Crazy oversteer / wheelspin with Michelin Pilot Super Sport

[jvincent]

Originally Posted by Ubersuber

I've yet to see any reference to any reliable source that actually contradicts anything I've said.

I suspect this thread may get even longer before that happens although I am confident no matter how long it gets there will be no such posting.

I thought you had already contradicted yourself in this thread. I guess you aren't a reliable source then.

[7thgear]

Originally Posted by Ubersuber

The point and purpose of my posts is to provide correct and useful information.

yes, you're so correct and informative that you can't keep the car on the road and spin out at the slightest hint of forward velocity.


while the rest of us have grip and are enjoying driving our cars at a spirited pace.

[DylanFRS]

Originally Posted by Ubersuber

Wheel radius isn't relevant to volume except as a number in the calculation. You need to calculate the volume of a torus which requires the inside circumference, the outside circumference and the cross section. Size of the torus doesn't affect the volume in the manner you may be thinking of.

The variables for bike tires are tire section (as for cars but there are fewer standard wheel sizes for adult bikes). Tire slip angles work differently for bicycles (and motorcycles) so comparing the grip of one type of vehicle to another is fairly pointless.

The volume of the tire and the tire pressure are correlated to load capacity in all pneumatic tires. Your remarks about adjusting tire pressures on bikes for ride and handling changes have no useful application to cars.

The point and purpose of my posts is to provide correct and useful information. The contradictory posts are mainly just that: contradictory.

I've yet to see any reference to any reliable source that actually contradicts anything I've said.

I suspect this thread may get even longer before that happens although I am confident no matter how long it gets there will be no such posting.

Honestly Ubersuber, all you need to do is to go look up the definition of "Normal Force" and apply that to the equation for pressure and I think you will get all of your answers. You're looking at this from the wrong side and making it more complex than it is. It's not about how the tires push on the ground, it's about how the ground pushes back.

[s2d4]

Speak with authority but gets it wrong, people correct him but he refuses to concede so they must be wrong. Therefore he must be right.
Even this logic is ridiculously stupid.

[Ubersuber]

Originally Posted by DylanFRS

Honestly Ubersuber, all you need to do is to go look up the definition of "Normal Force" and apply that to the equation for pressure and I think you will get all of your answers. You're looking at this from the wrong side and making it more complex than it is. It's not about how the tires push on the ground, it's about how the ground pushes back.

On my car nothing pushes. Really, quoting a version of Newton's Law (and the third one at that) helps this debate?

Your car is only held up in the manner you suggest when all four tires are flat.

The car is suspended on its tires at the hubs. The weight of the car hangs from the center of the wheel/tire assembly. The forces that hold the car off the ground are equally distributed inside the tire (which is round for practical purposes).

The weight of the car is held up by ALL of the tire ALL of the time.

The tire can do this only because of the air pressure inside the tire. Deformation of the carcass and the size of the contact patch are irrelevant to the "push/push" you refer to. Pressure, as you must know, exerts the same force everywhere inside the tire equally and in all directions which is what we mean by "pressure". All of that force holds the car off the ground, so in reality most of the tire holds the car up by "pulling" rather than "pushing". The contact patch no more holds the car up than the valve stem does. Bicycle wheels are a good illustration of this as the axle on a bike actually hangs from the spokes, the axle does not push on the spokes as must be intuitively obvious to anyone who thinks about it for a moment or two, well almost anyone I suppose.

The higher the pressure, the more air is in the tire and the more load it can carry.

The larger the internal volume of the tire the more load it can carry at any given pressure than a smaller tire at the same pressure because it contains more air.

This is pretty simple to understand.

The effect on the contact patch is another matter entirely. Tire grip is not proportional to contact patch size in the way many seem to think.

A review of other pages on that Barry's tire site provides even more food for thought on the underlying (har har) issue raised by the initial post in this thread...it'll be really interesting to see what opinions are posted after reading all of that!

[stonenewt]

Originally Posted by ZDan

Not saying anybody else is right, but this statement is wrong.

That was bad quote clipping. I was answering the sentence before that.

I mean why do heavy cars use larger tires but roughly the same tire pressure?

Not the second sentence that you quoted.

[stonenewt]

Originally Posted by Ubersuber

I've yet to see any reference to any reliable source that actually contradicts anything I've said.

You provided those your self as an attempt to support your stand point. This shows a lack of understanding.

[7thgear]

the worst part is that while in general, the discussion tire properties and construction is correct, Uber's application is inconsistent with the end goal.


Blindly following the manufactures recommendation for tire inflation when using a non-OEM tire is just stupid.

The end goal is to achieve a good balance of grip and control, there is no magic formula for this, you generally do it through trial and error until you get the results you want.


if the tire grips at a lower psi and the driver does not feel any negative steering feedback, then all is well in the galaxy.

