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My Venture into Autox

19K views 146 replies 10 participants last post by  4rd Tough 
#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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#2 ·
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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#4 ·
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.
 
#3 ·
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.
 
#5 ·
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.
 
#6 ·
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.
 
#7 ·
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
 
#8 ·
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.
 
#9 ·
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.
 
#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.
 
#11 ·
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.
 
#12 ·
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.
 
#13 ·
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.
 
#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.
 
#15 ·
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.
 
#17 ·
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?
 
#16 ·
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.
 
#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?
 
#19 ·
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!
 
#20 ·
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.
 
#21 ·
You aren't running with a group that follows the SCCA Classes. CAM-C is where our cars are classed using those rules.

I wouldn't worry so much about that. And, you aren't bad, you're just a Novice. Everyone starts out as a Novice. I was 12 seconds behind the slowest car on course at my first few events. I got beat by a PT Cruiser. It takes a season to get comfortable, so don't be too hard on yourself. It may seem like it's impossible to catch those other cars, but you'll start reeling them in soon.

Check out BRR-SCCA; they are an SCCA Club that will have some CAM-C cars at their events.
 
#22 ·
At the first event, I was the only American RWD car there. This last event there was a 2011 Mustang GT, C5 Z06, and C7 Grandsport. For the most part it is all small imports with the exception of some Feista ST's and Teslas. So there is no one to compare to. The guy that was running in front of me in the afternoon at the last event said he had a 96 GT.

A PT cruiser is a neon with a different body. There is guy that runs with this club that has an old Plymouth Neon 2 door and he does really well with it.
 
#23 ·
I compared my times in my first season to a Mazda 3 (Novice), an Acura Integra (Novice) and a GTI (regularly FTD). I used RAW times, not PAX. The cars didn't matter, it was the experience level of the drivers and the times they were running. Dividing their times by mine let me know I was keeping up with my fellow Novices and getting closer to the guy setting FTD. If you don't have direct competition in a similar car, this method lets you measure your progress.
 
#24 ·
The clubs I run with are SCCA and private. SCCA follows the rules which hampers some cars with standard mods that place the car in a non-competitive class. SCCA puts lots of restrictions on the street class whereas CAM is comparatively wide open. The private clubs very but generally, only look at HP, weight and tires. Formulas are used to adjust. I'm not a fan of either approach but it is what it is.

Given the limitations and scoring factors, for a novice driver I agree with Warhorse - compare times to other novices not cars. Maybe even look to see where you are against the fastest. The one universal truth with novices is that they generally overdrive or underdrive their cars. Either way the times are not optimal so comparisons are more likely a measure of skill/experience rather than car type/set-up. Also, since venues change as do the courses, comparing times from one event to the next is not helpful in isolation.

I'm also an advocate of holding variables to a minimum. For example, did I just shave off one second because of a better line, or some other factor? When first starting out it's often a mistake to "upgrade" the car. Fact is most of the newer cars are way more capable right out of the box than a novice driver can appreciate. So in the beginning, keep the mods to a minimum and work on driving. Seat time is the one variable one can see improvement on with no other changes. This isn't to say that the car's consumables and other safety issues should be ignored. But it is rather hard to tell if an improvement is due to a better line or some change to the chassis/suspension. Chassis/suspension changes have their time and place. Seat time is universal.
 
#25 ·
Its almost comical that any club looks at HP to classify an autocross car. HP has the least correlation to laptime in autocross than any single parameter that you could choose. I think that car color is probably a better predictor of laptimes:) Only half joking here.
 
#26 ·
It looks like most of the "fast" guys were 2 or 3 seconds faster at my second event. I was 6 seconds faster. So I was about 3 seconds faster. My car will be staying the way it is for rest of the year. At a minimum next year it will have new tires. I am debating on what size to go with. There are limited choices in Mustang friendly autox tires. If stay with 17's the only thin I saw in a 275 was a falken RTK615+. There are more options I go with a 245 but I don't know if I want a tire that small. Then I could step up to a 18'' with a 315 but I am not sure if that will fit and the tires get really expensive. If I go with an 18'' wheel I could put GT500 brakes on it eventually, but I am not sure brakes are all that important, like HP is not that important. Then I was also thinking if I could run the 18'' wheel with 315s and then put the GT500 14'' rotors on the car, I would be increasing my unsprung weight. How would that effect handling? It is kind of looking like 17'' wheels with 275 tires and then cobra brakes eventually is the best bang for the buck. I could also run a 275 front and 315 rear. I like to try to think things through so I only have to buy it once. I don't want to buy new 17'' wheels and tires and then decide I want GT500 brakes and need 18'' wheels and tires.
 
