Inventing the wheel (encumbrance from carts)

[younglorax]

If a horse is pulling a wheeled cart, how do you calculate the encumbrance?

Clearly it shouldn't just use the weight of the cart directly, because I can push a car down the street and I'm quite confident I don't have ST 34. But I don't know what formula to apply to get the proper value.

Thanks!

ETA: Answer is on B352

[Bruno]

See LIFTING AND MOVING THINGS, page 353 in the Basic Set (Campaigns book, in Chapter 10, Success Rolls.

Short version, divide by 10 for two wheels, 20 for four wheels, but then you become a slave to road surface conditions ;)

[Bruno]

You can also figure it out via mechanical advantage, if you've got the head for it. My high school science class sort of vaguely glossed over the lever and the wheel, unfortunately. I should probably read up on that.

[younglorax]

Originally Posted by Bruno

See LIFTING AND MOVING THINGS, page 353 in the Basic Set (Campaigns book, in Chapter 10, Success Rolls.

Short version, divide by 10 for two wheels, 20 for four wheels, but then you become a slave to road surface conditions ;)

I figured there was an answer in the book I was overlooking. Thanks!

[younglorax]

I'm assuming this is a "wonders of physics" example, not an error, but the numbers are pretty extreme.

A horse would have an easier time pulling a nearly 1-ton wagon than carrying a 50-lb bag on its back.

A saddle horse (ST 21, BL 88 lbs) pulling a full loaded wagon (1680 lbs) with four wheels (wt/20) on a smooth road (wt/2) would count as carrying ((1680/20)/2) 42lbs -- None encumbrance. Heck, a slightly strong person (ST 11) would only count as having light encumbrance to pull that cart!

[Philomath]

Ever pushed a car? How about lifted or carried an engine block?

I know which I would prefer to do.

[younglorax]

Originally Posted by Philomath

Ever pushed a car? How about lifted or carried an engine block?

I know which I would prefer to do.

Well, an engine block is closer to 300 pounds than 40.

Anyway, I definitely see that wheels on a road is easier -- I'm just surprised at how much easier. Like I said, it just seems odd -- I don't doubt it's accuracy (I mean, this is SJGames we're talking about).

Although, come to think of it, carrying a backpack with 5 gallons of water in it (42lbs) would probably be harder than pushing a small car.

[Bruno]

A car is about two tons, give or take. 4000 lbs /20 for the approximation of 4 wheels, /2 for nice road, 100 lbs. Which is why I, with my ST of roughly 6, can't push a car on my own at all, but most healthy people (ST 10) can, albeit at a speed like a slow walk (a yard a second).

So yes, that's The Wonders Of Physics at work.

The 1/10th and 1/20th effective weight are good approximations, btw, but just approximations - skateboard wheels do not equal cartwheels. I've been reading up on mechanical advantage instead of doing my work (oops) and the Ideal MA for wheels appears to be the ratio between the axle diameter and the wheel diameter, multiplied by the number of wheels. GURPS is assuming NON-Ideal mechanical advantage (a reasonable assumption!), which is why you get a bonus for nice roads, rather than a penalty for going offroading.

You'd probably get an even bigger divisor for a theoretically perfect surface and a theoretically perfect frictionless wheel/axle system. But unless you've got a magic cart and a magic road, you won't get those.

[Turhan's Bey Company]

Originally Posted by younglorax

I'm assuming this is a "wonders of physics" example, not an error

Yes. In fact, that's why you can push your car without having ST 34. I'll point something out, though:

Originally Posted by younglorax

on a smooth road

That's a very important condition. The horse pulling the cart does about as well as the horse with the heavy pack under ideal circumstances, but move to a poor road, to say nothing of a trackless wasteland or a hill (one of the Low Tech Companions will have more detailed rules for dragging up slopes) and the horse pulling the cart pretty much stops dead, while the one with the pack doesn't slow down at all.