I use them mainly to make wider tires than are available other than by special order from the silicone tire makers. I like as wide a tire as I can get to suit my needs. I use old worn down sponge tires with the big and full hubs such as made by JK, HTK, or Alpha on my 1/24 cars. This gives me at least a .450" inside diameter for inserts. I like them worn down to about .750" for rears or trimmed down to that size. Adjust for your needs by trimming. I make them about .030-.040" smaller than the desired finished size. That allows about a .030-.040" coat of silicone. I have found this brand of silicone to work the best so far: Permatex black silicone sealant available in 3 oz tubes at the local auto parts store.
I prepare the tires by truing to exact size on a tire truer of commercial or homemade type, or a handheld drill motor and sandpaper block. When truing, make sure they have a true tire shape with rounded sidewalls and a rounded edge to resist grabbing the slot or braid in corners. It also makes the silicone stick to the tire better and resist peeling at the edges. Very important point in keeping them intact for awhile while racing them. After truing them up, now you must clean them very well. I use lighter fluid and a clean rag. Wet them down several times and wipe off any truing dust or tire goop material, so the rag shows clean when done.
Mount them on a spare axle near the end so you can easily grip them by the axle without touching the tire.
Mount the tire and axle in a lathe chuck or use a small drill press or hand held drill motor, held in a vise to have control, of how they get worked on. Make sure the motor does not spin them too fast or you will not get the silicone to stick and get some thrown off in your face (messy).
Once mounted in the chuck, open the tube of silicone, and with a clean dry finger, apply a 1/4 inch long, ribbon of the silicone as it comes out of the tube to your finger and then rub it in vigorously into the tire surface working the first coat in firmly to get seated it into the tire surface completely. It will take at least three to four applications of the same size amount of silicone to coat the tire well enough to build up a coating of at least .030 -.040" to come to the desired diameter of the tire.
When all coats are applied, clean your finger off well. I recommend a finger wetted with spit or (water) to be applied to the tire surface to work the silicone now on the tire surface into a smooth and complete coating. Especially working it down around the sidewalls to the rim. Make sure the sidewalls have a good coating front and rear.
The spit or water will keep it from sticking to your finger, so it can move the silicone around where you want it. When it looks good to you. Stop and get out a smooth flat surface such as the recommended Lexan sheet, 1/8 inch thick by at least 6-8 inches long. A piece of glass or a mirror will work as well. The sheet is then wet with water or (spit) and applied to the tire surface either by bracing the bottom side against the nearest hard surface, or as I prefer just hand-hold it against the tire surface and lightly press against the tire to make a good true flat surface. If you press too hard, you will run the silicone over the edge too far and have to work it back to the center again. This will take some practice to get it the way it looks best. If you get a sharp edge, wet your finger again and work the sharp edge back to the middle and use the sheet again to flatten and true again.
Once it looks right and true, watch the run-out, remove the axle and wheel from the chuck without touching the tire. Place the axle end, in an upright position in a hole drilled in a block of wood so it will stand upright by itself. Then when both, or as many as you have done, are mounted in enough holes, place the block of wood under a 60 watt lamp to warm them up for at least three hours to dry the silicone out. When dry, you can true the tire up, or just run them in. I find as I get practice at it I can get my tires to within .010" enough for racing purposes.Many of them are ready to run right after drying and just a few laps of tracktime will true them right up.
I realize this is quick and dirty, so if you have questions please ask and we will try to give an answer. It looks easy but does take some practice. Don't attempt this on wheels with inserts as the silicone will tend to wrap around the sidewalls and get into the inserts and get messy. On plain wheels it is easy to clean it out and then add the inserts after.
Lucks of luck,I have some of these tires still around and usable from some I made in the middle '80s. The silicone tends to seal the sponge rubber from the air and does not allow it to dry out as it normally does. They stay soft for quite a while while fully coated.
Later on I found I could make a fixture out some old aluminum I had access to. It fit in my lathe and does make it very easy to get the tire diameter very close to each other using the lathe hand dials. I then mounted a piece of Lexan in it to smooth the silicone out and and keep it very close to level from side to side.
