Over the past few years, I've run a lot of different paddle combos on 4 different quads. I was looking through some picture files I had on my PC and figured some of you could use some help getting a visual on sand tire Roll outs and width.
First and most important is that what ever written or chalked on the side of your tire (ie. Skat Trak chalks a # usually 60 to 72) is not necesarily the correct rollout.
The size of the rims you use, the tire pressure, temperature, the manufactuers tire carcass design, and the number of buffs (ie. single buff, B-to-B buff, triple buff, comp cut etc) all affect the footprint and the overall diameter of your sand tire.
The rollout needs to the calculated based on the tire carcass, not including the paddle. There are two fairly easy ways I measure rollout:
(1) Take the sand tire (by itself) and slowly roll it across flat, smooth sand and pay close attention to when 1 revolution is complete, then pick up the tire - and measure the distance from start to end. You have to be careful when you start and stop the roll and go in a straight line and be precise.
(2) Another way is to take a paddle that is aired up (by itself) and place it on a hard surface such as your garage floor with the carcass (not paddle) touching the ground. With the paddle tire perfectly perpendicular to the ground, take an adjustable T-stick and measure the ground to the top of the tire carcass-only. Then measure the length in inches, and multiply by Pi (ie. 3.14) to get the rollout.
What you'll probably find is that your 21" tire is really not a true 21" and rather 20.5" etc.
Some things are pretty consistant: if you widen your rim width, you will also create a flatter profile (ie. less donut shape) and smaller diameter (ie. less rollout). Lower tire pressure reduces the static rollout of your tire, and definitely changes a paddle characteristic in the sand - there's a huge difference in running 3lbs air vs 5 lbs air.
Another thing, is if you go from an 8x8 rim to an 8x7 rim, the thinner rim width squeezes in the tire, resulting in a balloon-shaped tire, increasing the diameter by about 3/4ths of an inch = an addtional 2-3 inches in extra rollout.
So here's some pictures I had of some different paddle tire and rim combos to give you an idea of some combo's. I've had more combos, but I can't find all of the pictures over the years...
(Left to Right)
(1) 21x12x8 Skat Trak 6-paddle Extreme (chalk=67) on 8x8 rim vs. 21" STU Padla Brat on 8x7 rim vs. a 20" ITP Sand Star on 8x8 rim
(2) Same tires again, this time from tallest to shortest (left to right) Skat vs. STU vs. Sand Star
(3) This picture is the same 21x12x8 Skat 6-paddle Extreme (chalk=67) on an 8x8 vs. a 20x11x8" Skat 8-paddle on an 8x8 (chalk=64)
(4) This picture is a 21x12x8 Skat 6-paddle Extreme (chalk=68) on an 8x7 vs. 21" STU Brat on an 8x7
(5) This picture is a 22x11x8 Skat 7-paddle Hauler (chalk=70) on an 8x7 rim vs. a 21x12x8 Skat 6-paddle Extreme (chalk=68) on an 8x7
Whats interesting about picture #5 is that I had the 22" on an 8x8 rim first (I can't find the picture) and it was nearly identical in height and width as the 21" Skat Extreme (chalk=68) on an 8x7". But when I changed out the 22" skat from an 8x8 to an 8x7 rim, it narrowed the tire alot and increased the height by 1" = +3" more rollout. BTW - haven't run the 22" on an 8x7 at the dunes yet, but it will probably be more of a hill set up than a duning set up.
At the end of the day, in-glamis, my favorite "bang-for the buck" and "works great in any sand condition" set up on the 450's has been the 21x12x8 Skat 6p Extreme with a chalked 68 rollout, on an 8x7 rim
.... BUT - the Brats are about 1 length quicker up the hill for me AND double the price...
BTW - there is another factor to rollout, but I won't get into it - and that is the dynamic rollout of a paddle tire as wheel speed and revolution increases and the tire spins quicker, it increases the diameter - and different rubber compounds and ply thickness affect this...