Awesome tires and I don't even have them dialed in yet.

I'm getting conflicting air pressure readings from local drivers. Some are swearing by -30# while others are in the +40#. Even taking into consideration different car weights, a pretty great disparity remains.

I had great succes with Victoracers at 26/28#, but from what I understand at this point, the 710's have weaker sidewalls that require higher air pressure. In KUMHOS overview of the tire, there are no air recommendations or heat range presented.

I'd be interested in hearing your findings, including where you started and where you ended up pressure wise.


..

205-15s tried air pressure from 38 down to 26 - best performance 28# cold on the big track. Ran thru it sevearal times - always ended up 28# cold.

Front camber -1.75 Rear camber -2.0

Ken

QUOTE

26/28#

Those are the #'s for a/x


KT

Fast guy with a Miata runs high 30's like 36 to 38 PSI for Autocross.
He took FTD for normal cars and PAX. Pretty much puts a whoopin on everybody all the time.

I did our last two AX events last year with my Kuhmos. I found #32 front and #34 rear worked well in my 70 with a 2.0L. Oh they are 205 50 15 size.

I went from falkens to the kuhmos and gain about 1 1/2 to 2 sec. It was enough for me to win my class both days

All the way from 26# to 38#...

Well... there ya go....

Guess I'll be forced to do some experimenting at the AX this sunday.

I've googled all over and can't find any real info on them. And it's odd to me that kumho provides nothing.

Please pass on any helpful info you run across.

..

I think this is what is happening to my car on sticky tires. running low air pressure will put a bigger foot print on the pavement and provide alot of grip. Enough to flex the sidewall to the point that the tire deforms, lifting the inside edge off the ground. This Very quickly turns into snap get loose and oh shit no traction.

Running higher pressure keeps the tire casing shape more uniform and while being stiffer tends to slide in a more linear fashion. More controlable and easier to drive. Actually I was faster by 2 seconds with higher pressures. 73 runs on Hoosiers was pretty much a bad idea anyway.

It just takes some time. Depends on car setup and event.
Start at 38# cold, after each "run" drop the pressure 2#s. You will "feel" the grip changing. In my experiance the grip got better until the pressure got too low. Go back up in 2# steps. In other word there was a noticable point whre the the grip was best. Do all 4 tires the same regardless of the "hot" pressure. Let cool and check pressure.
You can tweek front to rear after you find your "best" pressure.
Ken

Unfortunately we get so many drivers showing up to events that 4 timed runs is all we get. Fun runs are just that if there is time before it gets dark.

Ken, your procedure would take several events of which the course would change also. However local "get together" events might be a perfect place to do this.

Something else to note your new Tires will NEVER have more grip than the 1st event. So make it count. National level drivers buy a new set of tires before a National tour event and then religate that set to practice runs afterwards. Then get a new set of the Same tire for the next event.

You can move in 4# steps - the idea is to determine the area of best grip then tweek it in. And yes it may take several events to get to the "best" pressure.

Ken

QUOTE (Joe Ricard @ Mar 28 2006, 10:03 AM)

running low air pressure will put a bigger foot print on the pavement and provide alot of grip.  Enough to flex the sidewall to the point that the tire deforms, lifting the inside edge off the ground.  This Very quickly turns into snap get loose and oh shit no traction.   Running higher pressure keeps the tire casing shape more uniform and while being stiffer tends to slide  in a more linear fashion.

Joe- I think those are real good observations and not just because I agree with them.

Your comments made me replay last weekends AX with PCA I do just for fun (only time I get to use 4th). I started out with 28# settings (which works very well for Victoracers) and in the first heat did a snap 180 spin (talk about a low polar moment of inertia). I went to 37# for the 2nd heat and on the same corner the rear came out a bit but was easy to catch. Testimony to the predictability you mention of higher pressures.

Also my times were about a second faster, but I know that can come about from simply becoming more familiar with the course and improving lines and braking points. You know, using our skills.

Maybe there is something to say for staying away from either extreme while going for the lowest pressure that does not present problems.

Garold- you didn't specify, are you running Victoracers or 710s?

Ken- BTDT as a process with Yoks & Hoosiers over the last three years. I was hoping to discover a concensus to start off with (as I did with Victoracers). I have found that empty parking lots and off ramps can really help balance out my AX findings.

As JP sez... it'sa black art.

Thanks you'all and I'll pass along my experiences.