#27 ·
The unmodified Fox chassis does limit wheel/tire choices. On my 86 (old style fenders), I ran 17x8 01 Cobra wheels with 255/40s square. Had a .5" spacer on the rear and sn95 a-arms/spindle up front. (FYI, the sn95 a-arms are about 1.25" longer than the stock Fox chassis arms. This means front tract is increased by 2.5" which makes fender clearance an issue. But because the 86 K-member has the a-arm pick ups about .5" more inboard than the later 87+ v8 cars, track compared to those cars is only about 1.5" wider - or +.75" per side. Still creates clearance issues but not nearly as bad.) So long as I had ride height at 25" ground to lip and -2.5* camber they worked without hitting anything. However, with the same ride height and camber setting when I moved to a 95 Cobra R 17x9 with 255/45s they did hit the front edge of the fender. I also had to remove my .5" spacer from the rear. This car had no fender rolling.

The short answer is the 01 Cobra and 95 Cobra R wheels have different off-set/backspacing. So pay attention to wheel backspacing and don't get too greedy with wide tire choices. While a 275 will fit a 9" wheel, current thinking is that combo is too pinched to yield a full patch especially in dive while cornering. A 255 or perhaps a 265 would be better.

As for tire choices, what is your budget and how often do you want to buy tires? For example, my wife and I drive the 2016 Mustang and a 2010 MINI S. The Mustang runs MPSS (300 TW) on the stock PP wheels while the MINI uses Potenza RE-71Rs (200 TW) on light-weight 17x7.5s. I chose the MPSS because the Mustang is still a DD and because of cost (about $300ish a corner). However, a quick look at Tire Rack will show that moving up to a good 200 TW tire is only about $20- $30 more per corner. We chose the 71Rs because we swap the MINI's wheels/tires from all seasons to the 71Rs at the event. Also, due to the size the 71Rs are about $170ish a corner and because they are dedicated last longer.

The MPSS work very well, give great feedback and are progressive at the limit. They are also comfortable as a daily, with low noise and great wear. The current set have two A/X seasons, four track events (HPDEs) plus DD duties. Haven't measured them but they appear to still have about 6/32s. The 71Rs are a little noisy as a daily and wear is not great (we've had to use these as dailys a few times due to unforeseen conditions). But they grip. My wife is still working these out but she is not an aggressive driver. She is into the second A/X season, one track event and very limited daily use (down to about 4/32s). I've only used the car a few times and haven't found the sweet-spot but can tell they have a lot of promise.
 
#28 ·
4rd Tough,

I always recommend going as long as possible on the tires that are already on your car. Stepping up to bigger/more expensive tires when you’re just starting out has downsides…

1. The best tires cover up a lot of mistakes Novices make, and can lead to bad habits forming.

2. You will chew up good tires much faster if you overdrive the car, and they cost a lot of money.

Driving around the limits of your car and your tires will make you a better autocrosser. I used NT555s (300TW) for my first season, then stepped up to NT05s (200TW) for a while. I wanted to learn on relatively cheap (and not very good) tires before stepping up to the BFG Rival S tires (which are very expensive and very good). I went with Rivals when I got within 2 seconds of the fast local guys in CAM.

One of my good friends runs the 275/40/17 Falken Azenis RT615K+ on his 17x9 rims. He’s very happy with them (and very fast). I prefer less sidewall, so I use 18 inch rims.

Pinching the tire .5 inches off the measuring rim width isn’t that bad. A lot of people do it. I ran 275/35/18 Rivals on 18x9 inch rims with no issues. The most common size aftermarket rim width for these cars is 9 inches, so a 275 on a 9 is widely used. It’s not ideal, but I know a lot of fast Mustang drivers that use that combination without issues.

