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Discussion Starter #1
I did my first auto x 2 Saturdays ago. My car is supposed to have 245 tires all the way around, but I have 275's on the rear. The factory pressure for the 245 tires is 30 psi. I ran 32 psi. I have some wear along the edges of the tread on all 4 tires. Should I be running my air in my tires?

 

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That looks pretty good to me. Honestly, if you only got that much wear on the shoulders at 32#, then I would guess you weren't pushing all that hard. Which is actually a good thing - most first-timers push waaaay too hard and tend to really wear the shoulders of their front tires. If you do more auto-xing, depending on what tires you have, how much negative camber you're running, and how aggressive you're attacking the corners, you may find that something more like 40# is necessary up front to keep from rolling over onto the shoulders too much. Lower pressure (about normal street pressure) will probably work just fine in the rear.

One somewhat common trick is to use the wear bar indicators on the shoulder of the tire as a reference point. The indicators aren't the same on every tire, but in many cases it's a little arrow or triangle, like so:

If you can see wear is coming off the tread face and onto the sidewall to about the tip of the arrow, that's fine. If you're rolling over onto the shoulder so much that you're scrubbing well down the arrow, then you need to up the tire pressure (to firm up the sidewall and help keep the tire from rolling over) and/or be a bit less aggressive in the corners.
 

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Checking heat across the tire with a pyrometer is the proper way to see what the tire is doing. It will tell you if pressure is correct and if camber is correct. Observing the sidewall is pretty useless. Now, on my autox car I havent done that, but I do run 275/35 18 RE71's square at 28f and 26r with much success. Sometimes 25r if the pavement is very slick. For autox you want the tires to heat up quickly.
 

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Discussion Starter #4
That looks pretty good to me. Honestly, if you only got that much wear on the shoulders at 32#, then I would guess you weren't pushing all that hard. Which is actually a good thing - most first-timers push waaaay too hard and tend to really wear the shoulders of their front tires. If you do more auto-xing, depending on what tires you have, how much negative camber you're running, and how aggressive you're attacking the corners, you may find that something more like 40# is necessary up front to keep from rolling over onto the shoulders too much. Lower pressure (about normal street pressure) will probably work just fine in the rear.

One somewhat common trick is to use the wear bar indicators on the shoulder of the tire as a reference point. The indicators aren't the same on every tire, but in many cases it's a little arrow or triangle, like so:

If you can see wear is coming off the tread face and onto the sidewall to about the tip of the arrow, that's fine. If you're rolling over onto the shoulder so much that you're scrubbing well down the arrow, then you need to up the tire pressure (to firm up the sidewall and help keep the tire from rolling over) and/or be a bit less aggressive in the corners.
There were parts of the course that I could take pretty hard then there other parts of the course that were pretty complex and I didn't want to miss a cone or get lost so I took it easy. I had an instructor riding with me and he said the main thing holding me back was not knowing the course.The guy that designed the course missed a cone. They said this course was not a good course for a beginner. I only did morning runs, so I only got 4 runs. If I would have stayed all day, I would have got 6. I felt like on the 4th run I was starting to get the hang of the course. If I could have got my other 2 runs I think I could have done better. I may up my pressures a little and hopefully I will get the hang of the course fast Saturday. I'll keep the wear bar trick in mind.


Checking heat across the tire with a pyrometer is the proper way to see what the tire is doing. It will tell you if pressure is correct and if camber is correct. Observing the sidewall is pretty useless. Now, on my autox car I havent done that, but I do run 275/35 18 RE71's square at 28f and 26r with much success. Sometimes 25r if the pavement is very slick. For autox you want the tires to heat up quickly.
I was thinking about using an IR thermometer. I know it won't be as good as a pyrometer but it may help some. How hot should the tires be, or will that vary from tire to tire? I'd like to have 275s or 315's on the front. Right now I am try to make do with what I have. I'm not sure if I am going to keep this car much longer.
 

