Is it possible for a truck that is traveling at a constant 100km/h to have a wheel detach and the wheel travels faster than the truck for a period?
Assume instant detachment of the wheel. The truck does not change speed after detachment.
Would it change things if the wheel is on a driven axle or a lazy axle?
Would it change things if the truck was accelerating or braking?
Stealth said:
Is it possible for a truck that is traveling at a constant 100km/h to have a wheel detach and the wheel travels faster than the truck for a period?
Under the circumstances described, no.
Assume instant detachment of the wheel. The truck does not change speed after detachment.
Would it change things if the wheel is on a driven axle or a lazy axle?
Would it change things if the truck was accelerating or braking?
If the truck were braking at the time of detachment, under most circumstances, the wheel would overtake the truck, since it would retain the momentum (and thus speed) it had when it detached, while the truck would slow down.
It all does depend on whether the wheel stays upright. The vehicle will be slowing due to the drag. If the wheel can go on rolling it will often travel further than the vehicle.
roughbarked said:
It all does depend on whether the wheel stays upright. The vehicle will be slowing due to the drag. If the wheel can go on rolling it will often travel further than the vehicle.
if it detaches at 100kph, gyroscopic forces will ensure that..
stumpy_seahorse said:
roughbarked said:
It all does depend on whether the wheel stays upright. The vehicle will be slowing due to the drag. If the wheel can go on rolling it will often travel further than the vehicle.
if it detaches at 100kph, gyroscopic forces will ensure that..
Yes, unless it striks an obstacle on the way.
Anecdote, my MiL was driving when a wheel detached from an oncoming car on the Nullabor. She must have been mesmerised by it as she allowed it to take out the radiator rather than take evasive action. Though that may be a harsh assessment because I wasn’t behind the wheel. There may not have been any apparent evasive action to take.
Assuming a road without significant bumps, the acceleration of the truck becomes significant.
If the truck has positive acceleration all of the force causing that acceleration comes from the interface between the tyres and the road. This causes deformation in the tyre, with associated strain energy.
At the instant the wheel becomes disconnected the forward force on the wheel will be unchanged, but the connected mass will reduce by a factor of Truck mass/Wheel mass, so the wheel acceleration will increase dramatically. The force on the truck will reduce by half (assuming two drive wheels), but its mass will hardly change, so its acceleration will reduce by half.
The wheel will continue to accelerate until all the strain energy is converted either into kinetic energy or heat, and since rubber has a very high strain energy capacity this will give the wheel a large additional velocity, before it starts to slow down.
By similar reasoning, if the truck is braking, the wheel would slow down rapidly after detachment, and might even go into reverse.
This is all hypothesis by the way, I haven’t checked if that is really what truck wheels do.
roughbarked said:
stumpy_seahorse said:
roughbarked said:
It all does depend on whether the wheel stays upright. The vehicle will be slowing due to the drag. If the wheel can go on rolling it will often travel further than the vehicle.
if it detaches at 100kph, gyroscopic forces will ensure that..
Yes, unless it striks an obstacle on the way.
Anecdote, my MiL was driving when a wheel detached from an oncoming car on the Nullabor. She must have been mesmerised by it as she allowed it to take out the radiator rather than take evasive action. Though that may be a harsh assessment because I wasn’t behind the wheel. There may not have been any apparent evasive action to take.
nope, even if it hits a bump or slope. at that speed, it will be sure to stay upright…
https://www.youtube.com/watch?v=OO1NFrBeaBE
The Rev Dodgson said:
Assuming a road without significant bumps, the acceleration of the truck becomes significant.If the truck has positive acceleration all of the force causing that acceleration comes from the interface between the tyres and the road. This causes deformation in the tyre, with associated strain energy.
At the instant the wheel becomes disconnected the forward force on the wheel will be unchanged, but the connected mass will reduce by a factor of Truck mass/Wheel mass, so the wheel acceleration will increase dramatically. The force on the truck will reduce by half (assuming two drive wheels), but its mass will hardly change, so its acceleration will reduce by half.
