EV racing rule #1:
More Efficient = Faster


Inertia... IS the enemy!

The single most influential design factor for a race car is weight or more properly; mass.
The greater the mass, the harder it is to accelerate, change direction and slow the car.

Imagine that you are designing a race car in a world where each gallon of gas weighs 237 pounds.
How much emphasis would you put on getting good gas mileage?

Since energy storage (batteries) is a larger part of the weight of an electric vehicle than gas is on a standard race car, even small changes in efficiency have a far greater effect on the weight required and hence, the competitiveness of the electric race car.

To illustrate the scale of the difference, here is a comparison of a similar design choice between an ICE race car and an electric race car:

Consider a gas powered, less than 2.5 liter, production based GT racer.
You have an opportunity to make it 10% more efficient.
The car gets 5 miles per gallon while competing in 30 mile sprint races.
This means the car uses 6 gallons of gas during the race.
The gasoline weighs 6 lbs per gallon for a total of 36 lbs.
Since the car starts with a full tank and finishes with an empty tank, the actual gasoline weight carried during the race is ½ of the 36 lbs or 18 lbs.

The effective weight of the gasoline saved by being 10% more efficient is 1.8 lbs.

Let's look at the same situation with the Electric Imp.
We use around 1.25 kW-hr per mile.
This means 37.5 kW-hrs to complete a 30 mile race.
It takes around 19 lbs of our cutting edge Kokam High Power cells to supply each kW-hr at the 450 amp draws we need to be competitive.
This adds up to a 712 lb pack.
We carry the full weight of the pack from start to finish.

The same 10% efficiency improvement which saves the gas car 1.8 lbs will remove 71.2 lbs of batteries from the electric car.

Every component on an EV should be judged by its' actual weigh and the efficiency penalty weight.
When we compare two motors of equal weight but one is 1% less efficient, it can be considered 7.12 lbs heavier under these race conditions.

Efficiency can be speed dependent.
One motor might be more efficient at low speed while the other is more efficient at high speed.
Then which is the most efficient motor will depend on whether it is a high speed or low speed track.

The efficiency penalty will be different for different race lengths (greater for longer races), and different batteries (greater for heavier batteries).

The weight per kW-hr will be also depend on amp draws (see Peurket's equation)
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