Run flat tires

[xlrlist01]

The Porsche Carrera GT was known to be difficult to drive and very unforgiving. A very narrow "forgiveness band" with little warning of going past the envelope. Considering the number of owners, and very few miles this car had on it, I would be surprised the tires were not ate up with flat spots. If I were driving a car like this I would replace tires much more frequently. Goes back to doing what's right for the application.
Porsche Carrera GT in Walker crash had six owners in its cross-country life - Autoweek Racing car news - Autoweek

Porsche Carrera GT

Porsche Carrera GT

At the risk of making a mess of this, here are some notes about the hazards of low profile tires.

Start with an 'ordinary' tire. Lets give it a profile of 70% (technically its low profile, but not much). Lets go round a curve at a speed that is the limit of grip and give that a rating, I give it a 5. Just stay with me. Now, lets go a tad faster. The tire can't get round the curve but still grips at a value, lets call it 4.9. A bit faster again and the grip is lets say a 4.8. The thing to note here is that 4.9 and 4.8 isn't much less than the 5.0 I started with.

OK. Lets change that tire to a 35% ratio. Same curve. Same speed. Tire gives a grip of 5, enough to get round that curve. Lets go a bit faster. Good news, the tire gives a 5.5. Faster still and lets say the tire manages a 6. Lets assign that 6.0 as the limit, ie the 35% tire is gripping more in the curve. Sounds good hey? Now lets go a little faster. Whoa, the tire now gives a 5.0, a huge drop from that 6.0. Lets go a little faster still and wow, that tire is giving me a 3, that is lower than the standard tire I started with.

OK, I have made up the numbers, but the description is about right. A lower profile tire gives a higher grip in a curve than the more standard tire, but it does so by sacrificing the safety margin if you go too far. When it lets go, a very low profile tire lets go, no warning, no build up, no gentle recovery.

The top racing drivers can deal with this. Ordinary good drivers can't. There are far too many who think they can, but the bottom line is, they can't. Stabiltrac is a good thing, it tries to give the ordinary good driver more of the edge that a top racing driver has, never switch it off unless you really, really know why you are doing so. But it cannot beat the physics, ever.

Now, I know that the above has holes in it, I'm illustrating some of the concepts that form the compromise that is any vehicle. Yep, you can change this for that, but it always causes something else to happen, and most of the time the something else is not so good. Not always, because cars are also built to a price and there are things you can make better simply by spending more $$$. Generally, though the flip side is not so good. This isn't a problem if you know what you are getting into.

I run the rear anti-sway bar. The stiffer the rear of a car, the less margin for the switch from under-steer to over-steer there is (generalization). True over-steer is always a bad thing, it is very dangerous indeed and all manufacturers ensure that there are huge safety margins to avoid it. I know I have taken away a small amount of that margin, but it fixes a an undesirable behavior caused by the active suspension and there is still a healthy margin of under-steer left, so I'm OK with that, the problem with the active suspension is much worse than the slight loss of under-steer protection. Selecting lower profile tires involves a similar choice, but I don't see it discussed much. I don't like the ride quality of extra low profile tires, so prefer the 'correct' tires, but I know that that is my take. I like a very wide 'forgiveness band'.

 

[Phrede]

At the risk of making a mess of this, here are some notes about the hazards of low profile tires.

Start with an 'ordinary' tire. Lets give it a profile of 70% (technically its low profile, but not much). Lets go round a curve at a speed that is the limit of grip and give that a rating, I give it a 5. Just stay with me. Now, lets go a tad faster. The tire can't get round the curve but still grips at a value, lets call it 4.9. A bit faster again and the grip is lets say a 4.8. The thing to note here is that 4.9 and 4.8 isn't much less than the 5.0 I started with.

OK. Lets change that tire to a 35% ratio. Same curve. Same speed. Tire gives a grip of 5, enough to get round that curve. Lets go a bit faster. Good news, the tire gives a 5.5. Faster still and lets say the tire manages a 6. Lets assign that 6.0 as the limit, ie the 35% tire is gripping more in the curve. Sounds good hey? Now lets go a little faster. Whoa, the tire now gives a 5.0, a huge drop from that 6.0. Lets go a little faster still and wow, that tire is giving me a 3, that is lower than the standard tire I started with.