..

the lower you go the more "unstable" the car will *feel* but you'll actually *gain* "stickage" ...

sidewall flex does not kill your times once you learn to drive with it. it takes time to get used to it as it feels very "unnatural" ...

i run my goodyear schlicks at 16# cold ...
Andy

There really is only one right way to set pressures. Temperature. The rest are just approximations...

All cars are setup slightly different. And chassis setup goes a long way to determining tire setup. You want the temperature of the tire to be close to even across the tread. _Slightly_ higher on the outer edge, and progessively cooler to the inner edge.

"feel" will only get you sorta close. And different people like a different "feel" to the car. So driver A might like the way the car feels at 36 psi, and driver b might like it better at 28 psi.

Take the temperatures as soon as possible after coming off the course. Two or three runs, and you should have them pretty close.

Pyrometers can be had for around $100 or less nowadays. And don't get the IR laser pointer cr*p. Get one with a real probe. You need to measure the temperature of the rubber -in- the tread, not the very surface. And after you've spent nearly $800 on just _one_ set of tires, a pyrometer is a valuable one-time investment to protect your many thousands of dollars of racing tires you'll go through in the course of a couple seasons... You will get more life out of the tires, and the car will handle better too...

-Josh2

There's a lot I think I know about tires, but in reality, I know a bit about my own set up....and am still learning.

I prefer the method Ken is talking about. I do it a bit different, but not enuff to mention....I'm definetely in agreement with the "several events" search for the ideal pressure. Since pressure is variable with temperatures, it can be a bitch to get a handle on it at any single AX. Seldom do I get my tires up to 140 deg....no buggers on my treads....this is not gud....I think

I liked the way my past Kuhmos & Hoosier R dots felt at a given pressure. Should these pressures happen to coincide with your "like the feel", it's coincidential, me thinks.
The tires I run now are straight up & down side wall jobies that I could prolly run 10 psi pressure in.....but haven't tried as I got happy at about 18 psi....now if I could just get the fronts as hot as the rears.
The only place I got em' hot was on a skid pad and it was incredible, neck stretching sumbitch. The shitbox just hunkered down & said " is that all *you* can take?"

I have a two day a/x this weekend.
Should be about 70-80 heavy hitters.

I'll tell you how I stacked up on 26-28.

I started very high and worked down to this psi.

I don't know if you saw my last in-car ( in my blog ), but it was good enough for TTOD.

Last one was, too.

Same pressures. This works. Or they are all slow


KT

QUOTE (trekkor @ Mar 28 2006, 05:03 PM)

Same pressures. This works. Or they are all slow KT

Do I detect the "big frog" syndrome?
We gonna have some fun at the WCC.

QUOTE

"big frog"

All croak?

I'm a wide mouthed bull frog...

I wuz thinkin' "big frog, little pond"

We will see.....Teeners attack norcal

I think tire pressures are overrated at times. However I'm more of a low pressure believer when talking about DOT Radial Slicks. I run my Hoosier DOT AX tires around 25 PSI on 8" rims. One of the faster drivers in a Boxster running Kuhmo DOT radial slicks pretty much proved to me that tire pressures in AX dont really make a huge difference. He ran the first session with lower pressures around 24 PSI and then second half of the day he ran pressures all the way up to 37 PSI and ran times a little faster. He ended up having fastest times of the day.

For me focusing on driving not pressures makes my times faster. I typically set my hot pressures to one point and drive around my tires. ..Does that make sense?

Yea big frog little pond. I had that happen when I wnet to Dothan alabama. Put a whuppin on most of the local hot shoes. Cept for 2 EVO school grads that eeked out a few 10ths on me.
Went to Trans Louisianna Autocross 1 ( 4 regions show up all in one place) and got my ass handed to me. Talent seems to congregate.

QUOTE (Joe Ricard @ Mar 28 2006, 08:26 PM)

Yea big frog little pond. I had that happen when I wnet to Dothan alabama. Put a whuppin on most of the local hot shoes. Cept for 2 EVO school grads that eeked out a few 10ths on me. Went to Trans Louisianna Autocross 1 ( 4 regions show up all in one place) and got my ass handed to me. Talent seems to congregate.

I hear you, I'm going to do the SCCA regional at Milwaukee....talk about a

If this thread drifts any further, we're gonna need a Gilligan's Island smilie.

AND if it continues to be hi-jacked by you left coasters, I demand a pirates face!

..

