will big rimes slow me down??

I have a 2000 4.3 and i wanted to put some big 20" rimes on it and i was just woundering if they would slow me up a whole hell of alot.

Getting a larger tire radius is like having a smaller rear end gear ratio. Up to a point, it will increase fuel efficiency. This of course assumes that your overall tire radius with the 20's is larger than with your stock 16's. Can't speak from experience, but I wouldn't expect much of a difference.

I have 20's on my truck. I find it harder to spin the tires (I have a lot more rubber touching the road now). The acceleration was only slightly slower, but top end is higher. Unless you get a programmer your speedo, odom, and trip counter will be off also.

The key is keep the overall tire diameter as close to the same as your stock tires as possible. The 20"s will most certainly be wider and that will be the only thing that will hinder the performance, but it will not affect your speedo as long as you keep the diameter of the tire the same as stock.
:2cents:

Will the 4.3 with a some mods spin the tires or not????

I had a 96 4x4 with the 4.3 and a 5-speed and I could spin
the tires just fine even w/o mods, so you shouldnt have a
problem either.
:)

Are you wanting to race the truck, or just wondering if it will slow you down in general? I only went up to 17s for the sole purpose of keeping my 1/4 down. I run stock tahoe wheels with BF Goodrich street slicks at the track.

Thanks for answering all of the questions and input on the whole topic. With what I know now I probably will end up going with the 20s and not the 18s. Bigger is always better!!