OK, I have made up the numbers, but the description is about right. A lower profile tire gives a higher grip in a curve than the more standard tire, but it does so by sacrificing the safety margin if you go too far. When it lets go, a very low profile tire lets go, no warning, no build up, no gentle recovery.

The top racing drivers can deal with this. Ordinary good drivers can't. There are far too many who think they can, but the bottom line is, they can't. Stabiltrac is a good thing, it tries to give the ordinary good driver more of the edge that a top racing driver has, never switch it off unless you really, really know why you are doing so. But it cannot beat the physics, ever.

Now, I know that the above has holes in it, I'm illustrating some of the concepts that form the compromise that is any vehicle. Yep, you can change this for that, but it always causes something else to happen, and most of the time the something else is not so good. Not always, because cars are also built to a price and there are things you can make better simply by spending more $$$. Generally, though the flip side is not so good. This isn't a problem if you know what you are getting into.

I run the rear anti-sway bar. The stiffer the rear of a car, the less margin for the switch from under-steer to over-steer there is (generalization). True over-steer is always a bad thing, it is very dangerous indeed and all manufacturers ensure that there are huge safety margins to avoid it. I know I have taken away a small amount of that margin, but it fixes a an undesirable behavior caused by the active suspension and there is still a healthy margin of under-steer left, so I'm OK with that, the problem with the active suspension is much worse than the slight loss of under-steer protection. Selecting lower profile tires involves a similar choice, but I don't see it discussed much. I don't like the ride quality of extra low profile tires, so prefer the 'correct' tires, but I know that that is my take. I like a very wide 'forgiveness band'.

I think this over simplifies the complex components of automotive handling and tire features. If it was only so simple as tire profile. Tire compound and design are also major players in the tire department well beyond profile. Things like unsprung weight, drive train design, damping factors, suspension design, alignment and many, many more things come into play when looking at the total system.

All things are a compromise and ride comfort is just one reason I do NOT run the 'correct' tire. The OEM factors in many things when selecting individual components, if one is willing to accept the all the factors of modifications, gains are there to be had. It all goes to what your personal preferences are. I would no go so far as to say "...most of the time the something else is not so good". What is good or not is a matter of opinion.

Just one example is in line with the discussion here. It is generally accepted that non-runflat tires are lighter, less expensive, more available, ride better and out perform the OEM run-flat versions. The opposite side of the coin is that you run the risk of getting a flat and should be prepared. In my opinion, not such a bad thing. Not for everyone, make your own decision based on your comfort level. In addition, I think a lower profile tire would provide better performance. However, the risk of road hazard damage and worsened ride do not sufficiently offset the gains for me. Again, not better or worse just what works for me and what I want.

While you consider oversteer a bad thing, I think it can be a lot of fun.... to a point. It's all about opinions.

 

[Eslic1]

Wow...

I think this over simplifies the complex components of automotive handling and tire features. If it was only so simple as tire profile. Tire compound and design are also major players in the tire department well beyond profile. Things like unsprung weight, drive train design, damping factors, suspension design, alignment and many, many more things come into play when looking at the total system.

All things are a compromise and ride comfort is just one reason I do NOT run the 'correct' tire. The OEM factors in many things when selecting individual components, if one is willing to accept the all the factors of modifications, gains are there to be had. It all goes to what your personal preferences are. I would no go so far as to say "...most of the time the something else is not so good". What is good or not is a matter of opinion.

Just one example is in line with the discussion here. It is generally accepted that non-runflat tires are lighter, less expensive, more available, ride better and out perform the OEM run-flat versions. The opposite side of the coin is that you run the risk of getting a flat and should be prepared. In my opinion, not such a bad thing. Not for everyone, make your own decision based on your comfort level. In addition, I think a lower profile tire would provide better performance. However, the risk of road hazard damage and worsened ride do not sufficiently offset the gains for me. Again, not better or worse just what works for me and what I want.

