Autocross: Outside front edge tire wear

[Dana Pants]

the 1 inch aftermarket bars are way too stiff. You want the smallest step possible in the right direction. Either a gt350r OEM bar or crushing the ends of the bar you have on a press and drilling some new holes.

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[SteveW]

I've given that advice. Doesn't apply here

In low speed elements I can use a little throttle to slightly reduce required steering input, but everywhere else, it is edge of understeer. Since I drive the car to the edge of understeer as much of the time as I can, more front wear than rear is obvious. It's the shoulder wear that is infuriating.
I've been increasing tire pressure in response to hellish wear to try to save money at the expense of being fast. This costs me grip, but I don't add steering input past the slip angle of peak grip (I've been autocrossing a few decades, last two events were 1st and 2nd in pax, even with the handicap of the high front pressure and wrong car for the class).

Sounds like the only actionable advice here is to go with a stiffer rear bar to take some of the demand off of the front tires. All the adjustable bars I'm finding are 1". Is that the go-to size? I don't want to go too crazy. This is my wife's daily driver ahead of autocross priorities

Hope you don't mind a few questions...

What shocks do you have?

What are the toe alignment settings front and rear?

Rear tire pressure?

Can you describe your corner driving technique? Are you generally on the throttle at least somewhat to balance the car mid corner or is it understeering so badly from entry that you have to wait to apply throttle?

 

[NightmareMoon]

Here is the wear I've been getting with the jacked up pressures. Is the carcass of the RT660 curved so there is more tread ply under that edge, or are these a few runs from trash like the previous tires when they got to this point?

Glad to hear you aren't a noob overdriving the fronts, just an aggressive driver overdriving what a "mustang" can do in all aspects.

Those look melty. How many runs on those?

 

[Rocwandrer]

Glad to hear you aren't a noob overdriving the fronts, just an aggressive driver overdriving what a "mustang" can do in all aspects.

Those look melty. How many runs on those?

A mix of surfaces and drivers. Drivers have been me, a codriver who drives roughly like me, and a come at it from the bottom codriver.

48 runs (~80 second runs) on a mix of a single corner on space shuttle braking zone runway concrete (very rough on tires), a little regular runway concrete, and a lot of easy on tires asphalt runway/taxiways/aprons. Half me and half the come at it from the bottom codriver.

35 runs on abrasive super sticky runway apron concrete (~50 second runs), 2/3 aggressive runs.

 

[NightmareMoon]

Here is the wear I've been getting with the jacked up pressures. Is the carcass of the RT660 curved so there is more tread ply under that edge, or are these a few runs from trash like the previous tires when they got to this point?

Hard to say, I'm personally about 80 runs into my first set of RT660s and they they're not as worn as yours yet. Mine haven't given up yet, so I don't yet know how many runs before they'll go out on me. The local sites are not too abrasive, but those 80 runs include 3 track sessions. If you can see the rubber color or texture change on the outside edge, you might be through the good stuff and into the structural stuff below.

83 runs on concrete, yeah I'd guess you're nearly done, and you might be through the good rubber on the shoulders. Storage counts too.

FWIW, on the RE71Rs, the main sign they were heat cycled out (and/or just out of the good rubber on the shoulders) was a significant drop-off of front cornering grip (i.e. onset of bad understeer).

 

[Rocwandrer]

Hope you don't mind a few questions...

What shocks do you have?

What are the toe alignment settings front and rear?

Rear tire pressure?

Can you describe your corner driving technique? Are you generally on the throttle at least somewhat to balance the car mid corner or is it understeering so badly from entry that you have to wait to apply throttle?

Stock ford performance package dampers. Zero static toe rear. A hair of static toe in in the front. Rear tire pressure 34-36 psi (this gives even wear and seems pretty close to right for grip). Front toe bushing compliance on this car is so sloppy, who knows what the dynamic toe is doing at any given moment.

High speed corners:

I'm just even throttle for an even apex and so on, but bumping up against an understeer limit behavior. A quick throttle lift usually does not induce any rotation at all, so it is pretty far away from idea.

Slow corners:

Slow corners are weird. This car is different from hundreds of others I've driven. I wrote the description and looking at it, it seems pretty normal, but it doesn't feel that way, so I did a poor job of describing it. Here it is anyway: There are two possibilities and they are distinct, I have to commit to one or the other.

1.) If I roll into a low speed corner at nearly as fast as is possible, any small amount of throttle pushes it very wide. A little more throttle pushes it wider still.