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Tire size, rim size and sidewall size all play a role in how hard you can attack. What tire size are you running? What rims are they on? If you have a 275 on an 8 inch rim, your tire is pinched and that will impact when the tire rolls over.

If you have a lot of sidewall, dropping pressure will lead to the tire folding over a little and having less steering response.

Also, your tire pressure will go up on every run. If you started at 32psi, it could be at 36psi after your first run. Be sure to check your tire pressure between runs and adjust accordingly. It looks to me like you could have dropped a few psi. But, I need to know more about your tire and rim size to be sure.

The wear should be closer to the lower edge of the tread block.

I run 315/30/18 Rival S tires front and rear on my New Edge cars at 26psi.

My advice to novices is to do a season of autocross before you start making major changes to your car. Driving around the limits of your car will make you a better driver. Putting the best tires on your car too early will cover up a lot of mistakes you are making behind the wheel. Get seat time and instruction. Learn the car. Then build the car to suit your driving style.
 

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Discussion Starter #6
Tire size, rim size and sidewall size all play a role in how hard you can attack. What tire size are you running? What rims are they on? If you have a 275 on an 8 inch rim, your tire is pinched and that will impact when the tire rolls over.

If you have a lot of sidewall, dropping pressure will lead to the tire folding over a little and having less steering response.

Also, your tire pressure will go up on every run. If you started at 32psi, it could be at 36psi after your first run. Be sure to check your tire pressure between runs and adjust accordingly. It looks to me like you could have dropped a few psi. But, I need to know more about your tire and rim size to be sure.

The wear should be closer to the lower edge of the tread block.

I run 315/30/18 Rival S tires front and rear on my New Edge cars at 26psi.

My advice to novices is to do a season of autocross before you start making major changes to your car. Driving around the limits of your car will make you a better driver. Putting the best tires on your car too early will cover up a lot of mistakes you are making behind the wheel. Get seat time and instruction. Learn the car. Then build the car to suit your driving style.
I'm running 245/45R17 and 275/40R17. The fronts are a factory wheel, 17x8? The rears are a 17x9.

I went auto xing today. I had instructor ride with me on my 3 morning runs. We got 4 runs in the afternoon and an instructor rode with me on 2 of them. My goal for today was to get a 55 second run, but I did not tell anyone. The instructor that was riding with me got super excited when I ran a 54. I walked the course 3 times today. This course was a simpler course than the course was the first time.
 

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The 245/45/17 and 275/40/17 have the same amount of sidewall, which is good. The rim size should be stamped into the back of the rims. A factory rim would be 17x8. With that amount of sidewall, you probably don’t want to go below 30psi.

Having said that, you will experience more tire wear (especially on the edges) the lower you go and the harder you attack. In addition to keeping the tire from folding, higher pressure helps keep the wear in the center of the tread. No matter what, you will be decreasing the life of your tires by autocrossing.

Check your air pressure after each run. Remember, if you pull out 3-4psi every run as the tires heat up, you will need to put air in before you drive home.

Your 245/275 setup will create more understeer. But, the description of your car says you have D-Specs. You can adjust out some of the understeer caused by the staggered rims and tires using the struts/shocks. You might also need to use less air pressure in the front tires to help with understeer.

As for walking the course, I would suggest doing as many walks as you can. If your club does a Novice Course Walk, do that too. It can also help to shadow experienced drivers on their course walks.

I have a few “Mustang Autocross Tips” on my Warhorse Racing YouTube channel. If you have some time, check out the “How to Attack the Course…”, “Duration of Acceleration” and “A Tale of Two Seconds…” videos. They cover some very important aspects of autocrossing these cars.

Here’s a link:

https://www.youtube.com/channel/UCOEWzAT17XoeGzSWysT1NXw/videos
 

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Discussion Starter #8
The 245/45/17 and 275/40/17 have the same amount of sidewall, which is good. The rim size should be stamped into the back of the rims. A factory rim would be 17x8. With that amount of sidewall, you probably don’t want to go below 30psi.