While you consider oversteer a bad thing, I think it can be a lot of fun.... to a point. It's all about opinions.

I agree...

 

[mtrocket]

I'll be surprised if my michelins last more than 11.000 miles. Very poor ware on my 2006
I'll be surprised if my Michelins last more than 11,000 miles. Very poor ware on my 2006 XLR

Something's amiss, methinks. I've had good tire wear performance on my '06. When I replaced my 18" wheels, my tires still had like-new tread on them after 12K+ miles, even tho' the car needed a 4-wheel alignment (according to my dealer, Red Noland in COS). All I'd done was to rotate them (front-back, same side) every 4K miles, and I kept the tire pressure at 32 psi.

I'm sure others will chime in with 4-5 times as many miles as I've experienced. FWIW

Tim

I have an '07, replaced the tires last October (2013), right before I put her down for her long winter's nap. I had about 25000 miles on them. The outer and inner 1" of tread had peeled off each tire... the tread was pretty wore as well. Probably should have replaced them long before, but unless I got down and inspected each tire very carefully, the peeled tread was not noticeable.

 

[buki]

Y'all r all standing on shaky ground.

I am astounded by most of the concepts expressed in this thread.

But then, I have learned over time that you never grow old until you lose your capacity to be astonished so I am invigorated.

That said I hope you will ponder the following:

1. Your car was designed by a team of world class engineers and stylists at the largest auto maker in the world.

2. It is one of very few cars ever made that is essentially timeless. Anyone who sees it will never realize that it is between 5 and 10 years old.

3. It was built with technologies so advanced for their time that many manufacturers have never yet offered them. In fact, the Magnetic Ride suspension on your XLR is a $27,000 option on the Mercedes AMG.

4. Your car was tested on the most trying venues in the world under the most harrowing conditions imaginable by a team of test drivers who took it to places you will never experience.

5. The suspension and tires are the result of a combination of the very best chassis and tire engineers anywhere to deliver PROVEN performance under very exacting specifications.

6. Unless you are Michael Shumacher, the XLR is more than capable of giving far more than you will ever be able to take.

7. To think that you can improve any aspect of this incredible car after the millions and millions of dollars spent to create it is ludicrous.

8. And finally do you REALLY think a jack and a can of fix-a-flat will get you home after a 100 MPH blowout?

It is what it is for all of the right reasons.

Enjoy.

May the ranting begin.

 

[airmike]

As to #7---"I" may not be able to improve on any aspect of the incredible car, but I didn't make the headlights that craze either. So I don't think it is quite perfect ..and I like the whine from the supercharger, so how can it not be improved on if the cai lets the sound out?

I thought Ludicrous was a rapper/singer..

I am astounded by most of the concepts expressed in this thread.

But then, I have learned over time that you never grow old until you lose your capacity to be astonished so I am invigorated.

That said I hope you will ponder the following:

1. Your car was designed by a team of world class engineers and stylists at the largest auto maker in the world.

2. It is one of very few cars ever made that is essentially timeless. Anyone who sees it will never realize that it is between 5 and 10 years old.

3. It was built with technologies so advanced for their time that many manufacturers have never yet offered them. In fact, the Magnetic Ride suspension on your XLR is a $27,000 option on the Mercedes AMG.

4. Your car was tested on the most trying venues in the world under the most harrowing conditions imaginable by a team of test drivers who took it to places you will never experience.

5. The suspension and tires are the result of a combination of the very best chassis and tire engineers anywhere to deliver PROVEN performance under very exacting specifications.

6. Unless you are Michael Shumacher, the XLR is more than capable of giving far more than you will ever be able to take.

7. To think that you can improve any aspect of this incredible car after the millions and millions of dollars spent to create it is ludicrous.

8. And finally do you REALLY think a jack and a can of fix-a-flat will get you home after a 100 MPH blowout?

It is what it is for all of the right reasons.

Enjoy.

