Posted on 07/28/2013 11:23:11 AM PDT by AtlasStalled
Your Dad’s car must have had a manual transmission.
You are correct in that the polar moment of inertia is a factor in a car’s handling. And whether or not you are putting power through the drive wheels as well. But the moment of inertia is a constant, determined by weight distribution and as such not determined by torque to the wheels. I guess that statement threw me off.
In any case, let me add that I do *not* recommend coasting downhill in neutral. That we can agree on. There are, of course, many factors affecting your car’s behaviour when driving through a curve. What it comes down to (the limiting factor) is always how much force (forward/rearward/lateral) the tires are able to handle. When you add torque through the drive wheels while close to the limit of adhesion, you’ll get understeer on a FWD car and oversteer on a RWD car. Neither of which you’d really want (unless showing off for friends...:-)) which is why I scoffed at your ‘torque’ statement. But I realize you probably weren’t talking about a ‘close to the limit’ situation.
Drive safely and have a great day!
Well, there’s really no point in trying to have a discussion with you.
Your tag line tells me that.
You’re right about the way I worded my original posting; the polar MOI is constant — unless you do some serious weight shifting in the vehicle.
“You are truly a child.”
Why do you say that?
Who else would equate putting a manual transmission in reverse with the difficulties that were being discussed on this thread?
You really don’t understand that your “readout” was nothing but software that tracked throttle position vs vehicle motion??
>> “There is really no need to have fuel going into the cylinders when coasting” <<
.
The need to have some fuel going to the chambers at all times is rooted in the fact that cars these days have only a front pump, and no longer use a rear pump, thus it the engine has no fuel and stops running everytime you take your foot off of the throttle, you would have to use the starter to restart the engine.
The car I have now has a low pressure pump in the tank, and a high pressure pump feeding the injectors that is driven off of one of the camshafts. That’s two pumps.
I believe all engines that inject directly into the combustion chamber (rather than into the intake ports) have two pumps.
This includes cars made by Audi, VW, Lexus, Ford, Honda, Chevy, Cadillac, and so on.
As for the fuel shutoff, obviously, fuel flow has to be restored to prevent the engine from shutting down as the car comes to a stop.
There are, of course, a few non-hybrid cars that are designed to shut off their engines when stopped, and restarted when the accelerator is pushed.
Did you read the articles at the links that I provided?
No, I guess not.
The second link mentions actually hooking an oscilloscope to the injector’s control wires, and observing that the electrical activity on those wires stops completely when coasting. No power going to the injector means no gas going to the engine.
As for the “gimmick” readout, the information that it gives you is developed from the computer’s knowledge of fuel flow rates, the length of time the injectors are opened, and the speed of the car. Knowing all that and doing the required calculation gives you MPG. And accumulating this data over time gives you an average MPG.
The average MPG numbers that I see in my case are a little on the optimistic side (maybe 5% high), but allowing for this bias, they do correlate well with MPG calculated at fill-up time.
This “gimmick”, as you call it, is actually quite useful as it allows a driver to correlate his/her actions with real-time MPG numbers.
Listen, brainiac:
Throwing a car in reverse is a very bad idea if you are flying down the road in a forward direction. You do it with your car all you want. Just please don’t do it around any other vehicles who don’t deserve to be wiped out.
If a driver is in a panic situation due to a stuck accelerator they are likely to be pressing hard on the brake. If the road surface is slippery then there may not be enough traction to keep the wheels turning if they are not engaged. Shifting into reverse in that situation can allow the driven wheels to stop rotating long enough for the auto transmission to engage reverse. The result is locked up drive wheels and then then guess what? They crash.
I said throwing a car into reverse in a stuck accelerator situation should not be done because it could in some instances lead to locked drive wheels. You told me that was nonsense. Problem is you are wrong.
Instead of convincing yourself you are the smartest person on FR (see your tag line) maybe you should pay attention and LEARN for a change.
Now piss off and quit sticking your nose into things you are not capable of thinking through.
Do you have any idea what you’re talking about?
Yes, what you’re talking about is starting with a car that is already going at a high speed, and ending up a car that’s completely out of control going at a high speed.
Not a good situation at all. There’s a good chance you will die, and even worse, you could take others with you.
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