Join Date: Nov 2003
Can´t remember where i got this article, but i think it´s a good explanation about foam tires.
Even though word says that almost all foam comes from the same rubber supplier in Japan, there will always exist differences in final product between foam manufacturers because foam tires are ultra sensitive to many factors regarding raw material storage, process and construction of the tire.
The first and most important difference that distinguishes one manufacturer from the other is the period and condition of storage of the raw foam. Some manufacturers store the foam plates at room temperature in their warehouse, and then work on them as orders come in. Others instead, have storage facilities with controlled temperature, light and humidity, where the foams plates are kept to mature for a certain period before working on them (just like wine, ham or cheese), and then have preservation time and ambient conditions of finished products based on their experience.
Another difference factor that affects grip is the type of glue used to fix the foam on the rim. The main characteristic that this glue must have is absolute resistance to high temperature, because at high temperature tracks, the friction of the foam over asphalt can make them reach temperatures of around 100ºC.
In theory, the best adhesive to glue foams would be some type of cianoacrilite, but this type of glue has the characteristic of hardening and crystallize the parts in contact, so the tire will not wear in a uniform way, forming small harder steps in the points of gluing, compromising traction and drivability.
Off course, each manufacturer has its own “secret” gluing formula, which must be resistant and flexible in the point of contact. The best gluing is the one that cannot be seen and felt.
Another difference that can condition the performance of foams is the type of cutting of the foam plates. Three types of cutting are known. Knife cutting, High-pressure water cutting and Laser cutting.
Each one of this methods will cause different behavior of the tires, specially the Water cutting method, which consists of a powerful jet of water mixed with and additive, and depending on the additive and its proportion to water, will vary a lot the tire behavior.
Then there is the Knife cutting method in which two high sharp plates turn in circle at high speed cutting the foam plate giving form to the final donuts to be glued on the rims. With this type of cut, the natural characteristic of the foam is kept unaltered, but you cannot modify the behavior, and you get fewer tires out of the plate because of the lesser precision of the cut.
Finally, there is the Laser Cut method, that offers absolute precision, but the heat that emanates from the ray tends to dry out the foam causing problems in the gluing stage.
Another difference in the characteristic of the foam tires is obtained by varying the internal diameter of the donut, depending on the desired behavior and wear of the tire. Even though it might seem insignificant, a difference of 1mm change, affects the tire behavior.
Finally the rim, which in the last years is having a very important roll in the development of foam tires. More flexible, so as to have a faster grip of the tire to the track, firmer rims so as to have more slide over the track.....but it depends on the car, some brands work better with flexible rims, others work better with firmer rims. In addition, you can have rims from the same mould, but made with different materials, and they will render a different behavior of the foam. Finally, it is important that the rim be resistant to hits.
To conclude; the variables that can affect the performance of foam tires are so many, that those who sustain that they are all the same, because they are made from the same foam supplier, are wrong big time.