Introduction:

Back near the dawn of the automotive era, a fellow by the name of John Sipe was looking for a way to make his deck shoes more slip-resistant on wet boat decks. He came across the idea of cutting parallel slits in the rubber soles. He tried it and it worked! One thing led to another and the use of "Siping" for automobile tires soon caught on.

Siping is a process that involves no removal of rubber, just the insertion of slits into the tread blocks. It is very common in all-season automobile tires, but not too common in off-road, "Mud Terrain" type tires, which feature large, monolithic tread blocks. However, there are benefits to be gained from siping these kind of tires.

How to do it:

A couple of guidelines for siping:

• For tires used off-road, siping is usually confined to only the center tread blocks to minimize the possibility of "chunking" the outer tread blocks on rocks.
• The siping is usually kept 1/2" back from leading and trailing edges of tread blocks.
• For a good effect, siping cuts should be spaced approx. 1/4" apart and run at right angles to the direction of travel.
• The cuts should not be more that 1/4" (or the depth of the tread block - whichever is less) deep.
  • It is better to do shallow cuts then renew them as the tread wears down.
• I would also recommend letting the tread block design dictate the exact spacing and location of the slits.
  • Since tread blocks vary in size and shape around the tire, you may get 3 slits in one block, 4 in the next and 5 in the next.
  • If you feel averse to free-handing it, make a "story board" out of a stick with marks at 1/2", 3/4", 1", and so on to use in laying out the cuts.
    • I found a blue ink, ball-point pen works good for marking on rubber.

For a cheap tool, I took a utility knife with an old blade, broke it off and ground it down to a sharp point that projected a bit less than 1/4" from the knife body. You can leave the tire on the vehicle as long as it will turn freely, otherwise take it off for the siping process. Try out the siping tool both pulling and pushing it and use whatever technique feels most comfortable (I found alternating between pushing the knife on the nearest blocks and pulling it for the farther away ones worked best for me).

Below, you can see two of the tires I siped, one a 33x9.50 BFG MudTerrain and the other a 33x15.50 Super Swamper TSL-SX. THe Swamper was actually easier to sipe as it has very soft rubber.

Keen Swamper-Spotters will notice my "chevrons" are not quite factory spec. Before I siped them, I wanted to "soften" the tread up a bit by deeply grooving the center of each block to allow them to flex and conform to the terrain better. To do this, I took a circular saw, equipped with a carbide-tipped blade and set the depth at about 3/8" and then cut each block at the "V". It makes a pile of rubber crumbs and smoke but otherwise works quite well. The saw blade leaves a kerf a bit over 1/8" wide.

How it works:

The siping cuts allow the tread blocks to flex and conform to the ground easier than a monolithic tread. In wet and icy conditions, the siping cuts act like "squeegees" to cut through the water and allow contact with the surface below. They also help dissipate heat and prolong tire life.

I siped my BFG M/T tires which had about 25,000 miles of use as well as a pair of Super Swamper TSL/SX tires with about 2000 miles. The improvement on the M/Ts was impressive. With my rear locker, it was almost impossible not to chirp a tire when accelerating around a sharp corner, now, it I have to really try to break it loose. I also tested it in the rain with similar results. On ice, I was able to climb a steep hill covered with glare ice in 2WD with ease. Normally this hill requires 4WD to get up in this condition. While it was possible to spin the tires, if I backed off the throttle, they regained traction and pulled nicely.

I'm sold (and siped)!

Cost:

   Basically free and some time, less than 15 minutes/tire.

Project Rating:

For More Information:

• The SAF-TEE Tire Siper Process
• There's an excellent article on Tire Siping in the Mar. 99 issue of Peterson's 4WD and Off Road magazine.
• Some tire stores also do siping for about $9/tire.