Getting a Grip on HO Tires

Rear tires of different widths,diameters and compounds can have a dramatic effect on your cars acceleration.straight line speed, cornering capability and overall lap times. Just like in real full size racing,simply changing tires can affect your cars gearing and stance. Originally,your car came from the manufacturer with a set of rear rubber compound tires. These provide adequate traction and there is nothing wrong with them as long as they remain pliable. As time, temperature, humidity (or lack thereof) and normal wear take its toll ,the tire will necessarily need replacing. You can opt for stockers or use something different.
Upgrades are available from Wizzard,Scale Auto,Slotech,Twinn-K,HO Express and others. "Graupners" are a relatively inexpensive upgrade ranging in price from $1.00 - $8.00 a set. Let's take a look at what is available in general and see the changes and developments which have occurred in HO tire technology.
One of the first changes which came upon the HO scene was the sponge compound tire, Sponge "rubber" has a couple advantages. First, it can be reduced in circumference and ground to the desired size, either using the run sand method (tires fitted to an actual car) orby using a homemade or store bought tire mandrel fitted to your moto-tool of drill using various grits of automotive sandpaper (200-1500 grit).This method will true the tires surface for smoothness, lower the tires overall profile and round off sharp edges in the hope of improving traction and eliminating the dreaded "flips" under acceleration and cornering. The tire diameter can be checked using a set of calipers,micrometer or with one of the new tire templates offered by Scale Auto or Vanbo Racing. Sponge tire can vary +or- .001" depending on athmospheric pressure and ambient air temperature.
Sponge tires should be glued to the rims you are using with contact or rubber cement to avoid slipping when running your car. The next phase in the tire evolution cane the Silicone Compound tire. These are available under many names and come in an assortment of colors. Silicone tire cannot be ground and they only come in 2 diameters that I am aware of. They can be slightly improved with run sanding on some fine grit paper with synthetic oil added to provide a "scuff" which can aid slightly in cornering and reducing lap times. (clean them off before you use them though). Silicone tire can be fitted to most rear rims whether delrin plastic, aluminum or other materials since they are self molding to the rim.
The most recent change in tire technology and the only true competitive choice currently is the Applied Silicone/Sponge tire. These are available from a variety of manufacturers and come in a multitude of widths and more importantly diameters in increments of .002".
The tire come already mounted to high tech rims (usually molded and machined lightweight delrin plastic) which require special mounting and removal using a wheel press or puller available from your hobbyshop, mailorderhouse or raceway. These tires come in variu=ous sponge densities and different grades of silicone for different adhesion situations depending on the class of competitive car you are building. They will run well on plastic track or routed/epoxy coated layouts. They also last longer than plain sponge tires.
A less expensive alternative is to create your own homebrewed silicone/sponge tire. As mentioned previously,a pair of regular new sponge tires can be purchased, ground and trued. Once you are satisfied with this, you can proceed to mount each tire on a suitable rim and then place each rim on a rear axle. Secure them in a vice (use old axles as this step will distort them and make them useless). Purchase some clear silicone in a tube (G.E. Or Dow Corning work well). Mix the silicone with mineral spirits in a disposable container. (3 parts silicone to 1 part mineral spirits). Mix well and apply using a modeling spatula or clean finger to the tires outside and sidewalls. Allow to dry overnight. Do not handle them after the mixture has been applied. Make it as smooth as possible and work quickly before the mixture sets up. The result will be a set of low budget "skins".
Regardless of which tires you choose to use for your application, it is important to keep the clean. For routine maintainance and cleaning use a good quality masking tape. Roll the tape onto a flat surface, tacky side facing up. Then roll your tire over the sticky tape. This does a fine job of removing dust, track debris and other surface dirt. I recommend doing this before racing, after each heat and again before you put the car back into your pit case. For a more thouough cleaning, use isopropyl alcohol or lighter fluid. and allow to air dry. Tire should be monitored for wear, dryness and loss of pliability and chunking. Clean and replace them often.