May the ranting begin.

 

[cubby558]

I don't take much stock in his rant--He's a radio DJ!! Some of the other posters in this thread are engineers. I think they know what they are talking about!

As to #7---"I" may not be able to improve on any aspect of the incredible car, but I didn't make the headlights that craze either. So I don't think it is quite perfect ..and I like the whine from the supercharger, so how can it not be improved on if the cai lets the sound out?

I thought Ludicrous was a rapper/singer..

 

[Phrede]

Sadly so wrong on many accounts.

1. Your car was designed by a team of world class engineers and stylists at the largest auto maker in the world.

Toyota is the largest car maker in the world and sells more cars than GM.

2. It is one of very few cars ever made that is essentially timeless. Anyone who sees it will never realize that it is between 5 and 10 years old.

I do love the styling, but to say no one knows how old it is presumes ignorance.

6. Unless you are Michael Shumacher, the XLR is more than capable of giving far more than you will ever be able to take.
Just flat false, do you even know what it feels like when the speed limiter kicks in? You presume that just because you could not handle more performance, no one else can? How is it you know my skill level so well?

3. It was built with technologies so advanced for their time that many manufacturers have never yet offered them. In fact, the Magnetic Ride suspension on your XLR is a $27,000 option on the Mercedes AMG.
4. Your car was tested on the most trying venues in the world under the most harrowing conditions imaginable by a team of test drivers who took it to places you will never experience.
5. The suspension and tires are the result of a combination of the very best chassis and tire engineers anywhere to deliver PROVEN performance under very exacting specifications.
7. To think that you can improve any aspect of this incredible car after the millions and millions of dollars spent to create it is ludicrous.

To think that there were not compromises in the design and build of the car is what is ludicrous. The engineers are not given free reign in any product design, cars included. The marketing people have WAY more input on the product than the engineering team. There are many things that have engineers hands tied. EPA and other regulatory constraints, noise limits, ride requirements, manufacturing cost constraints, technology availability, serviceability constraints, marketing opinions are but a few things that limits the design engineers to building what they want. To think that the best of everything was used in a $100k car is also a grandiose delusion.

As nice as what it is, it is not a perfect car. A perfect car does not exist. Since everyone has their own opinion of perfection, there is no way a manufacturer can produce this car. This is what drives the aftermarket parts industry and provides customers to the custom build shops. GM is not infallible and EVERYTHING can be improved on.

8. And finally do you REALLY think a jack and a can of fix-a-flat will get you home after a 100 MPH blowout?
I hope you do not think a run-flat tire is immune to a blow out. For your own safety you should educate yourself on what a run-flat tire is and is not. Most all blow outs today are a result of improper tire pressures and maintenance. The main purpose of run flat technology is NOT a blow out but a leaker. The ability to tell when a tire is minimally low by driving characteristics is not that difficult. Even then, the TPMS watches your pressures for you.

 

[buki]

Y'all r all standing on shaky ground.

I am astonished by most of the concepts expressed in this thread.

But then, I have learned over time that you never grow old until you lose your capacity to be astonished so I am invigorated.

That said I hope you will ponder the following:

1. Your car was designed by a team of world class engineers and stylists
at the largest auto maker in the world to completely reposition an aging
brand. The stakes were extremely high. The best of the best built it for the lucky few who own one.

2. It is one of very few cars ever made that is essentially timeless.
Anyone who sees it will never realize that it is between 5 and 10 years
old at this point in time. Think what it will be 25 years from now.

3. It was built with technologies so advanced for the
time that many manufacturers have never yet offered them. In fact, the
Magnetic Ride suspension on your XLR is a $27,000 option on the Mercedes
AMG.

4. Your car was tested on the most trying venues in the
world under the most harrowing conditions imaginable by a team of test
drivers who took it to places you will never experience.

5. The suspension and tires are the result of a combination of the very best
chassis and tire engineers on the planet to deliver PROVEN performance under
very exacting specifications.