QUOTE (Joseph Mills @ Mar 28 2006, 06:34 PM)

If this thread drifts any further, we're gonna need a Gilligan's Island smilie. AND if it continues to be hi-jacked by you left coasters, I demand a pirates face! ..

wow, I didn't know that MS and MN were on the left coast

QUOTE (Dan (Almaden Valley) @ Mar 28 2006, 08:36 PM)

QUOTE (Joseph Mills @ Mar 28 2006, 06:34 PM) If this thread drifts any further, we're gonna need a Gilligan's Island smilie. AND if it continues to be hi-jacked by you left coasters, I demand a pirates face!  :D .. wow, I didn't know that MS and MN were on the left coast

Hey I'm not talkin'bout them.


You inland impaired guys started it!

..

what do you mean "inland impaired"? I am like at least 15 miles from the beach

Sorry,

What were those tire pressures again.

Well I'm taking Andy's # and Trekkors # and adding them together.

Should be about right.



15 miles huh! You're about 1 mile short of the east side of the fault line.

..

QUOTE (grantsfo @ Mar 28 2006, 06:21 PM)

I think tire pressures are over rated.

i dis-agree ...

the difference on my car between 16# and 26# is that at 16#, the car sticks like glue, but "feels" spoongy, at 26# the car "feels" tight, but i can't keep the rear-end planted, i constantly fight to keep the rear-end from passing the front ...

10# difference on the initial cold setup makes for a completely different car ...

for me, that's a pretty clear indicator of the importance of tire-pressure ...
Andy

QUOTE (SirAndy @ Mar 28 2006, 08:02 PM)

QUOTE (grantsfo @ Mar 28 2006, 06:21 PM) I think tire pressures are over rated. i dis-agree ... the difference on my car between 16# and 26# is that at 16#, the car sticks like glue, but "feels" spoongy, at 26# the car "feels" tight, but i can't keep the rear-end planted, i constantly fight to keep the rear-end from passing the front ... 10# difference on the initial cold setup makes for a completely different car ... for me, that's a pretty clear indicator of the importance of tire-pressure ... Andy

I gotta agree with Andy there. Tire pressures can make a -world- of difference in how a car both feels and handles. Even a 4 lb change can be significant.

-Josh2

Just have to say I have seen same driver go from low to high pressure on DOT slicks without major impacts to times. I honestly cant feel much differnce on Hoosiers between 24 and 32 PSI. I think its funny that there are two camps that swear by high and low pressures with DOT slicks. Tells me that there isnt much difference. I stand by my position that there isnt much difference for DOT tires like 710's in AX. Of course its important to experiment, but I just havent seen a signficant difference.

Andy isnt talking about DOT slicks.

I'm not an autox guy..
nor do I play one on TV.

but I gotta say that tire pressure makes a ton of difference..
thus the reason you can go out onto a track and feel the tires go "off" through a session... you come in to fine 6-8 lbs difference in pressure.

thats a huge feeling difference out of 6 lbs. AT TEMP.

I'm going to switch over to nitrogen this summer if things work as planned just to avoid this 6lb pressure increase.

I agree with Josh that temperature is key and a probe is the way to judge it scientifically... validly... measureably... and repeatedly...

I am only guessing... (remember I don't know Sheet about autox and have only done 1 in my life) guessing.... that if pressure really doesn't make that much difference in autox, then the tires are not up to their operating range. Because once tires are up to their correct operating range, pressure really does make a difference.

oh... one more thing. lets not confuse this thread between D.O.T. tires versus Slicks. They are two very different things, with different requirements, and different air pressure needs... make sure that new people reading along don't make any mistake. D.O.T. tires are NOTHING like slicks.

brant

tire pressure in slicks is a big deal. Not to mention the temps. go out on a really cold day on cold slicks and see how it goes....

In NASCAR (no flames please) how often have you heard them say the car is pushing so we are going to increase the pressure in the right front by 1/2 pound? 1/2 pound makes a difference so what do you think 6 pounds makes. Even on a DOT R tire.
Or drop 1/2 pound for some other handling quirk. It must do something...either that or DEI, Childress, Gibbs, Rousch and all the rest don't know squat....

I think that the key here is that in AX the tires rarely get up to operating temps. Why do you think folks like reruns....they get some heat in the tires and then get to do it again right away...

And, you gotta be careful about the "recommended" pressures from the maker.

For example, Hoosier say 40-44psi...No good.
Feels skatey.

We found that 25-28 psi on the "A" Hoosiers was good.

Same with the 710's. I started high.

Found the lower psi's work best and the tires will "catch" you when you start to lose it, as opposed spinning out with the high pressures.

I've been enjoying the 710's abilty to recover.
I used to spin a lot

Plus- I've found them to be excellant track tires.
Long life.