Having said that, you will experience more tire wear (especially on the edges) the lower you go and the harder you attack. In addition to keeping the tire from folding, higher pressure helps keep the wear in the center of the tread. No matter what, you will be decreasing the life of your tires by autocrossing.

Check your air pressure after each run. Remember, if you pull out 3-4psi every run as the tires heat up, you will need to put air in before you drive home.

Your 245/275 setup will create more understeer. But, the description of your car says you have D-Specs. You can adjust out some of the understeer caused by the staggered rims and tires using the struts/shocks. You might also need to use less air pressure in the front tires to help with understeer.

As for walking the course, I would suggest doing as many walks as you can. If your club does a Novice Course Walk, do that too. It can also help to shadow experienced drivers on their course walks.

I have a few “Mustang Autocross Tips” on my Warhorse Racing YouTube channel. If you have some time, check out the “How to Attack the Course…”, “Duration of Acceleration” and “A Tale of Two Seconds…” videos. They cover some very important aspects of autocrossing these cars.

Here’s a link:

https://www.youtube.com/channel/UCOEWzAT17XoeGzSWysT1NXw/videos
I'm not concerned about decreasing the life of my tires. I ran 34psi in the front and 32psi in the rear. I went up with my pressure because I was going to push harder. I think it was the wrong move, my tire wear still looks about the same. I think I need to run a lower pressure. I was thinking about 30/30. It may even need to go lower. This club does a walk for first timers, but a guy just leads you around the course, nothing special. When I worked the course, I got a spot in the middle, where I could watch the whole course to help learn it too but this course was real simple in comparison to the last one.

I've watched a couple of your videos. I'll be sure to check out some more.
 

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I think 30/30 is a good place to start. I’m not sure I would go too far below that with your sidewall height.

If your shocks are on a stiff setting, you might also want to consider softening them up. On my solid rear axle cars, I set the Tokico Illumina 5-way adjustable shocks and struts to 2 FRONT, 3 REAR (5 is the stiffest setting). Softer up front to reduce understeer; a little harder in the rear, but not so hard that you lose grip.

There are a lot of variables in terms of suspension, but an autocross setting is often softer than what feels best on the street. You’d be amazed how well these cars respond to a minor adjustment of the shocks and struts.

Identifying the 5 or 6 important cones among the hundred cones on course is a skill that takes time. The more you autocross, the easier it gets to find the areas where you can attack. The awesome thing about autocross is that the course is never the same twice.

Thanks for checking out the videos. I created the channel to help Mustang drivers new to autocross get the most out of their cars on course. I’m happy to answer any questions you might have.
 

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Discussion Starter #10
I'm pretty sure my shocks are at 5 front and 4 rear. I'm going to try a tire pressure adjustment next time, 30/30. Then I may get brave and play with the shocks the same day. I don't want to mess with too much on the car right now. I am the biggest variable and it may be tough to tell what it working, but at the same time I'd like to have things dialed in.

The two events I have been too were by the same club. It seems like at the end of a long slalom they like to setup two cones that you have to go the same way around. So I know to watch out for that.

I'm going to check out some more of your videos now.
 

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It’s definitely a good idea not to make too many changes when you first start out. You have the exact right mentality: work on the driver first. When you are ready to make adjustments on the shocks and struts, I would suggest softening the fronts. The D-Specs have 7 turns of adjustment, if you are at 5 turns in, you are almost at full tight up front. And you are tighter up front than in the rear, which can cause understeer. Being that stiff up front will make you more likely to fold the front tires over at 30psi.

I would suggest trying the 30/30 setup to see how it feels. Do a few runs at that pressure setting. Then experiment by setting the shocks at 3 FRONT and leaving them at 4 REAR. Not knowing your entire setup, I can’t say this will be perfect, but you should feel a difference. Go easy; when you take out understeer, you can add oversteer, which means you can go sideways or spin.

