[G30M]

i admit i have been watching too much youtube but something made me curious

why do cars squat when people try to launch them by holding the brake and pressing the gas pedal?

or maybe i had too much to drink on a Friday ...

[chassis]

Suspension geometry, primarily the arrangement of the lower control arm pivot points relative to wheel center and tire contact patch.

Older related concepts to read about include anti-dive and anti-squat suspension geometry. Gillespie’s vehicle dynamics book is one of many references to learn more.

[10"]

yeah you had too much too drink.

[overcoil]

I believe original VW Bus actually raised when launched as described above

[G30M]

Originally Posted by overcoil

I believe original VW Bus actually raised when launched as described above

so force applied on the static driveline causes suspension to squat?

interestingly i watched a X drive launch and both the front and rear axles squatted, would that also be consistent?

[G30M]

Originally Posted by chassis

Suspension geometry, primarily the arrangement of the lower control arm pivot points relative to wheel center and tire contact patch.

Older related concepts to read about include anti-dive and anti-squat suspension geometry. Gillespie’s vehicle dynamics book is one of many references to learn more.

ah, i thought those were mountain biking words!

i can understand when the car moves but i can't understand how it happens when the driveline is static.

but thanks

[overcoil]

Originally Posted by g21

ah, i thought those were mountain biking words!

i can understand when the car moves but i can't understand how it happens when the driveline is static.

but thanks

Don't you think the rotating crankshaft generating heat and power at the clutch - even if the transmission is not rotating that the engine is pressing massive amounts of power up against those cinched brakes or computer stalled transmission ?

[HighlandPete]

Originally Posted by g21

i can understand when the car moves but i can't understand how it happens when the driveline is static.

Another way to try and understand how it moves when static... Imagine huge torque to drive shafts strong enough to literally 'twist' each suspension assembly off the car, with brakes powerful enough to resist any slip. What we see is the movement in the suspension assemblies resisting the applied torque against the brakes. It's a case of equal and opposite reaction. Parts/bushes moving/twisting to equal the applied torque.

[chassis]

Originally Posted by g21

i can't understand how it happens when the driveline is static.

Halfshaft torque is reacted at the brake caliper/rotor when the vehicle is not moving and torque is being supplied. The caliper force reacts against the knuckle (upright, wheel carrier, vertical link, whichever term you like) and the knuckle torque is reacted by the control arms and links. The resultant forces and torque result in squat.

During a launch after the brakes are released, there is no torque because the wheel bearing by design does not resist torque. The wheel bearing reacts the tractive effort (force) at the contact patch which is delivered to the vehicle via knuckle and suspension links. The opposing reaction from the vehicle center of gravity, which is being accelerated, results in squat.

Read about anti-squat and anti-dive suspension geometry and report back.

[Rocket455]

Originally Posted by chassis

Suspension geometry, primarily the arrangement of the lower control arm pivot points relative to wheel center and tire contact patch.

Older related concepts to read about include anti-dive and anti-squat suspension geometry. Gillespie’s vehicle dynamics book is one of many references to learn more.

[XutvJet]

The only vehicles that will squat on brake boosting (i.e., torque braking or brake stalling) are planetary automatics with torque converters.

In simple terms, the torque converter, essentially two fans facing one another with fluid as the transfer media, has a stall speed (typically 1,400-2,000rpms) in most street cars. This stall speed allows you to apply the brakes and throttle to load up the torque converter usually just below it's stall speed. This loading effect twists the motor in it's mounts because the drivetrain is trying to turn the tires which are being held back by the brakes. Since the tires aren't moving and the drivetrain is loaded up, it starts pushing against other components in the suspension which obviously move and have some flexibility (i.e., bushings). Due to this, the rear suspension typically starts to squat down as this loading effect happens. Much like accelerating hard from a stop (ass end squats down).