KT

I do think that tire pressure is very important in AX, and each tire has an optimum setting for a particular car, driver and course surface. And it's an elusive bitch!

But I also think Grant made an interesting point about the range of the 710s.

As an AX'er, I haven't found the pyrometer to be as effective for AX as it obviously is for track. Here are some of the problems I've ran into. In AX the inside of my rear tires get cooked sitting still in staging from the engine and exhaust header heat. And the outside of the front tires are worked to death from constant cornering and transitions in directions. These get evened out on a race track after several laps, but I haven't figured out an effective way to interpret the pyrometer readings in AX situations.

To compound the problem, the tires produce very little temp change in a short AX run. My tires just don't heat up much! They never reach anything near the recommended operating ranges. So the readings become more minute. We made radical changes in air pressure and we just couldn't get significant and constant readings to base further changes on.

Although I do bleed them between runs, it is very rare that they gain more than 1-3# of air pressure from a run.

I've been more successful dialing in tire pressure thru observation of how the tire is behaving, perceived cornering speeds, braking thresholds, turn-in, transitions, amount of stick, etc.


Grant - Interesting point about you make about being out of the temp operating range - from what I have been told, with the 710's, KUMHO has made a tire that sticks great when they're cold or warm, but quickly loose their grip when hot.

I think for AX maybe the best way to utilize a pyrometer would be in an empty parking lot. Maybe I need to try one again.

No simple answers to this stuff.

..

QUOTE (Joseph Mills @ Mar 28 2006, 10:52 PM)

I do think that tire pressure is very important in AX, and each tire has an optimum setting for a particular car, driver and course surface. And it's an elusive bitch! But I also think Grant made an interesting point about the range of the 710s. As an AX'er, I haven't found the pyrometer to be as effective for AX as it obviously is for track. Here are some of the problems I've ran into. In AX the inside of my rear tires get cooked sitting still in staging from the engine and exhaust header heat. And the outside of the front tires are worked to death from constant cornering and transitions in directions. These get evened out on a race track after several laps, but I haven't figured out an effective way to interpret the pyrometer readings in AX situations. To compound the problem, the tires produce very little temp change in a short AX run. My tires just don't heat up much! They never reach anything near the recommended operating ranges. So the readings become more minute. We made radical changes in air pressure and we just couldn't get significant and constant readings to base further changes on. Although I do bleed them between runs, it is very rare that they gain more than 1-3# of air pressure from a run. I've been more successful dialing in tire pressure thru observation of how the tire is behaving, perceived cornering speeds, braking thresholds, turn-in, transitions, amount of stick, etc. Grant - Interesting point about you make about being out of the temp operating range - from what I have been told, with the 710's, KUMHO has made a tire that sticks great when they're cold or warm, but quickly loose their grip when hot. I think for AX maybe the best way to utilize a pyrometer would be in an empty parking lot. Maybe I need to try one again. No simple answers to this stuff. ..

Just go to an SCCA board or GRM board and ask similar question about 710s. See answers you get, they are all over the map.

QUOTE

Although I do bleed them between runs, it is very rare that they gain more than 1-3# of air pressure from a run.

Hmmmm

I bleed of 3-5 psi after *every* run.

Never got 'em greasy yet.

I'll try to remember to record tire temps this weekend.


KT

PLease do Trekkor. If you run that airport roundy round thing I would imagine the runs would be long enough to get some temp in them.

I have reached 160 degrees on a new set of Hoosiers. 8 runs two drivers on blistering hot concrete ambient air temp as 98.

next event was a night event managed 130 degrees warm asphault ambient temp about 85. one driver

I also have to ask a hypothetical question that is a bit off topic. If I'm running 29 PSI on all four corners with DOT slicks and then decide to lower just front pressures to say 26 PSI. What will happen? Will the car push more or will it oversteer?

Trick question Grant, if 29 PSI was determined to be optimum grip then going below that threshold will reduce grip. Hence the front will slide violently as the tire side wall rolls and deforms the contact patch.

QUOTE (Joe Ricard @ Mar 29 2006, 07:46 AM)

Trick question Grant,  if 29 PSI was determined to be optimum grip then going below that threshold will reduce grip.  Hence the front will slide violently as the tire side wall rolls and deforms the contact patch.

