New Member Starting Autocross Build
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I've been autocrossing Foxes and New Edge SRA and IRS cars for years. They are always a blast to get out on course. Autocrossing can cost a lot of money (especially if you run in CAM), but there are also lots of relatively inexpensive mods you can do to get your Mustang competitive without breaking the bank.
Yeah I run in CAM (Costs A Million), the one nice thing about it though is I can work on my car without looking through a rule book first. I got my Mustang in the middle of the season last year and ran it just how I bought it and I had more fun than anyone else on course for sure. Should be a bit more competitive this year though, practically rebuilt the car over the winter. Right now I'm trying to find a shop to weld in the full length Maximum Motorsports subframe connectors I got.
If you could let me know some of the cheap mods you recommend I would really appreciate it.
If you could let me know some of the cheap mods you recommend I would really appreciate it.
There are some basic mods a solid rear axle car needs to deal with the factory-installed understeer and throttle-induced oversteer that holds these cars back on an autocross course. A good set of adjustable shocks and struts, and Steeda's adjustable rear sway bar make a huge difference, because they allow you to get the car neutral (which is the most important thing when autocrossing a Fox/SN95 Mustang). Just doing those relatively inexpensive (around $600) mods will change the personality of the car. It's also important to make sure your chassis is braced really well. In addition to full length subs, strut tower, lower chassis and rear shock tower braces help a lot. I've used Stiffler's FIT System on 2 cars and it's really amazing (but there is a ton of welding involved).
I'm too new to post links on this forum, but I have a couple of budget autocross videos on my Warhorse Racing YouTube channel. I also have a video about chassis bracing. They might help you decide on your setup.
I'm too new to post links on this forum, but I have a couple of budget autocross videos on my Warhorse Racing YouTube channel. I also have a video about chassis bracing. They might help you decide on your setup.
Thank you so much for the advice. I already put on a strut tower brace for chassis stiffening, and I have BMR springs with cheap KYB shocks and struts right now. Eventually I'm going to get some adjustable Konis but right now the funds are low. I was going to get a K-member brace, but I needed a whole new exhaust and someone was selling used long tubes for so cheap I couldn't pass them up, and I'm not sure if that brace would clear them.
That is the trouble for me because I don't know how to weld, and the cost of the equipment makes it prohibitive. So until I find a way to get welding done at a reasonable price I'm limited with the chassis bracing.
I found your YouTube channel so I'll watch all your videos before I ask anymore questions, because boy do I have a lot.
That is the trouble for me because I don't know how to weld, and the cost of the equipment makes it prohibitive. So until I find a way to get welding done at a reasonable price I'm limited with the chassis bracing.
I found your YouTube channel so I'll watch all your videos before I ask anymore questions, because boy do I have a lot.
I'm happy to help. I created the channel to inspire Mustang owners to autocross their cars and provide driving tips and real world, race-tested reviews of parts. I always tell people it's not about spending the most money, it's about spending the right money. A well-built inexpensive car can beat cars that cost 5 times as much.
Welding is pricey, but a stiff chassis makes for a better autocross car. A stronger chassis will make every suspension mod you do work better.
Thanks for checking out my videos. Feel free to ask any questions you might have.
Welding is pricey, but a stiff chassis makes for a better autocross car. A stronger chassis will make every suspension mod you do work better.
Thanks for checking out my videos. Feel free to ask any questions you might have.
Your videos are fantastic! Incredibly informative and entertaining, and they answered a lot of my questions. My one question now is about tires since you are a novice instructor and this is only my second season autocrossing. My plan was to buy a cheap set of decent summer performance tires to start off with, that way I can focus on learning to be smooth without destroying $800 worth of tires in a couple events. I have also heard that going right to the best tires as a novice can cause you to learn some bad habits.
I have a set of 17x9 inch wheels that I bought used with some dry rotted 245/45R17 tires on them, and that size rubs the front fender liner on the driver side when turning. So I think 245/40R17 is the size to go with. For this year I was going to get Sumitomo HTR Z III tires, and once those wear out I'll get some 200tw tires.
What are your thoughts on this plan? Should I get cheaper, harder tires and hope they last longer, or should I go right to 200tw tires?
Thanks again for the awesome videos, keep them coming!
I have a set of 17x9 inch wheels that I bought used with some dry rotted 245/45R17 tires on them, and that size rubs the front fender liner on the driver side when turning. So I think 245/40R17 is the size to go with. For this year I was going to get Sumitomo HTR Z III tires, and once those wear out I'll get some 200tw tires.
What are your thoughts on this plan? Should I get cheaper, harder tires and hope they last longer, or should I go right to 200tw tires?
Thanks again for the awesome videos, keep them coming!
