Question about spinning?
10-24-02, 11:19 PM
#2
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Crowned roadway so the rain runs off of it, and after being stationed at Ft. Campbell, I know you get a lot of that!
Anyway, crowned road, gravity, and dynamic friction instead of static friction for the rear wheels, so they slip sideways down hill.
Anyway, crowned road, gravity, and dynamic friction instead of static friction for the rear wheels, so they slip sideways down hill.
10-25-02, 12:07 AM
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OK, I'll try.
The roadway is crowned so the rain runs off. Even it it looks flat, it really isn't or else the rain would puddle in the middle, so there is a very small slope to the right.
So ordinarily when a wheel is rolling, it is rolling without slipping. This means that the relative velocity of the contact patch of the tire has the exact same velocity as the roadway that it is in contact with for that instant in time (meaning zero velocity....think about that for a second and let it boggle your mind. If your frame of reference is the road, and you chose a point on a wheel, it has a circular path right? meaning there is relative velocity between that point and the roadway, until it actually touches the road, at which point its instantaneous velocity must be zero....smack smack...sorry, back to english)
When two surfaces are in contact and have zero relative velocity, then they have STATIC friction between them. If two surfaces have relative velocity, then they have DYNAMIC friction. Static friction is always greater than dynamic friction, its a law of physics. Its approximately twice as great. If you have any doubt, try pushing your couch across the room. Its hard to get started, but once it starts moving it only takes about half as much force to keep it sliding. This is why anti-lock brakes work better. More braking force is achievable as long as the wheels have static friction with the road.
So you spin your tires really fast in second or third gear, and all the tires have is dynamic friction with the road, or half the traction that static friction provides. Since there is a very slight slope with a crowned road, your rear tires start to slide down hill, to the right.
This is even more pronounced in the snow, and I learned all about this my first winter driving at age 16.
The roadway is crowned so the rain runs off. Even it it looks flat, it really isn't or else the rain would puddle in the middle, so there is a very small slope to the right.
So ordinarily when a wheel is rolling, it is rolling without slipping. This means that the relative velocity of the contact patch of the tire has the exact same velocity as the roadway that it is in contact with for that instant in time (meaning zero velocity....think about that for a second and let it boggle your mind. If your frame of reference is the road, and you chose a point on a wheel, it has a circular path right? meaning there is relative velocity between that point and the roadway, until it actually touches the road, at which point its instantaneous velocity must be zero....smack smack...sorry, back to english)
When two surfaces are in contact and have zero relative velocity, then they have STATIC friction between them. If two surfaces have relative velocity, then they have DYNAMIC friction. Static friction is always greater than dynamic friction, its a law of physics. Its approximately twice as great. If you have any doubt, try pushing your couch across the room. Its hard to get started, but once it starts moving it only takes about half as much force to keep it sliding. This is why anti-lock brakes work better. More braking force is achievable as long as the wheels have static friction with the road.
So you spin your tires really fast in second or third gear, and all the tires have is dynamic friction with the road, or half the traction that static friction provides. Since there is a very slight slope with a crowned road, your rear tires start to slide down hill, to the right.
This is even more pronounced in the snow, and I learned all about this my first winter driving at age 16.
10-25-02, 12:38 AM
#6
English for the "cornfed boys":
The road is curved (crowned) to drain water to the sides.
If you put a puddle of water, it will drain to the lowest point because of gravity.
When your tires are spinning, they offer no traction, so your car acts just like that "puddle" and will drift to the lowest point on the road.
You drive on the right side, so you will pull to the right.
The road is curved (crowned) to drain water to the sides.
If you put a puddle of water, it will drain to the lowest point because of gravity.
When your tires are spinning, they offer no traction, so your car acts just like that "puddle" and will drift to the lowest point on the road.
You drive on the right side, so you will pull to the right.
10-25-02, 12:40 AM
#7
Makes you wonder why they slope the fast lane so much, esp. coming around a gradual turn on the hiway... I see it all the time cars slide right off the road.. Stupid engineers.
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10-25-02, 12:54 AM
#8
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Originally posted by Suparslinc
Makes you wonder why they slope the fast lane so much, esp. coming around a gradual turn on the hiway... I see it all the time cars slide right off the road.. Stupid engineers.
Makes you wonder why they slope the fast lane so much, esp. coming around a gradual turn on the hiway... I see it all the time cars slide right off the road.. Stupid engineers.
What do you think is worse, haveing a crowned road that upsets your center of gravity somewhat, or a puddle in the middle of the roadway that is guarenteed to ruin your traction, and will eventually damage the pavement and create potholes, costing $$$$$ to repair?
