# Tutorial: How to model a variable dimension driven car Tire in Solidworks 2013

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1. ### Step 1:

Like in the first tutorial first you have to define (Add) your global variables: Right click on Part tree>Hidden Tree Items>Equations>Show.
You can choose and enter the numbers in mm, inches, degrees or just blank integers.

The Rim Width is normally shown as 10J meaning 10 inches. Rim Diameter is also in inches and the Tire Width is in millimeters. The aspect ratio is the ratio between the Tire Height and Tire Width.
For easier calculation I defined the Tire Height out of the Aspect ratio like shown in the picture.

2. ### Step 2:

First create the Axis like shown in the picture above.
The Dimensioned Axis are Rim Fits. If you are already modeled the Rim you know that the Rim Width is the whole width of the rim – so in order to fit the Tire into the rim you must enter the equation: ˝RimWidth˝ - 10mm (because on my Rim there is a 5mm Flange on either side of the rim).

Align the axis so that they will be centered: for the dimension just click on the new created dimension and divide it by 2.

3. ### Step 3:

Now add another axes for other dimensions.
The widest axes are the TyreWidth and its alignment.
And the horizontal axes are: ˝RimDiameter˝/2 and on top of that is the ˝TyreHeight˝ dimension.
Now you should have all axes finished.

4. ### Step 4:

Next create an easy tire cross section.
I defined the coincidence of the vertical arc with equation: ˝TyreHeight˝/2. Don't use Tangent relation here or else you will get errors once the RimWidth is Greater than TyreWidth.
I have defined the Upper surface with the equation: ˝TyreWidth˝*0.85.

5. ### Step 5:

Next create an offset of the sketch contour and erase the upper entities and connect it with an horizontal line like shown above.

Next mirror the sketch over the main vertical axis.

6. ### Step 6:

Next use the revolve feature to create an basic tire geometry.

7. ### Step 7:

Next create an Surface offset and hide it – this will be the rib depth later on– you can also make this variable driven – this way you can change the tire ˝wear˝.

8. ### Step 8:

Next create an sketch on the cross section of the tire like shown in the picture.
The equations are based on tire width so the ribs are varying with the tire width.
[1]= ˝TyreWidth˝/200
[18,846]=˝TyreWidth˝/13
[4,9]=˝TyreWidth˝/50

The tire width here was 245 mm so you don't get confused by the numbers – don't pay attention to the values, because I have change them a lot in order to get it working.

9. ### Step 9:

Use the revolve feature to create the Ribs.

10. ### Step 10:

Now comes the ˝complicated˝ part – creating the tire pattern.
I have gone for an easy one – partly because of the low computing power and partly because of the easier presentation.

You can create your own ones but be sure you make them properly driven, so when you change other dimensions it won't get messy.

Here I've used some reference points like shown in the picture and then i have connected them using arcs.
Try to avoid the splines because it is hard to fully define them.

11. ### Step 11:

After you are finished with the initial contour, just mirror it once through horizontal axis and then once more through vertical axis. Then make the first mirror contour for construction.

12. ### Step 12:

Next create an Cut Extrude and select up to Surface. Here you will select the Surface we have created before.

13. ### Step 13:

Next we have to create an Circular Pattern of this Cut Extrude.

Select the Cut Extrude and click on the Circular Pattern. Select Full Crown /360 degrees – Equal Spacing. In the Number of Instances type in the equation: ˝RimDiameter˝/20 and click OK.

Maybe you will get some errors – just select the same options like in the picture and you should get rid off them:

14. ### Step 14:

Just create a sketch as shown in the Picture. You don't have to create variable driven dimensions here, because the major rib pattern is ratio-dimensioned and the distances will stay about the same – but if you want you can also dimension this ribs with global variables.

I also had a problem because my computer started to work very very slow – thats why I didn't payed further attention to more details.

15. ### Step 15:

Finally create a Circular Pattern with the same equation for Number of Items like for the previous Cut Extrude. ˝RimDiameter˝/20.