Car wheel coming off driving at 40 mph

shown73

I knew if I waited long enough another Allegro driver would pop up! Only us old codgers would remember, but there was once a spate of well meaning diy'ers changing their own rear wheel bearings, and giving the hub nut a good old wrench to tighten. Result, overheated bearings, hub disintegrates, driver quickly learns the truth, or otherwise, of the wheel overtaking!

darich

i've had a wheel come off my car - a few years ago.
The wheel did not, does not and could not, overtake the car unless an outside force either slowed the car down, or accelerated the wheel.

Sounds very much like a homework question to me.

pcfixmanchester

Am pretty sure that if you lose a wheel while driving you will brake pretty quickly or at the least take your foot off the gas. So the car will slow but the wheel will carry on at its current speed.

I hope we all get a good grade on this assignment ;-)

Andy ;-)

uktyler

If the wheel that came is off is under power, and the car is wheelspinning, i.e. in snow, then the wheel will be rotating faster. Therefore when it leaves the car it will speed up.

Also if the tyre has low pressure the weight of the car will compress it, reducing its radius. When it comes off the car and the weight is taken off its radius increases, but its rotation stays the same, meaning it will increase speed.

Did you pass?

Hintza

But the simple solution is it is one of the drive wheels. As soon as the wheel comes off a drive wheel the forward drive on the car will cease and friction etc will slow the car down quicker hence the wheel overtaking.

PayUpMrBookie

Ive been in a car when it lost its wheel.... my old grandpa 'R.I.P' was a Lada lover and while on our way to the caravan for a few days break we were travelling along the road from Ayr to Stranraer when one of the rear wheels came off the car... Yes the wheel overtook the car, but only because the arseend of the car started scraping along the road. Very scary experiance, anyway, before you guys start with the age old Lada jokes... The blame lay with the guys at Arnold Clark who serviced the car the day previous, they forgot to tighten the wheel nuts.

uktyler

Hintza wrote: »

But the simple solution is it is one of the drive wheels. As soon as the wheel comes off a drive wheel the forward drive on the car will cease and friction etc will slow the car down quicker hence the wheel overtaking.

Not necessarily, if it was a six wheel drive then theoretically you could loose a drive wheel and continue driving.

Gordon861

Surely when the wheel comes off it's diameter will increase by a small amount (due to lack of weight on it) but it will keep spinning at about the same rpm. This should result in an small increase in real speed on the road.

darich

uktyler wrote: »

Also if the tyre has low pressure the weight of the car will compress it, reducing its radius. When it comes off the car and the weight is taken off its radius increases, but its rotation stays the same, meaning it will increase speed.

Gordon861 wrote: »

Surely when the wheel comes off it's diameter will increase by a small amount (due to lack of weight on it) but it will keep spinning at about the same rpm. This should result in an small increase in real speed on the road.

Both wrong.
Laws of physics would require to be re-written for this to be the case.
There is a certain amount of energy in the spinning wheel regardless of it's radius - kinetic energy which is dependent on mass and speed (rotation in this case)

If the the mass of the wheel doesn't change (it doesn't) and since energy can't be created by the wheel without an outside force, the increased radius would result in a loss of speed (ignoring wind resistance and friction).
Have you ever watched an ice skater spinning on the spot and get faster as the arms and legs are pulled in? They also slow down when the arms are extended.
Exact same principle. Increased radius means the object has more energy, transferred from the movement.
Increase the radius of the tyre and the wheel will slow down.
Decrease it and the wheel will accelerate.

But since neither can happen, and since no outside forces act on the now detached wheel (other than friction and wind resistance) it slows down.
It cannot pass the car unless the car slows at a faster rate.

harveybobbles

psarinuk wrote: »

You as a driver just realized that the wheel is overtaking you…

I think as a driver that I'd notice the car handling badly before I noticed the wheel coming past me...