Explain this track tire wear

Swapping the tires for a track day and I noticed a weird pattern.  There is a bit of a trough worn about 1/4 of the way in from the outside on a front tire   The other front doesn't seem to have it  and the rears don't either  

Front:

rear:

these are nitto nt01 315/30-18 and the tire was on the outside (rf running ccw).  Some high speed turns and one long left 90-100 mph sweeper. 
 

i was running about 26-28 hot. 
 

was I under-inflated?  

Was the track clockwise, counterclockwise and was this the driver's side or passenger side front?  Once you figure out why I'm asking you'll have a big part of your answer.  I bet you had both fronts set to the same pressure.  And I know your track has 360 degrees more turn left or right.  As a result, one front will almost always show significantly more wear.  You set up the car for the track you are racing, or you live with uneven wear.  
 

Or you can swap fronts more often to help even the wear, or set up a 4 tire rotation.

Considering that you're just about to the wear bars on the rest of the tire that wear isn't bad.  You could try a little higher pressure but I think what you really need is a little more camber.

Ccw and rf so it definitely took more of a beating.  
 

agreed on more camber.  That's happening after I do bushings. Which is next on the list. 
 

i was wondering if this is a common indication of too little pressure?  Or too little camber?  Or of anything at all...

The wear on the first tire you show is weird.  Yes, it's wearing more on the outside shoulder and wanting more camber, but it's also got a line of heavy wear about 70-80% of the way out, with lighter wear in the 80-90% range.  I've run through a lot of NT01s on my M3, and I don't think I've ever seen it do that.

What kind of car is this on?

C6 z06

i wondered if the pressure was too low and the tire was folding a little on LH turns??

I was actually thinking pressures might have gotten too high.  It seems like the fronts may have gotten too hot/high pressure and that was where the tire bulged/buckled a bit under the load.

We've had many races where the tires wear 2" in from the edge. We're severely camber limited and I've always chalked it up to that.

So RF on a CCW track.  You are heating up the RF a lot more, so that may be part of the issue.  Again, I'd probably start a tire rotation program.  I'd also think about starting the RF a bit lower in pressure knowing it'll heat up more.  And I'd see if there is an easy way to add negative camber.  Outside of those things, you'll get more complicated and more controversial, but setting the car up to turn left would help a lot. 

What pressures are you targeting hot?  I don't like to see my NT01s much over 36 (measured in the paddock after the session is over, so probably a bit higher than that if measured immediately after a hot lap in the pits).

How many sessions are on that tire?

So these tires have about 6 days on them, but only one of the days (this last one) had a bunch on time (about 70 minutes total). 
 

the days have been different directions on different tracks and I have been rotating them.  Although only on this last day did I think to place them relative to the direction of the track compared to the last day. 
 

for example I have another event this Saturday and we are running a different track cw so I will leave them in the same position as they were for the last ccw. 
 

I've been running 27 or so hot.  I definitely staggered pressures from side to side but not by much. 
 

We took temps across the tires on a hot lap and they weren't bad.  Definitely need more camber (and this discussion is leading me to do it for this next event instead of waiting). 
 

i just wonder if I was running pressures too low....   hard finding data from guys I trust in these sizes (315/30 and 335/30). 
 

jfryjfry said:

Ccw and rf so it definitely took more of a beating.  
 

agreed on more camber.  That's happening after I do bushings. Which is next on the list. 
 

i was wondering if this is a common indication of too little pressure?  Or too little camber?  Or of anything at all...

What camber are you running right now? I have C6 Z06 and had similar wear on Rivals. It got better when I went from 2° camber to 3°, if you are pushing the front needs a lot of camber if you are running stock bushings. If you keep stock bushings I would say you need at least 3°, potentially more if you are pushing the car hard.

What are you looking to replace the bushings with? I know the stock ones deflect way too much under load.

I try to stay around 36psi hot. That means I am usually starting my sessions at 24-26psi. I think the general consensus is mid-30s is a good hot psi for these cars, at least for street tires and I see good wear at those pressures.

Could you adopt a square tire setup to reduce rear grip or increase front grip, and allow a 4 tire rotation?  

Yeah, 27 sounds pretty low to me.  I'd suggest running the next set mid-30s and see if that improves things.

That said, 6 days out of a set of NT01s isn't bad.  I'm getting 3 before they start to lose grip, with one more before they cord.

In reply to codrus (Forum Supporter) :

Different car/weight/size, but I've been running NT01's on a Miata for multiple seasons now. I've tried going as low as 26 and as high as 38 (hot ofc) and settled around 34-35 for most situations, confirmed with pyrometer. It can be hard to judge based on others experiences, I aim for 20 20 minute sessions before cording. Depending on the track/weather/etc I usually get more like 16. Other Miata dudes with the same (stock) power might get half a year, really depends how much you're pushing. Everyone thinks they're killing it of course...

What's the pyrometer say, OP? Looks similar to the wear I had when I was working the fronts and my pressures were a bit too low.