Oh, my... Don't you have mercy?
Well, I don't, so another long answer.
Now, Alejandro, compadre, hermano, listen to me for a minute, please.
First, simple: what twists a tyre is torque. Stay there, don't let trick questions confound you. You slip the tyre at max torque more easily. End. No "ifs", "buts" or "I guess".
Second, my daily nag:
For the love of Pete,
in the name of James Watt's sacred slide rule, please, people. This is a technical forum. No steaming piles, please.
a. There is no shame in answering: "I don't know" or "I was mistaken". It's called scientific method.
b. Also, there is no shame in saying: "Look, these are my numbers. What do you think?" instead of implying people is stupid, ehem, even if
we (and I'm included there) are. Concentrate on the original question.
So, autogyro, JerseyTom stop it.
Third, allow me to complicate my life. Imagine, for sake of simplicity, that:
a. you have a small engine, so its power it's not enough to make the tyre slip.
b. you don't shift gears
c. you slam the throttle and keep it there (as God intended)
When do you have more force on the wheels? (twisting them, of course) Read ahead if you want a few ideas (and a recommendation to win your drag races).
Your car has a power-rpm "curve" like this one:
232 hp @ 8500 rpm
159 lb-ft @ 5500 rpm
Damn, we also have to deal with gringo units... (I'm starting to become racist
).
So, 8500 rpm and 232 hp is like (wait a minute)... All right, these are my numbers
Alelanza's car numbers (in bold, the power curve numbers, in italics my calculations, in colour red and blue, the important numbers)
Now, even if you don't read this (and maybe you won't, I understand),
your car engine axle gives you 194 newtons at one meter distance when you're at max power (last number in red, lower left) or
it gives you 216 newtons at the same one meter fulcrum when you're at max torque (red number, row 9).
Like this (for dummies!):
Your car has a gearbox and wheels (I think).
Imagine your gearbox and rear/front transmission have a gear relationship of, I don't know, 9 to 1.
That is, when your car is in first gear, for every turn of the engine, the axle at the end of the gearbox turns 3 times and your differential box also turns 3 times per each revolution of the gearbox, for a final relationship of 9 to 1.
In English: every time your engine turns 9 times, your wheels turn 1 time. That would be more or less typical for the kind of cars I drive.
So, you multiply your torque per nine. Power stays the same, because the rotational speed (how fast your wheels turn) is 9 times slower.
In the end your car receives a force of 595 kilograms when at max power, or 660 kilograms at max torque (blue numbers, bottom of the worksheet, assuming 13 inches radius wheels) that impulses it forward.
Amazingly, when you have 25% or so less power (232 hp at max power vs 167 hp at max torque)
your force on the ground, the force that really counts, is 10% larger (as I said, 595 kg of force at max power vs 660 kg of force at max torque)
So, your tires slip easier with max torque. The force on them is larger. QED
Of course, your wheels can develop, more or less, the same force as the weight of your car on them. You have two wheels that transmit power (unless you drive a 4x4), so each wheel receives 300 (max power) or 330 kg of force (max torque).
If your car, I don't know, weighs 1.000 kg (a number I picked because I can divide it by 4 easily) then each wheel has 250 kg of weight on it, assuming perfect 50/50 weight distribution (more like 25/25/25/25).
So, tyres will slip anyway, either at max torque or max power. The force you're trying to put on the tyres is larger than its weight (I'm also assuming you have tires with a friction factor of 1).
However, seriously: if you want to win your drag race, learn at what rpm point your tires slip (hear them screeching). Now, put the pedal to the metal and when you're reaching that rpm (which means you reached max torque), go easy on the throttle. Past that point, squeeeeeeeze again the throttle (
gentle there, remember I said 10% difference: can you move your throttle forward in ten steps? I can ).
Why (I think) engineguru00 gives a different answer, in his experience? Easy: when you hold the clutch at mid-point, what you're doing is changing the final gear relationship. The clutch is slipping, so your 9 to 1 engine turns per wheel turn doesn't apply. What does it means?
That his car has not enough power to slip the wheels, so, he's trying to apply more force (using more torque, burning some millimeters out of its clutch). Actually, I bet the car weighs more than 1.000 kg and/or tyres give him more than 1.0 coefficient of friction (in real life, high spec tyres give you something like 1.5 cf).
Finally, if I'm wrong (autogyro, are you listening?), thanks, people. I want to learn and answer the original question, instead of starting a row, no matter if you're right (and you are, JTom).