The awesome thing about turbos is that brake stalling creates some boost because turbos are load dependent devices. This effect adds additonal torque for the launch hence a harder launch assuming the tires can handle it. Manual and DCT cars can't brake stall thus cannot generate boost on launch unless they're employing some aftermarket tuning wizardy like anti-lag or a two-step which are downright hell on a turbo's longevity.

The best way to launch an automatic with a street-based torque converter is to flash stall rather than sit there for a long duration of time, like multiple seconds. Stalling a torque converter creates a ton of heat and really isn't good for the transmission longevity. A flash stall is were you go hard on the brakes by pressing down relatively hard, then lifting up slightly on the pedal and then pressing down hard. You should feel the brake pedal get very firm and hard. Now the brakes have maximum bite. Then put your foot lightly on the throttle and get the rpms to around 1,000rpms. Right before it's time to go, stab the throttle about 50% while keeping your foot hard on the brake and release the brake pedal in about one second. This will flash stall the torque converter and help the tires plant and not go up in smoke. With turbo car, you may need to flash stall more like 2 seconds to get the turbo boosting up a bit.

[Bruuuce]

from my 4 wheeling friends

[c1pher]

Weight transfer from kinetic energy?

[chassis]

Originally Posted by c1pher

Weight transfer from kinetic energy?

After the brakes have been released, acceleration (change in kinetic energy) of the center of gravity causes weight transfer to the rear axle. I am guessing you are thinking about the right principal but strictly speaking kinetic energy does not result in weight transfer.

[c1pher]

Originally Posted by chassis

After the brakes have been released, acceleration (change in kinetic energy) of the center of gravity causes weight transfer to the rear axle. I am guessing you are thinking about the right principal but strictly speaking kinetic energy does not result in weight transfer.

I must have slept at the wrong Holiday Inn Express.

[G MONEY]

Originally Posted by XutvJet

The only vehicles that will squat on brake boosting (i.e., torque braking or brake stalling) are planetary automatics with torque converters.

In simple terms, the torque converter, essentially two fans facing one another with fluid as the transfer media, has a stall speed (typically 1,400-2,000rpms) in most street cars. This stall speed allows you to apply the brakes and throttle to load up the torque converter usually just below it's stall speed. This loading effect twists the motor in it's mounts because the drivetrain is trying to turn the tires which are being held back by the brakes. Since the tires aren't moving and the drivetrain is loaded up, it starts pushing against other components in the suspension which obviously move and have some flexibility (i.e., bushings). Due to this, the rear suspension typically starts to squat down as this loading effect happens. Much like accelerating hard from a stop (ass end squats down).

The awesome thing about turbos is that brake stalling creates some boost because turbos are load dependent devices. This effect adds additonal torque for the launch hence a harder launch assuming the tires can handle it. Manual and DCT cars can't brake stall thus cannot generate boost on launch unless they're employing some aftermarket tuning wizardy like anti-lag or a two-step which are downright hell on a turbo's longevity.

The best way to launch an automatic with a street-based torque converter is to flash stall rather than sit there for a long duration of time, like multiple seconds. Stalling a torque converter [...]

I wouldn’t call rolling boost wizardry now a days. Is it hard on the turbo, sure. But if tuned correctly and done properly, you will be fine. It’s the only reason I borrow my brothers GTR. Rolling boost with 1300 WHP is addicting. Lol. Make sure your tires are warmed up.

[Bc2005]

In the old drag racing days it was common to use front shock absorbers that had asymmetric damping. They allowed the front end to easily rise as the car left the line, and then slowly let the front end drop. This shifted more weight to the rear tires as it took off (better traction) and then slowly leveled the car out to help steering as it went down the strip.

This was in the days before there was any traction control other than that provided by the rear axle. Positraction-style rearends helped, but once you broke both tires loose the rear of the car usually went sideways and your only option was to reduce throttle to get back some traction. Drag racers never want to let up on the throttle unless it’s to shift.

[G35POPPEDMYCHERRY]

to make gains