Hoosier A6, Tire Pressure

michaelsmiller · **Posted:** Tue Sep 28, 2010 8:55 pm

I have always managed to be the last one to the party. Unlike everyone else, I have just purchased my first set of Hoosiers. I have been running 225/45-17 Kumho V710’s on my C Stock 2006 MX5 for the past 3 seasons. The tire pressure has been set at 34 psi in front and 37 in the rear plus or minus one pound depending on conditions. I get about 124 autox runs per set. After hearing everyone’s problems with Hoosiers cording quickly, I want to make sure that I run the right tire pressure this weekend. Any suggestions from people driving cars with camber gaining suspensions would be much appreciated. It sound like the strut cars run a little higher pressure. My alignment is 1.1 camber all around and 7.2 castor. The Kumho’s cord a little further than 1/3 of the distance from the outside edge of the tire. Basically, the wear is as even as a stock car can hope for. :?:

Les Davis · **Joined:** Fri Aug 29, 2003 2:04 pm **Posts:** 2059

michaelsmiller wrote:

I have always managed to be the last one to the party. Unlike everyone else, I have just purchased my first set of Hoosiers. I have been running 225/45-17 Kumho V710’s on my C Stock 2006 MX5 for the past 3 seasons. The tire pressure has been set at 34 psi in front and 37 in the rear plus or minus one pound depending on conditions. I get about 124 autox runs per set. After hearing everyone’s problems with Hoosiers cording quickly, I want to make sure that I run the right tire pressure this weekend. Any suggestions from people driving cars with camber gaining suspensions would be much appreciated. It sound like the strut cars run a little higher pressure. My alignment is 1.1 camber all around and 7.2 castor. The Kumho’s cord a little further than 1/3 of the distance from the outside edge of the tire. Basically, the wear is as even as a stock car can hope for. :?:

I would first recommend more static negative camber, pretty much as much as you can get out of the stock suspension even though it will sacrifice some of that caster. Other than that your pressures seem okay, you can probably get away with less pressure for more grip, but it might cost some tire wear.

Karl Shultz · **Posted:** Tue Sep 28, 2010 9:47 pm

Les Davis wrote:

michaelsmiller wrote:

I have always managed to be the last one to the party. Unlike everyone else, I have just purchased my first set of Hoosiers. I have been running 225/45-17 Kumho V710’s on my C Stock 2006 MX5 for the past 3 seasons. The tire pressure has been set at 34 psi in front and 37 in the rear plus or minus one pound depending on conditions. I get about 124 autox runs per set. After hearing everyone’s problems with Hoosiers cording quickly, I want to make sure that I run the right tire pressure this weekend. Any suggestions from people driving cars with camber gaining suspensions would be much appreciated. It sound like the strut cars run a little higher pressure. My alignment is 1.1 camber all around and 7.2 castor. The Kumho’s cord a little further than 1/3 of the distance from the outside edge of the tire. Basically, the wear is as even as a stock car can hope for. :?:

I would first recommend more static negative camber, pretty much as much as you can get out of the stock suspension even though it will sacrifice some of that caster. Other than that your pressures seem okay, you can probably get away with less pressure for more grip, but it might cost some tire wear.

What Les said. I'd get as much camber into the front of that car as you can.

What we run:
Front:
- 2.0 deg camber <-- maximum we can get
- 5.x deg. caster <-- maximum we can get after setting the camber
- 0 toe, although, we've just started running a shade of toe out
- 34psi

Rear:
- 2.0 deg. camber <-- this is just what we like - the car will take 3+
- 1/16" total rear toe in
- 30psi

michaelsmiller · **Posted:** Tue Sep 28, 2010 10:13 pm

1.1 deg of camber is all of the way to the stops on a stock Miata. The castor is large just because there is more adjustment there and it seems to help. It took 3 tries at allignments to get to where I am now. I wish that I had as much adjustment as the S2K and Solstices. The Miata seems to have a lot of camber gain due to suspension geometry. Thanks for the guidance.

Karl Shultz · **Posted:** Tue Sep 28, 2010 11:09 pm

michaelsmiller wrote:

1.1 deg of camber is all of the way to the stops on a stock Miata. The castor is large just because there is more adjustment there and it seems to help. It took 3 tries at allignments to get to where I am now. I wish that I had as much adjustment as the S2K and Solstices. The Miata seems to have a lot of camber gain due to suspension geometry. Thanks for the guidance.