10-25-02, 01:59 AM
#10
Originally posted by Strider
As an engineer I take exception What do you think is worse, haveing a crowned road that upsets your center of gravity somewhat, or a puddle in the middle of the roadway that is guarenteed to ruin your traction, and will eventually damage the pavement and create potholes, costing $$$$$ to repair?
As an engineer I take exception
What do you think is worse, haveing a crowned road that upsets your center of gravity somewhat, or a puddle in the middle of the roadway that is guarenteed to ruin your traction, and will eventually damage the pavement and create potholes, costing $$$$$ to repair?
of
tire wear + steering box wear+ LSD wear + head-on collision repair (not to mention loss of life) + median barrier damages
compared to:
pothole repair + brainy engineer salary
J/K J/K
10-25-02, 02:40 AM
#11
Is that all that contributes to the pull to one side? I was always under the impression that there was the additional rotational force of the engine that acted on the rear end.
Looks like I'll be doing some tire spinnin' in the center and on the left hand side of the road to test it.
Looks like I'll be doing some tire spinnin' in the center and on the left hand side of the road to test it.
10-25-02, 07:51 AM
#14
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like nimrod said, if this happens on the left side wont it pull to the left. i understand what yall are saying.. but awhile back in some rain, i was going down the center of a road and ran 1st to about 5500 and dumped into second and started spinning, but the rear went both ways. i was around 6200-6600 spinning and it went to the right first, then came back to the left for a little, then went straight. i have done burnouts in dirt before, and it does go straight (guess there was no slope)
i agree with S2-13BT, it just does
i agree with S2-13BT, it just does
10-25-02, 09:19 AM
#15
84SE-EGI helpy-helperton
Gyroscopic precession from the rotating engine components, driveshaft, rear differential (except LSD), and wheel/tire unsprung weight contributes to this, also, even on smooth, even, paved roadways.
I will agree, however that it's most likely due to road camber and a reduced coefficient of sliding friction from a tire rapidly accelerating beyond the limit of adhesion, especially shifting to 2nd or 3rd. 1st gear starts will normally spin straight ahead, as you haven't overcome the static friction, yet. HTH,
I will agree, however that it's most likely due to road camber and a reduced coefficient of sliding friction from a tire rapidly accelerating beyond the limit of adhesion, especially shifting to 2nd or 3rd. 1st gear starts will normally spin straight ahead, as you haven't overcome the static friction, yet. HTH,
10-25-02, 11:00 AM
#17
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Not sure if this will help any, but do a burnout
(sitting still) and see if the car goes sideways. Which ever way the *** end goes you need to preload the spring on that side some. My mustang had this problem, got an airbag and kept adding air till it did nice burnouts. Once I got that figured out the 60' dropped into the 1.5's and it lauches nice and straight. Also when it loses traction going down the street it goes nice and straight. Not that instantly looking out the passenger window stuff
(sitting still) and see if the car goes sideways. Which ever way the *** end goes you need to preload the spring on that side some. My mustang had this problem, got an airbag and kept adding air till it did nice burnouts. Once I got that figured out the 60' dropped into the 1.5's and it lauches nice and straight. Also when it loses traction going down the street it goes nice and straight. Not that instantly looking out the passenger window stuff
10-25-02, 12:28 PM
#18
Tennis, anyone
I have to ask. Mike, car has LSD ? Thats how 'most' rear wheel drive cars 'act' with 300 + hp . Try this,,, next time
your gonna launch from a dead dig,start at the line, put it in reverse , and back up some first, then move back up to the line, It's kinda like winding up a spring, and see what happens The crowned road could be it too.
Here we find ourselves fighting gravity, with the wheel(s) spinning there is no resistance , so it slips downhill,
just like the water would. take a drop of water, and drop it on your arm, what happens ?? it rolls off the side that is steeper/the less resistance.
your gonna launch from a dead dig,start at the line, put it in reverse , and back up some first, then move back up to the line, It's kinda like winding up a spring, and see what happens The crowned road could be it too.
Here we find ourselves fighting gravity, with the wheel(s) spinning there is no resistance , so it slips downhill,
just like the water would. take a drop of water, and drop it on your arm, what happens ?? it rolls off the side that is steeper/the less resistance.
