# Dropping clutch

hi,
I am currently building a drag racing game and I am wanting it to be as physically accurate as possible. my question is, when a driver drops the clutch in a vehicle what needs to be taken into account to calculate the force acting on the vehicle while the wheels are spinning? is it possible to come up with a general formula?

so far i've got
the c/f of the tyres
size of tyres
speed wheels are spinning
weight of vehicle
maybe current speed of vehicle will need to be taken into account?
I want to get the forward force acting on the vehicle

turbo
Gold Member
It's a LOT more complex than you expect. Width of the slicks, inflation pressure of the slicks (which controls the size of the tire-contact patch), front-to-rear weight distribution, extension/compression ratio of the front shocks... Good drag-racers have to be fanatical about the details and be willing to change stuff on the fly to compensate for local temperatures, track traction compounds, etc, etc.

rcgldr
Homework Helper
"Dropping the clutch" is done by on many street cars where the clutches have limited dynamic friction, usually by design to reduce shock to the drive train. The car ends up launching better, or at least more consistently, by spinning the tires, rather than slipping the clutch. Then the trick is to find what initial rpm produces the best launch.

Cars modified for drag racing have clutches with high dynamic friction, and in this case it's bettter to slip the clutch than the tires. At the high end of drag racing cars, alcohol and nitro-methane buring drag cars, the clutches are mechanically programmed via weight and springs to optimized clutch slippage for maximum acceleration without spinnning the tires, so although the driver just drops the clutch, the clutch self regulates it's slippage.

For a drag racing game, it would be difficult to model a drag racing clutch where the driver modulates clutch pressure to control acceleration.

The other situation where dropping the clutch is done is high end road racing cars. These have clutches with high amounts of static friction, that they are amost all or nothing clutches. In addition there's little angular inertia in the engines (Formula 1 cars have 4 lb "flywheels" to allow fast shifting), so the clutched is dropped at high rpms to prevent engine stalling when exiting the pits.

I'm not trying to model top fuel type dragsters more like tuned street cars. the main focus of the game is a much more complicated tuning 'engine' where instead of clicking "turbo upgrade" the player can choose exhaust sizes, turbo sizes, a/f ratio, timing advance, boost control method, etc. I am currently training to become a software engineer and once I get better I want to turn it into a 3d game so both tyre and clutch slippage will eventually be modeled. I'm not looking for formulas with nasa type accuracy but I want something that will be competitive in the market