Rubbing the tire on the road, is it really mathematically simple?

When I was in high school I was taught, or I read, that it's bad to turn
the steering wheel when the car is not moving. It's hard on the front
tires, wears out the tread, and one should be moving the car at least a
little when turning the wheel. Did they say that? Do they still?
I've been thinking about this and now I have doubts.
Seems to me any extra wear on the tread because of turning the direction
in which the tires point will be the same whether the car is moving or
still. It's harder to relate to the sliding motion of the tire on the
road surface when the car is moving, but it's clear when the car is
still. That seems to me to be the difference, but the vectors that
indicate rubbing seem the same either way.
I included the math group first because it seems like they would have
opinions.
Reply to
micky
obviously all the wear is on one spot on the tire
na, it is distributed all along the tire face, not in one spot
Reply to
SergIo
micky amok-crossposted to sci.math, sci.physics, and rec.autos.tech: ^^^^^ Please post here using your real name.
Yes, of course. However, this is just a rule of thumb; the amount of wear depends on the surface and the type of tread. For example, the wear from turning a still tire on ice or snow is negligibly small compared to the turning on asphalt.
You have not thought this through.
It is not. When the car is moving relative to the ground surface (road), and the wheel and tire are rotating the tire?s tread is experiencing mostly rolling resistance/friction/drag with the road. When the car is at rest relative to the road, if the wheel is turned, the tread is experiencing mostly kinetic friction with the road.
The magnitude of the friction (a force) between two surfaces is calculated as the friction coefficient (commonly: µ, mu) for the contact of the two surfaces for the respective situation times the magnitude of the normal force F_n on the body with significantly less mass (lighter body):
F_f = µ F_n,
whereas
F_n = F_g cos ? = m g cos ?
is the force with which a body is pressed against the ground surface by gravity (actually the force that the ground surface must exert on the lighter body to prevent it from continuing to fall freely towards the center of energy?momentum of the heavier body, e.g. the center-of-mass of Earth).
? is then the angle of the ground surface to the tangent surface of the heavier body:
. :`. : `. : `. : `. m : `* cos(?) = F_n/F_g : F_n .^:`. F_n = F_g cos(?) : .' ?: `. : .' : `. : `. : F_g `. : `. : `. : `.: `. ^ :__ v `. : n __ : | ?`. : |PE '--------------------------`----'--
(? = 0 ? F_n = F_g cos(0) = F_g × 1 = F_g as expected, so this works.)
The coefficient of rolling resistance is generally much smaller than that of kinetic friction ? which is why the wheel was invented in the first place. For example, the coefficient of kinetic friction for car tire rubber on concrete is 0.6 to 0.85, while the coefficient of rolling resistance is only 0.01 to 0.015.
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For a car that has an average mass of 1 metric ton, on a horizontal road that makes a difference of friction of at least
F_fs = µ_s m g = 0.6 × m g = 0.6 × 1'000 kg × 9.82 m/s² ? 5'892 N
to
F_fr = µ_r m g = 0.01 × 1'000 kg × 9.82 m/s² ? 98.2 N,
i.e. at least 60:1. The greater the friction, the greater the wear. So, roughly speaking, turning a still tire wears it off 60 times more than turning it while driving, which means that its lifetime is reduced to 1/60 of its normal lifetime if this would be done continuously.
A tire is usually *rolling*, NOT sliding, on the road surface.
[If it would be sliding, then the respective vehicle would be out of control. One possibility for this condition is aquaplaning: the tire is sliding on the water on the road instead of rolling in proper contact with the road. Tires with a pronounced profile and suitable tread pattern reduce or avoid aquaplaning as the water can be displaced into the tread pattern so that the tire keeps in contact with the road.
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Most certainly they are not. In the rolling case there is an additional non-zero force vector in the direction of the wheel?s axial rotation:
___ ___ : : : : : .-:----> F_fk : -------> F_fk = F_res ^ : : : F_fr : : : : : : : =:=*=:= =:=*=: : : : : : : : : : : : : : : : : :___: :___:
rolling, at rest, turning left turning left
(friction is always opposite to the direction of motion)
Since the tread profile is optimized for the wheel rolling in the direction of axial rotation, NOT sliding, sidewards sliding of the tire at rest is detrimental to the lifetime of the tire and quality of the tread, particularly when the vehicle has a great mass and it is done on a horizontal road (as then the friction is greater; see above). Also, one can imagine that the greater torque required to turn a still wheel (to work against the greater friction) produces additional stress and wear for the steering.
Please do not do that again.
?No article in the world is relevant for more than a few newsgroups. If World War ? is announced, it will be announced in news.announce.important.?
?attributed to Peter da Silva
F?up2 sci.physics
Reply to
Thomas 'PointedEars' Lahn
Paul in Houston TX amok-crossposted: ^^^^^^^^^^^^^^^^^^ Please post here using your real name, ?Paul in Houston TX? #74656.
What is the basis for your assumption?
F?up2 sci.physics
Reply to
Thomas 'PointedEars' Lahn
A lot of stuff you learn in high school is theoretical and a lot of the times not practical. As a practical matter, most times you can avoid turning the front tires while stopped. Sometimes you can't. All the math and theory in the world won't change that fact. Don't worry about this and be grateful that you have power steering. As they say, don't sweat the small stuff.
