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Power Calc Software

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This is an interesting program that I used to experiment with bicycle designs. In the right hands, it might even give some insight into our beloved Honda Insight.

www.machinehead-software.co.uk/

Note: I am using the following values:
drag coefficient: .25
frontal area: 1.9 m^2
coefficient of rolling friction: .0066 (listed for the B381 tires, not the RE92)
weight: 900 kg

I used this program extensively when getting ready for the Tour De Sol Rally in 2006. Basically, it doesn't look like much to start, but once you have your settings in place, you can calculate the effect of small changes to Cd, frontal area, tires, weight, etc.

It also can be used to get a rough estimate of horsepower per mph for your car. (my Insight is roughly 6hp to go 50mph - So "lean burn" mode which gets 150mpg requires no more than 50 mph on a flat.)

Dropping the side mirrors would buy 1-3mph at the same gas mileage. It also shows how much dropping the frontal area can effect this. (Turn the Insight into a flat top convertible for example.)

Note: Dropping weight doesn't appear to do much for the mpg. Though it does show up when you program a slight hill. I don't remember the numbers, but you can estimate the acceleration that you want to use in regular driving. This shows how dropping just 200 pounds would make the car accelerate much more efficiently.

Finally, after all is said: It taught me the three important techniques for efficient driving:

1) Brakes are "throwing away" gasoline. Don't hit the brakes if can avoid it.

2) Drag increases as the square of speed. So, try to avoid high speeds if possible. (You might need to drive the slow parts faster to hit time goals.)

3) Know your engine's efficiency requirements. The Insight likes to drive hot, and doesn't like heavy acceleration. (Thus warm it up and try not to push hard enough to engage the electric boost.)


SOFTWARE:

As for this software.

1) Note how on the top left corner, you can enter the Cd. Look this up online for your car. Also, you need to know the frontal area. You might need to click the mouse a second time to make it work.

2) The gradient can be used for acceleration (if you remember the acceleration formula and can convert Kg to Lbs, etc.)

3) Set the speed and it shows you the power requirement to go that speed. You will likely want to create a graph for your car that indicates the speed and mph conversion. This requirements diligent testing, but isn't too hard to create.

Once you have the basics in order, you can play with the Cd and even use the program in reverse to calculate how much of a change an aerodynamic mod does to the Cd.

Tip: It does go to show how important it is to do measurements at very accurate speeds and consistent temperatures.


Tip 2: Be sure to look up the "Rolling Resistence" for your tires. It is downright AMAZING how much they differ. This is one of the mpg secrets of the hybrids on the market. A regular tire can be .02, while the Potenza RE92's eat 1/3 of the energy.

Thus, reducing the mass of an Insight doesn't have as much of an effect on MPG on the highway as a regular car with "sticky" tires.