17" vs 18" with racing in mind. . .
02-20-04, 03:09 PM
#126
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A huge key point that we never really thought of (but which was spoken of by the other people) is the concept of frictional mu going DOWN as force goes up. This is unintuitive in that it doesn't follow the increasing mu paradigm.
"For rubber tires, the coefficient of friction decreases with contact
forces. The net effect is that past a certain load, the frictional
force needed to overcome inertia of a cornering automobile cannot
keep up with the centrifugal force. This means that the heavier the
car, the worse it corners on the same size tires. This makes sense
from experience, but not necessarily from physics. Again, the reason
behind it is that the coefficient of friction of tires drops with
increasing load.
This means that if you want to corner harder, you need more surface
area to decrease the contact pressure, and hence get wider tires."
We never really thought of that... so, in closing..
WE WIN, Damon LOSES.
(kidding)
"For rubber tires, the coefficient of friction decreases with contact
forces. The net effect is that past a certain load, the frictional
force needed to overcome inertia of a cornering automobile cannot
keep up with the centrifugal force. This means that the heavier the
car, the worse it corners on the same size tires. This makes sense
from experience, but not necessarily from physics. Again, the reason
behind it is that the coefficient of friction of tires drops with
increasing load.
This means that if you want to corner harder, you need more surface
area to decrease the contact pressure, and hence get wider tires."
We never really thought of that... so, in closing..
WE WIN, Damon LOSES.
(kidding)
02-20-04, 03:27 PM
#130
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Originally posted by clayne
Let's have some healthy post-debate desert, shall we?
Let's have some healthy post-debate desert, shall we?
02-20-04, 03:54 PM
#131
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Originally posted by DamonB
Didn't you learn the difference between "desert" and "dessert" in school? "Desert" is the dry place with all the sand. "Dessert" is what you get after dinner. The way you remember is that you always want two desserts (it's got two s's). Get it?
Didn't you learn the difference between "desert" and "dessert" in school? "Desert" is the dry place with all the sand. "Dessert" is what you get after dinner. The way you remember is that you always want two desserts (it's got two s's). Get it?
02-21-04, 09:23 PM
#132
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Originally posted by SleepR1
You start this whole damn controversy, and this is all you have to add to the fray?
You start this whole damn controversy, and this is all you have to add to the fray?
To be honest, given the discussion that ensued, I think I did good. A lot of relevant discourse, and thinking. But in the end, we are pretty much back to wider is better....
Last edited by PVerdieck; 02-21-04 at 09:29 PM.
02-21-04, 10:13 PM
#133
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Originally posted by PVerdieck
A lot of relevant discourse, and thinking. But in the end, we are pretty much back to wider is better....
A lot of relevant discourse, and thinking. But in the end, we are pretty much back to wider is better....
02-26-04, 10:54 AM
#134
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Some thoughts on tire width from Mark Ortiz. Ortiz is a respected racecar engineer and a noted contributor to Racecar Engineering magazine. His entire list of articles is in the Suspension and Handling Links sticky.
Mark Ortiz on tire width
More thoughts from Ortiz on weight distribution
Mark Ortiz on tire width
More thoughts from Ortiz on weight distribution
02-26-04, 07:27 PM
#135
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In the first link, Mark Ortiz doensn't provide much data...mostly his experiences and common sense. That's not good enough for us scientists/engineers. I think we all agree that wider tires are needed for cornering, but it's not so simple when considering longitudinal forces is it?
I couldn't open the second link, so I can't comment on the weight distribution piece.
I couldn't open the second link, so I can't comment on the weight distribution piece.
Last edited by SleepR1; 02-26-04 at 07:30 PM.
04-08-04, 06:54 AM
#138
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Paul Haney's book "The Racing and High Performance Tire" is highly recommended; it's in our Suspension and Handling Links sticky.