The wheel will continue to accelerate until all the strain energy is converted either into kinetic energy or heat, and since rubber has a very high strain energy capacity this will give the wheel a large additional velocity, before it starts to slow down.
By similar reasoning, if the truck is braking, the wheel would slow down rapidly after detachment, and might even go into reverse.
This is all hypothesis by the way, I haven’t checked if that is really what truck wheels do.
Yes most of the hypothesis looks good. Though if the wheel is braking before it detaches, there will be forces that most likely will cause it to topple and possibly bounce off some part of the vehicle. Which could point it in any direction.
stumpy_seahorse said:
nope, even if it hits a bump or slope. at that speed, it will be sure to stay upright…
Well, while it is still flat round and concentric, yes.
roughbarked said:
stumpy_seahorse said:nope, even if it hits a bump or slope. at that speed, it will be sure to stay upright…
Well, while it is still flat round and concentric, yes.
flat and concentric has nothing to do with it.
while it is still spinning on an axis is what will keep it upright
stumpy_seahorse said:
roughbarked said:
stumpy_seahorse said:nope, even if it hits a bump or slope. at that speed, it will be sure to stay upright…
Well, while it is still flat round and concentric, yes.
flat and concentric has nothing to do with it.
while it is still spinning on an axis is what will keep it upright
if flat and concentric don’t come into it then how is the axis there?
roughbarked said:
stumpy_seahorse said:
roughbarked said:Well, while it is still flat round and concentric, yes.
flat and concentric has nothing to do with it.
while it is still spinning on an axis is what will keep it upright
if flat and concentric don’t come into it then how is the axis there?
there is no rule that it must be flat and concentric to have an axis.
example, get a square of cardboard.
Poke a pencil through the centre and spin it like a top on the point of the pencil.
it will remain upright while it is still spinning sufficiently.
It is neither flat, nor concentric
Nice video ss.
Roughbarked, it will still maintain its angular momentum, no matter what shape it is, but what is going to make a tyre change into non-tyre shape anyway?
the rear wheel off my landrover overtook me. smartarse mate in cruiser reckoned it was the fastest he’d seen one move.
ChrispenEvan said:
the rear wheel off my landrover overtook me. smartarse mate in cruiser reckoned it was the fastest he’d seen one move.
Were you accelerating when it came off?
Actually thinking about it, you wouldn’t need to be accelerating. Just the force required to maintain constant speed of the vehicle would be enough to give a large acceleration to the tyre when it separated.
The Rev Dodgson said:
Assuming a road without significant bumps, the acceleration of the truck becomes significant.If the truck has positive acceleration all of the force causing that acceleration comes from the interface between the tyres and the road. This causes deformation in the tyre, with associated strain energy.
At the instant the wheel becomes disconnected the forward force on the wheel will be unchanged, but the connected mass will reduce by a factor of Truck mass/Wheel mass, so the wheel acceleration will increase dramatically. The force on the truck will reduce by half (assuming two drive wheels), but its mass will hardly change, so its acceleration will reduce by half.
The wheel will continue to accelerate until all the strain energy is converted either into kinetic energy or heat, and since rubber has a very high strain energy capacity this will give the wheel a large additional velocity, before it starts to slow down.
By similar reasoning, if the truck is braking, the wheel would slow down rapidly after detachment, and might even go into reverse.
This is all hypothesis by the way, I haven’t checked if that is really what truck wheels do.
I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
Brief discussion by some post-grad physicists here:
http://ask.metafilter.com/49668/Why-does-a-detached-tire-roll-faster-than-the-car
I reckon my engineer’s explanation is better than anything these so called scientists came up with :)
ChrispenEvan said:
the rear wheel off my landrover overtook me. smartarse mate in cruiser reckoned it was the fastest he’d seen one move.
As a very young lad on our way out to get mallee roots on a rough track, I was daydreaming out the window when sudden;ly a wheel rolled past us going way faster. I was watching it go and said to dad, “Someones wheel just went past”. He was hanging on to the steering wheel tight and said, “I know, it is ours”.
