Texture Animation questiion

Not sure if I should be asking here or in a texture forum, but I need advice, please, on llSetTextureAnim.

I am working on a wheeled vehicle, and i want to make the wheels go round, or seem so to do. Since it's a physical wheeled vehicle, the obvious solution (if it weren't physical), llTargetOmega, seems a bit anti-social, so I'm animating textures, instead.

The spokes are fine. That's not a problem. But the tires themselves are proving more tricky, at least when the vehicle is moving slowly enough for them to be seen. They look fine when the vehicle is stationary, but when I start the animation, it over-rides, of course, all my repeats and offsets and the treads look very strange indeed.

My question is this. I know that, by playing round with the sizex and sizey values in

llSetTextureAnim(ANIM_ON | SMOOTH | LOOP , ALL_SIDES, 1, 1, 1, 1, 1);

I can sort of emulate repeats but I don't really understand how.

I've had to rotate my texture through 90 degrees in the edit window to make it run round the rim of the wheel prim (another bit I don't really understand, since the wiki suggests this should be cancelled out), but I can't find any permutation of the sizex and sizey values that seems to reproduce the approximate effects of my horizontal and verticle repeats when the texture is not animated.

Can anyone point me in the right direction? Or should I be looking for a texture that looks right at repeats of 1 horizontal, 1 vertical and 0 offset under normal circumstances?

I think that's the right approach, and one that doesn't need to be rotated.

However this is not something I fiddle with much.