What will hurt your performance is a staggered setup. Staggered wheels and tires add understeer. Understeer is not good for an autocross car. A staggered setup negates other suspension mods you make to get the car neutral. And, you can’t rotate a staggered setup. You will have to rotate your tires much more often if you continue to autocross. I get 3,000 miles out of a set autocross tires doing everything I can to manage the wear on the outer edges. Your front tire edges take a beating; they will wear out fast if you can’t rotate your tires.

In my opinion (and based on my personal experience), the best hassle-free setup for a 1994-2004 Mustang is to run 18x9.5 inch rims with 275/35/18 tires. This allows for many more tire options. There aren’t a ton of rims available in this size. I used the SVE 2000 Cobra R wheels (+20 offset). They weigh 28 lbs. each (which is a lot), but they are relatively inexpensive. Miro makes a set of 18x9.5 inch rims; they are more expensive, but lighter. I know someone who uses them and he’s very happy with the quality. That +20 offset is the key for fitting 18x9.5s on our cars.

Trying to fit 18x10s with 315s on a 1994 Mustang will require some cutting and flaring of the fenders (front). You MIGHT be able to do an 18x10 with a 275, but that combination doesn't fit on every car.

Honestly, if you know your front rims are OEM 17x8 Bullitts, you could get 2 more for the rear and run a 245/40/17. That gets you less sidewall than stock, more steering feel, and the money you save on tires can be better spent on other mods or more events. Do a season on those tires and upgrade from there. But, some Bullitt wheels don’t fit over bigger brakes.

As for the brakes…

The OEM 94-04 brakes are not great. 99-04 cars have better 2-piston calipers, but even those get overmatched under heavy braking.

I have used 13” OEM 94-04 Ford Cobra brakes with Hawk HP-Plus pads on all 3 of my cars. I am frequently entering tight elements at the rev-limiter, which is about 65 mph. The brakes do everything I ask them to do: great initial bite and no fade. 14” brakes cost a TON of money and they are more suited for track applications. Bigger brakes don’t actually stop the car better, they just dissipate heat better. Well, if you use your brakes as little as possible on course, they won’t fade from getting too hot. Why pay a bunch of money for something you are trying to use less and less every time you autocross?

A really good set of pads and SS lines will make a huge difference, even on stock brakes.

Contact MPS Auto Salvage in Georgia; they rebuild OEM 94-04 Cobra brakes. I’ve used them for years without any issues.
 
#29 ·
When I think of tires for a 94-04, I think of 245, 275, and 315 on a 17'' wheel or 275 and 315 on a 18'' wheel with an aspect ratio that matches stock height. 245s seem small too me, not much bigger than what a miata runs and a mustang is a way heaver car. Tire choices for auto x seem to be limited in these sizes. I probably do need to branch out and look at 255, 285 and 295 tires. I thought about getting MPSS when I bought the nittos, but they did not come in a 275/40R17. I don't have a budget in mind yet, but I don't think I want to be paying $300 a tire. I have had this car 10 years and have driven it about 10-12k miles. So my tires are going to dry rot before they wear out. So a tire that wears out fast won't be an issue. The only reason I am considering tires, is because my old tires are getting dry rotted. I agree, that a square setup would be best so I could rotate my tires. If I do 275s all the way around, I'll need 2 wheels. I could just bite the bullet and buy 4 so I could run 18s.

How much does MPS charge for the calipers? I was thinking about getting some from an auto parts store or rock auto. If I found a used set, I could rebuild them. I'll remember the Hawk HP plus pads for when the time comes. I saw where the guys on a corvette forum like autozone pads. They sell a set of high performance pads with a lifetime warranty. I won't be doing brakes anytime soon. I'll wait til my brakes need replaced. I know clean brake fluid also improves the pedal.
 
#30 ·
4rd Tough,

If you keep autocrossing, tires will become a major focus. 200TW tires for autocross require a little more attention than “normal” tires. They can’t be stored in near or below-freezing temperatures. Most people keep them in a temperature-controlled dark area when they aren’t in use. Basically, you want to limit the heat cycles to when you are autocrossing. They will get hard and lose grip if they stay outside year-round. You can generally get a season out of 1 set of tires (if you flip them on the rims). I get about 20 events out of a set of Rivals.

