The Truth About Cars » unsprung weight The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Sat, 19 Jul 2014 17:00:13 +0000 en-US hourly 1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » unsprung weight Heresy Unsprung, Lotus Engineering: Unsprung Weight Doesn’t Really Matter Much Fri, 19 Apr 2013 14:49:46 +0000

Protean Electric In-Wheel Electric Motor

It’s April, when automotive engineers from all over the world gather in Detroit for the SAE World Congress. Protean Electric, which has been promoting the electrification of cars with their in-wheel mounted direct drive motors for the past few years, used the occasion of the World Congress to introduce the production version of their motor, which will start being assembled in a Protean owned factory in China next year.

Protean is also looking to license their technology to OEMs. The Protean motor can fit on standard hubs inside wheels that are 18 to 24 inches in diameter and the power units are also compatible with disk brakes, with mounting bosses for calipers. They can be used as part of a hybrid system, or since they have a continuous output rating of 86 HP per motor, they are powerful enough when used in pairs to drive pure battery electric vehicles. A self-contained unit with integral electronics and controls, the Protean motor can even be retrofitted to used cars. Protean is selling the fact that it’s a bolt on solution to turn a conventional combustion powered car into a hybrid. It’s actually pretty nifty and the motors allow for reverse torque so with the proper electronic controls torque vectoring is possible, allowing for very sophisticated traction and stability control. Theoretically, with a motor at each wheel it could also make parallel parking a snap by turning on the car’s own axis. Their in-wheel motor, though, is not why I’m writing about Protean. The real reason why I’m writing about Protean is a study the company commissioned Lotus Engineering to do on the real world impact of unsprung mass. A study with a somewhat counter-intuitive conclusion.

Surprisingly, Lotus, which knows a thing or two about chassis dynamics, said that tires and suspension tuning have a greater impact on ride and handling than adding the 68 lbs per wheel that the Protean system weighs. That sounds like heresy in an automotive world that has chanted “reduced unsprung mass” as a mantra for the past 50 years, at least. Reducing the mass of the parts of the car not supported by the suspension, in other words the mass of the suspension itself, has long been considered essential to better handling. Since they’re mounted in the wheel, hub motors are on the wrong side of the unsprung mass equation. Lotus says that while adding weight to the wheel has an effect on ride and handling, that effect can be offset by normal suspension tuning procedures.

Click here to view the embedded video.

The choice of Lotus Engineering to do the testing was not coincidental, because of Lotus Cars’ reputation for making what are arguably the best handling cars in the world. Cars that have supple road manners in addition to their cornering grip. The fact that Lotus cars can deliver that kind of cornering performance while still maintaining a comfortable ride on real world loads has not been lost of reviewers and car enthusiasts. Essentially, Protean was thinking that if Lotus gives them a pass, so will all the car guys who are asking, “But what about unsprung weight?”

Here’s what Steve Williams of Lotus Engineering said:

Whilst it is true to say that the vehicle dynamic performance was degraded by the increase in unsprung mass, the degree to which this was noticeable was small and could be said to have moved the overall dynamic performance of the test vehicle from class leading to mid class. Further more, the understanding gained from this study has led Lotus to believe that the small performance deficit could be largely recovered through design changes to suspension compliance bushings, top mounts, PAS characteristics and damping, all part of a typical new vehicle tuning program.

Add the powerful benefits of active torque control and Lotus’s finding make a strong argument for the vehicle dynamics benefits of hub motors as an EV drivetrain.

White paper (PDF) on the study here. Powerpoint presentation here.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can dig deeper at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks – RJS

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Positive Post Of The Day: Mazda To Add Lightness Thu, 12 Nov 2009 17:05:52 +0000 A return to form? (

Brace yourself ladies and gentlemen, because an automaker is taking on one of the American market’s greatest bugbears: size and weight bloat. Mazda’s vehicles have gained 80 pounds on average with each recent redesign, according to Robert Davis, senior vice president of product development and quality for Mazda North American Operations. Davis tells Automotive News [sub] that increases are coming “mostly in larger tires and wheels, and safety equipment,” resulting in a 2010 Mazda3 that weighs 2,868 pounds compared to a 2003 Protege’s 2,634 pounds. And, says Davis, that’s all about to change. He promises “typical” weight reductions of 220 pounds per vehicle on future Mazda models, through a combination of measures. For one thing, dimensional creep is a thing of the past, with some Mazda models scheduled to lose as much as three inches in length.

