Expert Advice - Rollers

Every Mini 4wd has to have rollers. Without rollers, it would be impossible for a car to run on tracks. Rollers come in all sizes and shapes. The current rollers can be divided into five categories: plastic rollers, plastic rollers with ball bearings, aluminum rollers, aluminum rollers with ball bearings, and ball bearing rollers. Below I'll talk about these different kind of rollers.

Plastic Rollers

These are rollers that come with a Mini 4wd kit or hop-up parts (ex. Sliding Dampers). Some of these rollers have rubber o-rings on them, and others are just plastic. For those of you using these, I have one thing to tell you all: these are the worst kind of rollers ever! They are plastic, and of course, breaks much too easily. The ones with o-rings are even worse because o-rings slow down your car. But no matter how bad these rollers are, they are still useable.

Plastic Rollers With Ball Bearings

Unlike their cousin, the simple plastic rollers, plastic rollers with ball bearings are the best kind of rollers that gives your car top speed. These rollers have a very thin edge, making the lowest contact with the wall of the track, allowing it to go very fast. Ball bearings are in the middle, lowering the friction, and making the rolling process smoother. There's one thing that's not so good about this type of roller, though. Because the edge of these rollers are so thin, it gets worn out real quick, and the plastic roller needs to be replaced. Unfortunately, Tamiya doesn't produce this type of roller. Still, these are truly the best rollers you can find.

Aluminum Rollers

Aluminum rollers are the second best rollers after the plastic rollers. They are made of aluminum, of course, and is stronger than plastic. All these rollers have rubber o-rings, and if put on a car, slows it down greatly. So if you want to use these rollers, take the o-rings off. These rollers are not suggested for super fast cars.

Aluminum Rollers With Ball Bearings

Anything that has ball bearings is better than those without it, so naturally, these rollers are better than the aluminum rollers that doesn't have bearings. The aluminum rollers that have plastic o-rings and not rubber o-rings are the best, because creates less friction. These rollers are very common, but still aren't better than plastic rollers with bearings.

Ball Bearing Rollers

These rollers are simply ball bearings. They are quite effective, but are also quite heavy. It is useful to weigh down the front of the car so that it doesn't fly. 6mm Ball Bearings can also be used. They are very light, and makes your car go quicker compared to other ball bearing rollers.

Where To Put Them?

Now you know the basic roller types. But where do you put rollers, and what's the best place to put them? Let's first begin with the basics. A fast car needs a total of eight rollers; four in the front bumper, and four in the rear roller stay. With this design, you get two levels of rollers, giving you a much more stable car. That was all you needed to know, and eight rollers are what you need to add. Now let's go on to small details.

You'll notice that the front rollers are bent at an angle of up to 15 degrees. But why is that so? Mini 4wd has been designed this way so that a car won't fly. If you try to pull the head of the car to a 0 degree position, it'll definitely fly. As a car is running, the front of the car needs to have a force that pulls it down to the track, and that's what the angle does. So if your car flies alot, you might either want to pull your bumper down a bit more or sand the plastic which the bumper is screwed onto to make an even larger degree. But remember this: The more the degree, the slower the car will be, but has a less chance of flying. The less the degree, the car may be faster, but has a better chance of flying.

Flying is horrible, but there are even more ways to prevent flying. On some plastic rollers and aluminum rollers, you'll see rubber o-rings. These create friction and slow a car down. It also keeps the car on the track, therefore lowering the chance of flying.

After making sure that your car won't fly, it's time to study the height and positioning of the front rollers. The first two lower rollers usually should be attached directly underneath the front bumper. This type of positioning lowers the chance of flying off the track. The other two rollers would of course be located above the front bumper, usually 17-19mm away from the bottom rollers. The rollers in the rear would need to have a distance of 23-27mm away from each other. Of course, you don't really need to follow that rule. Just remember this: The higher your rollers, the more stable your car would be, but will become more slow. The lower your rollers, the more unstable your car would be, but will be faster.

Roller Sizes

Rollers come in different sizes, and are measured by their diameter. Different roller sizes used on a car can greatly effect its speed. The diagram above shows three cases which will be explained below.

1. Front and back rollers at the same size
The car will run straight. Minimizes the power loss, and is the best possible setup.

2. Rollers larger in the front
Front roller diameter is bigger than that of rear roller. Suitable for courses with many corners since this pushes your car towards inside of the course when rollers contact a wall.

3. Rollers smaller in the front
Smaller in front: Rear roller diameter is bigger than that of front roller. This makes your car run along with a wall. Gives stability during cornering, but creates power loss.

That's pretty much all the knowledge there is for the rollers on a Mini 4wd.