Acceleration is based on a multitude of factors including engine size, vehicle weight, road surface, incline, and driver skill.
As a result there's no way to determine concrete numbers for a given vehicle's ability to accelerate.
The entries here are a simple guide to give a very rough idea about how a car of a given weight will perform with a given engine.
To drive in reverse simply set your target speed to anything less than 0 (zero) MPH/KPH.
Hitting the Redline
You'll hear a lot of players make reference to the “redline”. This is the 150mph mark on your speedometer. all other numbers and tick marks following the 150mph mark used to be red, in an older version of the speedometer graphic. Hence the “redline”.
Like a real car, if you put the 'accelerator' pointer past the redline, the power tires (either front wheel drive or rear drive) have a tendency to spin, losing traction and making the vehicle a real challenge to handle. If you put the accelerator pointer just under the redline, your power tires will not spin and all engine power is transferred to the ground in TRUE acceleration.
When in a race, you might want to have it 'past the redline' at all times making the car easier to drift into and out of corners. If you are on an asphalt track, (or out in the wilderness on a paved road) you might not want to have the tires spin so much so you can keep a better straight-line on the pavement allowing better control of your car.
Using the accelerator correctly is a learned personal skill that takes time to master and know when and where tire spin is necessary and where it would not be beneficial.
That being said, the fun is in the learning and you'll find that “Red-lining” is where your accelerator will spend most of its' time in different situations.
There is a small controversy surrounding the redline. While the developer has indicated the redline has no effect on cars in the game, players have reported that cars handle decidedly differently above and below the redline. Other players have reported that once you reach a target level that is beyond the engine's maximum torque output at its current speed, raising the target level further has no effect.