Learn something new every day - I'd have guessed a Miata would have a lot more than that.

JamesShort · **Posted:** Wed Sep 29, 2010 9:09 am

Karl Shultz wrote:

michaelsmiller wrote:

1.1 deg of camber is all of the way to the stops on a stock Miata. The castor is large just because there is more adjustment there and it seems to help. It took 3 tries at allignments to get to where I am now. I wish that I had as much adjustment as the S2K and Solstices. The Miata seems to have a lot of camber gain due to suspension geometry. Thanks for the guidance.

Learn something new every day - I'd have guessed a Miata would have a lot more than that.

NBs can get more than that...I think a stock NB can get the rear into the low 2.x* on stock eccentrics.

jeremy gast · **Posted:** Wed Sep 29, 2010 10:09 am

it is weird some can and some cant and no one knows why.

JamesShort wrote:

Karl Shultz wrote:

michaelsmiller wrote:

1.1 deg of camber is all of the way to the stops on a stock Miata. The castor is large just because there is more adjustment there and it seems to help. It took 3 tries at allignments to get to where I am now. I wish that I had as much adjustment as the S2K and Solstices. The Miata seems to have a lot of camber gain due to suspension geometry. Thanks for the guidance.

Learn something new every day - I'd have guessed a Miata would have a lot more than that.

NBs can get more than that...I think a stock NB can get the rear into the low 2.x* on stock eccentrics.

JamesMilko · **Posted:** Wed Sep 29, 2010 10:25 am

Are the NBs like the NAs where you'll be on the bump stops the entire run on stock springs anyway?

michaelsmiller · **Posted:** Wed Sep 29, 2010 12:22 pm

I can get 2.5 + degrees of camber in the rear. Combine that with a big front sway bar and you get a car that pushes horribly. I set the rear at 1.1 degrees camber in order to balance the cars handling. It's the front suspension that is limited to 1.1 degrees. Just hitting the throttle gives me 1 extra degree of rear camber due to squat. At my last allignment, before making any changes, we hung from the rear of the car and read 3.5 degrees of camber. Really soft rear springs and a suspension with high camber gain, make for interesting handling. I imagine that in CSP where the suspension can be optimized, the NC should be a very good car. Look at the last nationals, the first 3 places in C stock were MSR NC's.

JamesShort · **Posted:** Wed Sep 29, 2010 12:59 pm

michaelsmiller wrote:

I can get 2.5 + degrees of camber in the rear. Combine that with a big front sway bar and you get a car that pushes horribly. I set the rear at 1.1 degrees camber in order to balance the cars handling. It's the front suspension that is limited to 1.1 degrees. Just hitting the throttle gives me 1 extra degree of rear camber due to squat. At my last allignment, before making any changes, we hung from the rear of the car and read 3.5 degrees of camber. Really soft rear springs and a suspension with high camber gain, make for interesting handling. I imagine that in CSP where the suspension can be optimized, the NC should be a very good car. Look at the last nationals, the first 3 places in C stock were MSR NC's.

C stock yes, but the NC does not have the power to weight ratio of a CSP NA or NB with a 01+ VVT engine and 1990 dashboard etc etc etc. The single line in CSP for 90-05 Miata's makes for UPBD heaven

.

Maybe going forward the ND an onward might stay on the same line as the NC and have a very nice (and easily swappable engine) to make the NC more competitive in CSP.

Did you ever try more camber in the rear but with some rear toe out to mitigate the understeer?

Keith Vail · **Posted:** Wed Sep 29, 2010 3:38 pm

JamesShort wrote:

C stock yes, but the NC does not have the power to weight ratio of a CSP NA or NB with a 01+ VVT engine and 1990 dashboard etc etc etc. The single line in CSP for 90-05 Miata's makes for UPBD heaven

.

Mike, I would probably start at 40 psi up front and see where the tire rolls to. You can always reduce pressure after a run or two but if you start too low you can drastically reduce the tires life.

James, the NC is competitive in CSP. One won Nationals in 08 and was driven to the event as it still had AC and such. No one has built one to the level that the other top NA/NB chassis cars are at since Brian sold his right after Nationals. They can easily be right in the mix but they are more expensive to build since the chassis is that much more expensive. You can get a 90-93 NA chassis for cheap and then you have the lightest car and just put the power and handling stuff in it.

