Tire Wear

[Three Cobras]

The basics: 12.5K miles, always inflate to stock spec or maybe stock plus two PSI. Always check after major temperature changes. No uneven wear side to side or any apparent improper alignement wear.

I have noticed in the proper light that both the front and rear tread surfaces are slightly, but noticeably, concave. You can see it when the shadows are just right on the tires. Aha! Underinflated says I!. Not, says the gauge (a fancy, schmansy round gauge, not a ballpoint pen-type POS). Last night I got out my calipers and measured the tread depth. The tread depth either side of the center tread bar is about 60 thou (maybe 1/16") LESS than the tread depth one groove in from either side. Aha! That expalins the convexity, but my vexity was just beginning. That also says 'overinflation' to me.

My questions: 1. Anyone else with some miles on the car see this too? 2. Anyone else with almost no miles on the car see this too? In the case of #2, I was wondering if the tires were just naturally dished in. I know some tires have different hardness rubber in different areas across the width of the tread, so I was wondering if that was the case here and that Goodyear had intentionally dished the tire.

My normal inclination would be to increase the inflation pressure to flatten the tread center, but of course that would increase the center wear.

Thoughts anyone?

[SCGT500 Co Pilot]

We will have a research team on site this weekend there buddy. I'm sure we will take everything into consideration and have some facts to post upon our return back to the forum.

[Alloy Dave]

The basics: 12.5K miles, always inflate to stock spec or maybe stock plus two PSI. Always check after major temperature changes. No uneven wear side to side or any apparent improper alignement wear.

I have noticed in the proper light that both the front and rear tread surfaces are slightly, but noticeably, concave. You can see it when the shadows are just right on the tires. Aha! Underinflated says I!. Not, says the gauge (a fancy, schmansy round gauge, not a ballpoint pen-type POS). Last night I got out my calipers and measured the tread depth. The tread depth either side of the center tread bar is about 60 thou (maybe 1/16") LESS than the tread depth one groove in from either side. Aha! That expalins the convexity, but my vexity was just beginning. That also says 'overinflation' to me.

My questions: 1. Anyone else with some miles on the car see this too? 2. Anyone else with almost no miles on the car see this too? In the case of #2, I was wondering if the tires were just naturally dished in. I know some tires have different hardness rubber in different areas across the width of the tread, so I was wondering if that was the case here and that Goodyear had intentionally dished the tire.

My normal inclination would be to increase the inflation pressure to flatten the tread center, but of course that would increase the center wear.

Thoughts anyone?

I haven't looked at this. Slowly creep through a small puddle of water and drive out of it...leaving a wet pattern on the road. Does the entire tread meet the road? If so, I wouldn't adjust anything. If you notice that the outer edges show "wet" on the road, but the center does not, then perhaps you should increase pressure a bit. Do you have stock wheels/tires? Too wide of a rim can cause what you describe.

 

As for pressure gauges, I worked in a tire shop for 8 years. The only gauge I'll use is the pencil type. Good luck.

 

Dave

[Three Cobras]

As for pressure gauges, I worked in a tire shop for 8 years. The only gauge I'll use is the pencil type. Good luck.

 

Dave

 

Seriously? Seriously?

 

Stock tires and rims.

[mach1fever]

The old 03/04 cobras did the same thing because there was not enough camber adjustment. I don't know about the gt500 because its a different suspension, but a friend of mine put in 4-way caster camber plates and the problem went away. Doesn't explain the back though?

[Three Cobras]

Mach -

This is not camber wear - it's symetrical across the tread and concave exactly in the center, not offset. That's what puzzles me.

[Dropping__Chronic]

Mach -

This is not camber wear - it's symetrical across the tread and concave exactly in the center, not offset. That's what puzzles me.

 

My buddy used to work at the Proving Grounds in Midland Tx for Firestone. He told me that when a tire is under speed, that it actually ends up 'running' on the outer edges of the tires while at speed, as centrifigul force bows out the tires a bit for maximum grip. He also said something to the effect of that allowing for the tires to then flatten on turns to put the full footprint down and give maximum traction. I think it's by design that it does this, and that overinflating may do more harm than good.

 

We had this discussion quite a while ago, but that's basically how I remember it.

 

\____________/ Normal - at rest

 

\___/----------\____/ At speed

 

 

Is this how you are seeing the wear, with more at the endges than the middle?

[Alloy Dave]

The old 03/04 cobras did the same thing because there was not enough camber adjustment. I don't know about the gt500 because its a different suspension, but a friend of mine put in 4-way caster camber plates and the problem went away. Doesn't explain the back though?

Camber will only affect wear one ONE side of the tire..not both.

[Alloy Dave]

My buddy used to work at the Proving Grounds in Midland Tx for Firestone. He told me that when a tire is under speed, that it actually ends up 'running' on the outer edges of the tires while at speed, as centrifigul force bows out the tires a bit for maximum grip. He also said something to the effect of that allowing for the tires to then flatten on turns to put the full footprint down and give maximum traction. I think it's by design that it does this, and that overinflating may do more harm than good.

 

We had this discussion quite a while ago, but that's basically how I remember it.

 

\____________/ Normal - at rest

 

\___/----------\____/ At speed

Is this how you are seeing the wear, with more at the endges than the middle?

I would agree with this, but only at very high wheel speeds. However, you raise a good point....if someone is doing a lot of burnouts...the tire may be deforming like you say DURING THE BURNOUT and wearing the center.