Reply to
dsi1
More importantly, it's hard on the steering linkage, which tends to be a lot more expensive to replace.
Mind you, with modern power steering, clueless drivers, and longer warranties, manufacturers have probably beefed up that part of the mechanism.
Still, when you trust your life to a machine, treating it well seems like a no-brainer.
Sylvia.
Reply to
Sylvia Else
What they really say; Don't sweat the petty things but don't get caught petting the sweaty things.
Reply to
Xeno
My method of avoiding excessive tire slippage when parallel parked is to use a floor jack to lift the front tires off the ground and swing the entire front end clear of the car in front. This saves excessive strain on the tires, steering linkage, the steering rack, and the power steering pump. Never having to replace the entire front suspension is pretty much a no-brainer. Thanks to years of practice, I can pull out of a space in only 2 minutes!
Reply to
dsi1
If it was so hard on the steering, manufacturers would never have fitted power steering to cars.
Nope, the parts were sufficiently strong enough before the advent of power steering.
All driving instructors (should) tell their students to roll the car fore or aft slightly when turning the steering. It is amazing just how much of a difference that makes to steering effort. What you are effectively doing is transferring the energy to the tread blocks and they are sufficiently flexible enough to absorb the energy involved. After all, it's the tread blocks that are giving you slip angles at higher road speeds.
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Reply to
Xeno
power steering is force multiplier, makes it easier to steer.
but along the way companies cheapend out the power steering, mostly the pump, and it is less reliable, in some cars not replaceable if it breaks, you can only get another from a junk yard and put it in, but it is just as bad, plastic tanks that crack....
true, I think all cars have power steering now, know of any that do not ?
Reply to
sergIo
When you are driving along the road, the tread stays gripped to the road surface. If it didn't you would be in deep shit at the first corner. At speed, any speed, the tread blocks are sufficiently flexible to allow the wheels a small change in steering angle yet still remain gripping the road surface.
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Rather than opinions, I'll direct you to relevant texts on the topic;
Tires, Suspension and Handling, Second Edition John C Dickson
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This text covers the subject in more detail;
Steering Handbook Editors: Manfred Harrer, Peter Pfeffer
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Chapters 1 through 5 should more than adequately cover your needs.
If you really want to delve heavily into the mathematics of it all, then this book should do it;
The Automotive Chassis Engineering Principles, 2nd Edition J Reimpell, H Stoll, J.W. Betzler
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The above cover steering, including tyres, from an engineering perspective and I suspect that's what you're after. The Along the way you'll get a good grounding on all the effects of steering geometry.
Reply to
Xeno
Plastics are the *new vanguards of planned obsolecence*.
Wide tyres, powerful engines and front wheel drive, with attendant torque steer, have guaranteed it.
Reply to
Xeno
Too slow. Go electric built-in. How to park in tight spaces -
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Faster way to get out of tight spaces -
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Reply to
Sanity Clause
Japanese slider cars. Yonaguni, Okinawa, Japan received 14.4 inches of rain in 6 hours.
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Good for sliding cars.
Reply to
allisellis851
I just got home and I have time now to read this detailed answer carefully, but it's been two weeks and many may miss my answer now, let alone if I wait longer, so this reply just addresses non-technical points.
To comment on the technical points of this and a post by Xeno, I have to read the links. That will take a few more days.
In sci.math, on Sun, 12 May 2019 01:14:45 +0200, Thomas 'PointedEars'
Sure, but I was figuring "all things being equal".
"Mostly rolling", but if you integrate the sliding** portion over the time the wheels are being turned, I think the amount will equal no matter whether the car is going quickly, slowly, or not at all.
**kinetic friction you call it.
Maybe entirely.
Sorry, I can't abide by your request. People from the math group red my first question and they are interested in all the answers. Especially since you put so much effort into this one, I'd think you'd want anyone who might be interested to see it.
Plus I think it's a violation of Usenetiquette to drop groups. Were that done in 2 or 3 of the 3 groups I posted to, I'd have to read all 3 groups to see all the answers.
I dont' know who he is, but even if he's right, I only posted to 3 newsgroups.
Reply to
micky
The point is that when you steer the car while rolling, there is actually no sliding involved, or at least quite a bit less. This answer would be different if you were talking about a metal or wooden wheel. But when you turn a wheel with a rubber tire, the rubber tire twists. One way you can look at it is that the tread of the tire that is in contact with the asphalt is still aligned straight ahead, while the tread in front of that patch is angled to the left. There is indeed heating of the tire that comes from such distortion if the rubber, but this is quite distinct from the tire tread sliding against asphalt, which it doesn?t do.
A simple thing to notice is the sound your tire makes when you lock the brakes at low speed, which IS a case of kinetic friction. Do the tires make that noise when you make a rolling turn? Try it.
Reply to
Odd Bodkin
In sci.math, on Sun, 12 May 2019 01:26:41 +0200, Thomas 'PointedEars'
Hmm. That sounds right.
"Total tire wear would be the same". That's because of the law of conservation of tire wear. Or, iow, one does't get something for nothing so the wear would have to be the same. Or greater, but I don't see why it would be greater.
When the car is not moving, all the wear would be in one place, but surely when it's moving, the wear would be spread around the circumference of the tire.
I put back the other two groups. Otherwise I, and everyone else, has to read all three newsgroups to see all the answers.
Reply to
micky

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