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).