I put a call into Hoosier Tech support to try to get some clarity as we were seeing such disparity in people's pressures.
I spoke to Tim who was very patient with me and pretty funny.
I actually told him about this thread to which he laughed (seems he has heard this story before).

I will greatly paraphrase what he told me.
He basically told me we are all correct.
The tire doesnt have a target pressure. It has a range that is within the design parameters I guess. He said when I was using 38 hot that was at the higher end of the spectrum and the guys in the low 20s are at the lower end.
The radial slick has an optimal temperature range. Thats what we should be shooting for.

He went on to say we (collectively as drivers) have to stop thinking about pressures manipulating contact patch. In the radial slick any pressures within reason will not alter contact patch.
What it is manipulating is the spring rate of the tire. He said its all driver preference.
Some drivers like / need less spring rate out of the tire, some want more.
A lower inflation gives the sidewall less spring rate, feels softer more compliant like softer springs.
More pressure makes the tire have more spring rate, stiffer and more direct like stiffer springs.
Air pressure = spring rate, nothing more.

I think he said that every Lb of air pressure equals 33 lbs of spring rate in the tire. I dont know if that is linear across all sizes, he and I were talking about 245/580-15s. I didnt ask if that was a consistent metric.

He said he has Runoffs level podium finishing SCCA customers at both ends of the Radial slick pressure spectrum because its what they like or what works for their car setup or driving style.

As long as we are getting the tire to the target heat range (Im think he said 180-225) and the most uniform temp possible across the tire face via alignment settings thats the goal.
So it seems like anywhere between 22 and 39 are the target pressure(s).

Hope that sheds some light on things... It was a great phone call. I thanked him profusely for the knowledge dump.

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PostPosted: Thu May 31, 2018 4:48 am 
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Wow thanks for doing that! I got the most out of the pressure not changing the contact patch. And that also backs up my suggestion that the S radials are stiffer spring-wise than the A/R DOT tires.

Is the number 180-225 - is that for S80s or S100s? Or either?


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PostPosted: Thu May 31, 2018 4:51 am 
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Awesome info, thanks for updating the thread. I've called and talked to them before and was only given the target pressure and temp ranges- which were then scribbled on my trailer wall and have since faded away...

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PostPosted: Thu May 31, 2018 5:40 am 
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Radial tire spring rates are a function of load and air pressure, and vary according to the tire size/model number so the 33 lbs that was mentioned is for a specific tire.

However, the variation is not all over the place. My information showed between 32 and 40 lbs per pound of air for different tires, but the actual spring rate for a given tire could vary by 50 lbs for the same air pressure with a 200 lbs difference in load.

This information is probably more confusing than helpful, but what I have found as the toughest thing to get used to when switching from bias ply to radials is that air pressure has a lot less effect on grip. Everyone wants to know what pressure to set them at, because that is what we use for bias ply tires, but it is not as important with radials. What I tell people to do is start with your bias ply pressures and keep increasing the air pressure until the driver doesn't like it any more, and then back down to where it felt good. One of the main advantages of the radials is reduced rolling resistance, and that improves as the tire pressure goes up, so you want that to be as high as possible.

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PostPosted: Thu May 31, 2018 8:36 am 
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I think its kind of a pain that Tim and Adam who are supposed to be equivalents in their roles, offer essentially different (I'll use the word "opinion" at this point) on the same topic when asked within 24 hours of one another.

Adam was very definitive that the tire has a pressure target of 28-30psi.

Tim seems to side with temps and pressure not being as important.

The overlap of philosophy is probably pretty large leading them to likely both be correct, but it would be better to explain the entire picture.

To boot, Jimmy's and my suspension and drivetrain configuration are identical, and our hp and weight are fairly similar too I would guess.

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PostPosted: Thu May 31, 2018 8:42 am 
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tschreyer wrote:
I think its kind of a pain that Tim and Adam who are supposed to be equivalents in their roles, offer essentially different (I'll use the word "opinion" at this point) on the same topic when asked within 24 hours of one another.

Adam was very definitive that the tire has a pressure target of 28-30psi.

Tim seems to side with temps and pressure not being as important.

The overlap of philosophy is probably pretty large leading them to likely both be correct, but it would be better to explain the entire picture.

To boot, Jimmy's and my suspension and drivetrain configuration identical, and our hp and weight are fairly similar too I would guess.

n
As with all data YMMV, I have always gone with testing as the best way to get there. Sometimes all the engineering data in the world will not be nearly as fast as SOP and Stopwatch. I fully appreciate what the folks at Hoosier bring to the game.

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PostPosted: Thu May 31, 2018 9:31 am 
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I know some of those guys fall back to the setup sheets and just quote from it.

I honestly don't blame them; I can only imagine what it's like to deal with the public on a daily basis.

"My car is slow and I spent $xxx on these tires, so what do I do."

I can only imagine how I'd respond :shock: :lol:

Fair warning, I am and have been a Hoosier Guy since the late 80's. I wouldn't have whatever successes I have, without them.


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PostPosted: Thu May 31, 2018 9:42 am 
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Joe Harlan wrote:
tschreyer wrote:
I think its kind of a pain that Tim and Adam who are supposed to be equivalents in their roles, offer essentially different (I'll use the word "opinion" at this point) on the same topic when asked within 24 hours of one another.

Adam was very definitive that the tire has a pressure target of 28-30psi.

Tim seems to side with temps and pressure not being as important.

The overlap of philosophy is probably pretty large leading them to likely both be correct, but it would be better to explain the entire picture.

To boot, Jimmy's and my suspension and drivetrain configuration identical, and our hp and weight are fairly similar too I would guess.

n
As with all data YMMV, I have always gone with testing as the best way to get there. Sometimes all the engineering data in the world will not be nearly as fast as SOP and Stopwatch. I fully appreciate what the folks at Hoosier bring to the game.


I think that's perfectly fine to say then!

My conversation asked is there a target pressure: "YES" what is it?: "28-30psi is where we want that tire".

That is way different than: "YES" what is it? "Anywhere from 20-40psi will work safely, but will require further testing"

When you break down run cost, the last thing you want influencing your testing time/money is misinformation - so you spend the entire day and entry fee messing around with a tire at exactly 28-30psi because thats the information you received from the right source, but likely trying everything else to come to find out you can let 8psi out for a change of 264lbs on a corner? That's kind of a big deal I guess.

I guess why I am frustrated is I asked Tim this 12mos ago when we switched to these tires. The feedback was run them exactly like we ran the R7's. We couldn't get them to work, tried things, called back, got a different answer, then 24 hours later there is a different answer.

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