Sand conditions differ from location to location, beach located riding areas (Pismo, Coos Bay) tend to require more tire than say Glamis, Dumont, or Sand Mountain. It has been my experience that about the time you rule out a tire you find a situation that you need it, so never say never when it comes to racing.
HP and gearing play a major part in set up, so here are some guidelines when selecting a tire. As stated earlier rollout is a major factor in traction. Rollout is the total circumference of the tire, so if your tire has a 72 on the side, that means with 10 psi in the tire it measures 72" if you were to wrap a tape around it, or it will travel 72" before it completes one full rotaion. If it's a 80 rollout tire then it measures 80" @ 10 psi in total circumference and so on. Rollout is important for both launching and accelerating. The more rollout you have the larger the foot print of the tire touching the sand is. Most think of side width when talking about surface area, but front to rear surface area is much more critical. A 80 rollout 10 paddle Glider will launch harder than say a 70 rollout 10 paddle Hauler/Extreme because there is more surface area. It's all about flotation and how much tire, not how much paddle is touching the sand. You can have 14 paddle extremes in the sand and be the first one to hit oil because they will dig faster, but the key is staying on top and moving forward, the larger rollout provides this for you.
The other advantage rollout provides is the ability for the tire to skinny at high speed and pull the paddles out of the sand. The skinnier the tire gets the less drag you have, the greater the MPH will be. Think about what a NHRA top fuel dragster tire does during there burnout, they get skinny the faster they spin. Skinny rims allow more rollout as do strictly buying larger rollout tires. Drag is created by the paddles themselves, it's not the amount of paddles on the tire that create drag, but the height of the paddle sticking in the sand that will deter MPH while creating more drag. As an example lets imagine 2 sets of tires with the exact same rollout 72. One set has 10 paddle Extremes the other has 10 paddle Gliders. The Extremes will launch harder and run the 1st half of the race stronger while the Gliders will launch slower, but run the second half of the race up to 2 mph faster than the Extremes due to less drag. Speed kills!
Weight is always a factor when racing, but can be an advantage when it comes to rollout. Do larger rollout tires weigh more than smaller tires? Absolutely, but when racing the added weight actually helps the tire to bite sooner and hook before a lighter tire will with more "hook up" due to surface area and weight. The weight is only detrimental in the initial drop of the clutch, because it takes more power to spin 16 lbs than it does 13 lbs. of tire, but from that point forward it is an advantage. It takes very little power to maintain the rotating mass once moving in comparison to initiating the spin.
It's difficult to make tire and gearing recommendations for the majority because everyones builds and set ups are different on top of the sand conditions, but here are a few guidelines. If you are a recreation rider who dunes the majority of the time I would recommend the least amount of paddles as possible on a 70 - 72 rollout tire. This will help the handling and allow the bike to be thrown some body english while still providing adequate traction to climb. To much paddle and the bike will not want to turn.
If your a hill shooter that spends most of your time at the hill I would choose a tire with the most rollout and the least amount of paddle that fits your HP application. The heavier the bike/rider is the less amount of paddles will be needed to hook the bike. The lighter the bike/rider is a higher amount of paddles will be required to launch the bike.
300 ft. racing is all about getting out of the hole, but mph is a tuning tool as well. Normally your mph reflects you 60 ft. times and how well you are coming out of the hole. Faster launch = higher mph, Slower launch = lower mph. It is a helpful indication as to where and how to make tire and gearing adjustments. You have to find the happy medium between launching and mph. OEM frame bikes on gas should go with large rollout tires and 12-14 paddle Extremes. Powers Adder bikes with NOS or Turbo will need 80+ rollout staggerds with 16 - 20 paddle Extremes depending on track conditions.
Gearing is much more complicated and power plays a huge role in what gearing to run. Here are a couple of tips to remember. Normally you want to gear your bike so that it will accelerate through the highest RPM that you are making power at. If you over gear a stock bike it will not pull 5th gear with any rpm because of the lack of power in that rpm range. On a 3 mod bike that might be 6500 rpms, on a race bike maybe 8500 rpms, so gear your bike with your riding style to run in that rpm range as much as possible. If you are a racers you want to gear your bike 1 tooth off the rev limiter as you cross the line. So, if your gearing is 15 x 38 and you just touch the rev limiter as you cross the line, go to 15 x 37. 1 tooth on the front countershaft sprocket = 3 rear teeth. Every 2 points of tire rollout equals 1 tooth on the rear sprocket, If your running 15 x 38 with 72 rollout tires and change to 80 rollout tires, you need to add 4 teeth to run at the same rpm that you were with the 72s. The new gearing would need to be 15 x 42 or 14 x 39 to compensate for the larger diameter tire. Remember going down on the front sprocket size is lower gearing, increasing the teeth is higher/taller gearing. The opposite is true for the rear sprocket, higher/taller gearing is a smaller rear sprocket, lower gearing is more teeth or an overall larger rear spocket. Also something to remember, for every 1 tooth on the rear spocket that you add or subtract it is equal to approx. 250 rpms up or down on the power band. 1 tooth up or down on the front countershaft sprocket is equal to approx. 750 rpms.
Alot of this has come from trial and error and much of it is never discussed amongst racers. Hope some of you can benefit from this information.