Thanks for checking out the videos! I hope they helped.
Tires are one of the most important choices for autocrossing. And they are a very personal choice. Knowing how you want your tires to "feel" takes a lot of seat-time. I tell novices to run whatever tires they have until those tires are used up. As long as those tires aren't dry-rotted or corded. You are right, putting great 200tw tires on your car will cover up a lot of mistakes and get you into some bad habits. You will also chew those tires up learning on them, so they won't last nearly as long as they should. If you don't have Caster/Camber plates in the car, you will also wear out the shoulder faster. I don't have personal experience with the Sumitomo HTR Z III tires, but I think going with a 300tw tire is a really good idea for now.
Every car is different, and rim size and backspacing vary, so it's hard for me to be 100% sure these next suggestions will work on your car...
All 79-04 Mustangs are "wall-eyed"; the tires poke out more on one side than the other up front. Factory tolerances weren't great back then. If your tires are rubbing the inner fender liners (splash shields), you can use steering rack limiters to keep them from rubbing. One or two rack limiters should allow you to run a 245 easily. If you are hitting the metal anywhere on the fenders, your overall tire diameter is too large (you need a lower profile tire), or the offset on the wheels isn't right.
Caster, camber, ride height and suspension mods all impact tire fitment when trying to shoehorn wider tires onto a Fox. But, here's what I would suggest (and PLEASE check that this will fit your car BEFORE buying the tires)...
The Sumitomo HTR Z III tires in 245/40/17 are a good choice, but will be slightly "stretched" on a 9-inch rim. Those tires also come in 255/40/17, which is 10mm wider. The overall diameter is 25" (compared to 24.6"), so there's a bit more sidewall (which isn't ideal), but they will fit better on a 9-inch rim. There are lots of variables, but you will basically get 20mm (almost 1 inch) more tire per axle. In my opinion, the 255s are the better choice (they are about $11 more per tire). If they fit your car.
But, you will have to take some time to make sure the 255 tires will fit (the same process as in the "Fitting 315s" video on my channel). Rack limiters and wheel spacers might be necessary. And it's always possible that they just won't fit. The fitment in the front should be the hard part, but always make sure they also fit in the rear.
Fitting tires is always an interesting challenge. No two Mustangs are the same. I always try to get the widest tires possible (without pinching them on the rim) in a square setup, so I can rotate them. You will have to do the same fitment tests with the 245 and the 255 on the 9-inch rim, so it might be worth considering the 255s.
Tires are one of the most important choices for autocrossing. And they are a very personal choice. Knowing how you want your tires to "feel" takes a lot of seat-time. I tell novices to run whatever tires they have until those tires are used up. As long as those tires aren't dry-rotted or corded. You are right, putting great 200tw tires on your car will cover up a lot of mistakes and get you into some bad habits. You will also chew those tires up learning on them, so they won't last nearly as long as they should. If you don't have Caster/Camber plates in the car, you will also wear out the shoulder faster. I don't have personal experience with the Sumitomo HTR Z III tires, but I think going with a 300tw tire is a really good idea for now.
Every car is different, and rim size and backspacing vary, so it's hard for me to be 100% sure these next suggestions will work on your car...
All 79-04 Mustangs are "wall-eyed"; the tires poke out more on one side than the other up front. Factory tolerances weren't great back then. If your tires are rubbing the inner fender liners (splash shields), you can use steering rack limiters to keep them from rubbing. One or two rack limiters should allow you to run a 245 easily. If you are hitting the metal anywhere on the fenders, your overall tire diameter is too large (you need a lower profile tire), or the offset on the wheels isn't right.
Caster, camber, ride height and suspension mods all impact tire fitment when trying to shoehorn wider tires onto a Fox. But, here's what I would suggest (and PLEASE check that this will fit your car BEFORE buying the tires)...
The Sumitomo HTR Z III tires in 245/40/17 are a good choice, but will be slightly "stretched" on a 9-inch rim. Those tires also come in 255/40/17, which is 10mm wider. The overall diameter is 25" (compared to 24.6"), so there's a bit more sidewall (which isn't ideal), but they will fit better on a 9-inch rim. There are lots of variables, but you will basically get 20mm (almost 1 inch) more tire per axle. In my opinion, the 255s are the better choice (they are about $11 more per tire). If they fit your car.
But, you will have to take some time to make sure the 255 tires will fit (the same process as in the "Fitting 315s" video on my channel). Rack limiters and wheel spacers might be necessary. And it's always possible that they just won't fit. The fitment in the front should be the hard part, but always make sure they also fit in the rear.
Fitting tires is always an interesting challenge. No two Mustangs are the same. I always try to get the widest tires possible (without pinching them on the rim) in a square setup, so I can rotate them. You will have to do the same fitment tests with the 245 and the 255 on the 9-inch rim, so it might be worth considering the 255s.