Tires for 17 inch rims do cost less than tires for 18 inch rims. And, the best 275/35/18 tires will cost around $300 a tire. It’s a big, continuing expense. I always encourage people to make the decision that will allow them to attend the most events. If running 17s means spending less on tires and more on seat time, do it. If you can go with 18s and still do a ton of events and schools, I think 18s will be better in the long run.

That said, I know a couple of people who run 245/40/17s and they’re really competitive. Yes, it’s a small tire, but people make them work. Part of the process of getting better at autocross is getting the most out of your tires, no matter what size they are. Running a great 245 can make you faster than running an average 275.

MPS usually charges around $400 for their rebuilt calipers. But, if you can rebuild your own, you can find Cobra or Bullitt front calipers on Ebay for less. They are getting harder to find and more expensive. OEM is always better than reproduction, in my opinion.

The difference between the best brake pad AutoZone sells and an HP-Plus is night and day. They are not even in the same universe in terms of initial bite, heat handling and consistency. They are well worth the extra money. Use up the brakes you have, then consider upgrading once you’ve gotten your braking down to the bare minimum on course.
 
#34 ·
I knew that summer tires should not be exposed to cold weather and that you should not move a car with summer tires in below freezing temps. I did not know about the heat cycles. It is sounding like I need a second set of wheels for auto x. I could keep them in the basement which is cool. How many times do you run at an event?

Calipers from the auto parts store or rock auto, are OEM calipers that are rebuilt. I would have to pay the core charge since I would not have a core to turn in.

HP-Plus pads do squeal and they do eat up rotors faster than less aggressive pads. It looks like I will get 2 seasons and 1 Evo School out of my HP-Plus pads and Power Stop rotors (the equivalent of about 25 events).

The OP has put 10-12k miles on his car in 10 years; he doesn’t drive it that much. He has also stated that he has very little time between runs. Hopefully, we have all convinced him to do as many events and schools as possible in the near future. I suggested using his existing pads up before swapping to more aggressive pads.

I used Hawk HP pads for 3 seasons. They are very good pads, but they eventually became inadequate as I got faster. If the OP is looking for pads that will make his rotors last longer, they are a good compromise. But, he might need to upgrade before they are worn out as he gets faster.

I respectfully disagree with the point that AutoZone brake pads will work for a Novice for several reasons:

1. The factory brakes on 1994-2004 Mustang GTs are not great.

2. The longer you are on the brakes, the less you are on the gas.

3. As you learn to autocross, you are actively trying to use the brakes as late and as little as possible.

4. Sometimes, that initial bite from an aggressive pad is all you need to set your speed into a slalom, or to transfer weight to the front end to get the car to turn.

So why would you use pads that require you to be on the brakes longer, don’t stop as well and have less initial bite? It will only cost you time.

If the OP is going to change pads because his current pads need changing, why buy pads that will last multiple seasons and not provide optimal braking?

The best advice I can give is to wait on the upgraded brake/pad decision as long as his current brakes will allow. That will get him more familiar with the car’s braking strengths and weaknesses and help inform his decision about upgrades that suit his driving style.
The only reason I mention brakes, is I don't want to buy 17'' wheels and tires then a year two, decide to upgrade my brakes to GT500 brakes. My rear pads are getting down, but rear brakes don't apply much on a car. No more than I drive it, they may last another 10 years. As I was typing this message, I got sidetracked and was looking closer the the Fully torqued racing GT500 conversion. I am not too crazy about that setup.
 
#31 ·
Pads are a consumable. HP-Plus tend to use rotors and squeal. For a non-dedicated car/DD I'd stay with the Hawk HP or move to a Porterfield. Agree that the AZ/AA brands are not suitable for advanced AX work but work fine at the novice level. Brake modulation is useful so a pad that permits progressive input is better than one that doesn't. Stock or performance street tend to be less grabby (initial bite). Brake heat is not that much of a concern for AX unless you start doing a lot of back-to-back runs - such as a T&T or school. But the pads do need heat in them to work optimally. So a stock type pad will get to operating temp faster than a track focused pad. However, if you want to open track the car then move up to a pad that takes heat better.
 
#35 ·
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