[DylanFRS]

Originally Posted by Ubersuber

The higher the pressure, the more air is in the tire

Wrong.

When you say "more air" are you talking volume or mass? Because they are different. And you keep talking about "more volume" and "more air". For a given tire on a given rim, volume is basically constant... (static tire deformation is negligible). So, then pressure is dependent on the mass of air in the tire at that point AND temperature.

Originally Posted by Ubersuber

The larger the internal volume of the tire the more load it can carry at any given pressure than a smaller tire at the same pressure because it contains more air.

Wrong, and you jump around too much. Are we talking pressure or loads?

The loads a tire can take depend on A LOT of things including tire construction AND pressure (not volume, they are different).

Listen, talk all you want about hanging and how the car acts on the tires and all that but here is the simple math for you...

A car weighs Fcar. That means, for a car to sit at rest and not fall into the earth, the ground pushed back on the car EXACTLY Fcar. Of course it is pushing back directly on the tires. So the force on each tire, in the simplest case, is Fcar/4.

Ftire = Fcar/4

That means that the pressure one tire is exerting (Ptire) is:

Ptire = Ftire/Atire

Where Atire is the contact patch of a single tire in square units of length.

Now here is the real kicker, this is gonna blow your mind.

Ptire is also the air pressure in the tire!!!!!!!!!! Boom!

Because, the air in the tire has to push back on the inside of the tire with the same pressure for the tire to stay rigid. Amazeballz!

[stonenewt]

Originally Posted by DylanFRS

Wrong.

When you say "more air" are you talking volume or mass? Because they are different. And you keep talking about "more volume" and "more air". For a given tire on a given rim, volume is basically constant... (static tire deformation is negligible). So, then pressure is dependent on the mass of air in the tire at that point AND temperature.



Wrong, and you jump around too much. Are we talking pressure or loads?

The loads a tire can take depend on A LOT of things including tire construction AND pressure (not volume, they are different).

Listen, talk all you want about hanging and how the car acts on the tires and all that but here is the simple math for you...

A car weighs Fcar. That means, for a car to sit at rest and not fall into the earth, the ground pushed back on the car EXACTLY Fcar. Of course it is pushing back directly on the tires. So the force on each tire, in the simplest case, is Fcar/4.

Ftire = Fcar/4

That means that the pressure one tire is exerting (Ptire) is:

Ptire = Ftire/Atire

Where Atire is the contact patch of a single tire in square units of length.

Now here is the real kicker, this is gonna blow your mind.

Ptire is also the air pressure in the tire!!!!!!!!!! Boom!

Because, the air in the tire has to push back on the inside of the tire with the same pressure for the tire to stay rigid. Amazeballz!

Dude, you should be a teacher

[stonenewt]

Originally Posted by Ubersuber

Dont follow this advice. The center of the tread will wear out long before the outside ribs.

I didn't just read that did I?

[7thgear]

Originally Posted by stonenewt

I didn't just read that did I?

exactly why I drew that picture

[Tcoat]

HA HA HA HA HA
I once told some body to "be carful of the info on here as some guys can't even agree what tire pressure to use".
That was before I ever even saw this thread!

Do you guys just follow each other around to debate?
Once again tried to learn something and came out knowing less then when I went in because don't know just who to believe.
Torn between Wparsons and Stonenewt as the most credible at this point.

[wparsons]

Originally Posted by Ubersuber

I've yet to see any reference to any reliable source that actually contradicts anything I've said.

I suspect this thread may get even longer before that happens although I am confident no matter how long it gets there will be no such posting.

Challenge accepted.

The link you posted:

Originally Posted by Ubersuber

http://www.tirerack.com/tires/tirete...nd_Feeding.pdf

Point number 1:

Originally Posted by Ubersuber

Note the difference between track pressures and auto cross pressures. Street use would require even higher cold pressures.

Originally Posted by MichelinArticle:Page8

note: Though autocross hot target pressures are the same as those for road racing, you may need to start at a higher
cold inflation pressure to compensate for the lower pressure
gains in autocross racing.

Point number 2:

Originally Posted by Ubersuber

Find one technical source that says reducing rear tire pressure from factory specification will reduce oversteer. It isn't possible.

Originally Posted by Ubersuber

This increases the tendency for this chassis to oversteer. It really doesn't need the help.

Originally Posted by Ubersuber

No it didn't. Lowering rear tire pressure below recommended will reduce understeer. It cannot reduce oversteer, physically impossible.

Originally Posted by MichelinArticle:Page17

Decrease oversteer, lower rear tire pressure

I REALLY hope you're better at fact checking before using anything in a court room than you are with arguing online. Although, I would LOVE to see you in action where you present evidence to defend someone that actually incriminates them further.

Will you go away now?