Thanks for the input! Going with the 300tw tires will definitely help the budget stretch a little farther. The used wheels I bought came with 245/45R17s on them so I was able to test fit them. The top of the front left tire rubs so it's a diameter issue, also the clearances elsewhere are tight. The sidewall is close to the strut in the front, and close to the quad shocks in the rear (I already flipped them). I got caster/camber plates installed in the front so I was going to get the alignment done first before I make a final decision, but I'm not sure the 255s would fit
The interesting part is if you look at the spec table the 245/40s look to be a step in between the 245/45s and the 255/40s:
Hopefully you can see that table from Tire Rack, but the tread width is 0.5 inches wider on the 245/40s compared to the 245/45s, and the 255/40s are only an extra 0.3 inches. The section width definitely depends on the measured rim width but the tread width shouldn't.
The interesting part is if you look at the spec table the 245/40s look to be a step in between the 245/45s and the 255/40s:
Hopefully you can see that table from Tire Rack, but the tread width is 0.5 inches wider on the 245/40s compared to the 245/45s, and the 255/40s are only an extra 0.3 inches. The section width definitely depends on the measured rim width but the tread width shouldn't.
You're welcome! It's possible the 255s just won't fit. And, there will be much more hassle (and possibly cost) involved in getting them to fit. If the wheels are close on the inside, but not touching, a 1/8 wheel spacer can give you more room. Just check the "poke" on the outside to ensure you don't hit the fender lips.
You will find that tires vary tremendously, and autocrossers spend a lot of time obsessing about the right size, width, etc. I know I have. I looked at the Tire Rack specs when you mentioned the Sumitomos and the difference does seem minimal. I'm just programmed to try to get as much tire on the car as possible. I think you'll be fine with the 245/40s.
But, in the crazy world of autocross: 0.3 + 0.3 = 0.6. Over half an inch more tread width per axle. Not bad for $44, if they fit.
If you aren't running poly spring isolators top and bottom in the front, they can add about 1/4 inch of space between the fender lip and tire. And these cars like to be a little higher in the front. They are a cheap way to get clearance. If you decide to do them, put them in prior to aligning the car.
Align the car with the tires you are going to race on. If your "test fit" tires are worn, they are not a 100% accurate indicator of tire size. If your tolerances are really close, you can align the car into interference. Then you have to align the car again. Better safe than sorry.
Also, consider that a lot of negative camber up front will introduce rotation. Which means the car will go sideways easier. This can be both good and bad. I set my Fox at -2 degrees up front and used the Steeda Adjustable Rear Sway Bar to keep it neutral. That provides better turn-in without oversteer. If you go for more negative camber without a way to compensate for the added rotation, you will end up fighting the rear end more than you need to.
You will find that tires vary tremendously, and autocrossers spend a lot of time obsessing about the right size, width, etc. I know I have. I looked at the Tire Rack specs when you mentioned the Sumitomos and the difference does seem minimal. I'm just programmed to try to get as much tire on the car as possible. I think you'll be fine with the 245/40s.
But, in the crazy world of autocross: 0.3 + 0.3 = 0.6. Over half an inch more tread width per axle. Not bad for $44, if they fit.
If you aren't running poly spring isolators top and bottom in the front, they can add about 1/4 inch of space between the fender lip and tire. And these cars like to be a little higher in the front. They are a cheap way to get clearance. If you decide to do them, put them in prior to aligning the car.
Align the car with the tires you are going to race on. If your "test fit" tires are worn, they are not a 100% accurate indicator of tire size. If your tolerances are really close, you can align the car into interference. Then you have to align the car again. Better safe than sorry.
Also, consider that a lot of negative camber up front will introduce rotation. Which means the car will go sideways easier. This can be both good and bad. I set my Fox at -2 degrees up front and used the Steeda Adjustable Rear Sway Bar to keep it neutral. That provides better turn-in without oversteer. If you go for more negative camber without a way to compensate for the added rotation, you will end up fighting the rear end more than you need to.
Yeah the alignment is something I will double check once I get the final set of tires on, and I definitely see the desire for the 255s. I only have poly spring isolators on the top in the front. I have BMR control arms, and after struggling to get the springs in with the lower isolators on for a few hours, I ended up taking them off.
I had them all greased up but the edge of the spring pocket kept digging into the isolator when I tried to move the spring over. I had my Dad helping me out and there was no way we were getting those springs in place with the isolators on, even without the isolators it was difficult. Both of the old front springs were actually broken about 1.5 coils from the bottom, so I can't say for sure how much the BMR springs lowered the car, but I did get poly offset rack bushings to hopefully prevent bump steer.
