Building Simple But Accurate Tires
and Wheels


Building low poly tires is a fairly simple process but a little preprocess research is the best place to start. The main thing you need to take into consideration is the application. I'll be using FSDSv1.6 to make the shape of a tire and wheel for a heavy duty vehicle, in this case a transit bus, but the same process can be used in just about any of the 3d programs, like gMax, for any type of vehicle. The important thing in low poly modeling is economy of design. In other words, make only what is necessary to get the job done. Use your texture for the illusion of detail.  
Many of the major tire manufactures have websites where you can find the basic dimensions of various sizes of tires. The tire size used on my transit bus is 11x22.5R75. This boils down to a Tire Cross Section of 11 inches, mounted on a 22.5 inch diameter wheel and the Tire Section Height is 75% of the Tire Cross Section. If you can find your tire size on one of these sites, look for the Overall Diameter and Tread Width. 

If you can't find the Overall Diameter you can get close by multiplying the Tire Cross Section by the Tire Section Height, then double it and add the Wheel Diameter. There is no easy formula for determining the Tread Width, so without published information you'll have to use your artisitc license. Luckily, I found that my tire has an Overall Diameter of 41.4 inches and a Tread Width of 10.8 inches. One other dimension to take into consideration is the recommended Rim Width. In my case it is 8.25 inches.  
Of course, if you have access to the real thing, that would be the best source for all of this information or prehaps your local tire shop will give you the required info. Most business don't mind a quick visit from you during their slow times if you explain what you're doing and come prepared.  
If you have a digital camera or even a regular camera and don't mind the wait for developing. take some time and go hunting. You'd be supprised what you can find on an overcast Sunday down in the industrial areas near you. Take some note paper and a tape measure and maybe even a couple of straight pieces of wood or 4 foot levels. If you can find a helper that will put up with your madness, then all the better.  
When taking images, I find that the overcast day is perfect as the light is more evenly distributed and I don't have to deal with shadows so much. If shadows are a problem, experiment with using your flash. Try and get your camera as perpendicular to the center of the subject as possible.  
Depending on your project you might want to expand your information gathering to include such things as lights and licence plates. Let your imagination be your guide.  
I am now ready to start my tire and wheel project. 

Depending on the measurment system you use, you might want to use Calculator to convert most of your measurments to either decimal feet or meters before you start. I use decimal feet. Since my tire overall dimeter is 41.4 inches, I first convert to decimal feet. 1 divided by 12 is 0.0833. 41.4 times 0.0833 is 3.45. (my tire diameter in decimal feet) So my Radius is 1.725 feet. If you start this as an independent project you can save the part out and use it in any other project where you need a part like this. I start by adding a tube pluging in my Radius. I set the Points/Section to 15 as this will give me a fairly round object with a flat area on the bottom. My length is 20 feet but you can use what ever you feel works best for you. On a piece of scratch paper I have sketched out the profile of the object and determined the 7 sections will do the job. By setting the Tube to Structured, I can add more sections if I find it necessary. I make the Tube closed at both ends and I want it built along the X axis with its origin and center at 0,0,0. 

In point mode, select the the two sets of end points and scale them to the diameter of the WHEEL. Using Calculator, I find the scale factor I want. 22.5 inches (the diameter of my wheel) divided by 41.4 inches (the Overall Diameter of my tire). So I want to scale these points on the Y and Z axis by this factor of 0.5434782. 

Select the next set of points in from each end.  
Scale these points to about 60%  
Repeat for the next sets of points in.  
Scale them to about 85%  


The two inner most groups of points will become the top edges of the tread. Since my tread is 10.8 inches wide, I want to translate each set of these points to their proper location. Using Calculator, 10.8 inches times 0.0833 my conversion factor = 0.9 decimal feet. I divide that by 2 and I end up with 0.45 decimal feet. This is the distance I want these points on each side of 0. Checking the X location of a point I see I need to translate this set of points 0.979 decimal feet. The set on the other side will have to be translated +0.979.  
I repeat the process for the next set of points outward. These points need to be at the Tire Cross Section Width, 11 inches. This with the next two sets will make the sidewalls. 11 inches (my tires Cross Section Width) times 0.833 = 0.9166 decimal feet. Divided by 2 = 0.4583. 4.286 minus 0.4583 = 3.8276 decimal feet.  
7.143 minus 0.45 = 6.693


Next I translate the outer most point groups to the Rim Width. 8.5 inches times 0.833 =  
0.7083 decimal feet. Divided by 2 = 0.3451 decimal feet.  
10 minus 0.3451= 9.6485 decimal feet.  
The basic tire is finished and ready to be textured. It only has 107 polys so it is very frame rate friendly. If you are using in a situation where the polys on the backside can't be seen, you could eliminate those polys too.  