The Rev Dodgson said:
ChrispenEvan said:
the rear wheel off my landrover overtook me. smartarse mate in cruiser reckoned it was the fastest he’d seen one move.
Were you accelerating when it came off?
Actually thinking about it, you wouldn’t need to be accelerating. Just the force required to maintain constant speed of the vehicle would be enough to give a large acceleration to the tyre when it separated.
this. yep.
stumpy_seahorse said:
I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
The Rev Dodgson said:
Nice video ss.Roughbarked, it will still maintain its angular momentum, no matter what shape it is, but what is going to make a tyre change into non-tyre shape anyway?
Simply the tyre blowing out will change it’s shape and stuff.
Any spinning top will also topple if it bumps anything. The momentum may cause it to right itself, as has been said.
ChrispenEvan said:
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
OK that’s interesting. That doesn’t seem to fit with my strain energy hypothesis.
The Rev Dodgson said:
stumpy_seahorse said:I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
Yep. there isn’t much of that but on a laden truck it may be greater. If only for a nanosecond, the tyre stops on the surface, it will have some effect though momentum will still apply.
ChrispenEvan said:
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
I was a passenger in a beetle when the wheel came off.
The best thing about themwas the old style hubcaps, which contained the lug nuts and we were able to put the wheel back on after retrieving it from down the road.
Had a wheel come off the buggy when i was navigating at a scouts rally once, it skipped across the estuary and we had to go swimming to retrieve that one
The Rev Dodgson said:
ChrispenEvan said:
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
OK that’s interesting. That doesn’t seem to fit with my strain energy hypothesis.
The wheel, once disconnected spins faster due to release of strain hypothesis?
roughbarked said:
The Rev Dodgson said:
stumpy_seahorse said:I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
Yep. there isn’t much of that but on a laden truck it may be greater. If only for a nanosecond, the tyre stops on the surface, it will have some effect though momentum will still apply.
Why do you say there isn’t much. The force at the tyre/road interface is mass x acceleration (less a little bit for wind resistance).
The Rev Dodgson said:
stumpy_seahorse said:I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
there’s still between 3 and 9 tyres still on the road (depending on truck type) that would still be braking.
(ruling out brake lines being split in the process of the tyre detaching)
stumpy_seahorse said:
ChrispenEvan said:
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
I was a passenger in a beetle when the wheel came off.
The best thing about themwas the old style hubcaps, which contained the lug nuts and we were able to put the wheel back on after retrieving it from down the road.Had a wheel come off the buggy when i was navigating at a scouts rally once, it skipped across the estuary and we had to go swimming to retrieve that one
Watched a bloke in a Jag x10 come through a dip approaching me fast. All four of his hubcaps detached and went in all four directions just like in the cartoons.
The Rev Dodgson said:
roughbarked said:
The Rev Dodgson said:But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
Yep. there isn’t much of that but on a laden truck it may be greater. If only for a nanosecond, the tyre stops on the surface, it will have some effect though momentum will still apply.
Why do you say there isn’t much. The force at the tyre/road interface is mass x acceleration (less a little bit for wind resistance).
because of the actual contact area, which is very small.
roughbarked said:
The Rev Dodgson said:
ChrispenEvan said:
i was being towed. by the cruiser. the wheel overtook him. i would imagine that there would have been a slight slowing. but the wheel went past pretty instantaneously.
OK that’s interesting. That doesn’t seem to fit with my strain energy hypothesis.
The wheel, once disconnected spins faster due to release of strain hypothesis?
The “wheel acceleration comes from the strain energy due to drive force at the tyre/road interface” hypothesis.
stumpy_seahorse said:
The Rev Dodgson said:
stumpy_seahorse said:I think because the friction causing braking is on the axle, not the wheel, if braking when it detaches, it (the tyre)will retain momentum while the truck itself will slow
But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
there’s still between 3 and 9 tyres still on the road (depending on truck type) that would still be braking.
