maybe you should change to 1/5 scale 20% model instead of a 1/4 25% model.
You will be able to buy some parts, like tires and brakes (disc brakes) off the shelf.
You still could make your own chassis (carbon monocoque) etc.
I would not try to make my own tires, that seems a lot of hassle - if you want to make real rubber tires.
Foam tires is o.k. and not too difficult to make, but maybe they don´t look the part.
There is a world championship for 1/5 scale gas powered R/C cars.
A friend of mine used to race them in Australia.
They use air/foam filled rubber tires, even rain tires - you can buy them.
And best/funnies thing of all, they even use tire warmers/blankets.
A 1/5 gas powered F1 car looks like this.
Touring car like this
more info´s here:
http://www.fg-modellsport-gmbh.de/FG-In ... la1_e.html
http://www.fg-modellsport-gmbh.de/PDF-A ... b-safe.pdf