Sure, it's difference is about this big:
No really.. can you please be even LESS exact with asking questions?
have you seen rack and pinion setups ?
I've seen pinions as small to fit on the tip of your thumb
and big enough to barely fit the palm of your hand.
FORGET rack and pinion! (really.. forget about it...)
you want to have it as light as possible: use the fewest parts possible, then reduce their weight
ANd really.. I understnad your intention, but keep all your solarcar related questions to ONE thread maybe,
that way it's much easier to get the context of your questions.
[and with that I'll merge a few]
'sid