Autocross: Outside front edge tire wear

[Rocwandrer]

275's on 9" wheels on the front of a 17 gtppp in FS. -2.0 camber. Every tire I've run on the front of this car (5 autocross sets in 2.5 years) has corded the outside edge well before the center of the tread. The last set was GY SC3 run at 38 psi. Outside corded with 5/32 left in the middle 5" of the tire. Calibrated tire pressure gauge. Rears still had 4/32 even tread left at the time. It was worse when I was running take off new PS4S, although I had a little less camber back then, too.

I'm running RT660's now, with 48 PSI front. The car understeers a lot compared with an otherwise identical setup competitor's car with pressure at 37 psi, because of the high pressure. I'm on my 3rd dual driven event and the front outside edge has no tread left. I definitely have a lot more center tread than inside, and more inside tread than outside. I'm out of ideas. Do people really put up with this?

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[Dana Pants]

Video please. I run a strano rear bar and got 149 runs from Yokos recently (rotating front to back via dismount from time to time). I ran rt660 at 35 psi front and saw no strange wear.

The car should be a little murdery to dance around cones:

new vs dead yokos:

 

[nbjeeptj]

48 seams high for any tire I have run. I have found the following pressures hot to work good on my car for track days. I run 275's on 10" wheels with 0 tow and -2deg camber front.

RT660 36psi
R888R 34-35psi
595rs-rr 38psi
595rs-pro 36-37psi

Seams like any past 40 on any of these options the car just does not feel right as it transitions into a turn, almost like there is the body roll then it rolls onto the sidewall in 2 stages, hard to describe this feeling but its been the case on 2 different track cars I have had when the tires get overinflated.

 

[Dana Pants]

Additional point: an rt660 set has 8 edges to destroy. 6*2*3*4= 144 runs per set of tires. A totally workable number.

6 runs per event times 2 drivers times 3 events to rotatation times 4 tire mounting positions.

 

[TeeLew]

The fact that it's the fronts wearing is a result of your understeer. The outside edge is because of a limited range of adjustment on your camber setting.

You can't really change the camber situation in the street class, so your only play is to reduce the understeer other ways. Rake is very effective. Also, if you are one who grabs a handful of steering lock while understeering, then you need to limit that.

 

[NightmareMoon]

275's on 9" wheels on the front of a 17 gtppp in FS. -2.0 camber. Every tire I've run on the front of this car (5 autocross sets in 2.5 years) has corded the outside edge well before the center of the tread. The last set was GY SC3 run at 38 psi. Outside corded with 5/32 left in the middle 5" of the tire. Calibrated tire pressure gauge. Rears still had 4/32 even tread left at the time. It was worse when I was running take off new PS4S, although I had a little less camber back then, too.

I'm running RT660's now, with 48 PSI front. The car understeers a lot compared with an otherwise identical setup competitor's car with pressure at 37 psi, because of the high pressure. I'm on my 3rd dual driven event and the front outside edge has no tread left. I definitely have a lot more center tread than inside, and more inside tread than outside. I'm out of ideas. Do people really put up with this?

You're not going to eliminate shoulder wear with 275s on 9" front wheels and only 2.0 camber. You'd need probably an inch more of wheel width, and another 1.5 degrees of camber. You're chasing an impossible dream.

Those of us who were fed up with the stock camber and shoulder wear have moved on to CAM where those mods are possible. That's basically one of the reasons I left FS (but also cause I got sick of driving an uncompetitive car in the class versus the BMWs and Camaros).

48PSI is EXCESSIVE for that tire. Drop 10lbs and enjoy having grip again.

Once in the tire's life you can dismount it from the wheel and flip it so you get a bit more total life out of the tire, but you'll take a hit on grip as it wears in to the new pattern after the flip. Flipping this way you should get 80-100 runs or so before the tire cords.

 

[Norm Peterson]

This ^^^


Norm

 

[TeeLew]

I hesitated commenting on the pressure as I've never ran those tires, but I'll echo the two above me. That is 15+ psi over what I've found on different tires.

 

[NightmareMoon]

I hesitated commenting on the pressure as I've never ran those tires, but I'll echo the two above me. That is 15+ psi over what I've found on different tires.

i’m not on 275s (295s in an 11” here) so I suspect the ideal pressures on his wheel are a couple poinds higher than mine, but I run 32-34 (hot pressures) front, and 45 is in a different zip code.

too high pressures -> bad understeer -> too much steering angle input to try to overdrive a front that won’t turn -> hellish shoulder wear -> even more tire pressure -> (repeat)

 

[NightmareMoon]

Your goal should be finding the tire pressure that maximizes grip, not the pressure that minimizes wear. Wear is unavoidable in FS so lets just try to get the most enjoyment out of all that money we’re throwing away on tires at least?

hopefullt then with grip maximized … then you can try to not overdrive the fronts and get some tire longevity back. If the car is understeering (ahem - Dana) and you then add additional steering angle while its understeering, you’re just shaving rubber off. This is a very common beginner/intermediate mistake! If understeer has developed, you need to reduce the steering angle (counter intuitive) a bit and/or shift some weight forward to get the front to bite and start turning. Adding steering while already understeering is adding insult to injury. More steering will never improve rotation rate until you loose so much speed the run will be wasted anyway. BTDT.

 

[Dana Pants]

If the car is understeering (ahem - Dana)

I hold the following to be true:

1) uncomfortable cheese grater is the preferred slip angle of yokos.

2) most of the sad tire noises in my videos are actually coming from the rear. The blooper reels make it more obvious because the noise scales with rear slip angle, not wheel input:

 

[Norm Peterson]

Norm

 

[Dana Pants]

Norm

Sarcasm title. The corner boss was missing many calls and the final event results show that run as not off course.

 

[Rocwandrer]

i’m not on 275s (295s in an 11” here) so I suspect the ideal pressures on his wheel are a couple poinds higher than mine, but I run 32-34 (hot pressures) front, and 45 is in a different zip code.

too high pressures -> bad understeer -> too much steering angle input to try to overdrive a front that won’t turn -> hellish shoulder wear -> even more tire pressure -> (repeat)

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

 

[Rocwandrer]

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?

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