Your goal is to get the car as close to neutral as possible.

This is one of the tricky aspects of autocrossing our cars: we want adjustability, but every available adjustment adds complexity to the setup. I always try to set the car up so that I only need to adjust air pressure. It makes life easy. The good news is you can usually dial-in a car one event.
 

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All the above is good info but the OP is a novice driver. Seat time rather than tire pressure/heat monitoring is more beneficial at his stage.

Nevertheless, I think we need to be clear when tire pressure is checked. I like to start at a cold pressure. For my last outing, I went with 33/28 F/R on a 19x9;19x9.5 wheel running 265/285/40 MPSS tires; 2016 Mustang GT PP.

At this cold pressure the tires increased to 37/31 psi after the hour drive to the venue. While in grid the D/S stayed pretty much the same while the PS decreased 2 psi both ends. Grid baseline heat (front only) was 140DS and 138PS measured at the center. NOTE: In grid the sun was on the DS while the car shaded the PS. Post run heat was 144 DS/142PS (DS sometimes145). These were 57 second runs with the fast cars in the 53s; 4 runs for the event. The L/R ratio was about even with the long sweeper being a left hander (working the PSF). PSI didn't exceed 38 on the DS front (I assumed the same spread F to R). Heat measures were with an IR thermometer with probe capability (not used). I was in the morning run group.

Feedback: On this course, the front was sticking pretty well but the rear let go twice causing throttle lift and steering correction. I concluded that I needed more rear pressure. For my next event this weekend, I'm starting at 35/31 cold.

Getting good heat measures with a probe is tricky at best and takes some time to accomplish (three probes per tire). Moreover, a 60 second course does not increase heat all that much whereas the sun does - unevenly I might add. So, unless the OP is already at the pinnacle of his driving skill and needs a bit more from the car perhaps monitoring heat and psi after each run is worth the time and effort. In my experience, these measures are not critical for a novice or even an intermediate driver.

With that said, I would set cold pressures and see how the car works during the day, but leaving them alone. Then based upon that experience, adjust for the next outing.
 

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I’m a Novice Coordinator for 2 clubs that get anywhere from 15 to 40 Novices per event. I’ve helped design and run Novice Programs and Novice Schools. I completely agree with you that seat time is the most important part of being a Novice. Having an instructor in the passenger seat would be ideal.

I’m not a big advocate of Novices measuring tire temps, but I do think it’s important for Novices (especially in older Mustangs) to check/set tire pressure as part of their pre-run routine. And, if they have some adjustability in their setup, it can be extremely helpful to get their car dialed-in better so they aren’t fighting the car.

Set your pressures cold in grid before your first run. Then check/set them right before each run.

I suggested softening up the front struts after doing a few runs at 30/30psi because my experience with these cars tells me that 5 is too stiff up front. And with his sidewall height, going below 30 might lead to the tires folding a bit during cornering. Softening up the struts will allow him to get more out of his tires without going too low on pressure. I’m just trying to get him to a good baseline setup he can run for the next few events.

Baselining your setup on the car allows you to better measure driver improvement.
 

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Discussion Starter #14
Tire pressure is checked cold. First event I ran 32psi front and 32psi rear. The second event I ran 34psi front and 32psi rear. The auto x was in the same parking lot and it felt slicker so I think I need to go down. That is why I am thinking about trying 30/30. With me being a novice, I feel like I am getting to know the course, and the event is over. So I think it would be tough for me get a good comparison to see if any adjustments help. 3 on the d specs is pretty soft. The car feels comparable to struts that are nearing the end of their life. I'm pretty sure 3 (need to check notes) is where I was running them to beat people at the stop lights.
 

