View Single Post
Old 02-29-2008, 09:18 AM   #3 (permalink)
optiwatch
mazdaspeed3 - 27 mpg
 
optiwatch's Avatar
 
Join Date: Feb 2008
Location: Georgia
Posts: 8

MS3 - '07 Mazda Mazdaspeed3 mazdaspeed
90 day: 27.85 mpg (US)

speedy3 - '07 Mazda Mazda 3 mazdaspeed3
Thanks: 0
Thanked 0 Times in 0 Posts
Calculating Horsepower requirements - including weight

Understanding that HP to overcome aero/drag is helpful. I want to include vehicle weight in my calculations to fully understand the impact of weight.

I came across this, but didn't get to an understandable value. I may just be overlooking some error in my calculations.
Pmotive=1/2*Cd*A*rho*v^3+Crr1*m*g*v
from http://www.geocities.com/greglocock/

My attempt at this calculation is attached on the second tab. Please let me know if anyone can fix it or provide the conversion from Pmotive to HP (or if you have a better spreadsheet). The first tab has the calculation from this discussion (The results look correct to me).

With significant investment, I think I can lower my weight by 200 lbs. Hopefully I can get some idea of the pay back. Spending most of my time at a stead speed (70 mph), I expect less pay back than the average vehicle. Taming my driving habits has already given me a 10% improvement (from average of 27 mpg to a max of 31.5).

I also want to find [easy] ways of reducing my RPMs at highway speeds from current 2750 to about 2200, but that's a different topic...

Thanks.
Attached Files
File Type: xls HP_requirements_calculations.xls (22.5 KB, 42 views)
__________________
power, performance, and fuel economy - can't they all just get along
  Reply With Quote