15x9 + 225 tire = odd wear?
 

I have had this happen on 2 sets of tires now, NT01's and Hancook C71's, I am getting strange wear in the middle/outside of the tire, check my crappy illustration below, pressures are around 32 hot. The wear is significantly worse where there carrots are in the illustration. All 4 tires are doing this.
Anyone have any experience with this? I am thinking of going to 30 hot to see what happens, is this just a result of the tire being stretched?

inside |-------^^---| outside

3 deg neg camber front
2.6 rear
1/16 total toe in rear
0 toe front

Sound like over inflation to me. With that much camber and stretch on a 9 you shouldn't have to use that much pressure. What do your temps look like after a run?

No temps unfortunately, I will try cutting the hot pressure, looks like they are going to be around 22psi cold!

The spec miata guys I know are running 30psi hot on Hoosier 205's. I know you need less with a bigger tire than a narrower one but I also know what is required varies by compound and structure of the tire. I don't have the answer but I would always try less air if the middle wears more than the sides.

Caster?

Techsalvager post.

:bowrofl:



OP: Do you rotate the tires? (rotation can mask issues in F/R alignment numbers)

What is your cold pressure, 26ish? I would drop about 1psi dead-cold (not: I only drove 10 miles, then let them cool for an hour. I mean dead-cold). What is your ride height and suspension? These factor in too. Your rear toe is 1/16th total in, which works out to about .08 degrees per side. I don't see that burning much rubber up, it's fairly mild. I see your issue as a result of high camber interacting with a slight over inflation.



[RANT]

The world needs to understand using degrees makes way more sense than this "X/16ths" or "minutes and seconds" bullshit. Hunter, who makes the vast majority of alignment machines, defaults to degrees when initially set up, You can explain it easier and you can describe it to customers easier. I don't have a frame-angle gauge, so when I need to, I do the trig to figure it out. But for the love of god I'm not interested in converting that bullshit into real numbers. I do this all day every day.



And fuck total toe. I can give you .16 total toe with toe-out on one side, and excessive toe-in on the other side to even it out. Kiss your thrust angle goodbye with that bullshit. Each sides toe needs to be within 0.01* of the spec, and with each-other. Rear Camber within .05* of each other (getting RR camber perfect is a bitch), front camber within 0.01*. This is ballasted or however the car will operate normally.

[/RANT

Thanks for the info, my c71's only have 3 sessions on them, no rotation on those yet. I am running max caster, dead cold pressures are around 24psi. Height is ~4" at pinch weld, 700/450 springs, koni race.
I will try dropping some pressure at TWS, going to flip them to hopefully balance em out.

Don't forget that track driving heats the tires much differently than autox or normal street driving. So when people mention XYZ pressure being ideal, make sure to understand the circumstance behind why that pressure is ideal for them. For instance, at autox, I run tire-pressures much below the conventional wisdom. Back to back testing, I'm faster with the lower pressure. I'm not a driving god by any means, and I don't doubt that under perfect conditions, the higher pressures probably generate more peak grip. But the lower pressures work well for me, so that's what I use. It's not the best or most ideal for everyone, it's my preference. Tire pressures are a lot like eggs. People know exactly what they like, and if it's not their way, it's wrong.


Don't be afraid to experiment. Do what works for you, because you're the one with the most to gain. ;)

You flaming ------. You ever type to me like that again on this forum and it will be the last time you make that mcsteak. Never again, son of bitch.

I lol'd.

From just a tire perspective I would go with over inflation, but 2lbs just doesn't seem like enough for you to really notice.

Forgive me for some off the cuff google searching and number spewing. I threw some numbers at a random website I found which calculates Tire Data. From my number spewing, the calculator gives this info for contact patch for a comparable tire that works with the calculator (225 on 8.5" wheel):

BND TechSource - Tire Data Calculator

Pressure - Contact Patch Width -Length - Area
32psig - 204.2mm - 153.7mm - 313.78cm^2
30psig - 204.7mm - 160.0mm - 327.48cm^2
28psig - 205.3mm - 166.9mm - 342.55cm^2
26psig - 205.8mm - 174.5mm - 359.22cm^2
24psig - 206.3mm - 183.1mm - 377.77cm^2


To see what's happening, slide your closed, but un-tensioned fist across a table backhands/sideways. Now do the same thing with a closed and tensioned fist. Note where the most friction occurs. Same thing happens when the tires have too much pressure during a turn.

So, how did it go? What was the successful cold tire pressure?

I started each session with 27psi on the driver's side (since TWS was CW), and 28psi on the passenger side, but then again, I'm not cornering as fast as you.

Same problem this time on A6's, I was 23 cold, 28/29 hot, keno said I was pushing the tires too hard causing the groove of death.

Hoosier A6 groove of death?