An envelope is a solid representation of a movable part in a sub assembly. It shows all the object´s possible positions. Even the most extreme positions, like full-compacted-suspensions.
In automotive design, a wheel envelope is a representation of a car’s wheel movement.
To design a brand new car body, is not a simple task. First of all, you need to decide the wheel specifications for your design. Then, be sure that the desired wheels meet the legal coverage regulations. After that, you would better have the wheel envelopes. Because without them, probably, you will never get that right clearance. Designers are really demanding when it comes to wheel’s clearance.
So, how we do get the wheel envelope? Well, this is a mechanical engineers dutty. Although, there are many departments involved. Initially we need to do an approximate bill of components for the car. Calculating the total car´s weight. We add to the final calculation the weight of the passengers and their luggages
We have now the basic values for the CAD software analysis. Engineers simulate all the potential positions of the tires under normal driving conditions. They take in consideration the suspension and the system´s elasticity limit. As well as, wheel deformation, maximum and minimum tire inflation. Certainly, we are considering here the snow-chains too.
Front fenders are the most difficult part to design. The wheels when steering, apply the maximum turn allowed by the mechanism. And is so easy to have a clash here between tire and fender.
Most probably, the entire tire family for a specific car model will be simulated. Then they will be checked against the current design. Engineers will also confirm that there are no clashes to the body.
Having the envelopes surfaces, simplifies a lot the design process. That help design´s convergence to the manufacturing phase.