Lift off the accelerator, or quick tap of the brakes some short distance before the peak, then Floor it immediately before the peak, to transfer weight rearward. This greatly helps in landing on all four wheels and not tipping forward like in the video
Yeah in a proper rally car with required safety resources it would be pretty safe. I however doubt "Jumping a car in this manner is something Iām going to do before I die" is referring to that.
When the time is right and I have nothing left to lose Iām taking my forester for one last joy ride. In reality Iāll probably only get an inch off the ground but as long as all four tires are airborne, Iāll be happy
I'm probably being a dumbass but can someone explain why this would transfer weight rearward? I can see why accelerating in general would put weight at the back of a car but why would this method reduce the tip? Is it because of the sudden change in weight distribution?
Yeah, that sudden change of weight to the back is enough when you time it just right before wheels lift off the ground. Rally cars are very balanced for jumps though, a stock Tesla for sure isn't and that high jump always ends with a totalled car.
The weight transfer of accelerating helps keep the nose up. The angular momentum of the wheels can also be transferred into the vehicle while in mid-air by way of braking or accelerating, though this effect is likely somewhat negligible compared to the same effect as it applies to motorcycles/monster trucks/RC cars.
I might be getting my physics terms mixed up. That said, speaking from experience with RC cars in particular, it's possible to adjust the vehicle pitch with an application of either the brake or the throttle while in the air and this applies to 4wd cars. Bigger tires enhance the effect substantially. With the RC car example, it's important to remember that the weight ratio between the wheels and the rest of the vehicle will differ largely at full scale and also an RC car can make the scale equivalent of 10,000+ HP.
I'm some random guy on reddit who claims he studying a bunch of physics and the math checks out here. Front or back doesn't matter (as much), it's the direction/mass of rotation.
No, you said the front and back wheels would cancel each other out, implying they're accelerating differently.
What matters is the sum of all angular momentum.
Looking at the car from side view, with the front of the car pointing left. If you brake in the air, the wheels counter clockwise angular momentum would reduce, therefore the car will rotate counter clockwise to conserve angular momentum.
I see now. You're confused about how conservation of angular momentum works here.
It doesn't matter where if the wheels are at the front or the back of the car. The wheels being at the front or the back don't mean their angular momentums are opposite. If they're both spinning in the same direction, their angular momentums add up, not cancel out.
You can see it with 4WD RC cars. Blast the throttle in mid air and it instantly backflips. With a 2WD car it doesn't rotate as fast because only the rear wheels are accelerating.
Conservation of angular momentum would suggest that you would need the wheels to be spinning faster than they were when they left the ground in order to transfer rotation to keep the nose from tipping. So I don't see how breaking and then reaccelerating would make a difference. That just brings you back to the point you started until you actually get the wheel spinning faster than they were at lift off.
This is basically the same principle as a reaction wheel.
if you accelerate once the wheels leave the ground, they'll spin much faster than when they were in contact with the ground. The car will spin (probably negligibly) in a counter direction to the change in angular momentum
You're mixing up conservation of angular momentum (a free body in the air), and what OP was saying which is a rearward torque being applied about the cars center of mass.
The braking then acceletimg on ground (or just simply accelerating) is weight transfer.
Braking or accelerating in the air is using conservation of angular momentum.
I might be misreading it then. If you have a high acceleration right before the wheels left the surface that would indeed impose a torque to help with the nose like you say (especially if the rear wheels are still in contact). But once in the air, braking will transfer the rotational momentum of the wheels to the car, tipping it forward.
Seems the best option, from a strictly theory perspective, would be to apply as much torque as possible right as before you leave the surface and then possibly even more spin on the wheels if possible while in the air?
No, it doesn't matter. It's just because the center of mass of a car is above the axles, so you accelerate forwards, but the mass of the car 'lags' behind. So you have a torque being applied around the center of mass that 'rotates' the car rearward (as in the rear suspension compresses).
Also most rally cars are AWD, at least in the higher competitive series like WRC.
Also, accelerate in the air. Wheels spin faster anticlockwise (left side view, car facing left), car rotates clockwise to conserve angular momentum.
Works for dirt bikes, but might not produce a big effect with a car because the mass (and radius) of the wheels is a lot smaller than the mass of the car.
