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## Main Question or Discussion Point

**Power and Tq Needed to keep a car rolling at speed**

Ok so im working on a personal project to formulate hybrid systems for a given car.

Before i can do any of the electrical math however i need to find how much power and tq it takes to no only get the car moving but keep it moving (flat & any given degree of climb)

I found a site that shows me some basic stuff on how to find the forces acting on a car by the air at a given speed

Road Load Force = a + bv + cv^2

a = Resistance from brake pads, or friction in the wheel bearings

b = Friction of the tires

c = Drag Coefficient

v = Velocity

The formula is great i'm sure..... BUT THEY DIDN'T GIVE ANY DAMN UNITS!!!!!

- some one help me please.

- How do you tie the Dc into every thing? I did some looking around and found a dc 0.31 for my car

- I also have no idea how to account for a car going up a slope, any one?

- How can i account for alt changes and temp changes? ( i think i need a simple formula for Pressure density)

I did find a quick and easy formula and found that i have about 446n acting on the front of the car at 120 kph or 75 mph. this in turns translates to ABOUT 16kw of power needed to keep the car at speed. what i'm wondering is where is this power applied. is this motor power? or just power needed at the wheel? i know from school that through gearing HP is divided by the gear ratio and Tq is multiplied by the gear ratio..... so how to i translate the 16kw it to Tq and HP at the Motor taking into account the tires?

Thank you for any help you guys/gals have to give. let me know if you need any other numbers.

just for Ref the car is a 05 Jetta TDI and weighs in at 3,300 lbs or 1,500 kgs

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