(ruling out brake lines being split in the process of the tyre detaching)
What happens to the rest of the vehicle doesn’t affect the separated wheel. It will still have a large deceleration force on a much reduced mass.
roughbarked said:
The Rev Dodgson said:
roughbarked said:Yep. there isn’t much of that but on a laden truck it may be greater. If only for a nanosecond, the tyre stops on the surface, it will have some effect though momentum will still apply.
Why do you say there isn’t much. The force at the tyre/road interface is mass x acceleration (less a little bit for wind resistance).
because of the actual contact area, which is very small.
The contact area has nothing to do with it. All of the braking force (other than wind resistance) comes through the tyre/road interface.
The Rev Dodgson said:
stumpy_seahorse said:
The Rev Dodgson said:But to slow the truck down there has to be an external force, and that comes from the tyre/road interface.
there’s still between 3 and 9 tyres still on the road (depending on truck type) that would still be braking.
(ruling out brake lines being split in the process of the tyre detaching)
What happens to the rest of the vehicle doesn’t affect the separated wheel. It will still have a large deceleration force on a much reduced mass.
there will be no deceleration force on it though as the brake will be either left on the truck, or free spinning with the wheel, not imparting friction on it to slow it down.
I think you were on the money with the higher torque:weight ratio of the wheel on its own compared to complete truck
The Rev Dodgson said:
roughbarked said:
The Rev Dodgson said:Why do you say there isn’t much. The force at the tyre/road interface is mass x acceleration (less a little bit for wind resistance).
because of the actual contact area, which is very small.
The contact area has nothing to do with it. All of the braking force (other than wind resistance) comes through the tyre/road interface.
Wish I could have told that to the bloke who tried to slap a circular saw to get the wobble out of it.
stumpy_seahorse said:
there will be no deceleration force on it though as the brake will be either left on the truck, or free spinning with the wheel, not imparting friction on it to slow it down.
I think you were on the money with the higher torque:weight ratio of the wheel on its own compared to complete truck
The same argument applies whether the force at the interface is forwards or backwards. At the moment of separation the mass greatly reduces, but there is still a force at the tyre/road interface because of the strain energy in the rubber.
The Rev Dodgson said:
roughbarked said:
The Rev Dodgson said:Why do you say there isn’t much. The force at the tyre/road interface is mass x acceleration (less a little bit for wind resistance).
because of the actual contact area, which is very small.
The contact area has nothing to do with it. All of the braking force (other than wind resistance) comes through the tyre/road interface.
how does all of the braking force come from the tyre/road interface?
Surely it starts at the point where the rotation speed of the tyre is reduced
stumpy_seahorse said:
how does all of the braking force come from the tyre/road interface?
Surely it starts at the point where the rotation speed of the tyre is reduced
If you look at the mass as being vehicle+tyres then to change the velocity of that mass you have to apply an external force, and that external force comes through the tyre/road interface. If the wheel starts to skid on a patch of ice with negligible friction then the wheel rotation will stop, but the velocity of the vehicle will be unchanged.
If you look at the mass as being vehicle+tyres then to change the velocity of that mass you have to apply an external force,
isaactly.
The Rev Dodgson said:
stumpy_seahorse said:there will be no deceleration force on it though as the brake will be either left on the truck, or free spinning with the wheel, not imparting friction on it to slow it down.
I think you were on the money with the higher torque:weight ratio of the wheel on its own compared to complete truck
The same argument applies whether the force at the interface is forwards or backwards. At the moment of separation the mass greatly reduces, but there is still a force at the tyre/road interface because of the strain energy in the rubber.
The Rev Dodgson said:
stumpy_seahorse said:how does all of the braking force come from the tyre/road interface?
Surely it starts at the point where the rotation speed of the tyre is reduced
If you look at the mass as being vehicle+tyres then to change the velocity of that mass you have to apply an external force, and that external force comes through the tyre/road interface. If the wheel starts to skid on a patch of ice with negligible friction then the wheel rotation will stop, but the velocity of the vehicle will be unchanged.
yes, but it will be the slowing (or speeding up in the case of acceleration) of the spinning momentum which causes the change in friction at the interface, you can’t have one without the other.
hence my questioning of your use of all of the braking force
The Rev Dodgson said:
stumpy_seahorse said:how does all of the braking force come from the tyre/road interface?