The biggest problem for me right now is there is still snow on the ground and salt on the roads, and I'm just itching to drive it.
The biggest problem for me right now is there is still snow on the ground and salt on the roads, and I'm just itching to drive it.
I've never encountered an issue like that, but I seem to recall the photos on BMR's website show the spring without a lower isolator in their A-arms. Perhaps that's how they fit on Foxes. BMR is always interested in feedback on their products. It might be worth giving them a call.
Offset steering rack bushings claim to help with bump steer, but they actually don't improve things. Maximum Motorsports makes a really good aluminum steering rack bushing kit for stock K-members that I've personally used and it really helps with steering feel. They have a great writeup on their website about why offset bushings aren't the best option for stock K-member cars.
Honestly, I have never worried about bump steer on my autocross cars. And, pretty much everyone I race with doesn't worry about it, either. We're not national champions, but we autocross a lot. The kit and the process can be expensive; that money is better spent on other mods. I'm not saying bump steer isn't an issue, but, in my opinion, it's not something you have to deal with immediately.
I know the feeling about wanting to get on course. I'm itching to try out that 315 square setup.
Offset steering rack bushings claim to help with bump steer, but they actually don't improve things. Maximum Motorsports makes a really good aluminum steering rack bushing kit for stock K-members that I've personally used and it really helps with steering feel. They have a great writeup on their website about why offset bushings aren't the best option for stock K-member cars.
Honestly, I have never worried about bump steer on my autocross cars. And, pretty much everyone I race with doesn't worry about it, either. We're not national champions, but we autocross a lot. The kit and the process can be expensive; that money is better spent on other mods. I'm not saying bump steer isn't an issue, but, in my opinion, it's not something you have to deal with immediately.
I know the feeling about wanting to get on course. I'm itching to try out that 315 square setup.
Thanks for the advice again. I got the BMR control arms from LMR and they didn't come with instructions, and I just looked at the ones on BMR's website and you are correct: no isolator in the pictures. I didn't see the isolators mentioned in the instructions at all but now that I think back on my install, the springs were an incredibly tight fit diameter wise with the isolator when I did some test fitting. My guess is the arms are not designed to be used with isolators.
And I just read the Maximum Motorsports article on the steering rack bushings. I guess I'll be ordering some of their aluminum ones and putting them in when I install their steering shaft which I just got. Thanks for making me aware of that.
Those 315s should have incredible grip, I imagine that's what I'm going to need eventually...
And I just read the Maximum Motorsports article on the steering rack bushings. I guess I'll be ordering some of their aluminum ones and putting them in when I install their steering shaft which I just got. Thanks for making me aware of that.
Those 315s should have incredible grip, I imagine that's what I'm going to need eventually...
I'm happy to help. It's possible the arms aren't meant to be used with isolators. The MM steering shaft is a good idea. The key to modifying these cars is all about addressing the weak links. But, don't do too many mods early on. Part of what I love about these cars is that they are hard to drive at the limit. Learning the car in stock form allows you pinpoint exactly what needs to be modified to suit your driving style. The most important mods are often done to the part behind the steering wheel. Once you've gotten a lot of experience, you can make selective mods that save you money.
I have never seen a New Edge with 315s square, so it will be interesting for sure. A Fox, without fender flares, is usually limited to 255 up front. A common setup is 255 front, 275 rear. If you can adjust out the understeer of that setup, it's a good one. If not, 255 square with BFG Rival S tires would be a nice setup on a Fox without flares.
I have never seen a New Edge with 315s square, so it will be interesting for sure. A Fox, without fender flares, is usually limited to 255 up front. A common setup is 255 front, 275 rear. If you can adjust out the understeer of that setup, it's a good one. If not, 255 square with BFG Rival S tires would be a nice setup on a Fox without flares.
Yeah I was going to leave the stock steering shaft in, but the rag joint is awfully close to the headers I put in. Just wish I could have put the MM shaft in when I had the engine, K-member, and steering rack out of the car...
I definitely agree with the too many mods statement. I also race dirt oval go karts, and that is my biggest rule: never make more than one adjustment at a time unless you know the adjustments will work together. I kind of treated this winter as a rebirth of the car, trying to remove all the weak links at once. It will feel like a completely different car, but hopefully for the better. Now that the car should be decent I can focus on the nut behind the wheel.
I definitely agree with the too many mods statement. I also race dirt oval go karts, and that is my biggest rule: never make more than one adjustment at a time unless you know the adjustments will work together. I kind of treated this winter as a rebirth of the car, trying to remove all the weak links at once. It will feel like a completely different car, but hopefully for the better. Now that the car should be decent I can focus on the nut behind the wheel.