Paul has this to say about tires with short, wide contact patches (wide tires) vs. tires with tall, narrow contact patches (larger diameter, narrow tires):
"In the section on lateral tread deformation we showed that deformation builds up along the length of the contact patch until the restoring force of the tread and carcass exceeds tread grip and sliding begins. A shorter contact patch at the same slip angle begins to slip at roughly the same distance from the leading edge (of the contact patch) as with a longer contact patch. But the shorter contact patch has more of its length stuck to the road than the longer, narrower patch; and therefore a larger portion of its overall area is gripping. A larger portion of contact patch area gripping means more total grip. So for the same load and same slip angle, a wider contact patch generates more grip than a narrow contact patch."
What's being said is that even if the area of the contact patches is the same in the wide vs narrow tire, the wide tire will still generate more grip because its contact patch does not have to distort as much as the tire rolls through a turn (slip angle) because the wide tires' contact patch is in fact short and wide vs tall and narrow. The tall, narrow patch MUST have much more distortion in it when an angle of slip is introduced (turning).
Paul has this to say about tires with short, wide contact patches (wide tires) vs. tires with tall, narrow contact patches (larger diameter, narrow tires):
"In the section on lateral tread deformation we showed that deformation builds up along the length of the contact patch until the restoring force of the tread and carcass exceeds tread grip and sliding begins. A shorter contact patch at the same slip angle begins to slip at roughly the same distance from the leading edge (of the contact patch) as with a longer contact patch. But the shorter contact patch has more of its length stuck to the road than the longer, narrower patch; and therefore a larger portion of its overall area is gripping. A larger portion of contact patch area gripping means more total grip. So for the same load and same slip angle, a wider contact patch generates more grip than a narrow contact patch."
What's being said is that even if the area of the contact patches is the same in the wide vs narrow tire, the wide tire will still generate more grip because its contact patch does not have to distort as much as the tire rolls through a turn (slip angle) because the wide tires' contact patch is in fact short and wide vs tall and narrow. The tall, narrow patch MUST have much more distortion in it when an angle of slip is introduced (turning).
04-08-04, 01:08 PM
#141
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okay...
I have the 17" CCW with 275/40/17
and my friend has the 18" CCW with 285/30/18
His wheelset is faster whether they are on my car or his car.
Oh yea, its on autocross. A timed event.
I have the 17" CCW with 275/40/17
and my friend has the 18" CCW with 285/30/18
His wheelset is faster whether they are on my car or his car.
Oh yea, its on autocross. A timed event.
02-14-06, 03:29 PM
#144
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Yet more from Mark Ortiz on wide tires
Excerpt from Ortiz:
Okay, summing up, what does a wider tire get us?
1. It runs cooler, and/or
2. it makes more efficient use of its contact patch by having a greater percentage adhering, and/or
3. it can run at lower inflation pressure and therefore actually have a larger contact patch, and/or
4. it can have greater lateral stiffness at a given pressure and therefore keep its tread planted better, and/or
5. it can use a softer, stickier, faster-wearing compound without penalty in longevity.
Note that most of these effects in turn play off against each other. We can blend and balance them, and get a tire that is somewhat cooler-running, has a somewhat lower operating pressure and somewhat larger contact patch, has somewhat greater lateral stiffness, and survives long enough with a somewhat stickier compound, all at the same time. That would explain an improvement in grip, wouldn’t it?
Excerpt from Ortiz:
Okay, summing up, what does a wider tire get us?
1. It runs cooler, and/or
2. it makes more efficient use of its contact patch by having a greater percentage adhering, and/or
3. it can run at lower inflation pressure and therefore actually have a larger contact patch, and/or
4. it can have greater lateral stiffness at a given pressure and therefore keep its tread planted better, and/or
5. it can use a softer, stickier, faster-wearing compound without penalty in longevity.
Note that most of these effects in turn play off against each other. We can blend and balance them, and get a tire that is somewhat cooler-running, has a somewhat lower operating pressure and somewhat larger contact patch, has somewhat greater lateral stiffness, and survives long enough with a somewhat stickier compound, all at the same time. That would explain an improvement in grip, wouldn’t it?
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