[Basic/High-Tech] Vehicles and fuel

[Sigrif]

I play a lot of post-apocalypse games. And in condition of limited resources I am always facing problems with vehicles' Range stat from Basic. High-Tech gave us fuel, but says nothing about consumption of it by vehicles.

The problem is that I can't say for how much Range ten gallons of diesel fuel, for example, can be used. And there is no way to get it from Range because we don't know vehicle's fuel load nor it's consumption rate. Some may say that this isn't important, but sometimes you have to use your Load for exta fuel to take.

So my question - is there some rules for it or any advice for this kind of situations?

[sir_pudding]

Use real world numbers?

[Rupert]

Originally Posted by Sigrif

I play a lot of post-apocalypse games. And in condition of limited resources I am always facing problems with vehicles' Range stat from Basic. High-Tech gave us fuel, but says nothing about consumption of it by vehicles.

The problem is that I can't say for how much Range ten gallons of diesel fuel, for example, can be used. And there is no way to get it from Range because we don't know vehicle's fuel load nor it's consumption rate. Some may say that this isn't important, but sometimes you have to use your Load for exta fuel to take.

So my question - is there some rules for it or any advice for this kind of situations?

Unfortunately there are no rules for this.

What I suggest is doing some research on the web (wikipedia should have capacities for the military vehicles, if that helps). You can derive fuel consumption per hour by assuming the listed ranges are on-road at the vehicle's on-road cruising speed. That will give you and hourly fuel consumption.

For high-speeds, Campaigns says 50% more fuel consumption, but that doesn't really reduce range sufficiently if you assume that's per hour. However, if you assume it's actually 2/3rds range (i.e. 50% extra fuel per mile, rather than per hour), it works out better and becomes much more of a choice between speed and range.

[Varyon]

If the vehicle's description states how much fuel it holds, you can simply divide Range by this to get the nominal Miles Per Gallon. If it doesn't, then for real-world vehicles you should be able to find the relevant information online. For fictional vehicles, you'll probably want to estimate it based on other vehicles.

[Stormcrow]

Originally Posted by Sigrif

I am always facing problems with vehicles' Range stat from Basic. High-Tech gave us fuel, but says nothing about consumption of it by vehicles.

Well, not nothing. "Cruising speed" (page B463) for ground and air vehicles is 60–70% of Top Speed. Aircraft can reach Top Speed by burning 50% more fuel, reducing Range (page B466).

The problem is that I can't say for how much Range ten gallons of diesel fuel, for example, can be used. And there is no way to get it from Range because we don't know vehicle's fuel load nor it's consumption rate. Some may say that this isn't important, but sometimes you have to use your Load for exta fuel to take.

This is in part because GURPS doesn't know what kind of fuel you're going to use with the vehicle. Fuel composition changes a lot over the years, as does fuel efficiency of vehicles.

It's also because vehicle listings tend to be generic in GURPS. Suppose you're driving a "luxury car" from page B464. Loaded Weight is 2.1 tons; Load is 0.6 tons. That means curb weight, including a full load of fuel, is 1.5 tons. For any luxury car. Clearly, not all luxury cars really have the same size gas tank, so this is a generic approximation.

So now we just need to look up a few real-world numbers. A typical sedan's fuel tank is between 13 and 18 gallons or so. The range of the "luxury car" is 500 miles. So you can guess that its normal fuel gives it very approximately 27 to 38 miles per gallon. Pick some numbers. Done. Regular unleaded gasoline is around 6 pounds to the gallon. Diesel fuel is about 7 pounds to the gallon. I'm rounding. Let's call the weight of the extra tanks negligible, since the fuel itself weighs much more. Now you know how much extra fuel you can pack.

Looking up anything more realistic than that is likely to run into the very wide margin of error for the details of a post-apocalyptic setting: fuel quality, state of repair of the vehicle, conditions of storage and operation of the vehicle. That much real-world detail wouldn't really apply to the setting.

[The Colonel]

Seem to recall Twilight2000 was very interested in this - and the relative values of gasoline and wood alcohol (don't recall diesel stats, which, come to think of it, is odd for a game set in Central Europe). If you can find a copy kicking about...

[Fred Brackin]

Originally Posted by The Colonel

Seem to recall Twilight2000 was very interested in this - and the relative values of gasoline and wood alcohol (don't recall diesel stats, which, come to think of it, is odd for a game set in Central Europe). If you can find a copy kicking about...

Ve2 was more detailed about this than anything 4e and had stats for many fuels. It still had to make assumptions about consumption based on a "cruising speed".

If it helps the energy content of alcohol is .50% of gasoline. Gasoline and diesel are close to identical at this level of resolution but only special "multi-fuel" engines can burn either. Mostly your engine is gasoline _or_ diesel and the other fuel is useless to you.

[Willy]

Don´t forget that older diesel engines can burn vegetable or animal fat. More modern engines may have trouble using them.

[Donny Brook]

I'd buy a 4e full treatment of vehicles design and specs. I wonder if anyone has thought of making such a book.

[thrash]

Originally Posted by The Colonel

Seem to recall Twilight2000 was very interested in this - and the relative values of gasoline and wood alcohol (don't recall diesel stats, which, come to think of it, is odd for a game set in Central Europe). If you can find a copy kicking about...

It does have diesel (same stats as gas and avgas), but biodiesel wasn't a thing when it was written.

Individual books are available from DTRPG, but the CDROM of the entire line is only $35 from Far Future Enterprises (although it looks as if Mr. Miller has an out-of-date SSL certificate or something).