Payload and power-to-weight ratio

[jcbrandon]

So I've been staying up late every night reading Tom Sheppard's Vehicle-dependent Expedition Guide and I'm fascinated by his discussions on payload, range, power, and the other compromises we all face when choosing a vehicle. Or making use of the one we've already chosen.

There's a table of weights on page 4.1-14 comparing the payloads and power-to-weight ratio of various potential expedition vehicles. The range starts with a Honda CR-V 2.0 (334 Kg payload; 66.32 horsepower per tonne of gross vehicle weight) to a Leyland 4 tonne truck (4715 Kg payload; 13.42 horsepower per tonne).

Curious, I did the math on my Power Wagon: 914 Kg payload (2010 pounds); 89.36 horsepower per tonne!

These are real-world figures. I weighed the truck and included a full tank of gas (34 gallons at 6.15 pounds per gallon) and me in the drivers seat. Subtracted that from the GVW (8510 pounds) to get the usable payload.

Anybody else want to do the math on your vehicle? I'd be quite curious to see how the Expo fleet compares to Mr. Sheppard's Defenders and Vauxhall pickups. Remember, a metric tonne is 1,000 kilos or 2,200 pounds.

 

[charlieaarons]

Unimog U500: payload 7200kg. Power/weight ratio 19.4 hp/tonne.
(600kg front axle, 6600kg rear axle payloads with tare weight 3800/2400)
Charlie

 

[mauricio_28]

That indicator, weight over HP, seems biased in favor of gas/petrol engines which produce more HP. For hauling, towing, and crawling over "expedition" terrain, I'll take torque (at low rpm) over HP anyday. But I'll play, nevertheless:

D40 TDI Nissan Navara
Weight: 1,960 kg
Max Payload: 820 kg
Power: 174 HP @ 4,000rpm
Torque: 402 Nm @ 2,000 rpm

Power / Weight: 89Hp/ton
Torque / Weight: 205Nm/ton

 

[jcbrandon]

That indicator, weight over HP, seems biased in favor of gas/petrol engines which produce more HP...

Power / Weight: 89Hp/ton
Torque / Weight: 205Nm/ton

I come up with 62.59hp per tonne on your vehicle. The equation is horsepower divided by gross weight. Agreed on the horsepower and torque question. For my Dodge truck that works out to 97.15 pounds-feet of torque per tonne of gross weight.

 

[michaelgroves]

Agreed on the horsepower and torque question. For my Dodge truck that works out to 97.15 pounds-feet of torque per tonne of gross weight.

The problem with maximum torque is that it's a pretty meaningless figure - the torque curve is all that counts (the flatter the better). Another truck could have the same maximum torque as yours, but at (say) 20% lower revs. Is that better, or worse? The answer depends on how the torques vary across the rest of the rev ranges of each engine respectively.

Driving in thick sand, for instance, especially in dunes, requires power. Low powered engines, no matter what their maximum torque, can't maintain the momentum to push their way through the thick stuff as well as a high powered engine can.

 

[Dowry]

I'll play:

Suzuki Samurai, ~2200lb curb
~800lb junk
66hp (carbed)

= 48hp/tonne

That sounds a lot better than it feels.

D

 

[R_Lefebvre]

Hmmm, not sure if I'm going about this the right way... my D2 had 217hp, and the GVWR is 6064lbs. Strangely, my two GAWR's combined add up to more than the GVWR. Anyway, specs are curb weight on the truck was 4600lbs, I figure 5064 with fuel, me, and the front bumper and winch, obviously this should be verified. That leaves 1000lb payload, or 454kg.

HP/metric Ton is 78. Not too bad!

I also am a disbeliever in the "torque is all that matters". While a healthy torque curve can make a low HP engine feel better, you are still very limited on how much work you can do. That means ultimately that you'll have slower acceleration, less hauling capability, and less power in sand. When pulling a load, torque only trumps hp in the bottom half of 1st gear. After that, hp is all that matters.

 

[1leglance]

The payload on my FJ Cruiser is terrible, I don't even want to talk about it...
Not sure of the HP but it does everything I ask and that is all that really matters...
I also enjoyed that section of the VDEG and it makes me lust after a diesel Defender 110 even more

 

[madizell]

. Anybody else want to do the math on your vehicle?

Jeep CJ-7, modified, 113.2hp/US ton; 124.5hp/metric tonne.

 

[Bella PSD]

So are we talking HP/TQ at the wheels or at the crank?

Louie

 

[madizell]

Probably crankshaft, since almost no one rates their vehicle with a chassis dyno. Auto makers usually express HP and torque at the crankshaft. Actual rear wheel HP changes with gear selections, transmission selections, and tire choices. Too many variables for comparison purposes, and so few vehicles have ever been on a dyno.

 

[Bella PSD]

Probably crankshaft, since almost no one rates their vehicle with a chassis dyno. Auto makers usually express HP and torque at the crankshaft. Actual rear wheel HP changes with gear selections, transmission selections, and tire choices. Too many variables for comparison purposes, and so few vehicles have ever been on a dyno.

Mine has been on a dyno many times. 32'',33" tires and with 35" tires. So I thought I could benefit from using real HP #'s at the wheels. If I was to guess I would be about 400-410 HP and 875 TQ at the crank.

I will plug those #'s in see what I get at 9000 LBS??

Louie

 

[michaelgroves]

As long as everyone is doing it the same way, it probably doesn't matter too much which one is used. I guess at the wheels would be the most meaningful, but as Madizell says, it's not a commonly available figure.

 

[ntsqd]

The most often quoted TQ/HP numbers in the US are an SAE standard, which is at the flywheel with all accessories mounted and driven. No idea what the European or Asian stds are, but since those numbers are always a point to some consumers I would imagine flywheel since they will be greater.

 

[michaelgroves]

The most often quoted TQ/HP numbers in the US are an SAE standard, which is at the flywheel with all accessories mounted and driven. No idea what the European or Asian stds are, but since those numbers are always a point to some consumers I would imagine flywheel since they will be greater.

Yes, same here in Europe, most of the torque and power standards refer to a flywheel measurement, including accessories. And torque at the wheels would not be that useful when comparing engines!