6. Unless you are Michael Shumacher, the XLR is more than capable of giving far more than you will ever be able to take.

7. To think that you can improve any aspect of this incredible car after
the millions and millions of dollars spent to create it is ludicrous.

8. And finally do you REALLY think a jack and a can of fix-a-flat will get you home after a 100 MPH blowout?

It is what it is for all of the right reasons.

Enjoy.

May the ranting begin.

 

[buki]

sorry! something resulted in multiple posts that i tried during i
a major storm last night. delete them if you can rob.

 

[Phrede]

sorry! something resulted in multiple posts that i tried during i
a major storm last night. delete them if you can rob.

Just in case you didn't know...... You can delete your own posts by using the "Edit Post" button near the bottom of the post.

HTH

 

[hawkeye372]

I am astounded by most of the concepts expressed in this thread.

But then, I have learned over time that you never grow old until you lose your capacity to be astonished so I am invigorated.

That said I hope you will ponder the following:

1. Your car was designed by a team of world class engineers and stylists at the largest auto maker in the world.

2. It is one of very few cars ever made that is essentially timeless. Anyone who sees it will never realize that it is between 5 and 10 years old.

3. It was built with technologies so advanced for their time that many manufacturers have never yet offered them. In fact, the Magnetic Ride suspension on your XLR is a $27,000 option on the Mercedes AMG.

4. Your car was tested on the most trying venues in the world under the most harrowing conditions imaginable by a team of test drivers who took it to places you will never experience.

5. The suspension and tires are the result of a combination of the very best chassis and tire engineers anywhere to deliver PROVEN performance under very exacting specifications.

6. Unless you are Michael Shumacher, the XLR is more than capable of giving far more than you will ever be able to take.

7. To think that you can improve any aspect of this incredible car after the millions and millions of dollars spent to create it is ludicrous.

8. And finally do you REALLY think a jack and a can of fix-a-flat will get you home after a 100 MPH blowout?

It is what it is for all of the right reasons.

Enjoy.

May the ranting begin.

Thanks for sharing this valuable info.


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[Stella]

Isn't one of the main reason why theirs run-flats on our cars is because there's no room for a spare? Now their might be other reasons like the customer feeling safe knowing they can still drive on it to get home or to a repair facility.
From what I've learned they didn't design a whole car. They borrowed ALOT of chassis,driveline,etc from a close cousin.
I don't think tires are at the top of a designer nor engineers list at cadillac. They meet their needs with their preferred vendors IMO.
There's so many factors to prolong the life of a tire,or on the other hand doing certain stuff can be fatal for any tire. If you properly maintain it your chances of catastrophe run flat or not are less likely. Just my two cents

 

[Eslic1]

I agree...

Isn't one of the main reason why theirs run-flats on our cars is because there's no room for a spare? Now their might be other reasons like the customer feeling safe knowing they can still drive on it to get home or to a repair facility.
From what I've learned they didn't design a whole car. They borrowed ALOT of chassis,driveline,etc from a close cousin.
I don't think tires are at the top of a designer nor engineers list at cadillac. They meet their needs with their preferred vendors IMO.
There's so many factors to prolong the life of a tire,or on the other hand doing certain stuff can be fatal for any tire. If you properly maintain it your chances of catastrophe run flat or not are less likely. Just my two cents

That's pretty much how I view things as well... I don't drive crazy or super aggressive, Although I do enjoy the occasional tire chirp I'm not looking to burn up half the block... I considered the fact they were chosen as factory install for a reason but I would love to have an even better ride from my tires if one exist.

 

[BoughtTheXLR]

I don't think tires are at the top of a designer nor engineers list at cadillac. They meet their needs with their preferred vendors IMO.

Exactly right. I was with a group of other Corvette owners at Corvettes@Carlisle who got a chance to discuss the upcoming C5 with several of the engineers. At one point, we expressed some dissatisfaction with the Goodyears that came on the C4. The engineers (after looking around briefly to see who else might be listening) said they had lobbied hard for Michelins, but were blocked by a corporate agreement. Years later, Michelins did appear on the the 04-05 XLR but after that it too went to Goodyears. (Except for the V, for which Goodyear didn't offer a runflat in the spec size).