So lets say 29 PSI is optimum. Then would one induce similar understeer characteristic by raising the front pressure to say 32 PSI?

http://rogerkrausracing.com/overundr.html

Ken

QUOTE (KenH @ Mar 29 2006, 08:37 AM)

http://rogerkrausracing.com/overundr.html Ken

Yet another good site to save to favorites

QUOTE (Joseph Mills @ Mar 28 2006, 10:52 PM)

...To compound the problem, the tires produce very little temp change in a short AX run. My tires just don't heat up much! They never reach anything near the recommended operating ranges. So the readings become more minute. We made radical changes in air pressure and we just couldn't get significant and constant readings to base further changes on...

If your tires are not getting up even close to optimal temperatures, one of a few things is going on.

1) Not driving hard enough.

...Yeah, I know. NONE of us are driving hard enough.

2) Wrong compound.

...For example, running R compound Hoosiers is not a good choice for autox as they are not designed to heat up quickly.

3) Too much tire.

...This is a problem I see more often than you'd think. If you have too much tire under the car, there won't be enough pressure on the tread face to generate heat. Especially at an autox. On a light weight 914, with a stockish motor, I would suspect that 225's might be as much tire as you can reasonably expect to get warm at an autox. More power, bigger meats in back... Why do you see people spraying down their tires with water at big autox events, they got enough heat in the tire, and don't want them to get too hot.

If you're not getting enough heat into the tire, look at 1,2 or 3. Certainly a 205 or 225 A compound Hoosier or Kumho -should- get up to temperature on a summer day at an autox. And if they're not, drive harder.


-Josh2

Grant,

A 3 psi change will result in a different feel depending on the direction. Assuming that the 29 psi pressure was optimal for the tire and the setup of the car, yes the 3 psi change in front is likely to induce understeer both ways. However, the "feel" of the car will be different.

Over pressure on DOT radials (and they're not "slicks", even if they don't have tread) will tend to result in the tire "skating" more. It will feel more responsive, as the sidewall is stiffer, but will tend to "skate" over smaller bumps on the pavement. Will feel a little rougher of a ride (we're talking shades of grey here), and while it will feel like it turns in better, will ultimately not provide the same level of grip.

Under pressure in the front will also ultimately result in understeer, but in a very different way. The sidewalls will be softer, and the tire will feel like it "takes a set" better. There is more compliance in the sidewall and will allow the tire to absorb more bumps before loosing traction. The tire will not feel quite as responsive (again, shades of grey here) as the over pressured tire, but may "feel" like it has more grip. It doesn't, it just feels like it takes longer to break the tire free of terra firma. That's the squishy sidewall talkin' there. And the reason it doesn't actually grip as well is that you're very likely loosing contact patch as the sidewall flexes more.

These are generalities. And will vary from tire to tire, and car to car....

This is assuming that the rest of the chassis is optimized. Shocks and alignment have a huge impact on how the car feels and responds. Dial in the chassis, and a 2 psi change in tire pressure is very noticeable. Watch the SCCA stock class autoxers, especially in the lower classes. Tire pressures are -everything- there, becuase they don't have much else to work with. Often times, tire pressures are used to "work around" other issues with the car that can't be changed. Like camber. On a camber limited car, the car will actually perform better with higher pressures in the front as the sidewall will flex less and help keep more of the contact patch on the ground. Take the same car, and dial in the necessary camber, and you can drop that pressure considerably. Same thing for wheels size. Put a huge tire on a small rim, and you're gonna need more pressure to keep the sidewall firm and keep the contact patch on the ground. Put a bigger wheel in ther ewith teh same size tire, and you can drop that pressure.

DOT Radials have very firm tread faces, and comparitively soft sidewalls. The sidewall is what talks to the tread and tells it what to do. Slicks on the other hand (Bias Ply slicks that is) have rediculously rigid sidewalls, and very compliant tread faces. The tread face is THE compliant surface, and tire pressures make a huge difference in the feel of the tire.

Okay, I've rambled a bit here.

Short story. If someone's lap times are exactly the same at 10 psi over and under, one of two things is going on. One, the rest of the chassis is far from optimized. Two, and more likely, the tire isn't being driven to the limit...

Just my $0.02... YMMV...

-Josh2

I always find these discussions interesting, as the ways people come to their "ideal" pressures often seem less than empirical. For example bringing pressures down over the course of the day doesnt account for tire and track getting warmer as the day progresses. Has anyone started low and gone up to see what happens? Why is it that the tire engineers indicate much higher pressures than what is often reccomended by some weekend AX drivers?

Has anyone ever done a test where they take a fresh set of Kuhmo 710s and run a skid pad then take another fresh set at a completely different pressure and run again?