Improved packaging should help reduce the impact on interior feel, while the use of more light-weight materials should also help decrease overall mass and weight. Though Davis does warn that “carbon-fiber roofs and hoods are great for a BMW M5, but they are not viable in our cost structure.” The weight reduction will not only improve fuel economy between three and five percent, it will also allow the use of more efficient engines without losing Mazda’s trademark sporty feel. And, frankly, it will provide a wonderful example to automakers like Honda who built their brands on light-weight, fun-to-drive cars before succumbing to dimensional and weight bloat over the past decade. Weight is not only the enemy of efficiency, it’s also the enemy of fun. If Mazda is serious about differentiating its vehicles with lower weights (and efficiency numbers on the last two generations of Mazda3s indicate that it probably should), this could possibly just herald a new trend that’s been a long time coming to the US market. Setting concrete goals like a 220 pound average reduction per vehicle is just the kind of challenge to the industry we’ve been looking for.

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Piston Slap: Design Weak: Big Ass Wheels Mon, 09 Nov 2009 22:26:45 +0000 "13's are OK if you are going for stock or restored look but as you say 13" tires are getting harder to find and in my opinion just look too small. There are 14" wheels out there with 4 lug patterns that look good on a II but even 14" tires are getting limited in size. I now think 15's are the way to go and with the aluminum adapters converting 4 to 5 lug, just about any wheel can be made to fit the II. Tire choices in 15's are unlimited so the correct look can be had by doing your homework on backspacing and wheel width. A nice set of Cragar 5 spoke 15's would look awsome on the II or you could stager and put 14's on front and 15's on rear." (courtesy

Mike writes:

Sajeev, what ever happened to 14-inch wheels?  I mean, seriously, does the Caliber really need to be shod with 17-inchers? Why does my dad’s new half-ton pickup have 17-inch wheels? His old one had what used to be the industry standard 235-75R15. He about had a coronary when he found out new tires would be over $100 each. Perhaps if I put on my tinfoil hat, I’d say the tire companies are behind this. So really, does the average family sedan or minivan really need anything bigger that a 15-inch wheel/tire?

Sajeev replies:

Of course the Caliber doesn’t need 17-inch wheels: they can’t possibly fix Chrysler’s rolling abomination.  But let’s think about why every modern car has big wheels.

Speaking from an Engineering Standpoint: wheels over 15-inches provide space for bigger brake rotors (and calipers) and a shorter profile tire in the same tire diameter.  The benefits are better braking in extreme conditions, like mountain roads or any form of towing. Shorter profile tires provide more road feel and tread grip, completely changing a car’s “turn in” during the act of corner carving. In theory: most cars lose these benefits above 18” wheels, as more unsprung weight and rubber band tires make things worse.

Furthermore, modern cars/trucks are heavy, straddled with more gizmos, bigger (and taller) cabins and more rigid bodies. When you add more weight, you need more stopping power.

Speaking from a Design Standpoint: styling is a major factor in the mass-acceptance of larger wheels. By the 1980s, both the downsized American icons and Japanese entrants required a certain passenger volume without resorting to the bulk and shocking overhangs (front and rear) of previous decades. Which required a taller DLO (Day Light Opening) for more trunk space—among other things—and created a taller car in the process.  And, in general, taller cars naturally look better with “taller” wheels filling out their wells.

And big wheels were here to stay when Ford sold Explorer SUVs like buttered popcorn, making everyone ride tall in the saddle. Hence the need for taller profile wheels and bigger brakes merging with America’s insatiable need for sleek sheetmetal since the 1950s.

Maybe 15” wheels can make a comeback, but vehicles need to ditch their platform shoes and go on a serious diet.  I’m not holding my breath.

[Send your queries to]

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