[Crushed 1LE]

This might seem like a strange question but what are the indicators that the tire has ended its useful track life? Lateral grooves all gone? Corded? No grip? This is my 1st set. 12 sessions on them now and they look a little tired. Times are still consistent, but not improving.

[rickybobby]

I am one of those that cords the inner band of the front tires with the oem track alignment settings. I am currently trying 0 toe up front and it may be improving this. One more track day will tell..
Its so annoying to be throwing away tires after 2-4 days because the inner band is cording. It seems to be worse at Laguna so my theory is that the car toes in under compression and T2 is scrubbing the tire as a result. Pure guess though as I haven’t done any suspension measurements.

[cdb95z28]

Originally Posted by rickybobby

I am one of those that cords the inner band of the front tires with the oem track alignment settings. I am currently trying 0 toe up front and it may be improving this. One more track day will tell..
Its so annoying to be throwing away tires after 2-4 days because the inner band is cording. It seems to be worse at Laguna so my theory is that the car toes in under compression and T2 is scrubbing the tire as a result. Pure guess though as I haven’t done any suspension measurements.

My .02. from observation, measurements and experimentation on my Gen5:

While I have not confirmed the bump steer/roll steer tendencies of the Gen6, my Gen5 is toe out in compression, toe in on rebound. Where did you hear that the Gen6 toes "in" during compression? Even if it does, toe in on compression, (RF during a left turn for example) the largest result is going to be a slight, maybe un-noticeable change in vehicle direction. I cannot see how a dynamic change to toe in causes the inner shoulder to wear abnormally. I do not see this as a probable result, it goes against the dynamics of what is happening to that tire.


So we all add static negative camber (-3* for example) to help grip and to get off the outer shoulder on that loaded RF corner in a turn and while driving straight, the tire will see more load towards the inner shoulder. Not all of the shoulder, but look at it as the entire contact patch is not seeing the same loading, just progressively more towards the inner shoulder.

Once you turn, the outer tire starts to load up and the chassis and tires roll. We add static negative camber because of the uncontrolled tire and suspension deflection. This causes this tire to move to a more flat contact patch, hopefully creating max grip and if you have enough static negative camber, minimal uneven wear of the tire. But on the inner tire in a turn, this static negative camber can be a big problem. We actually want this tire to dynamically move away from negative camber. An extreme example is If you've ever seen a NASCAR Cup car at Martinsville under caution on the straights, they run positive camber on the LF.

Since MacStrut cars don’t have great geometry for heavy loading, this LF doesn’t dynamically take enough of the static -3*camber away. A proper front suspension will allow caster to turn that static -3 to less than -3 on that LF when the steering wheel is turned.

So now we have that LF lose weight on it from the weight transfer to the RF in a turn and it is still in a negative camber situation.

Let’s add Ackerman. Pro-Ackerman causes the LF to dynamically toe out more than it’s static spec. Anti-Ackerman would dynamically toe in the tire. F1 cars sometimes use anti-Ackerman.
Toe out is used to help the turn in, yes, but it is because it is helping the inner, unloaded corner (LF in a left turn) build slip angle since it loses load during cornering. Pro-Ackerman builds more dynamic toe out on the LF to get that corner to play a little bit more part in the total grip. For example the static toe was set at toe out, maybe 1/8”. Now when we turn left the LF gains more toe out than the original spec. How much depends on the Pro-Ackerman and even the bump steer. The suspension travel plays a part also. Depending on the amount of roll, I think even the ZLE will go into a droop condition on this LF example.



Even with the variable of proper static camber, the inner shoulder isn't going to be the area that gives up first on that compressed RF. But it will on the LF.

Now with all the above variables we have a LF that has less weight on it, still is in a negative camber scenario, moving towards (more) toe out. The less loading will allow the tire to kind of just going along for the ride, only lightly contributing to grip generation. Add the left steering input along with more static toe out, we can see that the inner shoulder is being drug along at a possible inadequate slip angle. With little vertical load. Without adequate vertical loading of the sidewall, the tread just get drug along.

With that bump steer creating toe out on compression, think about what is happening when we step on the brakes hard. The front suspension compresses and the bump steer may create a greater toe out condition. More toe out than the static toe we had set on the alignment rack. And if you are a good trail breaker, that lengthens the additional toe out condition causing more inner shoulder wear.

Notice that the inner shoulder wear some of us experience is very narrow. If it was just a negative camber issue, the wear would be more progressive across the entire contact patch.


I just don't see toe out helping either LF or RF inner shoulder wear at all. It's counterintuitive. Toe out helps turn in and grip but it's about the unloaded corner, the LF in our example.

Car makers unusually add toe out on compression because it is the safe bet.

Zero toe is not enough. Go toe in. GM actually specs toe in for the Gen6 track alignment.

I've asked around, no one can confirm they have witnessed the bump steer characteristics of a Gen6.

[Evansa22]

The rest of the tire is wearing even, gm track spec alignment

[rickybobby]

Originally Posted by Evansa22

The rest of the tire is wearing even, gm track spec alignment

This is exactly what I get in the front with the gm track alignment specs. My tire temps indicate that the alignment is good so there is something going on with the cars geometry.