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Because the Mustang has a heavy front weight bias, we generally want about a 4psi cold spread front to rear (e.g., 34/30). Tire compound, whether an all season or full-on R-comp, aspect ratio, etc. determines where those pressures start. But that 4 PSI spread has been tested by many. This also assumes the wheel/tire combo is appropriately size-matched. For example, if you look at the wheel/tire combo Ford uses on the s550 GT350R, you can see that there is no sidewall bulge. In fact one might argue that the tires are stretched on those rims. If you watch enough vids showing what the tire does in dive while cornering (slip angle), you'll understand why. Hence why putting an oversize tire on an inappropriate narrow rim causes loss of grip.

In any event, there are lots of variables on course that happen very fast. Figuring all this out in short runs limited to say 4 for the day for me anyway, nearly causes info overload. Thus, I try to pick one or two things I want to work on for that event. Tire pressure is last if even on the list because I can set it cold and see how the day goes while working on the two improvements to my driving. Yes, I note how the car worked but I don't change anything because that injects another variable. Recently, looking ahead has been my focus which is easier said than done. But I'm a slow learner and have some bad habits to correct.
 

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I’m going to respectfully disagree with qtrracer on his first point. I have driven many s550s and a few GT350s; they are completely different beasts in terms of suspension/handling than an SN95 Mustang. The limit of the front and rear suspension is MUCH further out than a Solid Rear Axle 1994 GT. The only thing they have in common is front end weight-bias, and, due to many variables, a “one-size-fits-all” air pressure setup won’t work on cars from 1994-2019. I won’t comment on whether a 4psi spread is best for an s550, but I can offer some data from my own experience with 1979-2004 cars:

I autocrossed my 2000 GT with a Solid Rear Axle and my 2004 IRS-swapped V6 during the same season, on the same rims and tires. The GT has about 200 lbs. more weight up front than the V6. And, being a convertible means the GT’s weight distribution is MUCH WORSE than my near 50/50 V6. I never ran more than 1psi difference between the front and rear (lower in the rear). And I ran the same psi on BOTH cars. I started at 33psi front and rear and went lower as I chased grip. Once the car was dialed-in, I never ran more than 30psi front or rear in either car.

That setup didn’t change when I put an IRS in my GT. Now, with 315/30/18 tires on 18x10 inch rims, I usually run 27psi front and rear. That’s on BOTH cars, with almost identical mods; the main difference being the front end weight-bias on the V8.

The important takeaway is that both cars handled better (and beat s550s and some GT350s) with lower psi set the same front and rear. There is a danger in going too low, but that depends on what specific tires you are using.

The OP is running 245/45/17s on 17x8s up front, and 275/40/17s on 17x9s in the rear. A staggered setup creates understeer. His stiffer strut setting relative to the rear shocks creates understeer. From the factory, the car came with understeer. More importantly, the OP said it felt slicker when he went up in tire pressure on the same surface he’d been on the week before. That is because increasing front tire pressure in a car with added understeer will create more understeer.

Based on my experience and what he’s posting, I don’t think 34/30 is the proper setup for his car. I think 30/30 is the best place to start.
 

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Discussion Starter #17
Because the Mustang has a heavy front weight bias, we generally want about a 4psi cold spread front to rear (e.g., 34/30). Tire compound, whether an all season or full-on R-comp, aspect ratio, etc. determines where those pressures start. But that 4 PSI spread has been tested by many. This also assumes the wheel/tire combo is appropriately size-matched. For example, if you look at the wheel/tire combo Ford uses on the s550 GT350R, you can see that there is no sidewall bulge. In fact one might argue that the tires are stretched on those rims. If you watch enough vids showing what the tire does in dive while cornering (slip angle), you'll understand why. Hence why putting an oversize tire on an inappropriate narrow rim causes loss of grip.

