Crazy oversteer / wheelspin with Michelin Pilot Super Sport

[drewbot]

Stick to law, not engineering please

Sent from my OnePlus One

[FLYFISHR]

This got me thinking of how those tanker trucks will have extra sets of wheels that they can lower when they are fully loaded down thus increasing the size of the contact area that they have to spread the load arcoss.

[Dipstik-sportech]

Originally Posted by wparsons

I think he's going to shut up for a while after he posted an article that directly contradicts at least three things he has been saying.

Oh lord no he won't!!!! He's going to attempt to explain why he contradicted himself and somehow make it seem that he's right

[stonenewt]

Originally Posted by Ubersuber

????

This is dangerously incorrect.

As far as load carrying goes you absolutely can compare bike tires to car tires. The air that goes in them is the same.

No bike carries anything like the loading of a car tire but the same larger volume requires lower pressure to carry the same weight applies to both.

The physical limitations of the tyres that help define the pressures used in bike tyres & car tyres are different. With automotive tyres carcass generated heat is a problem, on bike tyres it isn't. On bike tyres the risk of pinch punctures is actually one of the key issues in getting the correct tyre pressure, for automotive use it's a non-issue.

Boyle's Law is a law of nature and does not vary in human experience.

Er... Think you need to read [ame="http://en.wikipedia.org/wiki/Boyle%27s_law"]Boyle's law - Wikipedia, the free encyclopedia[/ame] until the little animation in the top right actually makes sense.

Hint - "A modern statement of Boyle's law is:

The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system."

Just one reference ought to be enough:

http://www.schwalbetires.com/tech_in...ation_pressure

Find a technical site that supports the claim that tire pressure does not need to vary with internal tire volume when required to support a given weight.

Did you even READ that page?
"It is impossible to make a general recommendation on inflation pressure for a specific bicycle or a particular tire. The “right” inflation pressure depends mainly on the load exerted on the tire. This weight is mainly influenced by the weight of the rider and any luggage. Contrary to a car, the vehicle weight is only a minor part of the total weight. In addition there is a great diversity of individual preferences with regards to low rolling resistance or suspension comfort."

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

To increase the contact patch area. The heaver the load the larger an area you need on the road to provide grip. Put it another way, would you be comfortable driving a 1 tone vehicle with a contact patch of 1.6 sq"?

[EAGLE5]

[stonenewt]

Originally Posted by wparsons

How is making a car heavier affecting volume of the tire? You have to add more pressure because you have increased the weight on the wheels without changing desired contact patch size. This means more pressure required.

There's been a rule of thumb going around for ages to get the right tyre pressure on a bike. Adjust the pressure to get 10% static droop when loaded, at this point you'll not get the best of anything but you'll get a really nice balance between rolling resistance, comfort & bike handling.

If you hit 85-90% of the PSI limit of the tyre or rim then step up a tyre size. If you reach the minimum PSI of the tyre then drop down a tyre size. The maximum & minimum load of the tyre is directly proportional to the size of the tyres contact patch at 10% droop.

Two interesting points:
- It's completely independent of the wheel radius which kind of blows the whole volume theory out the water.
- You can't apply this rule of thumb or a similar one to car tyres.

[Dipstik-sportech]

Originally Posted by jsimon7777

Doesn't work on Tapatalk

[stonenewt]

Originally Posted by Dipstik-sportech

Doesn't work on Tapatalk

Also doesn't dispel any miss-information.

[troek]

Originally Posted by stonenewt

There's been a rule of thumb going around for ages to get the right tyre pressure on a bike. Adjust the pressure to get 10% static droop when loaded, at this point you'll not get the best of anything but you'll get a really nice balance between rolling resistance, comfort & bike handling.

If you hit 85-90% of the PSI limit of the tyre or rim then step up a tyre size. If you reach the minimum PSI of the tyre then drop down a tyre size. The maximum & minimum load of the tyre is directly proportional to the size of the tyres contact patch at 10% droop.

Two interesting points:
- It's completely independent of the wheel radius which kind of blows the whole volume theory out the water.
- You can't apply this rule of thumb or a similar one to car tyres.

Youve effectively convinced me, and got me to understand it as well.

[s2d4]

Yay, suberman ruins a handling thread again.

[ZDan]

Originally Posted by stonenewt

To increase the contact patch area. The heaver the load the larger an area you need on the road to provide grip. Put it another way, would you be comfortable driving a 1 tone vehicle with a contact patch of 1.6 sq"?

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

When you add load at a given pressure, you INCREASE the contact patch area.

When you add air pressure at a given load, you are REDUCING the contact patch area, not increasing it.

More contact patch area does not give greater load-carrying capacity. Too much tire deformation gives greater contact patch area and results in more heat into the carcass. You add pressure to reduce deformation and heat.

[7thgear]

[DylanFRS]

Originally Posted by Ubersuber

You are missing the volume effect. There is more air in the larger tire, i.e. the 215/45x17 tire has a smaller air chamber than the 225/45x17.

It is the volume of air that supports the load (technically the mass of the air). The higher the weight the more volume is required or more pressure. The mass of air is required to support the weight of the vehicle.

This isn't rocket science you know. Take all the air out of the tire and see what happens, then add back until the car is supported on the correct contact patch profile. You'll add the same amount of air to each tire but the pressure will have to be higher in the smaller volume tire, which it will be if the contact patch is to be the correct shape. Boyle's Law.

Tire construction affects this but not nearly as much as you might think. Run flat tires exploit the carcass rigidity in order to hold their shape without air but they need the air to work correctly. Hence the invention of TPMS, for run flats.

Oh man, how did I end up in this thread? I just have to quote this post so that people can re-read this. It is like you know just enough to be completely incorrect. It reminds me of people who get less than 25% on a multiple choice test. They know just enough to screw themselves.

[Ubersuber]

Originally Posted by stonenewt

There's been a rule of thumb going around for ages to get the right tyre pressure on a bike. Adjust the pressure to get 10% static droop when loaded, at this point you'll not get the best of anything but you'll get a really nice balance between rolling resistance, comfort & bike handling.

If you hit 85-90% of the PSI limit of the tyre or rim then step up a tyre size. If you reach the minimum PSI of the tyre then drop down a tyre size. The maximum & minimum load of the tyre is directly proportional to the size of the tyres contact patch at 10% droop.

Two interesting points:
- It's completely independent of the wheel radius which kind of blows the whole volume theory out the water.
- You can't apply this rule of thumb or a similar one to car tyres.

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.