Who's good at math and spread sheets?

[Dave]

Think I found some good info on what hp requirements there are based on speed, weight and frontal area. I assumed a drag cooeffience of .44 whick is common for a small truck. Lets you see why without enough hp, you hit the brick wall, the limit of speed.
Dave

[cgrey8]

Post the formula(s) and I'll see what I can throw together.

[Dave]

Chris, not sure if you got them but I sent them to the e-mail you have listed. Had trouble attaching the files here or to a PM
Dave

[cgrey8]

I cant get email here. I'll look when I get to work tomorrow.

[cgrey8]

I read the documents over and then looked at your spreadsheet. The things I didn't see in your spreadsheet were the shape coefficient taken into account as its own cell. It might have been amongst all the formula stuff that was converting all the cells into HP, but I couldn't tell. If it is, I would say break it out the way the document talks about in constant thrust measured in lbs. Then convert that to HP. That way, each step of the calculations can be seen and understood.

The other thing I didn't see was any calculations that handle wheel rolling resistance calculations. But I don't know where you get info on tire flex coefficients. While tire size could get you close, there are differences from one brand to another in the same tire size or even in the same brand/different line. For instance, I remember when we used to sell tires, we had one size that was available in our economy line, luxury/endurance line, low end sport line, and sport line. In each tire, you could push your finger into the sidewall and fell the stiffness and thickness difference.

The luxury line had a very thin and soft sidewall to get a much more cushy feeling. It was also the only tire we warrantied for 60k.

The economy line was thicker/stiffer, but the rubber quality itself was pretty low. Those tires wouldn't last much past 30k no matter what you did or what you put them on. I don't even think they were radials.

Both sport tires had an extremely thick and thus stiff sidewall.

Point is rolling resistance of the sport tires was much better and thus the effort the engine would have to put to the tires was much lower.

[Dave]

Chris, Finally had some time to get back to that spread sheet. Was blessed with five days of great weather and had a lot to do to get ready for winter, big yard and the leaves were starting to drift. Thanksgiving was 60 but Friday morning had that white curse on the ground. Went back and made the spreadsheet a little easier to follow. Including some more ref info. If sheet is corrrect, surprising just how much HP is used to break the wind at 60 and how much it increases at 70.
Dave
Edit: see I can't send a xls file so check your e-mail .

http://mb-soft.com/public2/car.html

2] Crr: Coefficient of rolling resistance (rolling drag). A value of 0.006 to 0.010 represents \low rolling resistance tires on a smooth surface; 0.010 to 0.015 represents ordinary car tires on concrete (see Wikipedia for other sample values). You can also calculate your CRR experimentally.

http://en.wikipedia.org/wiki/Automobile ... d_examples