How to choose foam tires for 4WD Touring Sedans (Part 2)
More on the cost of ownership: The main disadvantages of foam tires are that they tend to give less run-time than a rubber tire, and the rims are not as robust as those used for rubber tires. If you tap a wall or get hacked, the soft foam tires could be damaged or chunked (torn). Sometimes the tire can be fixed with thin CA, but usually lightly chunked tires become "practice" tires.
On hot asphalt, foam tires will give you the highest
level of traction available. Foam tires can be run more aggressively
because of better traction recovery characteristics when you spin the
tires. Rubber tires have a harder time regaining their grip after they
break loose. Another benefit of quality foam tires is that you don't need
to worry about unglued edges. I still recommend checking the tires
rim edge between rounds; but it's not as critical as with glued rubber
Another element of tire wear is related to the suspension geometry itself. If the suspension is not adjusted correctly or if the material used to make the rim is too flexible, the foam tire will not wear evenly. This means that the tire diameter won't be the same across the contact patch. This can induce handling problems in the car by creating an apparent camber angle or stagger (tires of different diameters on car). Typically, the softer the tire, the faster it will wear, and the easier it is for the tire to deform and for the contact patch to get coned out. All of these characteristics lower the useful life of a foam tire.
If you have access to a tire truer, it will greatly increase the useful life of the tires. It will also allow you to reduce the tires diameter to reduce side wall flex and make the contact patch more consistent. For most, a tire truer is a very big investment in the neighborhood of $200-350 depending on quality and features. If you are going to be running foam tires for most of the season, then a tire truer will almost pay for itself by allowing you to run the tires for a longer time. Not only this, but traction will feel more consistent from run to run. If you happen to have a lot of time on your hands, you can purchase foam doughnuts and mount/true your own tires at half the cost of buying the tire RTR.
Chassis Setup for Foam Tires:
We already know that foam tires have the highest possible level of traction than any other type of tire -Under the right conditions. What will all this extra traction mean in the setup department? The extra traction will be translated into extra body roll. If the chassis dampening is set too soft, then the car will roll-over.
Roll Over problems seem to be one the primary problems of beginning racers when they switch to foam tires. They forget to stiffen the shocks and the car spends more time on it's lid than on the tires! What can you do to "stiffen" the car if you don't have a box full of shock springs and a gallon of shock-oil at hand? The first thing is to do is to lower the ride height of the car. This will lower the center of gravity of the chassis, and make it harder for it to roll-over. The next thing to do, would be to decrease the droop on the suspension arms. This will limit suspension arm movement and help keep the car from swaying too much on the corners.
When I'm setting my car up for the large asphalt tracks I usually take my parking lot setup and set the camber to -2 deg all around. This is done to prevent the tires from coning out. Another setup change is done in the suspension department. I increase the shock fluid viscosity and go to the next stiffer springs front and back. I do this to take some sensitivity out of the chassis. If I still need less traction, then it's either a tire change or I stiffen the shocks some more or I dial out some traction with anti-roll bars to get the car tuned for the corners.
I like to keep tabs on tire wear with a caliper. I measure the inside and outside diameter of the tire. If the outside is wearing more than the inside then you need to increase the negative camber. If the inside of the tire is wearing faster then I reduce negative caster. On tracks with a lot of high speed right hand turns I also like to rotate the tires left to right to promote more even tire wear and extend their life.
Racing with Foam Tires:
I tend to do less tire swapping when I run foams, than when running rubber. This is because there are only a few tire choices available when you are running foams -that is, after you find a brand that yyou are happy with. Once you find your brand you will probably only need 3 to 5 different compounds. There is going to be a Hot/Warm/Cold base tire selection, but after you make your in initial choices, the rest is done with chassis setup.
It's not uncommon for electric racers to use traction additives on their foam tires. Electric race times are relatively short when compared to a 10-15 minute nitro main, This is one of the reasons why I don't recommend their use for racing conditions. Results are just not repeatable enough for me. Why introduce an additional sometimes uncontrollable variable into your traction formula?
Where do you start? Whatever the guys wining the races are using -that's what I start with! After the initial "roll-over" phase use your judgment as to the tires traction/wear/cost and take it from there. I like Super G's and TRC tires, there are a couple of new brands out there. If the tires aren't lasting you at least 4 Sunday races then you might have a very rough track or you are using very soft compounds. If you are clue-less as to what the compounds that you need then run RED (50) fronts tires and PURPLE (40) rear tires -that should be a good starting point.
A special note: If the track is very cold with outside air temps in the 40-50F then you may be better of using low-temp belted rubber tires. I've done this in the past with great results. While the "foam" guys where complaining about no traction I was clocking the laps with my rubber tires.
Once again -When running foam tires you will tend to have more traction that what you need and taking traction away with suspension settings is a lot easier than "creating" traction with suspension settings. This allows the beginner more room for error when setting up a car that runs on foam tires. The only drawback is that you need to stay away from the walls!
chart: Tire Manufacturer
I've compiled this short list of tire manufacturers to help you find
what you're looking for. This is in no way an endorsement from my part -I
can't guarantee that they will work for you! Looking at what the winners
are using is going to be a lot more valuable to you than what my favorite
Whoop some R/C car butt!!!
Eric Perez If you have any questions or would like to discuss any of the topics
presented in this article, feel free to e-mail
Tire Manufacturer Index:
I've compiled this short list of tire manufacturers to help you find what you're looking for. This is in no way an endorsement from my part -I can't guarantee that they will work for you! Looking at what the winners are using is going to be a lot more valuable to you than what my favorite tires are.
Whoop some R/C car butt!!!
If you have any questions or would like to discuss any of the topics presented in this article, feel free to e-mail me.
This page last modified: 07/26/11