What causes the car to lean back and forth between shifts?

[Based]

Like when you let off the gas to shift, the car leans forward, then you have to go super easy on the clutch or else the car will be pushed back. Is this the soft RMM causing this or is this a spring issue? Or maybe this could be fixed with a tune? I've read that a tune from Tune+ made one guy's car not "fall on it's face" on deceleration and it would just coast.

 

[jeffreylyon]

Weight transfer - the car squats when you're accelerating and goes neutral while you're shifting. I doubt that your car is "leaning forward" during the shift - it just feels that way because it was "leaning back" while accelerating. The car is diving, or leaning forward, when you brake.

"fall[ing] flat on it's face" is referring to a lack of power, not weight transfer (not directly at least).

 

[haste]

Physics.

 

[Sam4]

Physics.

Thank you......!

 

[Racer83L]

I will say, an RMM makes shifting much better than stock. I was going to buy metal bushings and a short shifter. After doing the RMM I'm happy (for now-I did catch the mod bug)

 

[LilPartyBox]

An aftermarket suspension setup that lowers the center of gravity and is stiffer than stock will eliminate a good portion of the weight transfer. But it will always be there to an extent.

 

[M-Sport fan]

Yes, more front damper rebound, and more rear damper compression will help lessen it, but this has to be carefully balanced to not mess up the neutral handling in other scenarios (unless you are ONLY drag racing the car).

 

[BRGT350]

A number of factors are at play, mostly weight transfer as mentioned above. Under acceleration, the weight is transferred rearward, making the car lighter up front. When you lift off the throttle to shift, the acceleration force goes away, and the weight shifts from the rear to the front, giving the pitching sensation. The other element on the ST is that it is a FWD car, so the engine torque causes the motor and transmission to roll fore and aft under acceleration and de-acceleration. On a longitudinal mounted engine, like a RWD car, the motor torque causes rotation left and right and not fore/aft. When you are accelerating, the torque causes the engine to move one direction and then lifting off the accelerator moves it in the other. Due to the massive amount of weight of the drivetrain, you feel it in the chassis when it moves. Those factors cause the pitching motion.

How to fix it? Well, there are a couple of options. First is to limit the amount of motion of the motor between acceleration and de-acceleration by using a stiffer bushing in the lower motor mount/rmm/torque mount/roll restrictor (same part, just a number of ways of naming it). Next is stiffer springs and matched dampers which will limit the amount the chassis pitches on the suspension. Finally, a shorter throw shifter to reduce the amount of time between shifts. The less time between shifts means less time for the weight to transfer from one end to the other and then back again.

 

[MeisterR]

Weight transfer is not a bad thing, the long as it is control.
A FWD car that put it's power through it's front wheel is slightly tricky because the weight comes off the drive wheel under acceleration.
But the long as the overall balance is good, that generally isn't a problem.

Suspension can play a big role in that, as the springs rate control HOW MUCH movement you get, and the damper force control HOW FAST it happens.

Jerrick

 

[BRGT350]

right, weight transfer is not a bad thing at all. Learning how to transfer the weight is important to proper driving. Lift throttle oversteer can be a great way to get a FWD car to rotate as the weight shifts forward upon deacceleration. The key is controlling weight transfer, both in terms of driving and car setup.