Can someone explain to me why my car wouldn't automatically stall when left in first gear on a hill with the parking brake on? A co-worker started my car for me and didn't shift it to neutral and somehow the front right tire spun down to the threads. My manager doesn't believe it's possible, and insists that it would have stalled right away. Can anyone help me with an explanation?
Tires are rugged by design
It takes several minutes of abuse to get a tire in relatively decent condition to pop and expose its steel ply.
The additional load of the drivetrain with the car being in gear should have resulted in the car stalling.
Even if the vehicle was running for a few moments the co-worker would've seen some tire smoke unless the car was on ice.
In my opinion, one of the following scenarios is applicable if what you say is true:
- the tire was in appalling condition to begin with
- the clutch is in appalling condition
- the car was somehow started and run in gear for several minutes at medium-to-high engine RPMs
- the tire that is now on the vehicle wasn't present at the time of the jump-start
Generally, parking brakes only affect the rear wheels of a car. Since your question implies that you have a front-wheel-drive car, the drive wheels weren't affected by the brake, and were able to spin (essentially) freely. But, the car couldn't move due to the rear wheels being stopped, so the front wheel with the lowest traction (the front-right) spun and wore itself down.
It is possible to do a "burn out" whereby a FWD car is run with the handbrake fully applied which can mean that one or both of the front wheels spin whilst in gear. If the car has an open differential, one wheel will spin. If it has a limited slip or lock diff, both wheels will spin.
I've seen that many times at the Worthersee Treffen Volkswagen meet in Austria. However, in order to take a tyre down to the treads you've got to give the car a significant amount of throttle for a sustained period. This Video shows the kind of abuse you've got to give a car and you'd have to do this for several minutes.
Indeed a car started in gear with the handbrake applied and, crucially; no throttle applied, will stall. I fear that your co-worker is telling porkies about what happened. Watch the video and decide for yourself.
Cars are designed to allow the drive wheels to spin at different speeds – this is to allow for the difference distances that the inside and outside wheels travel while turning or going around a corner. The part that allows this to happen is called the differential and it will also allow one wheel to spin freely while the other is locked.
So, based on what you've told us, this is how I think happened:
Your car either lacks a clutch interlock (which should have prevented starting the car unless the clutch was depressed), the interlock is broken, or your coworker wasn't thinking and didn't notice when s/he let the clutch out the tire started spinning.
You car must be front wheel drive (and not a SAAB, or other car where the parking/emergency brake acts on the front wheels). Or the car may have been resting against a curb with a brake that was unable to hold the wheel either because it was only partially applied or because it was out of adjustment (or moved forward until it hit a curb, but that would cause me to really wonder about your coworker). But somehow the tire was able to spin without moving the car.
The wheel with the damaged tire must have been on a relatively slippery surface and able to start spinning when the car was started or when the clutch was let out. If the surface was slippery enough, the spinning tire might have been relatively silent and hard to notice – especially if it was a noisy environment.
This is where it gets puzzling. For the tire to wear there needs to have been friction between the tire and the surface it was sitting on. The same friction that was wearing the tire should have provided traction that would have caused the car to try to start moving – but it sounds like you found the car in the spot where you left it. But if the tires had traction and the car didn't move then I would have expected the engine to stall. But perhaps the tire was sitting on a surface with some friction but not enough to stall the car or maybe the tire was already on its last legs (but unless something else is wrong, like an alignment problem, I would expect that other tires on the car would also be very worn down if this was the case) or perhaps the tires were sitting against a curb or something else was stopping the car from moving – then if the engine had enough torque perhaps it could spin the tire without stalling.
Everything that lands on a road surface (oil, grease, antifreeze, window washer fluid, gasoline, diesel fuel, battery acid, tire repair sealant car wax, beer, urine, dead rats, etc.) usually ends up next to the curb, and you were parked on a hill with the e-brake on which usually only applies to the rear wheels. Your coworker starts your car for you because its cold (I am assuming). The engine is racing on fast idle, the defroster fan is turned on high, who knows what the radio is up to. They let out the clutch and dont notice that the right front tire is spinning so they assume it is in neutral. Your tire starts wearing, your engine control computer keeps the engine from stalling.