The original tire came from a model kit. From there I made a mold, and cast a resin version of the original tire. I had a few things in mind that I wanted in a true competition urethane tire, so using the resin tire as a master, I proceeded to polish the center of the tire to .675. That is the basic size of the Pro trac/ H&R/ CB design wheels that we use. That Inside dimension makes this tire a glue on. You can use any type adhesive, but clear nail polish allows the most flexibility when mounting. I did this for many reasons.
1. I don't like the way stretching a urethane tire effects the sidewall.
2. A stretched urethane tire is in a constant state of tension, and will eventually tear if stretched far enough.
3. A relaxed sidewall offers up some very nice cornering at speed. it allows the tire to flex sideways, and helps keep the contact patch running parallel to the track surface.
That being said, I also turned the outside diameter of the new master to 29mm. That gives us plenty of room to true them up, and still maintain scale modeling appearance. The 12.5 mm overall width, allows it to fit under most bodies quite nicely as well as offering up a pretty healthy contact patch.
These tires have a sponsor logo on the finish side that is large enough to hand paint relative ease.
I also rounded the upper sidewall of this tire, so it would traverse Plastic track rails that sometimes stand proud of the track itself.
On to the process. I injection mold these tires using shore 40 dry, to reduce any air bubbles, and they are post cured at 150 degrees for 4 hrs. then they are naturally cooled down in a moisture free environment. The end result of all this netted me a very nice Race bred Urethane tire with performance in mind, that not only looks good, but is a great race tire for scratchbuilding. These are not made for RTR Cars. here are a couple of shots of them mounted on a couple of popular wheels.
