Quote:
Originally Posted by redpoint5
For the purposes of my example, imagine a very long and continuous hill. I'm used to driving up mountains around here, and it's not uncommon to travel many miles of continuous 5% grade. I can engine-off coast for about 10 miles when I'm descending Mt. Hood!
The 1hp example used above was an arbitrary number I choose for ease of math. Of course, the amount of power required depends on the weight of the vehicle and the angle of the slope. Calculating these requirements is possible, but difficult considering the varying slopes and weights of vehicles. I'd be curious to know the power requirement to hold a 3000lb vehicle on a 5% slope, as a baseline.
My Subaru Legacy averaged 27mpg, but on days that I traveled to the mountains, I could achieve 33mpg. I would drive in the highest gear possible while giving about 85% throttle.
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Force required to stay at hill is certainly interesting, I found this thread, which might be helpful for math part:
Work to push a sled up a hill: Friction, inclines,force,work
It is about sledge pushing up to slope, but from my understanding it is same for car, only base parameters need to be changed?
Perhaps members with stronger math skills can help with that?
From my understanding it would just need to put to excel or another spreadsheet program and input slope, weight and rolling resistance that should include any losses of drivetrain to be able to make fits for all calculator that outputs needed power for staying on hills, there one can even workout forces and thus power needed for different approaches of hill climbing.
I posted altitude profile of my shopping route earlier, it has highest climb of 7%, luckily not many miles, but there is good long climbing too, I'm getting to 1200rpm if I keep top gear and something like 80-90% throttle pedal down and there I need to shift down already, even turbodiesel has good torque and at low rpm it is not enough for these hills.
Because of no throttle butterfly I get better efficiency at low throttle than your gasoline Subaru, which make it possible to use low throttle and let speed decrease with top gear and use lower gear then to climb at slow speed low throttle. Good part of diesels is that you are having intake open to outside all the time, which helps greatly with low throttle efficiency.
However I'm not using really high rpm, just around 1500 with 4th gear, on steeper hills, speed can go below 60kph, so I save from air resistance enough even I use bit more diesel with lower gear.
But I'm not sure if it still is the best method, even I'm getting same or perhaps bit lower overall consumption at these hills than at level ground, maybe getting air resistance to enough low level might help with climbing at bigger speed and top gear, but this around 1300kg weight is bit of burden at longer and steeper hills. Easiest way to help with that is to get rid of driver's extra weight