Surely it starts at the point where the rotation speed of the tyre is reduced
If you look at the mass as being vehicle+tyres then to change the velocity of that mass you have to apply an external force, and that external force comes through the tyre/road interface. If the wheel starts to skid on a patch of ice with negligible friction then the wheel rotation will stop, but the velocity of the vehicle will be unchanged.
roughbarked said:
The Rev Dodgson said:
stumpy_seahorse said:there will be no deceleration force on it though as the brake will be either left on the truck, or free spinning with the wheel, not imparting friction on it to slow it down.
I think you were on the money with the higher torque:weight ratio of the wheel on its own compared to complete truck
The same argument applies whether the force at the interface is forwards or backwards. At the moment of separation the mass greatly reduces, but there is still a force at the tyre/road interface because of the strain energy in the rubber.
Yes. this strain energy is then unleashed and the wheel is thrown forward at a greater rate?
pops in
Or backwards, depending on the direction of the strain.
pops out
sings
You picked a fine time to leave me loose wheel…….
/kenny rogers
stumpy_seahorse said:
The Rev Dodgson said:
stumpy_seahorse said:how does all of the braking force come from the tyre/road interface?
Surely it starts at the point where the rotation speed of the tyre is reduced
If you look at the mass as being vehicle+tyres then to change the velocity of that mass you have to apply an external force, and that external force comes through the tyre/road interface. If the wheel starts to skid on a patch of ice with negligible friction then the wheel rotation will stop, but the velocity of the vehicle will be unchanged.
yes, but it will be the slowing (or speeding up in the case of acceleration) of the spinning momentum which causes the change in friction at the interface, you can’t have one without the other.
hence my questioning of your use of all of the braking force
I think he meant, on the one wheel?
stumpy_seahorse said:
singsYou picked a fine time to leave me loose wheel…….
/kenny rogers
beautiful. :)
https://www.youtube.com/watch?v=DGNB3Vy6YoI
https://www.youtube.com/watch?v=DGNB3Vy6YoI
Stealth said:
Is it possible for a truck that is traveling at a constant 100km/h to have a wheel detach and the wheel travels faster than the truck for a period?
Assume instant detachment of the wheel. The truck does not change speed after detachment.
Would it change things if the wheel is on a driven axle or a lazy axle?
Would it change things if the truck was accelerating or braking?
It maybe possible with the action of a differential that under braking in the case one wheel’s brakes don’t apply properly/equaly(or/and traction inequalities) that the rotating or driving force is disproportionately transfered to the more free wheel. So if one wheel is 20% slower than ground speed the other wheel will be 20% faster. To complicate things sometimes there’re differentials between drive axle sets or bogie drives.
A similar thing applies to drive axles involving differentials under power.
>So if one wheel is 20% slower than ground speed the other wheel will be 20% faster
Actually not quite sure i’ve conceptualized that perfectly, but i’m sure there’s a sunday seed of genius in the idea, halfway through my first coffee as I am.
of the many differentials (mostly smashed up spider gears) that ol’ destroyed in his youth, there was one occasion did managed to break an axle, smash the spider gears and have the differential lock up on one side, which changed the ratio as recall ( x2 i’d guess), the joy of it was that under power it pulled right, under deceleration it pulled left.
in the LJ Torana, had just broken a record for longest burnout, brakes on, went for about a kilometre, only thing that stopped us was tyre smoke in the vehicle.
back in the day, and it wasn’t unusual to be doing another differential change before the silicon had set from the previous replacement.
Thanks Rev, you comments on ‘strain energy’ is what I was thinking should be taking place. For a driven axel it seems obvious to me that when the truck is at constant speed the detached wheel would accelerate slightly, when he truck is accelerating it the wheel would accelerate more and when the truck is braking the wheel would decelerate. But for a lazy axle??? I think truck cruising = slight wheel deceleration, truck accelerating = strong wheel deceleration and truck braking = very strong deceleration, as in all scenarios the rubber would be in negative strain energy. Thoughts?