from motortrend.com
Hey There, Big Wheel
We're not saying "Don't" to oversized alloys and skinny rubber--but you need to consider what you're messing with.
By Kim Reynolds
Photography by the author & Brian Vance
Motor Trend, May 2004
So there you are, stopped at a red light with the wife and kid piled into your 10-year-old Camry, when you hear a thumping bass beat approaching on your left. You twitch your eyes sideways and confirm its source: Yep, a slammed SUV with ink-black window tinting is rolling to a stop next to you. As the screws holding your car's dashboard together slowly unwind due to the vibration, your daughter shouts, "Hey, look at those wheels--they're still turning!"
While spinner wheel spokes will certainly go the way of the leisure suit, tastefully executed, large-diameter wheels can be attractive. That's the reason car designers inevitably sketch them into their illustrations of upcoming models, why aftermarket-wheel sales have soared into the stratosphere, and why manufacturers themselves are offering bigger wheels; the Dodge Ram SRT-10's 22-inchers are the largest to date.
While aesthetics are in the eye of the beholder, we wondered how the substitution of mega-diameter wheels affects performance and whether they're safe on that 5800-pound truck. You should wonder the same before you shell out big bucks.
Although swapping on big wheels with short-sidewall tires (let's call them BWSSTs, see "dubs" in related Tire Testing story) is as simple as loosening and tightening lug nuts, it's nevertheless an act of significant reengineering. Those boring, standard wheels and tires you're so restless to replace are, in actuality, highly developed components, painstakingly integrated into the physics of your vehicle's suspension. By tossing them aside, you've just spun the roulette wheel of ride, handling, and braking performance outcomes. Feel lucky?
We did a few simple measurements comparing two wheel-and-tire packages: a pedestrian 18-inch wheel and P275/65R18 tire on a stock Lincoln Navigator and an Oasis-brand 23-inch alloy shod with 305/40R23 rubber unbolted from an aftermarket-modified Nav. On the scale, the standard wheel/tire set weighed 76 pounds. The BWSST package creaked the scale's needle to 84--that's a bit over 10 percent heavier. It's not a lot, but if these were the latest 26- or 28-inch models, the differential would be greater--and even more so with spinners. The increase is all unsprung weight, the worst kind.
Acceleration requires turning the rolling stock, too, so we must also include their rotational inertias. Here, the 23-inch wheel's big rim--spaced a crucial 2.5 inches farther from the wheel center--takes a second bite out of acceleration. We won't go into how we went about measuring this, but their added reluctance to spin is equivalent to four times the increase in wheel and tire mass. Last, this bigger wheel-and-tire package exacts a third performance price by adding 0.75 inches to the rolling radius as mounted on our trucks, making the final-drive ratio effectively five percent taller.
Heavier BWSSTs also guarantee an erosion of ride quality. Less obviously, this extra weight means they trace the road's profile less accurately, too, degrading cornering and braking. Racing wheel designer and builder Bill Jongbloed of Jongbloed Racing Wheels (currently developing wheels for the 2005 Indy 500) believes that braking is the most affected: "We did a test where we intentionally added weights to the wheels, and the consequence on braking distance due to the tires losing contact with the road was eye-opening."
There are no better alchemists of safety and speed than people who make their living building racing equipment. Relative to safety, Jongbloed notes, "As you go up in diameter, you increase the loads at the hub, and some of the hubs I've seen on the street have only about five-eighths of an inch of material under the lug. That would worry me." Bill adds, "Nobody really ever thinks about wheel maintenance, but in Indy-type racing, wheels are checked for cracks after every 10 races. On the street, wheels are never checked."
An army of vehicle-development engineers worked hard to give that H2 or G500 its world-class off-road prowess. By strapping on wheels and tires with little to no sidewall flex, you've tossed that rock-crawling ability out the door.
there was more right here but it wouldnt let me put it here and its to long to type
What safeguards exist to protect us from underengineered wheels even when new? Until now, the aftermarket wheel industry has had available a testing standard established by the SFI Foundation (Specification 5.0) which probes radial (rolling) and cornering durability. However, as of this writing, the Society of Automotive Engineers is about to weigh in with an aftermarket-wheel testing standard of its own (J2530) that promises to bring the same rigor to evaluating aftermarket wheels as has long been followed by the OEM suppliers.
Even J2530 won't soften the auto manufacturers's assertion that only they can properly engineer BWSSTs into a vehicle's suspension system. In some cases, aftermarket fitment will void your warranty. The natural concern is that even if the wheel and tire survive their reasonable lifetimes of pothole pounding, the suspension itself was never designed for this sort of expanded hammering. Bearings, spindles, and more are exposed to considerable, unanticipated stresses. We've heard of a manufacturer discovering, to its horror, cracks in suspension components after rigorous fatigue testing with large-diameter aftermarket wheels.
If you've just gotta have 'em, it's wisest to pick from established, reputable aftermarket brands, as many of these wheels are now made overseas and some see uncertain levels of standards testing. Look for an aftermarket wheel manufacturer's membership in SEMA, which indicates an interest in professional behavior, its being a partner with SFI (although many manufacturers perform similar internal tests). In the future, keep an eye out for wheels permanently marked with the SAE J2530 designation. Finally, don't go overboard on size choice. A well-chosen +1 or +2 wheel/tire combo can yield improvements in handling performance to go along with The Look. Replace your 18s with 26s, and you're long past diminishing returns.
And what about those spinner spokes? Engineer Finch says that American Racing Wheels has declined to jump on the bandwagon, due primarily to concerns about inquisitive small fingers getting pinched. But, gee, maybe a set of flashy, non-spinnerized 20-inchers might just make Dad's old Camry cool. Then again, maybe not.
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