Is it time to dial in more negative camber?

[dparm]

I chewed up an expensive set of PSC2 tires last season -- way faster than I expected to. There's a decent amount of wear on the outside edge of the tire (especially the front ones) which leads me to believe I need to add some negative camber. The inside edge has far less wear. I am not very familiar with this kind of thing so I figured I would ask here.

OEM spec is -0.6 F & -1.1 R with +/- 0.6 for both. GM actually publishes a "competitive driving" spec which recommends -2.0 front and rear. I already adhere to their competitive driving tire inflation instructions.

Is the outside edge wear indicative of needing more camber? I assume the trade-off here is that the inside edge will wear a bit faster on the street, and that the wear at the track will slow a bit.

[Richbot]

Have you experimented with more cold front pressure? Like, a lot more, and had somebody take hot pressures? Not a light car and not a very stiff tire sidewall wise. That wide wheel and that much camber should support the sidewall well enough

I think you should bump the camber up either way if you’re tracking the car the street wear won’t outpace a dead shoulder. No brainer. Yeah you’ll wear insides a bit more on street (and on track don’t forget that’s when you drag the inside of the tire across the road the most) but more wear is better than uneven/premature death or at least easier to take, emotionally, heh

[dparm]

Originally Posted by Richbot

Have you experimented with more cold front pressure? Like, a lot more, and had somebody take hot pressures? Not a light car and not a very stiff tire sidewall wise. That wide wheel and that much camber should support the sidewall well enough

I think you should bump the camber up either way if you’re tracking the car the street wear won’t outpace a dead shoulder. No brainer. Yeah you’ll wear insides a bit more on street (and on track don’t forget that’s when you drag the inside of the tire across the road the most) but more wear is better than uneven/premature death or at least easier to take, emotionally, heh

No, the owner's manual has a very specific inflation for competitive driving and even tells you how to measure/change it before and after the session. The on-board data recorder even shows me the tire pressures over the course of the session and validates their recommendation.

The sidewalls are actually very stiff since they're ZP. 285/30R19 up front, 335/25R20 in the back.

[Visceral]

Do you ever take a IR thermometer to track days? You can measure tire temp across your front tires (and rear) and get a light idea about what's happening.

My C6Z needed -2.5f/-1.5r to balance mid-corner steady state traction with corner exit rear traction, so there's some light precedent for more front camber, unless you begin to gain braking distance.

[dparm]

Originally Posted by Visceral

Do you ever take a IR thermometer to track days? You can measure tire temp across your front tires (and rear) and get a light idea about what's happening.

My C6Z needed -2.5f/-1.5r to balance mid-corner steady state traction with corner exit rear traction, so there's some light precedent for more front camber, unless you begin to gain braking distance.

I don't have one, but I can actually get tire temp data from the PDR (though it's a bit more rudimentary). How would I use the IR thermometer to understand alignment changes? Part of me just wants to stick with GM's recommendation as a safe-ground since the car is stock other than upgraded brake pads.

The C7's PTM is more sophisticated than yours and actually adjusts things based on tire temps.

[Visceral]

Originally Posted by dparm

How would I use the IR thermometer to understand alignment changes? Part of me just wants to stick with GM's recommendation as a safe-ground since the car is stock other than upgraded brake pads.

Measure temp of tire 1" from inside sidewall, middle, and 1" from outside sidewall. If you see more than 25deg F difference (side to side) you should make note for a camber change. If the center is hotter or cooler than the sides, then inflation should be considered (in combination with other handling information).

It's also a helpful tool for measuring brake disk temps.

A checkered/cool-down/yellow lap will slightly mute temp info, so measure asap and possibly consider coming in before the yellow lap.

edit: also measure both sides and consider the rotation of the track

[dparm]

I misspoke -- the PDR is logging the tire's air temperature, not the surface temperature (in addition to inflation). I suspect it is using that data to infer the surface temps.

So what you're saying is that if the outside edge of the tire is >25* hotter, add more negative camber?

[Estoril Blue]

As mentioned - reading tire surface temperature across the face tells you how much you are working the inside, center and outside of that tire.

IR thermometers are "okay" by the pen-probe are far more accurate.

Make a record of temperature readings:

https://www.joesracing.com/rt-4359-j...-download.html

Then you can make adjustments based on real measurements.

Are you working the curbs much? Because I had a student doing that and it chewed up his PSCs pretty well.

[dparm]

Originally Posted by Estoril Blue

As mentioned - reading tire surface temperature across the face tells you how much you are working the inside, center and outside of that tire.

IR thermometers are "okay" by the pen-probe are far more accurate.

Make a record of temperature readings:

https://www.joesracing.com/rt-4359-j...-download.html

Then you can make adjustments based on real measurements.

Are you working the curbs much? Because I had a student doing that and it chewed up his PSCs pretty well.

I rarely use the curbs due to the low ground clearance, small sidewalls, and extra wear-and-tear it adds to things.

[cherry-m3]

You should be running -3 or up. Not all tracks will do this, but the e9x likes to roll over on the outer sidewall. I've tried -2 at WGI and ate a set of trofeo's on the outer edge.

[dparm]

Originally Posted by cherry-m3

You should be running -3 or up. Not all tracks will do this, but the e9x likes to roll over on the outer sidewall. I've tried -2 at WGI and ate a set of trofeo's on the outer edge.

This is for my Corvette but I figured the fundamentals and theory are the same.

Some companies suggest going as high as -2.3 on this car but that's with dedicated track tires and wheels.

