There aren’t many motorsports out there where equipment takes as much abuse as it does in rally. In this modern era of composite materials and computer diagnostics, it’s easy to forget how important something as simple as a wheel can be. After all, a car isn’t much good if it can’t keep rolling. Of all integral systems onboard a rally car, the wheels often take the most abuse; a shredded tire certainly won’t stop a rally car from finishing a stage. Even with several miles to go, or even a jump in the mix, rally drivers don’t think twice about a flat.
For Subaru Rally Team USA, the wheel of choice is the Method MR502 VT-Spec. Method Race Wheels has been a sponsor and technical partner with SRT USA since 2013. When Method Race Wheels joined the program, the wheel they developed was specifically tailored to the demanding needs of the most successful rally program in the United states. While the wheel is a seemingly simple part, it’s one of the most vital in the championship winning equation. To find out more we decided to catch up with Method Race Wheels Engineering Manager, Sean Kleinschuster.
Method is certainly not new to off-road wheels. So, when development began on the MR502 VT-Spec wheel how much were you able to pull from previous knowledge and experience?
Sean – Prior to entering the rally market we were and continue to be very successful in the desert and short course off road racing communities. These two forms of motorsport present many of the same challenges as rallying while at the same time being drastically different. Overall it was a very natural progression for us into the rally segment because across everything we are involved in we deal with a dynamic, unpredictable, and unforgiving racing surface.
What were some of the factors you had to take into considerations when designing a wheel for rally racing? Were there any hurdles?
Sean – There are three basic load situations that a wheel experiences. Radial loading is essentially the weight of the vehicle pushing vertically down on the wheel. Next there is axial loading which is force applied perpendicular to the weight of the vehicle. Finally there is a bending load, which is seen when cornering. This is a torque applied to the wheel from interaction of the tire, suspension, and mass of the vehicle with the ground. There are three common design hurdles in all the forms of motorsport we are currently involved with. First are large impacts on course (varying axial and radial loads) due to large rocks, debris from other competitors, etc. The key to dealing with this problem is to strengthen the outer portion of a rim to avoid damage and flat tires while keeping weight within scope. This is the single biggest time sink in terms of design study and FEA simulation. The second issue we deal with is extreme suspension loadings from jumps and surface variations (large radial loading). This is where it really benefited us to be in a partnership with the best team in the series. I worked closely with Jonathan and Dan SRT USA’s engineers to get accurate values for the forces which are experienced so I could adjust my simulations used in the design process to optimize our rally wheel designs. Finally, there is a near zero tolerance for part failure with pit options being so limited. If a wheel breaks that could very well put the team out of contention for a win which is unacceptable. Overall the biggest differences from off road truck racing to stage rallying is the mass of the vehicles and how they are driven, neither of which has kept us from producing winning options.
What are the materials and manufacturing process used to produce the MR502 VT-Spec wheel?
Sean – All of our gravel wheels are pressure cast with A356.0-T6 aluminum. This process utilizes a mold into which molten aluminum is forced into a cavity that is the shape of the wheel with air pressure. Utilizing a pressure casting instead of a casting which is filled simply by gravity pulling the material into the cavity improves material properties and produces less scrap parts. The production facility that produces the wheels is TUV, JWL, and VIA certified meaning they are produced under the strictest process and quality control standards available in the industry.
What other stages might a wheel design go through before production?
Sean – In regards to our race wheels, performance is paramount. All of our wheels are the direct result of a ‘form follows function’ approach. Once the geometry has been established in terms of brake and suspension clearance as well as optimal scrub radius, the focus is to maintain the maximum required strength with the minimal amount of weight. Overall the process is very straightforward; I will get requirements from the SRT USA engineering team and make the necessary adjustments based on their data. If necessary, albeit rare, we’ll create a whole new design like we did going from 2013’s MR501 VT-Spec wheel to 2014’s MR502 VT-Spec. For 2015 we simply had to make an offset change to the 2014 wheel design to work optimally with the all-new 2015 car’s suspension geometry.
In terms of performance, what does Method bring to the table for SRT USA with their wheel design?
Sean – In terms of performance we have provided SRT USA with wheels that are both lighter and stronger than what was previously used. The MR501 VT-Spec has a 19% higher load rating than the competition while being 18% lighter. The MR502 VT-Spec has a 31% higher load rating than the competition while being 6% lighter. One of the greatest showcases of our wheel’s strength was at 2014 Oregon Trail Rally where David Higgins went for nearly 14 miles on a rim alone with confirmed speeds above 100mph and multiple crest jumps, enabling him to complete the stage without stopping to change a wheel or worse yet, no wheel at all. The wheel is now proudly displayed in our main conference room and is constantly generating conversations during meetings.
What has Method learned in terms of wheel design through their partnership with SRT USA?
Sean – We have learned quite a few things from our partnership. The information shared by SRT USA’s engineers about rally car suspension dynamics and loads is priceless. Simply put, the information and knowledge acquired over years of winning experience cannot be bought. Without this information a design would never be fully optimized. Additionally, we constantly are getting feedback from the drivers, mechanics, and engineers about details they like and some they don’t. It’s never a bad thing to get feedback that we can take back to the drawing board for future improvements. We are constantly pushing ourselves as a company and the partnership has enabled us to improve our product and presence in stage rally and rallycross to the point where people are lined up to buy the wheels that SRT USA uses for their own race cars and street cars.
As will most motorsports programs, the relationships between the race team, sponsors, and technical partners is a cyclical once. The experience and knowledge gained from racing helps develop a better component and feeds the development process, which in turn allows SRT USA to push even harder every year. The benefits of this process is not exclusive to racing teams, new technology is always trickling down and becoming available for consumers. With two years of development under their belt, Method Race Wheels will soon be releasing street wheels based on those used by SRT USA to win multiple national championships. They will be offering three different styles, the 501, 502, and the 203.