10-25-02, 12:49 PM
#19
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To add a bit to what Eville140 said: When you apply torque to the rear axle from the drive shaft, it will cause one end of the drive shaft to be forced down and the other end up. The force that is pushing down on the drive axle will cause one end to get more traction and it will push one side of the car harder than the other end gets pushed. What Eville is talking about is changing the corner weights on the car-this is what the Nascar guys are always talking about-to make the car looser or tighter in the corners. If there is more weight on the RR it will tend to make the back end of the car move right when it has less than full static friction. This will make a left turning stock car oversteer more. A road racing car should have the corner weights adjusted so that it is balanced turning either direction with your butt in the driver's seat (There could be a big difference between a scrawny little 135 pound guy and a 6'2" lard *** like me). A drag car is adjusted to get a straight ahead launch.
Don
P.S. I'd love to hear Strider convert this into Engineerese-it makes me all quivery inside when I hear that kind of talk.
Don
P.S. I'd love to hear Strider convert this into Engineerese-it makes me all quivery inside when I hear that kind of talk.
10-25-02, 04:14 PM
#21
Originally posted by mark perez
I have to ask. Mike, car has LSD ? Thats how 'most' rear wheel drive cars 'act' with 300 + hp . Try this,,, next time
your gonna launch from a dead dig,start at the line, put it in reverse , and back up some first, then move back up to the line, It's kinda like winding up a spring, and see what happens The crowned road could be it too.
Here we find ourselves fighting gravity, with the wheel(s) spinning there is no resistance , so it slips downhill,
just like the water would. take a drop of water, and drop it on your arm, what happens ?? it rolls off the side that is steeper/the less resistance.
I have to ask. Mike, car has LSD ? Thats how 'most' rear wheel drive cars 'act' with 300 + hp . Try this,,, next time
your gonna launch from a dead dig,start at the line, put it in reverse , and back up some first, then move back up to the line, It's kinda like winding up a spring, and see what happens The crowned road could be it too.
Here we find ourselves fighting gravity, with the wheel(s) spinning there is no resistance , so it slips downhill,
just like the water would. take a drop of water, and drop it on your arm, what happens ?? it rolls off the side that is steeper/the less resistance.
Hey randy when you wanna do some suspension and brake wrok to our cars? I wanna get mine done before the 'bodykit' LOL
10-25-02, 08:15 PM
#22
Originally posted by fmj355
To add a bit to what Eville140 said: When you apply torque to the rear axle from the drive shaft, it will cause one end of the drive shaft to be forced down and the other end up. The force that is pushing down on the drive axle will cause one end to get more traction and it will push one side of the car harder than the other end gets pushed.
To add a bit to what Eville140 said: When you apply torque to the rear axle from the drive shaft, it will cause one end of the drive shaft to be forced down and the other end up. The force that is pushing down on the drive axle will cause one end to get more traction and it will push one side of the car harder than the other end gets pushed.
10-25-02, 08:27 PM
#23
Could all this sidestepping be caused simply by an unequal suspension? Like a slightly stiffer spring on one side or something? Cause I do burnouts all the time in the TA and it stays pretty damn straight, unless i move the steering wheel. Strange...
10-26-02, 10:33 AM
#24
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Originally posted by LongDuck
Gyroscopic precession from the rotating engine components, driveshaft, rear differential (except LSD), and wheel/tire unsprung weight contributes to this, also, even on smooth, even, paved roadways.
I will agree, however that it's most likely due to road camber and a reduced coefficient of sliding friction from a tire rapidly accelerating beyond the limit of adhesion, especially shifting to 2nd or 3rd. 1st gear starts will normally spin straight ahead, as you haven't overcome the static friction, yet. HTH,
Gyroscopic precession from the rotating engine components, driveshaft, rear differential (except LSD), and wheel/tire unsprung weight contributes to this, also, even on smooth, even, paved roadways.
I will agree, however that it's most likely due to road camber and a reduced coefficient of sliding friction from a tire rapidly accelerating beyond the limit of adhesion, especially shifting to 2nd or 3rd. 1st gear starts will normally spin straight ahead, as you haven't overcome the static friction, yet. HTH,
10-26-02, 05:27 PM
#25
Originally posted by JEC-31
Also a tiny increment of streering will multiply quickly to going sideways if you're spinning fast enough. And with your setup, Mike-P28, you are probably well past the fast-enough mark.
Also a tiny increment of streering will multiply quickly to going sideways if you're spinning fast enough. And with your setup, Mike-P28, you are probably well past the fast-enough mark.
Well I noticed randy's 2.3 L turbo FB does it, the mustang I was racing that nite did it. So i know its not a rotary only thing.. Or a Rx-7 only thing for that matter...
I do need some new suspension components tho, but baby steps, baby steps LOL
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