 

Dave

[Alloy Dave]

Seriously? Seriously?

 

Stock tires and rims.

Yup, seriously.

[mach1fever]

Dave burnouts don't account for the front tires. If there is enough camber built into the suspension it would be both tires.

[Alloy Dave]

Dave burnouts don't account for the front tires. If there is enough camber built into the suspension it would be both tires.

Good point, I didn't pick up on the fact that he saw this on the front tires. However, I don't understand your camber comment....camber won't cause wear only in the center of the tire.

 

Dave

[Three Cobras]

My buddy used to work at the Proving Grounds in Midland Tx for Firestone. He told me that when a tire is under speed, that it actually ends up 'running' on the outer edges of the tires while at speed, as centrifigul force bows out the tires a bit for maximum grip. He also said something to the effect of that allowing for the tires to then flatten on turns to put the full footprint down and give maximum traction. I think it's by design that it does this, and that overinflating may do more harm than good.

 

We had this discussion quite a while ago, but that's basically how I remember it.

 

\____________/ Normal - at rest

 

\___/----------\____/ At speed

Is this how you are seeing the wear, with more at the endges than the middle?

 

My fronts and rears look like the 'At Speed' picture while at rest. The tread is worn more in the center, as though the tires were overinflated, but I have kept them at 35 - 36 PSI all the time, including adjusting for hot / cold temps. If they were overinflated, at rest the center would be bulged outward or at least level, but it isn't.

Slightly OT - who sells the tire pressure sensor bands more cheaply than Ford?

[mach1fever]

His tires were wearing toward the inside of the tire because ford had not built in enough adjustment to do a proper alignment. Nobody could align the car properly. One of the ford engineers admitted they had not built enough adjustment in the car. So he went with maximum motorsports 4-ways and had it re-aligned and it worked out. Ruined two sets of eagle f-1's in 13k miles of driving (to include the seabring sensation events)

[Three Cobras]

Mach1 -

Thanks. Camber wear is definitely not the problem for me - I do know it when I see it. These tires are not wearing abnormally fast either as I have 12.5K+ and I doubt I have even worn them half way. Just want to get ahead of any problem before it becomes major.

[Dropping__Chronic]

My fronts and rears look like the 'At Speed' picture while at rest. The tread is worn more in the center, as though the tires were overinflated, but I have kept them at 35 - 36 PSI all the time, including adjusting for hot / cold temps. If they were overinflated, at rest the center would be bulged outward or at least level, but it isn't.

Slightly OT - who sells the tire pressure sensor bands more cheaply than Ford?

 

That sounds like intentional dishing of the tire, but I can't imagine why it would be that extreme even while the tire is at rest.

 

Be on the lookout for bulges? I've not seen tires do that while sitting there myself.

[mach1fever]

Wish I was more help. I hope it works out. I know how frustrating diagnosing stuff like this is

[Three Cobras]

All -

Tire guys says 'overinflation wear'. Says he thinks Ford's tire pressure recommendation is too high - 'Try 32 PSI for a while."

Had the car on a lift with all four off the ground - all four tires dished in at center even with no load. I would have thought overinflated tires would bulge at center under no-load conditions. Hmmm.

This is not excessive wear at this point (approx 13K miles) so there's time to correct before writing off tire prematurely. I'd keep an eye on it for you others out there. If I see anything else worth reporting I will do it. I probably have one of the highest mileage cars at this point. Oh well, 13K down, 237K to go.

[Dropping__Chronic]

All -

Tire guys says 'overinflation wear'. Says he thinks Ford's tire pressure recommendation is too high - 'Try 32 PSI for a while."

Had the car on a lift with all four off the ground - all four tires dished in at center even with no load. I would have thought overinflated tires would bulge at center under no-load conditions. Hmmm.

This is not excessive wear at this point (approx 13K miles) so there's time to correct before writing off tire prematurely. I'd keep an eye on it for you others out there. If I see anything else worth reporting I will do it. I probably have one of the highest mileage cars at this point. Oh well, 13K down, 237K to go.

 

Aside from your tire issues, which it looks like you found the culprit for hopefully, I have to say I'm very impressed with your tire wear. On my Terminator, and the Cobra before it with the Independent rear end I would go through rear tires I'd say every 10-20k at best with pretty judicious driving. The wear would always be worn from the inside out, telling me the rear tires were off perhaps due to the IRS? I asked Ford about it and of course it was normal. I guess I'm just glad to hear a Cobra from the factory with the solid rear seems to keep the meat on the tires a bit longer. Having a daily driver that you have to replace the tires on every couple months was a real pain.

[LuckySnake]

All -

Tire guys says 'overinflation wear'. Says he thinks Ford's tire pressure recommendation is too high - 'Try 32 PSI for a while."

Had the car on a lift with all four off the ground - all four tires dished in at center even with no load. I would have thought overinflated tires would bulge at center under no-load conditions. Hmmm.

This is not excessive wear at this point (approx 13K miles) so there's time to correct before writing off tire prematurely. I'd keep an eye on it for you others out there. If I see anything else worth reporting I will do it. I probably have one of the highest mileage cars at this point. Oh well, 13K down, 237K to go.

Thanks for sharing this information. I'm going to drop to 32psi. I only have about 1400 miles and to early to tell about any funny tire wear. You might want to use another gauge to compare with the one you have been using. How has your clutch and transmission been doing?

 

Thanks