By using two valves, a bleeder and a standard tire valve, this team can inflate or deflate
The spun process is done a little differently. The original tube of metal is larger than the die and placed outside of it. It is then spun into the die and tightly against it. Since the die is machined perfectly and the shell is forced to conform to that shape, the result is a much better, almost perfect run-out with control of critical thicknesses in areas where we would see the most flexing and stress.
Spun wheels are more expensive due to the extra time in the process, the expense of the CNC machinery, and the quality control that is incorporated.
In choosing our wheels, we can sacrifice a little weight and still have strength by buying a heavier wheel at a lower cost if money is an issue. But if the budget allows, we should opt for the lighter, truer, and stronger spun wheel for all of the right reasons. In no event should we use a light wheel that may not have sufficient strength to endure the lateral forces that may be encountered. Time will tell, because if your wheel is not strong enough, it will eventually give up.
The center section is stamped and then spun to create the shape that is needed. The critical areas that need to be stronger (as in thicker metal) are where the wheel stud holes are located and where the edge of the center piece is welded to the shell. The metal between the studs and the shell mostly spreads out the forces and can be of less thickness.
A standard lug nut is shown on the left next to a spring mounted lug nut. Note the flange
Modifications have been incorporated into the design of the center section in order to accommodate the handling of the wheel, especially to help speed up the pit stops during a race. Reshaping the holes in the center section can help a crew member grab and hold onto the wheel as it is placed on the hub. Developing a deeper dish shape moves the holes closer to the outside of the rim so the tire handler does not have to reach as far into the shell to grab the holes in the center section as well as providing for better brake rotor cooling. The back side of the center piece where the holes are located can also be cambered to allow the studs to "find" the holes easier, and that lets the tire changer locate the wheel on the studs quicker.
Another reason the wheel stud hole areas need to be made thicker for some of the touring series teams is because they make pit stops during every race and those teams glue the lug nuts onto the wheel right before the race starts. After the race, the glue must be removed from the holes. Most teams use a metal wire wheel. Using this type of tool does a great job of cleaning the wheel holes and removing paint and glue, but the process also removes a small amount of metal. If the team uses the wire wheel long enough, that area of the wheel will become thinner and weaker. A small crack that originates here can grow all the way to the shell and cause a total failure of the wheel.
The two areas of the shell that need added thickness for strength are the rim area located next to the bead and the middle where the center piece is welded to the shell. As in the design of the center piece, the part of the shell that lies between the rim and the middle where the center is welded can be thinner than other highly stressed areas. In the spun process, this area is shaped so that some of the metal is forced into areas of high stress for added strength and that is one of the advantages of this process.
Again, we need to imagine where the forces are located and strengthen those areas as a priority. Racing wheels must maintain strength at both rims because the wheel might be used on either the left or the right side of the car. Mostly the "inside" rim, meaning the rim closest to the inside of the racetrack, is loaded from the lateral forces that occur while cornering. It would be a good idea to inspect those areas for deformities after each race. At least one racer has noted that the failure of the rim was noticeable once they knew what to look for.