In any event, there are lots of variables on course that happen very fast. Figuring all this out in short runs limited to say 4 for the day for me anyway, nearly causes info overload. Thus, I try to pick one or two things I want to work on for that event. Tire pressure is last if even on the list because I can set it cold and see how the day goes while working on the two improvements to my driving. Yes, I note how the car worked but I don't change anything because that injects another variable. Recently, looking ahead has been my focus which is easier said than done. But I'm a slow learner and have some bad habits to correct.
I'll keep the 4 psi spread in mind. For the next event I am going to try 30/30. I wish there was a place I could do some testing. There is a traffic circle in town......but it is across from the police department, so that probably would not be a good idea.:laugh: Do you have a link to any of those videos with the camera on the tire of the GT350R? I was thinking about putting a camera on my tires for a run. I also thought about mounting one to see how much side to side movement there is in the rear axle.

My goal the last time was time to learn the course better, so I walked it 3 times and when I worked the course I was in the middle, so I could see everything to help me learn it. Next time I am going to try to work on braking in a straight line, slow in fast out, and keep it tight. I really don't have much time between runs to do anything. I wish I had time to watch a video my previous run. I look far ahead, but I get caught up in what I am doing and then I'll be looking close up. At the last auto x I had a decent run going (for me) and there was 180* turn then a "dog leg" to the finish. I was trying to keep it real tight going around the 180* and did not have the car aligned very well to enter the dog leg. I see you are from MD. Do you ever run with the CDC?
 

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Discussion Starter #18
The club posted the results from last weekends event. There was only other Mustang, a 2011 GT at the event. My best time was 54 seconds his was 48. I think he was on Falken tires, maybe the RT615k+, I only glanced at the car as I walked by it in the paddock. My car is on old Nitto NT555 that are starting to dry rot. Since this was the only other Mustang there, how does my time sound in comparison?
 

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Sometimes it's better to track other Novices, not necessarily other Mustangs.

What was FTD for the event? Was the Mustang one of the fastest cars out there? What time did the fastest Novice run?

There weren't many Mustangs showing up when I first started, so I just picked 2 Novices and 1 faster driver than me and divided their raw times by mine. That let me know how I was doing relative to my fellow Novices and to a faster driver. I picked people that attended all the events so I could keep checking to see how I was improving over the season.

You've done a couple of events. Find a few drivers that were at both events and divide your raw time by theirs. If you got faster on each run and closer to their times at each event, you did great!
 

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Discussion Starter #20
Sometimes it's better to track other Novices, not necessarily other Mustangs.

What was FTD for the event? Was the Mustang one of the fastest cars out there? What time did the fastest Novice run?

There weren't many Mustangs showing up when I first started, so I just picked 2 Novices and 1 faster driver than me and divided their raw times by mine. That let me know how I was doing relative to my fellow Novices and to a faster driver. I picked people that attended all the events so I could keep checking to see how I was improving over the season.

You've done a couple of events. Find a few drivers that were at both events and divide your raw time by theirs. If you got faster on each run and closer to their times at each event, you did great!
I was trying to track someone with a similar time from the first event to the second event. The guy was at the second event, but he is not listed. There was a guy with a Genesis that did 52 and he was a novice. I guess I can go through the list from the first event and compare to this one. I remember see a notification on my phone from YT were you asked me if I ran Cam C. I did not see it when I replied to my comments tonight and just happened to think about it. Everyone is in the same class. They ask your weight, hp, tread rating. You get your time and a index time. They have an "optional class" like daily driver, sportscar, awd, etc. They also have a PAX class, maybe 10 people put something down for that.

I remember one guy from this both event and I think he is new too. The first event he did 57 and the second 51. I did 62 the first event and 54 the second. We both improved 6 seconds, lol. I found another guy that did 52 both times.

It makes it tough to tell how I am doing when I am going up against Miata's, S2000's, Miatia's, BRZ's, european cars, and I almost forgot Miata's. Someone even has an Exocet.

I had a good time, I am just trying to figure out how bad I am.
 
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