2.) But a moderate amount of throttle (quite a lot more than a little, but nowhere near full on power slide) allows a slither sort of navigation, where the wheel has to unwind a hair to clear the apex cone (not really countersteer, depending on who's definition you use). This approach seems to be much faster than approach number 1 (tenths faster in a 45' 2 cone slalom), but it requires finesse and commitment. In other cars, this approach is rarely the one I'd choose because it feels risky for little payoff. In this Mustang the payoff is huge.

 

[NightmareMoon]

Get some stiffer adjustable shocks and a swaybar on there ASAP. I’d suggest a front swaybar, having driven the car both ways. The rear shocks can be used to adjust your corner entry handling balance and on a stiff rebound setting they really will help the car rotate, and a front bar can help neutralize a little of that body roll that’s contributing to the wheel being pitched over and killing tires. Front bar will also increase front response at turnin and for slaloms.

i’d say go get a rear swaybar (that’s where I started), but the mild bar I have isn’t available any more and most of the rear bars for sale are too stiff A GT350R rear bar is closest, just not adjustable by default. I suppose you could drill it if you really want the car tail happy. I was able to go just as fast (with some practice) with a front bar and yes its an somewhat understeer biased setuo that way. Rear bar was a real handful on corner exit.

 

[TeeLew]

Slow corners:

Slow corners are weird. This car is different from hundreds of others I've driven. I wrote the description and looking at it, it seems pretty normal, but it doesn't feel that way, so I did a poor job of describing it. Here it is anyway: There are two possibilities and they are distinct, I have to commit to one or the other.

1.) If I roll into a low speed corner at nearly as fast as is possible, any small amount of throttle pushes it very wide. A little more throttle pushes it wider still.

2.) But a moderate amount of throttle (quite a lot more than a little, but nowhere near full on power slide) allows a slither sort of navigation, where the wheel has to unwind a hair to clear the apex cone (not really countersteer, depending on who's definition you use). This approach seems to be much faster than approach number 1 (tenths faster in a 45' 2 cone slalom), but it requires finesse and commitment. In other cars, this approach is rarely the one I'd choose because it feels risky for little payoff. In this Mustang the payoff is huge.

If you're rolling into a low speed corner nearly as fast as possible, then why do you suspect that *any* throttle is appropriate? I'm not being silly here, it's a genuine question. As you go to throttle you're shifting load from front to rear, squatting the rear, lifting the front and locking (as much as a Torsen will lock) the diff. If the car didn't understeer in that scenario, it would be loose as a bloody goose.

These cars do understeer and they are really limited on front negative camber in the Street class, but I think you could help yourself out quite a bit with a touch more throttle discipline. It sounds like you've driven a bunch of different Auto-X cars and, if you're comparing it with a Miata or some other Auto-X King Kong, you really do need to give it a moment mid-corner to turn before applying throttle.

I've mentioned this before, but I think the ABS really works against us if we try to trail-brake. I think when we combine relatively high G loads the ABS sees a crash coming and tries to straighten the car. Airbags work best with a head-on collision, and I think the ABS is trying to produce exactly that. To that end, I really try to limit my trail braking, even though I'd usually *want* it. I WISH there was an track specific ABS controller like with the S197.

 

[Dana Pants]

Complaints 1 and 2 are exactly why I run a rear bar. Throttle induced understeer is dumb. If a course forces you into a big constant radius or slightly decreasing radius turn, it’s game over every time if the back won’t move.

 

[SteveW]

Stock ford performance package dampers. Zero static toe rear. A hair of static toe in in the front. Rear tire pressure 34-36 psi (this gives even wear and seems pretty close to right for grip). Front toe bushing compliance on this car is so sloppy, who knows what the dynamic toe is doing at any given moment.

High speed corners:

I'm just even throttle for an even apex and so on, but bumping up against an understeer limit behavior. A quick throttle lift usually does not induce any rotation at all, so it is pretty far away from idea.

Slow corners:

Slow corners are weird. This car is different from hundreds of others I've driven. I wrote the description and looking at it, it seems pretty normal, but it doesn't feel that way, so I did a poor job of describing it. Here it is anyway: There are two possibilities and they are distinct, I have to commit to one or the other.

1.) If I roll into a low speed corner at nearly as fast as is possible, any small amount of throttle pushes it very wide. A little more throttle pushes it wider still.

2.) But a moderate amount of throttle (quite a lot more than a little, but nowhere near full on power slide) allows a slither sort of navigation, where the wheel has to unwind a hair to clear the apex cone (not really countersteer, depending on who's definition you use). This approach seems to be much faster than approach number 1 (tenths faster in a 45' 2 cone slalom), but it requires finesse and commitment. In other cars, this approach is rarely the one I'd choose because it feels risky for little payoff. In this Mustang the payoff is huge.

