cookiejar, I had a similar thought when researching this article--how incredibly complex the process is of analyzing all the variables and how they interact. Thanks for the input on the Citroen wheels. Interesting to know that such design considerations--aerodynamics and materials--were being looked at back then. I wonder if that's the Citroen model my husband and I rented in France in 1974.
Speaking of aerodynamics, both the Citroen SM and the (1954 - 1972) DS featured full and smooth wheel covers. Brake cooling was by separate ducts to inboard transaxle mounted disc brakes. Brake fade was unmeasrable. Interestingly, with front wheel drive, the very reliable CV drive shafts took the full force of braking - much higher than engine output. These FWD transaxles and components were a favorite of formula 1 cars for many years when used in the rear.
I find the engineering of Citroen awe inspiring because they certainly marched to a different drummer well ahead of the mob. The Citroen DS, which has more leg and head room than my 4050 lb Buick Lucerne weighed in at an amazing 2700 lbs. The current Fiat 500 weighs in at 2600 lbs. With its self adjusting air/hydraulic suspension, the DS rode perfectly under all loads, superior to my 2007 Lucerne CXS's magnetic ride.
The Citroen SM, introduced in 1972 had composite wheels as an option, but they really didn't catch on. Citroen was also known for its low drag aerodynamic designs tested in its wind tunnel that had a moving conveyor belt, as they maintained that the interface between the car bottom and the road had the greatest wind shear and hence presented the greatest drag. All Citroens, including the ugly 2CV had very smooth bellies.
If weight is important in the wheel tire assembly, then perhaps tire weight deserves another look. I've noticed incredible weight differences between different tires of the same size. I've also noticed that the heavier tires really bounce when dropped. Unsprung weight has significant effects on handling on uneven surfaces as well as ride.
The latest fashion for low profile tires reduces the amount of rubber and air cushion and increase the amount of rim.
Thank you Ann for inviting us to provide additional information here. There have been some excellent and insightful comments made by the readers and clarification is always good for both parties. If further information is required, your readers can visit us at www.evolvehybrid.com or stop by booth 325 at the upcoming SAE World Congress in Detroit, April 16-18 for a first hand look at the eVOLVE hybrid wheel.
Thanks to Lacks (James, I believe that's you commenting here) for weighing in on the testing issues, as well as giving us more info on the design tradeoffs between aerodynamics, cooling and esthetics issues.
Our testing shows that completely covering the wheel achieves better aerodynamics, that said cooling and design is compromised so it is not a realistic option. Wheels are as emotional as they are functional – especially considering the side on visual impact of the vehicle. The eVOLVE hybrid wheel philosophy is to balance, weight, aerodynamics, design and finishes all at the same time. We believe composite wheel technology provides the ultimate method to balance all attributes as best possible.
The Lacks composite wheel system has been proven with over 24 million wheel assemblies delivered to OEM's globally over the past 15 years. There have been virtually no field issues due to excessive brake heats from disc or drum brake systems. We routinely test our Chromtec wheels on-vehicle through the Death Valley Brake Fluid Boil protocols and also through similar on-vehicle high brake heat exposure testing through the Gros-Glockner drive route in Europe. These tests are used by most of the global OEM's to evaluate wheel products and technologies for durability and reliability. The Lacks composite is approved for virtually all production vehicle applications and its designs are intended to provide both sufficient cooling to the brake system and optimized weight and aerodynamic performance to the overall vehicle system itself...achieved through great design.
Our experience is that fuel efficiency related to automotive wheels is a relatively unexplored area of technology, although efforts have been focused on mass and inertia...as well as aerodynamics. The eVOLVE hybrid wheel is one of the first programs to focus on good wheel design from a structural and aerodynamic perspective, relative to the impact on fuel economy itself. Previously, most efforts considered either mass or aerodynamics seperately and usually for some attribute other than fuel economy. We believe the eVOLVE philosophy will greatly assist the OEM's in their efforts to improve fuel economy without sacrificing great design. The results and video showing the coast down and wind tunnel testing are available at www.evolvehybrid.com.
You're right, sensor_pro, and all of the automakers are already doing everything you mentioned here and more. Automotive engineers are looking at everything in an effort to get to 54.5 in the next 12 years. If they could find about 25 more things that improve mpg like this does, they'd be on the verge of success. The big question, though, is how much will all of these improvements cost? If we have to load the vehicle with composites and other lightweight materials, and the cost gets driven up by a factor of two or more, they're going to find a lot of consumers holding onto their old cars.
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