wnjj wrote:
You have to view the gearing change while considering RPM and MPH. That takes into account the amount of HP available and required at each speed.
Carcraft has a nice article that contained this paragraph:
Carcraft wrote:
Here's a reason low gears can be beneficial to dragstrip performance that you've probably never considered. Assume that a car is in a 1:1 trans ratio, has 26-inch-tall tires and 3.08:1 axle gears. When accelerating from 50 to 70 mph, engine speed increases by about 800 rpm. Put 4.10:1 gears in the same car, and engine speed increases by 1060 rpm-the difference is 40 rpm per mph with the 3.08s versus 53 rpm per mph for the 4.10s. The greater rate of rpm increase versus road speed provides greater acceleration. Since horsepower increases as engine rpm increases (up to the point when the torque curve drops off at a greater rate than engine rpm increase), the engine is able to overcome loads more easily with lower gears than with higher gears. This helps not only in acceleration but in maintaining road speed under a load such as when climbing a steep grade.
I realize this is about drag racing but pulling hills is about getting the most out of your engine and gearing just like the last sentence suggests.
I actually plotted available HP versus MPH throughout 1st through 3rd gear with both rear axle ratios up to 70mph, shifting each at 5000 rpm. I also plotted an assumed linear increase in demand HP on the same graph. You can see where the lower geared truck HP climbs away from the demand HP more quickly in each gear. I used an estimate of wheel size and assumed a flag torque curve from 3000 to 5000 which is reasonable along with the actual 6-speed ratios. I can try to post a picture if anyone's interested.
I would be interested in a picture.
