HP required to pull hills

[4x4ord]

Here is a formula that will give a rough idea of the flywheel HP required to tow a fifth wheel up a grade at speed.

HP= s(53000+gw)/31800

s = speed (mph)
g= % grade
w= weight of truck and trailer

It should give a fairly accurate number for most 5vers traveling 50 - 65 mph.

[Cummins12V98]

4x4ord does this help?

My HP was lower than the other guys with same HP engines because I let mine warm up too much before hitting the dyno.

I think I was 320's and others were 330's RWHP. Standard 20% loss would have been 308hp.

My 2011 HO was 304 out of 350 advertised.

[Cummins12V98]

goducks10 wrote:
How did you get through Ore dbl towing?

What R U talking aboot EH???

[goducks10]

How did you get through Ore dbl towing?

[4x4ord]

Cummins12V98 wrote:

4x4ord wrote:

Cummins12V98 wrote:
I will be pulling my 35k combined double tow thru 6% grades next week. What should my low speed be?

44 mph if you hit a long steady 6%. Sometimes there are short sections with a 6% grade where the sign is but the overall grade is considerably less. To really know the grade of the hill you'd have to know the elevation at two points on the hill and measure the distance between them. Here is a link to an elevation tool.

Edit: I was thinking you had 3.42 gears so 44 mph was figuring you'd be approaching the redline in 2nd gear. You've actually got 4.10's. The 4.10 gears will keep you in 3rd at a nicer rpm but you'll only be at about 40 mph.... maybe a touch over.

Must be that good AMZ/OIL top to bottom that nets me 5mph more than your calculation. The slowest speed from NW WA to SoCal was 45.

Could also be that the Cummins delivers more of it's advertised HP to the ground than what you calculated. This is at 35k combined double towing my MC trailer behind RV.

You are correct there are times that the 3.42's will out pull the 4.10's. I have owned both and have experienced this.

I plugged your values into my formula. It says it would take 372 flywheel HP for you to climb a 6% grade at 45 mph. At 2600 rpm your Cummins being able to put out 372 HP sounds a little optimistic but not unbelievable... My formula is close.... At 40 mph you'd be running about 2300 rpm and the formula says 40 mph up a 6% grade would require 330 HP. I figured 330 HP at 2300 rpm sounded about right. So I predicted 40 mph ... maybe a little more. Without a power or torque graph of the engine it is hard to preduct exactly what rpm the engine will pull down to. As well, if the hill is just slightly less than 6% grade less wheel torque is required so the engine can run a little faster where it makes more power. You might find it interesting to know that of the required 372 flywheel HP only about 75 HP is required to overcome drag and rolling resistance. The vast majority is being used to raise the weight.

[4x4ord]

Cummins12V98 wrote:

4x4ord wrote:

Cummins12V98 wrote:
I will be pulling my 35k combined double tow thru 6% grades next week. What should my low speed be?

44 mph if you hit a long steady 6%. Sometimes there are short sections with a 6% grade where the sign is but the overall grade is considerably less. To really know the grade of the hill you'd have to know the elevation at two points on the hill and measure the distance between them. Here is a link to an elevation tool.

Edit: I was thinking you had 3.42 gears so 44 mph was figuring you'd be approaching the redline in 2nd gear. You've actually got 4.10's. The 4.10 gears will keep you in 3rd at a nicer rpm but you'll only be at about 40 mph.... maybe a touch over.

Must be that good AMZ/OIL top to bottom that nets me 5mph more than your calculation. The slowest speed from NW WA to SoCal was 45.

Could also be that the Cummins delivers more of it's advertised HP to the ground than what you calculated. This is at 35k combined double towing my MC trailer behind RV.

You are correct there are times that the 3.42's will out pull the 4.10's. I have owned both and have experienced this.

It's possible that your truck is making more power than advertised but I think it is quite likely that the grades you are pulling are not actually as steep as the posted grade. I have taken elevations at several spots on steep grades and often find the posted grade is a little steeper than actual.

[Me_Again]

=s*(53000+g*w)/31800 in Excel produces the HP number.

=45*(53000+6*350000)/31800 is 372.1698 HP

[Me_Again]

Cummins12V98 wrote:

Could also be that the Cummins delivers more of it's advertised HP to the ground than what you calculated. This is at 35k combined double towing my MC trailer behind RV.

45 MPH, 6% and 35K coughs up 372 HP of your 385 HP. Chris

[Me_Again]

Looks pretty close. I put in 6%, 55 MPH and 24500 lbs and it spit out 346 HP, and I have 385 available. My travels in Western states seem to agree with this.

[wilber1]

JIMNLIN wrote:
I see this discussed on one hauler forum that has several BC Canada members. Their always talking HP per/weight per BC motor vehicle regs..
This from BC Weight

** 7.21 A person must not, without an overload permit, drive or operate on a highway a combination of vehicles unless the gross vehicle weight to the manufacturer's rated horsepower of the towing vehicle bears a relationship of not more than 150 kg to one horsepower.**

So reckon the chart may be of some us up there.

Not so much for RVers, that’s a lot of weight per HP. My truck and fiver both at their gvwr would have me at only 28.5 kg per hp.

[JIMNLIN]

I see this discussed on one hauler forum that has several BC Canada members. Their always talking HP per/weight per BC motor vehicle regs..
This from BC Weight

** 7.21 A person must not, without an overload permit, drive or operate on a highway a combination of vehicles unless the gross vehicle weight to the manufacturer's rated horsepower of the towing vehicle bears a relationship of not more than 150 kg to one horsepower.**

So reckon the chart may be of some us up there.

[Cummins12V98]

ShinerBock wrote:

Cummins12V98 wrote:

ShinerBock wrote:
Plugged the formula into Excel. This is what I come up with for 65 mph.

Looks like mine is off the charts!

I made that chart for my conditions, and I do not tow more than 22k GCW. I don't like DRW trucks so anything above 22k GCWR does not concern me.

I "FEEL" discriminated against. :B

[ShinerBock]

Turtle n Peeps wrote:
Thank you OP for the formula and thank you Shiner for the chart.

No problem. If you want the Excel spreadsheet then PM me your email and I will send it to you when I get back to work on Monday. The chart I posted changes the HP needed by inputting the speed, but I also made one to chart speed at different grades/weights by inputting HP.

[Turtle_n_Peeps]

So I finally had time to run the numbers on one of my trucks.

I ran the formula backwards to see where it came out.

I didn't have solid numbers but I had a pretty good WAG where they were. I knew pretty close what the grade was, what the total weight was and what the HP was. I knew exactly that I was going 28 MPH up this mountain.

So I punched in all the numbers and hit go and...……………….28.7 MPH!!! WOW!!! Now that was cool!

I was very impressed!

Thank you OP for the formula and thank you Shiner for the chart.

[ShinerBock]

Cummins12V98 wrote:

ShinerBock wrote:
Plugged the formula into Excel. This is what I come up with for 65 mph.

Looks like mine is off the charts!

I made that chart for my conditions, and I do not tow more than 22k GCW. I don't like DRW trucks so anything above 22k GCWR does not concern me.