In general, the less weight the better, but this is not absolute. For example, a vehicle with a high amount of unsprung mass will be less affected by minor road imperfections because the tires and springs filter these out. However, when range and acceleration are a priority, the less unsprung mass and rotational weight the better.
A vehicle with less rotational weight will require less energy to turn and operate at speed. Your vehicle will gain improved range if your rotational weight is less. It requires less battery energy to turn a lighter wheel and tire. Reducing unsprung weight also benefits the handling of the car on uneven roads and in cornering. The lower mass allows the springs and shocks to more effectively control the movement of the wheels and suspension. In summary, an electric vehicle with lower unsprung weight and by extension less rotational weight will result in a longer range.
The best way to reduce unsprung weight is by using lighter wheels. There are two popular manufacturing techniques for lighter wheels: flow forged and fully forged. Although they sound the same, the difference is critical. Flow forging involves liquefied aluminum in a cast and pressure is applied to the inner barrel, whereas fully forged wheels are made by forcing a raw block of metal into a shape with extreme pressure. Fully forged wheels are the lightest and strongest because of the process. Flow forging costs less, but the weight savings are minimal, if any.
At this point, you might be curious how do I know the range benefit of reducing unsprung weight for my vehicle? There are a number of mathematic formulas which are beyond the scope of this article. As a summary, for every pound of unsprung weight removed, it is approximately equivalent to reducing ~4 times of sprung weight! (1)
Let’s use an example of the 2022 Tesla Model Y Performance. Each 21” Uberturbine wheel weighs more than 38 lbs. If these four were replaced by Martian 20” MW03 fully forged wheels, the reduction per wheel is 13 lbs. for a total of 52 lbs. (A similar weight savings can be achieved on Model 3s as well.) With the smaller wheel size, the tires also weigh less. On average, each tire is 2 lbs. lighter or 8 lbs. for four. The upsprung vehicle weight is reduced by 60 lbs. [(13+2) x 4]. The total approximate equivalent sprung weight savings is ~240 lbs.! The total weight of a Tesla Model Y is 4,398 lbs. Theoretically shaving off 240 lbs. is equivalent to cutting 5.5% of the total mass of the vehicle.
As an additional benefit, fully forged wheels like the Martians are also stronger than the stock Tesla cast wheels. There are many stories of Tesla owners cracking their stock rims. (2)(3) This type of damage usually allows air to escape from the tire, sometimes leaving you stranded, requiring repairs or complete replacement. The MW03 wheels are an excellent balance of reduced weight and improved strength. Compared to the stock Tesla wheels, the Martians are nearly 30% stronger. This makes them less likely to be damaged by potholes or road debris. The Martian wheels are made from fully forged aluminum and in the event of damage, they are likely to sustain a bend instead of a crack and can often be repaired. For reference, the Tesla Uberturbine wheels are rated at ~1,800 lbs. whereas the MW03 wheels have a load rating of 2,200 lbs.
Back to our topic of weight reduction, as we focus on determining the ultimate range benefit. Studies of weight reduction impacts on EV range vary widely. One report revealed range benefits on the order of .1 miles for each 2.2 lbs. reduced.(4) Another study concluded that a 10% weight reduction improved electric range 13.7%.(5) A range improvement table from Teslike showed dropping a tire size results in about a 6% range improvement.(6) Based on these studies, we would expect an additional range from 11–23 miles for the Model Y Performance. As a comparison, studies on a conventional vehicle show a 10% weight reduction improves fuel economy by 6-8%.(7) To see what results we would achieve, we drove a 2022 Model Y Performance on both the stock 21” wheels and the Martian 20” MW03 wheels. The route we chose was a mix of both city and highway driving, specifically, 10.3 miles on the highway and 5.7 in the city for a total of 16 miles. We drove this one way and later returned on the same roads, so the roundtrip distance was 32 miles. On the highway, we set the cruise control to 70 MPH, but traffic sometimes affected that. For the city section, we obeyed the speed limits plus 5 MPH to match each route as closely as possible. We drove this route round trip a total of three different times on each of the wheels. There was a 52’ elevation change from the starting point to the end. After each route, we recorded the energy consumption. The link to our video is here.