I suspect that there is more than just a single variable of tire pressure at work during the course of a day at an AX event that leads to "grip" perception. I often feel grip on a paticular course change without making adjustments to my tire pressures. Taking a differnt line and hitting different section of pavement can often result in perception that grip has improved for me.

I know some people swear they gain as much as 2 seconds on an AX course by finding ideal tire pressure. That may be the case. Guess I'm just a born skeptic and general trouble maker around this subject since I have heard farily strong arguements from the high pressure and low pressure camps. However I am one of those lower pressure believers when it comes to DOT slicks (Dot radials without tread!)whether it be based in fact or my misguided perception.


I think no two cars are the same as mentioned above. I do concur that rim width, camber settings, spring ratings, etc will play a big role in where an individual sets their pressures. I dont think there is a general pressure one can set for a paticular tire. I know from my expereince running 8" wheels that I could run lower pressures more effectively than on 5.5 inch wheels.

I know more than a few people ( top flight SCCA autoxers) who will use up to three or four different sets of tires durring a test and tune day, trying to find the optimal tire pressures and suspension settings.

As Jake is so fond of saying, "It's all in the combination". Suspension settings, wheel size, alignment, and driving techique all will impact how a tire "feels".

What will make a tire perform at its optimal best? The -right- alignment, the -right- wheel size, and the -right- tire pressures. Tire pressures are often used to compensate for not having optimal setup somewhere else in the system.

Tire temperatures will tell you more in one day about what your tires need from the setup of the car. It'll tell you if you need more camber, it'll tell you if you need less camber. It'll tell you if the pressures are too high or too low. It'll tell you if the car is oversteering too much or understeering too much (that can be more driver related though...).

But you gotta get 'em warm...

-Josh2

And this really does help keep the warm.

asdf

QUOTE (jhadler @ Mar 29 2006, 11:22 AM)

If your tires are not getting up even close to optimal temperatures, one of a few things is going on. 1) Not driving hard enough. 2) Wrong compound. 3) Too much tire.

1) Well, to be honest, I don't know how much "harder" I can drive. Or maybe I don't understand what that word means.

I do tend to try to remain smooth in my driving efforts. There are a few "thrashers" in my region that I'm sure produce more heat in their tires than I do. And when they keep it together, they post some great times, but that has never been the fast way for me. I do try to continually push myself to the edge of barely being in control of the car. If I don't feel I've made a few "saves" on a run, I know I'm leaving something on the table.

My car and I are competitive enough to have won my class at the last AX, which included beating an 06 nat. champ in my class. I was ninth overall out of 120 entries. I'm certainly no hot shoe and have limited abilities, but I "think" I'm driving pretty hard.

But maybe I do need to try harder. I've got an AX this sunday. In my PAX class I'll turn it up and see what happens. Poor corner workers.

2) It appears to me that the 710s are perfect for AX since they perform so amazingly well cold (I am not the only AX'er who runs low temps). In my local region I've never seen anyone spray their tires except drivers running 710's. In fact, I see other brand tire drivers use a buddy driving as a "tire warmer".

3) I started to mention this in a previous post, but I think my car is definitely "over-tired". On faster courses it works well, but the short comings really become apparent on slow & tight courses. Fortunately in my region we run wide and fast so it's not so bad. I would consider going with smaller wheels/tires but I'm also considering doing a suby conversion, which if I do it would make my current setup pretty ideal. I agree that many AX car setups are prone to running too large of wheel/tire setup. The AX crowd is a diverse group.

Thanks for the pyrometer urgings. It's been several years since my experience and you have prompted me to give it another whirl. Nothing to lose right? I'm going to use it this sunday as much as my run intervals allow. Maybe I will learn a thing or two.

Yeah, the first two points were pretty much the rediculously obvious. But I had to say it anyway. The "too much tire" is one that sometimes gets confusing. Because more is always better right?

Too much tire, and you won't have enough pressure (lbs/sq in) pushing down on the tire to generate sufficient friction to heat up the rubber enough.

Get more power, you can use more tire (at least in the rear). There comes a point of dimishing returns on tire sizes. Both around the cones and at the track. At the track, you have more time, and momentum, to heat up the tires. But the wider tires present more rolling resistance as well. The early miatas in SSB would run narrow tires for the big tracks where they were down on power compared to the competition, and wider tires on the narrow tracks to improve their handling advantage. Weird...

I've considered going to 245's, and could -maybe- get enough heat into a set of Hoosiers. But the gearing would kill me, so I'm stickin' with the 225's...

-Josh2