More Contact Patch!

For those who couldn't care less how their 356 left the factory!
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David Gilliland
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Re: More Contact Patch!

#16 Post by David Gilliland » Tue Aug 08, 2017 6:37 pm

Stability under braking may be improved but my 305/50/15s sure make my 63 T6 a handful in the rain. Braking or not..
David Gilliland
63 Outlaw Coupe

Edwin Ek
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Re: More Contact Patch!

#17 Post by Edwin Ek » Fri Jun 07, 2019 12:57 am

Martin Benade wrote:
Mon Jul 24, 2017 11:17 pm
In your mention of Pressure = force/area, I understand the area, but what are pressure and force relating to? May be a dumb question, but I don't know the answer and I am trying to improve my understanding.
Martin, apologies but I just saw your question. Imagine a 120 pound woman wearing high heels versus the same woman wearing tennis shoes (shoes with a flat sole). Force is the force of gravity, i.e. why the woman's weight is 120 pounds. By comparison, since gravity is weaker on the moon (the moon has less mass), the same woman would weigh 20 pounds.

Pressure is force/area or commonly psi, pounds per square inch. Force and pounds are not the same thing, but in this common usage they are treated equivalently.

Back to the woman wearing high heels or tennis shoes. She is much more likely to punch through a flimsy floor wearing high heels because of the great pressure at her small heels. The force (her weight) is the same, but the area (heels vs flat soles) is quite different. The greater pressure overwhelms the integrity of the floor.

In car tires, the woman is the car and the shoes are the tires. I hope this is helpful.

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Harlan Halsey
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Re: More Contact Patch!

#18 Post by Harlan Halsey » Fri Jun 07, 2019 3:41 am

You fellows might find Paul Haney's book, "The Racing and High Performance Tire" subtitled, "Using Tires to Tune For Grip And Performance" illuminating.

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David Jones
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Re: More Contact Patch!

#19 Post by David Jones » Fri Jun 07, 2019 9:40 am

Read "The unfair advantage" by Mark Donahue. His dissertation on tires is illuminating. Wider can be better but one has to keep in mind not just contact patch but also tire compounds and how they react. Old wide tires with degraded rubber are going to be worse than new narrow tires. Way back in the 60's when rally cars were beginning to run special tires for stages I remember Saab using narrow 165 x 15 tires on their cars in the Monte Carlo rally and they ran away with it on the snowy stages because their tires bit through the snow and the oppositions wider tires just slid over the top. I would never go wider than 185 on a 356 because the car is just not heavy enough to justify that width and the degradation in road feel is not worth it. I like the way the car feels on 165's with less than 100 hp.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
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Robert Reed
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Re: More Contact Patch!

#20 Post by Robert Reed » Sat Jun 08, 2019 10:20 pm

Hey Guys;
You may want to think of it this way in regards to the contact patch...
The tire pressure being the main reason for the patch area.
Let’s say that the rear tire weighs 600 pounds sitting on the ground, if you put 25psi into that tire it should create a patch that is 24 square inches, (25/600=24).
Now pump it up to 30psi your patch actually shrinks to 20 square inches (30/600=20)
Hopefully that clears that part of the equation, it really is pounds per square inch.

Douglas Madsen
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Re: More Contact Patch!

#21 Post by Douglas Madsen » Sun Jun 09, 2019 7:47 am

Here is a tire data calculator that includes tire patch information.


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