 

[Phrede]

Exactly right. I was with a group of other Corvette owners at Corvettes@Carlisle who got a chance to discuss the upcoming C5 with several of the engineers. At one point, we expressed some dissatisfaction with the Goodyears that came on the C4. The engineers (after looking around briefly to see who else might be listening) said they had lobbied hard for Michelins, but were blocked by a corporate agreement. Years later, Michelins did appear on the the 04-05 XLR but after that it too went to Goodyears. (Except for the V, for which Goodyear didn't offer a runflat in the spec size).

This kind of thing happens a lot, and not only with tires. Many times the engineers are not the decision makers about which product to use despite being the most knowledgeable about the technical aspects.

 

[GizmoQ]

4. Your car was tested on the most trying venues in the world under the most harrowing conditions imaginable by a team of test drivers who took it to places you will never experience.

5. The suspension and tires are the result of a combination of the very best chassis and tire engineers anywhere to deliver PROVEN performance under very exacting specifications.

6. Unless you are Michael Schumacher (corrected spelling), the XLR is more than capable of giving far more than you will ever be able to take.

Just flat false, do you even know what it feels like when the speed limiter kicks in? You presume that just because you could not handle more performance, no one else can? How is it you know my skill level so well?[/COLOR]

Buki, I'm no Schumacher (I respect the man so I learned to spell his name right), but I've far exceeded the limits of the stock driveline and suspension. I understand I am one of the few exceptions on this forum, but the fact that there are more than one, two, three, four of us that I know of... proves you very wrong.

This is what drives the aftermarket parts industry and provides customers to the custom build shops. GM is not infallible and EVERYTHING can be improved on.

And for me, sticky, non-run flat tires were the first thing I acquired after adding more boost. Changed the suspension, got stickier tires. See a theme building here... I've found until you go full racing slicks, nothing improves safety and control at the limits of performance like a good set of tires and there's no such thing as a competitive run flat.

 

[nerkpowers]

Phede,
Love your Dilbert post. As an Engineer, I can attest that many of the things you state are very true.

I do have to say, that this is by far the coolest car I've ever owned, or driven for that matter. Of course past drives include a 1980 Pontiac Phoenix (my first car), 1984 Chrysler LeBaron (remember the K cars) and a 1987 Ford Taurus station wagon. Sometimes we just have to keep things in perspective. I have non-run flats but that was the way the car was when in bought it. After reading posts on this forum, I purchased a compressor and 'slime' kit made for the Camaro. Oh, and bought a plug kit as well.


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[Texas Shriner]

Phede,
After reading posts on this forum, I purchased a compressor and 'slime' kit made for the Camaro. Oh, and bought a plug kit as well.


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That's how I always rolled in my corvette. Oh, and a credit card and cell phone - Having the ability to dial 1-800-COME-GET-MY-ASS is the best back up of all.

 

[Crimson Pearl]

I recently checked the Sam's Club website and it appears that the Michelin P-Zero tires that came as original equipment on Crimson Pearl are still available, and at what I consider to be a reasonable price.

I have never considered the ride on my run-flats to be harsh. It seems firm when appropriate and softer when conditions allow. I recall being able to run about 50 miles on a freshly repaved Interstate Highway shortly after I purchased Crimson Pearl and the ride was as smooth as butter. It would appear to me that the Magnetic Ride Suspension does a fine job of adjusting the ride to the current manner of driving and road surface.

I've never been shy about installing different tires on my vehicle other than what came from the factory if I thought a different tire was going to serve me better. On the other hand, if I was very well pleased with the original set of tires, I would install the same type again when replacements were required. But changing from one brand to another is rarely as different as going from a run-flat to a conventional tire!

I believe that I will keep the P-Zero Michelins on Crimson Pearl as long as they are available. I have not been unhappy with them and I do like the added security of a run-flat. I know that it is no guarantee of never having a tire problem, but it probably lowers the chances of having a problem.