Camber Tires: Tires Get Tipsy
In 1839, Charles Goodyear accidentally discovered how rubber could be 'vulcanized.' Since then, the most notable tire advancements can be counted on one hand. Scot Robert Thompson invented the pneumatic tire in 1846. (Forty-two years later, Dr. John Dunlop had to reinvent Thompson's discarded idea.) Michelin patented the steel-belted radial in 1946. Tubeless tires arrived in 1954 followed by the first run-flat designs in 1958 and low-profile sidewalls in 1968.
Add to this list of fearless pioneers John Scott who recently offered us what he calls a Camber Tire for testing and evaluation. In our June 2010 issue, Automobile Magazine selected this as one of the ten most significant emerging technologies. Now that we've enjoyed a few miles over the road on these tires and had the chance to conduct two preliminary performance tests, we're more convinced that the Camber Tire concept is worthy of our acclaim.
Twelve years ago, Scott -- a successful Wisconsin car dealer and mortgage broker -- was inspired by the sight of a grossly overloaded Lexus sedan exhibiting excessive rear wheel and tire camber. Instead of running vertically, the tops of the rear tires were tipped sharply inward. While most of us would have moved on to the next item in our daily routines, Scott was convinced there was something to be gained by orienting tires in this braced sea-leg manner. With his father's backing he sketched his Camber Tire idea and hired an attorney to conduct a patent search. In 1999, he was issued US Patent 5975176 for a "tire with a constantly decreasing diameter." Scott had invented the asymmetrical profile with an inner sidewall significantly shorter than the outer sidewall. While negative camber angles up to ten degrees might be beneficial, the first experimental tires Scott had made are molded with the tread angled two degrees.
In conjunction with a suspension adjusted to suit this radically different cross-section, Scott's Camber Tire delivers a long list of claimed benefits:
- Quieter running
- Reduced tread wear
- More predictable response during emergency maneuvers
- Increased track width
- Improved handling, braking, and high-speed stability
- Improved straight-line steering
- Superior performance during oval track racing
(See Scott's website, www.cambertire.com, for the patent disclosure and detailed list of performance claims.)
This sounds like too much to be true. The skeptic in us wondered why the major tire makers weren't on to this trick if it really paid such handsome dividends. There had to be a hitch. Driving on Camber Tires at the ragged limits of performance was the only way to see if they lived up to Scott's promises. When he offered that opportunity with some experimental tires manufactured by his initial partner M&H, we were the first independent organization to put Camber Tires to the test.
Before adjourning to the track, this primer might be useful. The phenomenon called camber thrust is what a leaning motorcycle uses to assume a curved path. Tipping the tops of both tires towards the center of a bend develops lateral forces at the two points where the bike's tire treads contact the pavement. These lateral forces, in combination with small steering angles, are what allows motorcycles to follow a curved cornering path.
Camber thrust is also useful in four-wheeled vehicles. The main benefit associated with tipping the tires off a perfectly vertical orientation is compensating for the body's outward lean in a corner. Ideally, the entire tire tread should stay firmly and evenly planted against the pavement. Unfortunately, that ideal situation is disturbed by body lean and by the typical suspension system's inability to fully compensate for the tipping body.
Car and tire designers avoid significant camber angles because, if one front tire runs at a camber angle and the other doesn't, the car can feel twitchy and unpredictable on a straight path. Also, uneven tread wear occurs with tires rolling at steep camber angles.
The beauty of the Camber Tire is that its tread runs flat. Scott claims that his prototype tire treads showed normal life in long-mileage tests. But the more important benefit is the camber thrust available to enhance cornering ability without waiting for body roll or suspension deflection.
Forty years ago, racing driver-engineer Mark Donohue was so intrigued by the possible benefits of cambered tires that his crew constructed an experimental AMC Javelin for the Trans Am series combining cambered wheels with a live rear axle. Today, Goodyear is exploiting cambered tires in NASCAR. Since Sprint Cup cars only turn left on oval tracks, it's beneficial to have the outboard tires running at steep negative (top towards the car) camber angles while the inboard tires operate at steep positive (top away from the car) camber. In the middle of a high-speed corner, when the body rolls a few degrees, this setup provides the ideal upright orientation, allowing all four tires to generate maximum adhesion.
The tests we conducted at the Bosch proving grounds in Flat Rock, Michigan, over south-eastern Michigan public roads, and at the Tire Rack's testing facilities near South Bend, Indiana, were rudimentary by design and intent. The goal was to determine if the Camber Tire could deliver Scott's phenomenal claims. We used two Mitsubishi Lancer Evolution test cars - one with standard Yokohama Advan A13 original equipment tires and factory camber settings (see results chart), one with front and rear suspensions reset with negative camber. Scott's Optima Sports enterprise supplied two sets of Camber Tires for evaluation -- one molded with a 140 tread wear rating, the other with R compound tread rubber. (The reference Advans have a 180 tread-wear rating -- higher is better. R compound rubber is intended for gymkhana or race track use where traction is a much higher priority than tread wear. We owe a special thanks to Automobile Magazine reader Jermaine Holland who generously provided the reference Evo test car and OE tires.)
Our results confirm that Camber Tires do provide measurable advantages over conventional rubber designs. Optima's standard-tread design (second on the results chart) is a fairly close performance match with the original equipment Yokohama Advans. (After 23,000 miles of use, one Tire Rack customer rated these tires "simply the best tire an Evo driver can get. ") The R-compound Camber Tire delivered remarkable gains: versus the reference Advans, it shortened stopping distance by 11 feet and increased cornering grip by more than four percent (left and right lateral acceleration average).
Tire engineers would kill for any one-percent gain. Trimming braking distance by six percent while increasing cornering grip by four percent constitutes a major breakthrough.
We were also impressed at the subjective observations we noted with the Camber Tires. They turn in smartly with a purely linear and predictable response. The Evo's drift angle was significantly reduced over what was demonstrated by the Evo on Advans. At the limit of cornering grip, minor changes in steering or throttle position were enough to hold the car on the desired line. The feedback provided to the driver through the steering wheel and the car's minor movements were both clear and concise. The extra grip available here should be easy for any driver to use.
Even more amazing is how these radical tires performed on tattered Michigan back roads. They showed an uncanny ability to traverse pavement imperfections and potholes with much less trauma transmitted through the car's chassis. Instead of reverberating through the suspension and body structure, each bump was of short duration. The Camber Tires ride as if they're filled with marshmallows instead of cement.
Where from here? Scott is collaborating with M&H to construct more molds so that experimental Camber Tires can be evaluated in additional sizes. He also hopes to produce what he calls 'square' tires -- radials with identical compounding and construction, minus the camber feature -- to facilitate more equitable comparison tests. Plans are afoot for Optima Sports to sell some Camber Tires in the size we tested here to early adopters such as SCCA Solo competitors, track day users, and fanatic street drivers. But Scott's ultimate intention is to license this technology to major manufacturers with the means to further develop his concept. If and when the Camber Tire idea takes hold, John Scott will have earned his place next to the true tire heroes -- Goodyear, Dunlop, and Michelin.