A logical speed progression for increasing in size?

[flamewolf393]

Ive always thought that getting larger should increase your speed, simply because of gait length if nothing else. One of my players has come across a ten foot tall (at the shoulder) rat. I want to try and figure out how fast this creature realistically be able to move.

[exelsisxax]

Well if you want to talk about realistic...

the rat can't move. Its legs are insufficiently muscled to lift its bulk, and if they were, leg bones would break regularly. A rat of that size might also have to deal with various cardiovascular and respiratory problems that would lead to its death before it actually grew that large.

[flamewolf393]

Well if you want to talk about realistic...

the rat can't move. Its legs are insufficiently muscled to lift its bulk, and if they were, leg bones would break regularly. A rat of that size might also have to deal with various cardiovascular and respiratory problems that would lead to its death before it actually grew that large.

Haha, fair enough. :P

Lets say magic made it grow that large and allows it to function/act as a normal creature, just being its new size. How fast should it be able to move given how quick its smaller brethren are?

[Jowgen]

Speed is dependent on a lot of factors other than size. Compare a wallrus and a cheetah. The weight and built of the creature has a much bigger impact than its size. That being said, I do see it that it should have an impact.

For bipedal creatures, I'd simply go for a 10 ft increase per size category (same as the difference between a halfling and a human). For quadrupeds, I'd either make it the same of simplicty, or half it 10 ft per 2 size categories to account for acceleration difficulity.

[Larrx]

Ive always thought that getting larger should increase your speed, simply because of gait length if nothing else.

My wife uses this same argument to explain why she walks so much slower than me (wearing heels on cobblestone streets never has anything to do with it :smallsmile:).

But seriously, longer stride has little bearing on how fast you move. You need to move your feet further per step to accommodate your longer legs. The big factor in how fast you run is how fast you can move your feet, not how far you can move one foot before you switch to the other, and that's determined by things like mass and muscle power.

Now, that's over simplified. Gait does has some effect . . . it's just generally much smaller that training, fitness, and mass*, and for an abstraction like a TTRPG I would disregard it (despite the precedent set by the, honestly kinda dumb, speed rules for small PCs).

I mean . . . I'm 6'5" and a chubby housecat can totally out-run me. :smallbiggrin:

*I know mass and size have a close personal relationship, but your mass makes you slower the bigger you are, not faster.