Quickest way to get low end grunt & back to highway speed (sprocket q's)

[Roadinator]

I am do for a chain and sprocket.  I replaced the front with 19t to get a little improved highway cruising, but now I'm starting to play in the woods.  I was wondering if you could swap rear sprockets and have it 1) really make a difference 2) be done with one chain.  I could go to 17t up front and larger in the back (stock is 46t I think?), but did not know if I had two sizes for the rear I could swap them before a weekend of riding when I am mainly cruising the highway or playing slow and go on fire roads camping.  I was only interested in swapping the rear sprocket, but maybe that would not make enough of a difference?  Guessing you would have to have a chain to accommodate different size sprockets.

And yes I know the short answer would be "get a bike for the woods, not a '05 Girly," but that probably won't happen until next summer.   She's not that heavy 

[Mustang]

1 tooth on the front is equal to 3 on the rear
a 17 /48 combo you could use the same chain as stock and she would have some down low
a 16 tooth will be non existant to buy and chances of  finding anything bigger than 48 for the rear will be slim to none

[Roadinator]

Thanks Mustang.  With the 17/48 combo, what do you think 65mph would be like on the highway.  Would I still be able to hit 135?

[motoOzarks]

Here's a website set up to help figure all that out

http://www.gearingcommander.com/

[Roadinator]

Thanks for the web link.  That made it easy to see the difference!