[james1211]

Why is it that when you lift the clutch pedal and find the bite point, the nose of the car lifts? To my understanding they're just two friction plates that make contact, so what is it the lifts the nose under high bite points on hill starts?

Not a new driver btw, just always wondered.

[Sammydemon]

(Original post by james1211)
Why is it that when you lift the clutch pedal and find the bite point, the nose of the car lifts? To my understanding they're just two friction plates that make contact, so what is it the lifts the nose under high bite points on hill starts?

Not a new driver btw, just always wondered.

You are pushing the car forward from stationary so the rear suspension soaks up some for the forward force and causes the front of the car to lift slightly. This more obvious in rear wheel drive cars where the rear wheels literally lift the front of the car off the ground under high acceleration (same principle applies to motorcycles pulling wheelies). Watch an American car chase film from the 70s and see the noses of those soggy-suspensioned cars rise!

[james1211]

Yeah but it happens when i'm stationary so it cant be that.

[Sammydemon]

(Original post by james1211)
Yeah but it happens when i'm stationary so it cant be that.

But you're still applying a force to the wheels. I can't see how you would be stationary if you are at a strong bite point. Do you mean you have left the hand brake on?

[Hustler-1337]

(Original post by james1211)
Yeah but it happens when i'm stationary so it cant be that.

That's because the handbrake is still engaged and the vehicle can't actually physically move. If you apply more acceleration eventually the rear wheels will spin (in a rear-wheeled drive vehicle) and you will perform a burnout.


This was posted from The Student Room's iPhone/iPad App

[james1211]

(Original post by Sammydemon)
But you're still applying a force to the wheels. I can't see how you would be stationary if you are at a strong bite point. Do you mean you have left the hand brake on?

Picture doing a hill start, you need to find the bite point and revs before releasing the handbrake. So when you find it the nose lifts, what causes this? I find it hard to believe its because youre applying a force to the wheels are that force is being held by the brakes.

[ROG.]

Bite point or just beyond it with handbrake on and apply gas - oh boy will that bonnet lift!!

Try no gas for a start and see how that goes

My low tickover petrol car will move on clutch alone with no gas from setting off on a flat surface

[JC.]

Drive train is loading up the suspension.

Watch some videos of some drag cars pulling away from the line and you'll see how the weight transfers to the rear of the car.

[james1211]

I see,

[mf2004]

My best guess: when you get to the biting point the engine slows down slightly. This has to be caused by a torque on the engine by the car which means the engine is applying an equal and opposite torque on the car, this torque lifts the front of the car slightly. If this is true the car actually only lifts if your revs drop but they always will unless you have a ridiculous computer controlling the car.

When the car is rolling it's a different story, it's because the centre of mass direction of motion and point where the accelerating/decelerating force is being applied do not line up. (force is lower than centre of mass and direction of motion is horizontal) This causes a torque which lifts/lowers the front of the car.

[CurlyBen]

In most FWD cars the handbrake is acting on the rear wheels, and obviously the drivetrain is acting on the front wheels. That means the front axle's trying to move forwards while the rear axle tries to stay still - almost like the car's being stretched. There's a bit of movement in the suspension, so the rear end dips down, which feels like the nose lifting. I haven't tried it, but if you use the foot brake instead of the parking brake you'll probably find the nose won't lift. Rear wheel drive cars are a bit different, as the brakes and drivetrain are acting on the same axle.

[james1211]

(Original post by CurlyBen)
In most FWD cars the handbrake is acting on the rear wheels, and obviously the drivetrain is acting on the front wheels. That means the front axle's trying to move forwards while the rear axle tries to stay still - almost like the car's being stretched. There's a bit of movement in the suspension, so the rear end dips down, which feels like the nose lifting. I haven't tried it, but if you use the foot brake instead of the parking brake you'll probably find the nose won't lift. Rear wheel drive cars are a bit different, as the brakes and drivetrain are acting on the same axle.

Good explanation, thanks.

[Sammydemon]

(Original post by james1211)
Good explanation, thanks.

That's basically what I told you in the second post.

[CurlyBen]

(Original post by Sammydemon)
That's basically what I told you in the second post.

Is your post not talking about RWD? I'm not certain but I don't think what the OP's describing happens in RWD cars, as the handbrake and transmission are on the same axle, so the wheels don't turn until the brake is released. With a FWD the front wheels can turn a little without the rears turning, as they take up any travel in the suspension. That's a different effect to RWD's trying to lift the nose when launching - that only happens when you start moving, not when stationary at the bite point.

[KasanDude]

Basic physics. When the car moves forward for whatever reason, the back will slouch down and the bonnet will go up. This is because the wheels are going forward and the body of the car is just following.

Whats really fun is when you leave the handbreak on, give it the beans and get the clutch to its bite-point. Its like a bull getting ready to charge

[Sammydemon]

(Original post by CurlyBen)
Is your post not talking about RWD? I'm not certain but I don't think what the OP's describing happens in RWD cars, as the handbrake and transmission are on the same axle, so the wheels don't turn until the brake is released. With a FWD the front wheels can turn a little without the rears turning, as they take up any travel in the suspension. That's a different effect to RWD's trying to lift the nose when launching - that only happens when you start moving, not when stationary at the bite point.

Both, if you read carefully.