..::tyre tread::..

This type of effect can be quite difficult to reproduce, especially with some of the tread designs out there. Initially I was going to try to reproduce a standard radial design, but the student I was teaching that weekend (cheers Mike!) suggested not copping out and producing a simple design.

As I have recently been modelling out an Audi TT, producing the sports tyre designed for this particular car seemed logical. A simple search on a tyre manufacturer’s site, namely Michelin (in this instance) generated an image of the tyre, albeit slightly small but still legible.

Based on the Michelin Pilot Sport tyre as it fits the wheel of an Audi TT, the initial layout and design of this tyre pattern would confuse a novice modeller. But this doesn’t have to be the case. As with any emulation task, simply break down the problem into it’s core elements. For this particular tyre tread design, once the elements had been analysed it was a simple case of recreating the tyre design.

Okay, so what elements have we got to this design? Firstly we’ve got a uniform repeating pattern around the tyre. This pattern flows from the outside edge of the tyre into the centre circumference of the tyre, but the pattern distorts somewhat, like it’s been grabbed and pulled around the inner circumference of the tyre. The tyre’s side walls are also curved to meet the tread and are also shaped to fit the wheel. As the pattern is mirrored on the opposite side, once the geometry has been created on one side, it can be easily mirrored on the other side using the Symmetry modifier.

So how do we go around creating the geometry? Initially, a basic cylinder primitive with the required number of iterations and height segments is created and then collapsed to polygons so we can begin designing the tread. As it’s a repeating pattern, all we need to do is to work on one specific area, and this area can then be duplicated around the cylinder, thus completing the tread. Due to the amount of iterations set in the initial cylinder primitive, all we have to do to design our tread pattern is to select relevant edges and chamfer them to create a template for the inner parts of the tread. To create these, a simple negative extrusion is performed and vertices target welded to ensure the inner parts of the tread continue around the side of the tyre.

Reproducing the tread around the tyre is a simple procedure, but for this model we are not going to use 3ds max 5’s symmetry modifier to distribute it. The reason for this is due to the way the geometry has been chamfered and welded. Adding a symmetry modifier will add extra edges and vertices to the geometry which may not be present for every tread piece, which if we meshsmooth afterwards will result in an irregular-looking tyre! Therefore we delete the unwanted geometry and rotate clone the tread object. Afterwards, we simply attach all the tread pieces to the original tread geometry and weld the adjacent vertices together, ensuring the centre side vertices are also welded together. To create the stretched pattern around the circumference of the tyre, the middle polygons are selected, and with soft selection enabled, are rotated slightly. This will smear the polygons around the tyre, thus creating the desired inner tread pattern. The outer tread should be rotated the opposite way (also with soft selection) to create the required tread pattern. The side geometry is then extruded back way past the opposite side of the tyre to form the inner part of the tyre that can be attached to the wheel. Finally, a symmetry modifier is added to the tyre geometry so the entire tyre is mirrored and welded. As this mirrors one side of the object to the other, the inner tyre extrusion is also welded and therefore forms a tube from one side to the next. If desired, this internal tube geometry could be deleted as it will not be visible once the tyre is assigned to a wheel.

	Create a cylinder in the Left Viewport at 0,0,0 . I’ve used a radius of 52.647 and a Height of 35.926 as these dimensions fit the outline of the wheel on the image planes of the car I am working on. Use whatever dimensions are relevant to the image planes in your scene. Set the Height segments to 5 and Sides to 80.
	Select an edge loop along one side of the cylinder. Chamfer the edges twice to create a curved edge. Select the innermost polygon (the large one on the side) and move it inwards slightly to create a slight inset.
	Select edges running from the outside edge to the middle of the cylinder, and select ones running around the cylinder’s middle. Chamfer these a little as illustrated to create edges that we can extrude back to create the template for our tread.
	Extrude these new polygons back a little as illustrated. Target weld vertices created from the extrusion at the outer edge to the existing vertices on the outer edge as shown. Inset the inner large polygon and collapse. Select the required polygons to create a repeating pattern when rotated, invert the selection and delete the unwanted polygons.
	Rotate clone the object (not the sub-object polygons) 9 degrees and enter 9 as the number of copies. Select the original geometry and attach all copies. Select all vertices and weld them together. Select the inner vertices (previously the large side polygon) and collapse them.
	Select the side polygons, inset, reposition inwards a little, inset again and extrude backwards past the other side of the tyre. Slice the tyre to add extra edge rings between the middle and side of the tyre if desired. Select the middle ring of polygons, and with soft select enabled (as shown) rotate the polygons a little to distort the pattern. Select the outer ring of polygons slice them to add and with less soft selection rotate them a little the other way. Add a Symmetry modifier to mirror and weld the geometry.
	The final geometry. Additional chamfering could be made on the harsh edges to smooth the tread out somewhat and meshsmoothed if the tread has to be viewed at very close proximity.
	Zip file to accompany

..::tips::..

To get extra realism, I would recommend basing the tread on a tyre that is suited for the car you are modelling. Most tyre manufacturers have a list of tyres which are searchable by car manufacturer and model. This particular tyre has been applied to an Audi TT wheel in the final render as it was designed for this car.

To complement the wheel, try adding additional bump mapping to the tyre’s side wall. Additional bump decals such as manufacturer name, size, model, pressure information and any extra detail such as lines and patterns that would be difficult (and pointless) to model can be added this way to add extra realism to the tyre.

The final tyre texture should be a very dark grey around the tread, fading off to a slightly lighter grey around the side wall where the rubber is thinner and has accumulated dirt around any bump mapping. The inner parts of the tread should also accumulate dirt and debris from the road and should be added accordingly.

Due to the wide variety of treads out there, each tread design will require a slightly different creation method. This may range from different iteration values in the base primitive, different extrusion patterns, slicing, chamfering (etc). It may require a different modelling method depending on the complexity of the repeating pattern.

Initially published: 3D World magazine, Issue 41, August 2003.

Copyright © Pete Draper, August 2003. Reproduction without permission prohibited.

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