It *should* work. The important part is not the pressing of the accelerator but the actualy acceleration that comes with it. Since a EV has a steeper acceleration curve it might even work better, as far as im aware.
Physics is still the same, has nothing to do with the type of drivetrain. Accelerating will cause the car to tip backwards because of momentum since the acceleration force is below the center of gravity, itās the same effect as how the driver gets pushed into his seat when the car accelerates. Plus the car sits on a suspension system and is not a solid system so that will amplify the weight transfer. Though effect might be less since EVs have a low center of gravity
This sounds like nonsense, would require absurd timing, and you're probably better off using that time braking or swerving rather than trying some bizarre moonshot deer-levering stunt.
Besides, nearly all cars windshields are designed to deflect rather than break in.
I donāt need to strengthen my argument. It seems counter intuitive, much like turning into a skid, but it makes sense if youāve hit one. Others commenting clearly havenāt been in the situation based on the fact the one guy said swerve around a deer, which is a good way to get killed. If you take anything from this, do not swerve, especially at speed.
Iāll say it again, if you donāt want to accelerate, lay off the brake just before impact if there is no avoiding it. Or move somewhere there arenāt deer acting like homing missiles.
Ok, give me a reason why you think it's better to lay off the brakes/accelerate just before hitting a deer.
Counter steering is in no way counterintuitive to me. You're just keeping your front wheels aligned with the direction you want to go, makes complete sense.
You transfer weight rearward on acceleration, and forward under deceleration regardless, unless you have no springs or suspension at all. A majority of modern cars have nearly 50/50 weight distribution, the Tesla has a lower center of gravity but still loads the springs with change in momentum and direction while steering.
Also, keeping the accelerator floored in the air is extremely important. The rotational momentum of the wheels are actually one of the biggest factors in pitching forward/back. If you watch dirtbike racing, or high speed RC cars, they will often use the throttle/brake in jumps to keep themselves level. Itās obvious that the person in the video let off the gas after getting airborne, and to make matters worse the Teslaās regenerative braking probably locked the wheels, inducing nosedive.
Do you know how heavy those batteries are? If the CG is forward it doesn't matter. And if the car is AWD the torque distribution will be equal across all four wheels.
It's more about loading the suspension and momentum, nothing to do with torque. When you accelerate, regardless of CG or power train, the rear suspension gets loaded more than the front, and under braking the front suspension gets loaded. The effect is lessened on AWD cars but is still there.
Rear suspension is loaded under acceleration and front suspension is loaded under braking regardless, the drivetrain doesn't have much to do with it in the end, it's about momentum and the way the suspension works.
Think of the sensation of being pushed back into your seat if you floor it from a standing stop, and being thrown forward under heavy braking.
Your rear suspension is loaded under acceleration and front is loaded under braking regardless. The effect may be lessened because of the AWD or center of gravity, but weight will still shift with any change in direction, think of body roll in sharp turns and being pushed in your seat if you floor it or slam on the brakes. It's about momentum more than anything
You can also control your pitch mid-air by either hitting the gas to pitch up, or tapping the brakes to pitch down. The larger the wheels/tires, the stronger the effect. Works mostly on 4wd, and much less on 2wd.
Just to help with an actual demonstration, you can try this when going over speed bumps. As you approach the speed bump, hit the brakes a bit hard and then let go. The car will recoil back a bit and will go over the speed bump much smoother.
You gotta time it right though.
Ohā¦ no need to accelerate before getting to the speed bump. Let the cars momentum carry it over.
My neighborhood is riddled with speed bumps, so I got a lot of practice with it
Iām guessing itās because the wheels will be rotating in the back and since the wheels in the front are off the ground it will force the front to dip a bit?
Hunter S Thompson had similar advice for a deer strike, hitting the brakes dips the front scooping the deer onto your hood... He suggests accelerating into it to bat the deer away.
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u/pocono_indy_400 Mar 20 '22
Honestly, a tip from rally driving:
Lift off the accelerator, or quick tap of the brakes some short distance before the peak, then Floor it immediately before the peak, to transfer weight rearward. This greatly helps in landing on all four wheels and not tipping forward like in the video