<font color=purple>First things first, head out to some local events & get copies of the rules. Then, check out this link: GUMBO's Sanctioning Body Links
& check through some of the rules. You'll start to see some patterns. Are you planning mud "drags", or "bogs"? The setups are completely different for each - including tires & to a lesser extent, suspension.
Generally speaking, you'll want to stay away from 4-links & such as that will likely move you up into a higher class than a leaf-spring suspension, but it just depends on where you plan to race. For "bogs", run the largest allowed Swampers up front with matching size Boggers in the rear. If there is no Bogger in that size (say you want to run a 36" class), run Swampers front & rear. Do NOT drop down a size in order to run Boggers in deep mud (i.e. 35's in the 36" class). HEIGHT is where it's at! For "drags", you'll want 38.5X11 Boggers at all four corners (get 15" or 16" rims either way you go as you won't be able to air down your tires on 16.5" rims). For "bogs", I normally run 8-15 lbs of air up front & 5-10 in back depending on how rough it looks (more air for rough, less for smooth), & for "drags" ~5 lbs in front & 3-5 lbs in the rear. Your front & rear axle will not be the same width. The rear is narrower. For drags, this can be a big problem. To compensate, you'll need different wheel backspacing in order to get your rears to line up directly behind the fronts.
Not sure how much help this'll be, but maybe it'll get ya going in the right direction. Welcome to the world's most addictive sport! </font color=purple>
[img]/wwwthreads_images/icons/wink.gif[/img] Got Mud?
G.U.M.B.O. Mud Racing