[Richbot]

Hotter shoulder, colder inner ribs = needs more camber. If it's really begging for it, which I bet it is, you'll see 30+ degrees difference from the outer rib to the inner rib

Must be done immediately after a hot lap to be worthwhile. Especially if your cooldown lap is slow you'll be scrubbing the insides of the tires all the way around and temps will look fine by the time you get out and get the pyro out and get your clipboard out yada

IR is only useful for real-time logging IMO. Borrow a probe pyro, somebody at the track will have one

A design brief for driving the tires with no air pressure at 50mph for 50 miles max doesn't necessarily indicate the sidewalls are also going to stand up performance driving with the same camber settings a Civic has from the factory be nice to your track tires, and they are track tires, they wuv you, wuv them back, give them some camber.

Sounds like a nobrainer based on the wear you're reporting I'd hit the factory performance alignment for a starting point and go from there

EDIT: Yeah what they said

[dparm]

Originally Posted by Richbot

Hotter shoulder, colder inner ribs = needs more camber. If it's really begging for it, which I bet it is, you'll see 30+ degrees difference from the outer rib to the inner rib

Must be done immediately after a hot lap to be worthwhile. Especially if your cooldown lap is slow you'll be scrubbing the insides of the tires all the way around and temps will look fine by the time you get out and get the pyro out and get your clipboard out yada

IR is only useful for real-time logging IMO. Borrow a probe pyro, somebody at the track will have one

A design brief for driving the tires with no air pressure at 50mph for 50 miles max doesn't necessarily indicate the sidewalls are also going to stand up performance driving with the same camber settings a Civic has from the factory be nice to your track tires, and they are track tires, they wuv you, wuv them back, give them some camber.

Sounds like a nobrainer based on the wear you're reporting I'd hit the factory performance alignment for a starting point and go from there

EDIT: Yeah what they said

Fair point on the sidewalls, but what I'm getting at is that they're reinforced over a non-ZP version of the same tire. This is why cars with run-flats typically ride hard.

[Longboarder]

Originally Posted by dparm

I chewed up an expensive set of PSC2 tires last season -- way faster than I expected to. There's a decent amount of wear on the outside edge of the tire (especially the front ones) which leads me to believe I need to add some negative camber. The inside edge has far less wear. I am not very familiar with this kind of thing so I figured I would ask here.

OEM spec is -0.6 F & -1.1 R with +/- 0.6 for both. GM actually publishes a "competitive driving" spec which recommends -2.0 front and rear. I already adhere to their competitive driving tire inflation instructions.

Is the outside edge wear indicative of needing more camber? I assume the trade-off here is that the inside edge will wear a bit faster on the street, and that the wear at the track will slow a bit.

I just purchased a set of Cup2's for my stock ZCP suspension e92, and bought GC camber plates (like I did with my previous e92) to dial in a preferential alignment for street and track. I'm running -2.0 F street and will go nearly -3.0 F at the track (rears set at -1.8). I haven't been to the track yet with this e92 but have my first track day scheduled.

One thing I've learned with Cup2's on another car is that they like low tire pressure. My best laps are done starting with pressures in low-mid 20's and fastest times are achieved after the out-lap and maintain consistent until tires hit low 30's. By mid 30's they are slippery and upper 30's fairly dangerous.

Cup2's can last a long time with correct alignment and tire pressure. Fantastic all around tire.

[roastbeef]

-2 is a good balance between street and track. just know it will have more turn-in as you wrestle with that 'vette.

[dogbone]

Originally Posted by dparm

Is the outside edge wear indicative of needing more camber? I assume the trade-off here is that the inside edge will wear a bit faster on the street, and that the wear at the track will slow a bit.

Generically, I would guess yes, destroying the outside edge could be helped by more negative camber. I also found running a fatter tire along with more camber REALLY helped edge wear.

I don't know anything about a Corvette in terms of how suspension linkages go and such, but what I used to do on my M3/Vorshlag plates when it did both street and track was switch camber at the track to max camber, and then switch it to minimum camber for street. The toe change on the M3 between min and max was so minimal it wasn't worth worrying about (0.02). This worked great for me. The street tires lasted forever, and the track tires survived much better.

So, my question is, do you have camber plates that make it convenient to change camber? (On the M3, it required jacking up both sides of the front to be able to change the camber inward (more negative)).

[dparm]

Originally Posted by dogbone

So, my question is, do you have camber plates that make it convenient to change camber? (On the M3, it required jacking up both sides of the front to be able to change the camber inward (more negative)).

Sort of. You can remove washers from the upper control arm bolts but doing this repeatedly will probably wreck the threads on those bolts. Could convert to studs, I suppose, but it sounds like -2.0 F & R isn't really that crazy. Some of the aftermarket tuners and shops suggest -2.3 for more track-focused vehicles on dedicated tires. For additional context, the full track alignment spec provided by GM for all Corvettes is:

Front
Caster: +7.0
Camber: -2.0
Toe: 0.005 in

Rear
Caster: 0.0
Camber: -2.0
Toe: 0.005 in
Thrust angle: 0.0

Apparently the adjustable rear caster is adjustable with a special tool at the dealership (not all dealerships even have the tool), but the Corvette guys insist that this adjustability is a pretty nice feature.



My whole reason for asking this is that I would like to try and get more life out of the replacement tires. I'm going back to the PSS ZPs but am also going to trust GM's alignment spec.

Track wheels/tires are not in the cards just yet and I want to start understanding some of the more advanced concepts in setting up the car for the track.