Changing from 3.73 to 4.10 gears

rhagfo wrote:

4x4ord wrote:


To pull your 20500 lb unit up a 7% grade at a steady 55 mph would require very close to 290 rear wheel horsepower. (Exactly 210 HP to raise the load up the elevation gain plus another roughly 80 HP to overcome wind and rolling resistance) That means something like 342 engine horsepower. So long as the vehicle is geared appropriately it makes no difference whether that 342 HP is being generated by a diesel engine running at 2500 rpm, a gasoline engine running 4500 rpm or an electric motor running 1750.


Edit: I corrected a calculation error but even if your truck is capable of putting 85% of its engine's power to the pavement it would only be capable of 50 mph pulling 20500 lb gcvw up a 7% grade... and this assumes only 65 hp is being used to overcome wind and rolling resistance. I'm thinking the hill you've measured your speed on is not marked accurately or is not a constant 7% grade.

I forgot to mention that at the base of this climb is a 45 mph corner that is truly 45 mph when towing so I also accelerated to 55 while going up this grade.

At 2500 rpm your engine is only capable of about 90% of its peak HP which comes in at 2900 rpm. So either your engine is capable of making very close to 380 peak HP or that grade is not 7%.

I'll bet if you check the elevation gain between the bottom of the hill and top on this map and measure the distance along the road from the same two points in Google maps you'll find the hill is more like a 5 or maybe 5.5% grade.

https://www.freemaptools.com/elevation-finder.htm