Jumping doesn't seem to be covered in the rules, so I looked around the forums and found this thread http://www.autarch.co/forum/jumping-0 wherein Alex suggests a good house rule for it.
But it doesn't take into account very strong or weak characters. Substituting STR for DEX would then not account for highly dexterous or highly clumsy characters.
I gave it some thought, and I think I have a workable solution. I'd like to hear others' opinions on it.
It uses the raw strength score to determine how far a person can jump, but uses their dexterity bonus instead of their strength bonus to determine the modifier.
In feet, a human can:
-from a running start, jump 1.5*STR +/- their DEX Bonus - .5*stones of encumbrance
-from a standing start, jump .5*STR +/- their DEX Bonus -.5*stones of encumbrance
-leap straight up .25*STR - .5*stones of encumbrance
(These are maximums.)
For example, take a character with STR 12, DEX 16 (DEX Bonus +2), and 6 stones of encumbrance.
Running jump 1.5*12 + 2 - .5*6 = 17 feet
Standing jump: .5*12 + 2 - .5*6 = 5 feet
Leap straight up: .25*12 + 2 - .5*6 = 2 feet
A dwarf can jump half these distances.
An elf can jump these distances, plus 20%
Attempted jumps less than 1/2 the maximum are automatically successful.
Jumps over 1/2 the maximum require a strength throw with a target equal to the extra distance. For example, the character described in the example above needs to jump a 14' chasm with a running jump. His maximum distance is 17 feet. He could clear 9' automatically (half, rounded up), but the extra 5' requires a strength throw of 5+. His strength bonus is 0, so he doesn't get any adjustment. Success means he's standing on the other side of the chasm. Failure means he must make a dexterity throw of 10+, with his dexterity bonus applied. Success on the dexterity throw means he made it across, but landed sprawled on his face. Failure means he fell into the chasm. If he fell into the chasm, another dexterity throw at 10+ will tell if he managed to catch the edge and is dangling by his fingertips, or if he missed completely and is now falling into the chasm.
This is a little more complex than I'd like, but I think it gives reasonable ability to make reasonable jumps and provides reasonable risks for taking longer ones. It also makes a smart character disencumber themselves, if possible, before attempting to jump over dangerously deep obstacles.