JamesShort · **Posted:** Wed Sep 29, 2010 4:14 pm

Keith Vail wrote:

JamesShort wrote:

C stock yes, but the NC does not have the power to weight ratio of a CSP NA or NB with a 01+ VVT engine and 1990 dashboard etc etc etc. The single line in CSP for 90-05 Miata's makes for UPBD heaven

.

James, the NC is competitive in CSP. One won Nationals in 08 and was driven to the event as it still had AC and such. No one has built one to the level that the other top NA/NB chassis cars are at since Brian sold his right after Nationals. They can easily be right in the mix but they are more expensive to build since the chassis is that much more expensive. You can get a 90-93 NA chassis for cheap and then you have the lightest car and just put the power and handling stuff in it.

I agree, I didn't say it wouldn't be competitive, I said it wouldn't have the power to weight ratio of the NA/NBs. An incredible driver could win in one no doubt. But as you hit upon, you can have a perfectly prepped NA/NB for probably half the cost. I wonder if the ND will keep the MRZ style engine.

Steven Carter · **Posted:** Wed Sep 29, 2010 4:34 pm

sorry for the OT, but mentioning the 2012 MX-5 sent me off for a GIS...came back with this great quote...looking forward to the new iteration:

"That skin, by the way, will likely be more expressive than the rather safe MX-5 we have now, with Mazda's design chief Laurens van den Acker on record as saying the plan is for the car to "be more dramatic and give it some balls." "

http://www.autoblog.com/2009/03/24/next ... -electric/

michaelsmiller · **Posted:** Wed Sep 29, 2010 8:44 pm

I’m hoping that they only add horse power to the new Miata and don’t change the design too much. The only way that the redesign will be extensive is if Mazda never plans to do another RX8. The NC chassis is based on the RX8. Many people even run RX 8 sways on the MX5. As for trying other changes to the allignment, one eventually gets to a point that making more changes will most probably make the car worse than better. Right now, the car is perfectly balanced and very intuitive to drive. My son Anders at his second autox mastered the art of trail braking. The car is very easy to control at the limit and forgives you when you have greatly exceeded it. If Mazda made a club racer like Honda or the RX8 R3, then the NC would be one of the hottest handling cars available. The MRZ, otherwise know as the Ford Duratec, is a fantastic engine. The difference between the MRZ and the old Mazda 1.8L is that the torque comes on early and stays there until the rev limiter hits. The 1.8 delivers it’s power at high RPM’s. With direct injection, the MRZ 2L should be capable of 190 HP. If the MX5 does not gain weight, then the power to weight should be about 12.9 lb/hp. That’s very close to the S2K. The MX5 cup cars are running about 200HP with a reflash, headers, and intake.

Keith, Thanks for your thoughts on tire pressure. I’ll check the tires with a pyrometer after each run. That should help me tune it in quickly.

Steven Carter · **Posted:** Wed Sep 29, 2010 8:50 pm

michaelsmiller wrote:

I’m hoping that they only add horse power to the new Miata and don’t change the design too much. The only way that the redesign will be extensive is if Mazda never plans to do another RX8. The NC chassis is based on the RX8. Many people even run RX 8 sways on the MX5. As for trying other changes to the allignment, one eventually gets to a point that making more changes will most probably make the car worse than better. Right now, the car is perfectly balanced and very intuitive to drive. My son Anders at his second autox mastered the art of trail braking. The car is very easy to control at the limit and forgives you when you have greatly exceeded it. If Mazda made a club racer like Honda or the RX8 R3, then the NC would be one of the hottest handling cars available. The MRZ, otherwise know as the Ford Duratec, is a fantastic engine. The difference between the MRZ and the old Mazda 1.8L is that the torque comes on early and stays there until the rev limiter hits. The 1.8 delivers it’s power at high RPM’s. With direct injection, the MRZ 2L should be capable of 190 HP. If the MX5 does not gain weight, then the power to weight should be about 12.9 lb/hp. That’s very close to the S2K. The MX5 cup cars are running about 200HP with a reflash, headers, and intake.

From what I hear, I'm pretty interested...direct injection turbocharged---sounds like a RWD MS3 to me. Miatas are verboten in my house because the wife says they are too ubiquitous (true) but now I can say "Look honey, it's not a real Miata--it's an MX5 with a turbo!" (The old MazdaSpeed Miata didn't cut it for her--maybe this time it'll stick!)

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Hoosier A6, Tire Pressure

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