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Old 10-29-2008, 12:15 PM   #21 (permalink)
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^^ The data shows no reason for there to be a knee in the curve. It's shows there is no correlation between contact patch and stopping distance - we could have just believed what we learned in our physics classes, but it's nice to have an excuse to play with our toys {err, cars}.

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Old 10-29-2008, 12:20 PM   #22 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
^^ The data shows no reason for there to be a knee in the curve.
The data also shows ABSOLUTELY no reason to believe that there is NOT a "knee in the curve". The experience of every person that I've known that races is that there is a sweet spot on the pressure curve. A change of 1psi from that sweet spot can result in a second or more lost on a one-minute track. Lap Time is inversely proportional to grip. PERIOD.
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Old 10-29-2008, 12:57 PM   #23 (permalink)
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Quote:
Originally Posted by MazdaMatt View Post
Lap Time is inversely proportional to grip. PERIOD.
Grip is proportional to static Mu (mechanical system properties of rubber/road) and mass... Period... (<--or three of them )

Therefore

Lap time is inversely proportional to Mu and mass....
^I'm not seeing contact patch here.

Unless you're talking about drag racing... In which tires are designed to rely heavily on adhesion under conditions road vehicles/tires won't see...
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Old 10-29-2008, 12:59 PM   #24 (permalink)
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Originally Posted by bikin' Ed View Post
.........

1) DOT tires are tested to carry 15% more pressure and weight than is listed on the sidewall.

........
Ed,

Where'd you get that one? That is just not true!!
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Old 10-29-2008, 01:04 PM   #25 (permalink)
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Treb,i don't get your last post... changing from the 'sweet spot" psi brings you away fromyour best lap times. Therefore there is a drop-off in grip above the sweet spot. Simple as that. Throwing in a bunch of physics terms doesn't make you right when you are using them wrong. Go to a performance school. Ask if you should gradually adjust your tire pressures to find the sweet spot, of if you should pump them up to 100psi for max grip.
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Old 10-29-2008, 01:53 PM   #26 (permalink)
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When the conditions of driving on the road match the conditions of driving on the track, I'll be doing that... This isn't the case.

As for using physics incorrectly - you need to correct me if you're going to claim it to be wrong Additionally, I am not throwing anything around in the sense that it's unnecessary. I only brought up applicable information. If you're not going to correct me while stating it's being used wrong, you're simply throwing it away
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Old 10-29-2008, 02:19 PM   #27 (permalink)
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The conditions on the track EXACTLY match those on the road when you need to use the maximum tire grip on the road, such as when you need to avoid running over a child. 4 wheels on an asphalt surface being asked to provide as much cornering or stopping force as possible.

Let me clarify. You differentiated Mu from contact patch. However, you did not realize that contact patch is only a side effect of inflation, but the relavent side effect of inflation is mechanical grip, which IS in your loose equation. So yes, Mu*mass is a loose representation of your grip, however Mu is very much dependant on tire pressures, though not necessarily contact patch.
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Old 10-29-2008, 02:37 PM   #28 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
.........

Grip is proportional to static Mu (mechanical system properties of rubber/road) and mass.

.......

Sorry, but tires do not conform to the classical physics interpretation of friction: F= uM (gee, I wish I could post Greek letters!!)

That's because the tread rubber penetrates the road surface texture. That results in a situation where the max grip is acheived at a percentage slip - which classical physics says is the regime of sliding friction (and at a value lower than static friction).

See figures 6.7 and 6.8

Tire Technology, excerpt no. 2 from The Racing & High-Performance Tire
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Old 10-29-2008, 03:19 PM   #29 (permalink)
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OK, I give up ..too much magic not enough engineering

Guys, I quit Ecomodders !

People who tell you that WAY overinflated tires dont wear abnormally are dreamers, liars or drive like grandma. Wanna really saves ga ? Remove the brakes from your car -thy're HEAVY - the handbrake will do...

NO, I quit THIS list, serious, evolving discussion does not seem possible here. It's like those HHO lists where people claim to ignore thesecond law of thermodynamics abd make a perpetual motion machine...cause they wanna !

I only wished that serious people here would start another list with engineering and safety minded ecomodder discussions.

Adieu !

Denis
Lion sur Mer
france
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Old 10-29-2008, 03:23 PM   #30 (permalink)
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But denis, way underinflated tires don't work as well as perfectly inflated tires. So way overinflated tires must be WAY better!

I'm going to chug 9 mugs of coffee, i'll be back in 5 minutes. I'll get SO much work done!

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