By definition you must be over driving the entry to turns but it sounds like you have enough experience to know there's more to this understeer problem than just that. I reread your first post and you say another identical car doesn't handle like yours. Is that with you driving?

Another clue is throttle lift mid corner doesn't induce any rotation at all.

I gotta think that there are some worn out parts on your car like rear shocks and front tension link bushings.

Get some Konis, make sure you don't have any failed bushings then see how the car is. You might want a front bar or rear bar depending on what the car needs at that point.

 

[samstrano]

You need to loosen the car up. Through this whole conversation when I really haven't seen is anything indicating that the rear is trying to kill you. Somebody mentioned it earlier that you need it to dance. You don't want the car loose and uncontrollable, but if the car rotates a little bit into the corner that's just less you have to lean on the front.

For a long time I made an adjustable 22 mm bar that was solid. If people had interest I would do it again but it just wasn't a big seller because most people think bigger is automatically better and with 1 in bars that's wherever everybody went. Early on I decided that I wanted a rear bar option for those performance pack cars because it was pretty obvious to me the rear bar was a little soft. You can see that in the way the car would fall over on the outside rear tire when you hit the throttle and yank an inside front tire up.

Somebody also mentioned a set of dampers. Yeah that would be a big help. The chassis is a whole lot more stable and a whole lot more responsive and you can make it do things again to help it rotate on the way into the corner. Plus then you can also change how the good transfer comes off the front.

It's been a while since I've had a Mustang. It's been a good decade. But I've had one again since April. It's a little different because it's a Mach 1. But I can tell you that one of the absolute best things I've done to it so far was actually to put a set of shocks on it. And that's a mag ride car. But mag Ride can't deal with / isn't set up to autocross.

I've got a whopping two events on the car in its current state which is on A052s and a set of passive dampers. And it is good. Much better than it was with the OEM dampers. I've had it on a bunch of different tires from SC3s to the original PSC2, RT660s, a052s.

Anyway, I digress. Dampers in a rear bar. That's what you want. It doesn't appear that you have either of those things and they're the only two things left that you can do and both of them can affect quite a difference.

 

[Dana Pants]

I've got a whopping two events on the car in its current state which is on A052s and a set of passive dampers. And it is good. Much better than it was with the OEM dampers.

Your 22 mm rear bar is one of my prized possessions.

What dampers did you put in the Mach 1? Off the shelf Koni, Bilstein, or something fancy and custom from your extensive Motorsports network?

Edit: just saw the CAM post. Koni yellows for the win.

 

[NightmareMoon]

For a long time I made an adjustable 22 mm bar that was solid. If people had interest I would do it again but it just wasn't a big seller because most people think bigger is automatically better and with 1 in bars that's wherever everybody went. Early on I decided that I wanted a rear bar option for those performance pack cars because it was pretty obvious to me the rear bar was a little soft. You can see that in the way the car would fall over on the outside rear tire when you hit the throttle and yank an inside front tire up.

Agreed the 22mm solid rear bar is a great part, and its a shame it didn’t sell in the market because I feel like its the most neutral pairing with the common front bars.

I’ve had a few people ask where to get a bar like it. Not many, but a few, and I have to tell them they can’t get one, maybe go mod a GT350R bar.

These days its the CAM guys who have started with a large front bar and springs and finally have realized the car understeers too much and don’t want to overcorrect with a too large rear bar.

 

[samstrano]

Your 22 mm rear bar is one of my prized possessions.

What dampers did you put in the Mach 1? Off the shelf Koni, Bilstein, or something fancy and custom from your extensive Motorsports network?

Edit: just saw the CAM post. Koni yellows for the win.

I need more of you guys to tell folks that, I would make that again! I'm glad you like it.
Shocks/struts. Koni Sport but had to modify the rears some to work (but they are SCCA legal for Street). Not pretty but effective. I was trying this as a proof of concept before I considered Penske's on it. Not that I see how changed, I just might do that, but sort of depends on what happens with the classing for 22.

 

[strengthrehab]

I need more of you guys to tell folks that, I would make that again! I'm glad you like it.
Shocks/struts. Koni Sport but had to modify the rears some to work (but they are SCCA legal for Street). Not pretty but effective. I was trying this as a proof of concept before I considered Penske's on it. Not that I see how changed, I just might do that, but sort of depends on what happens with the classing for 22.

I was hoping to find one, but was relegated to getting the Pedders bar from you.

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