TECH CORNER
by Joe Finkle
Cer t if ied Por sch e Tech n ician Gold M eist er
Wh eel Align m en t Dem yst if ied
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our Porsche and a grocery shopping cart have something in common!...but we'll get to that in a moment. I'm here this issue, as it is Horizontally Opposed's 'Tire Issue', to discuss often overlooked wheel alignment. "But Joe! I park 2 feet away from any curb for fear of damaging my alloys, and pot holes these days are few and far between".
The same principal applies to the front end of your Porsche.
CASTER Back to that grocery cart commonality: simply, caster is what makes shopping carts (and your Porsche's) front wheels run straight. The steering pivot is in front of where the wheel contacts the ground in the direction of travel. This is positive caster. This forces the wheel to always track straight when the cart is pushed forward or backward without wandering.
handling, steering
Positive caster creates two primary benefits: CAMBER -
The industry convention is to check alignment, depending on mileage driven, every 6 months or at least once a year. It 's more important with your Porsche as handling is a hallmark element in the Porsche experience. Optimized alignment will pay-off in a better handling Porsche. Factory specs for alignment are established as a trade-off in tire wear and better handling. This is because of some basic geometric principals like camber, which can improve how your car ?feels? can also cause more than normal tire wear. It all translates to the kind of driving you do. If the time spent in your Porsche are drives without really 'exerting' the car, then factory settings are close to optimum. However, with tire width and construction continuing an inexorable march forward, you might want to revisit the factory settings.
improvements in vehicle maximum traction, and responsiveness.
1) I m pr oved st raight -line st abilit y at speed. The front wheels positioned forward of the upper ball joint/strut mount produces a self-aligning torque on the front wheels and tires. This is a fairly complicated engineering concept, but the idea is that positive caster creates a tension that wants to return/keep the front wheels pointed straight ahead while at speed.
You experience the benefits of positive caster and self-aligning torque every time the steering wheel naturally ?unwinds? back to 12 o?clock when exiting a corner. And without positive caster and the resulting self-aligning torque, the vehicle would be very inclined to wander at highway speeds. -
When viewed from ahead, camber the relation of the top of the tire to the bottom expressed in degrees. Positive camber is the outward tipping of the top of the tire. Negative camber is where the top of the tire is tipped inward and is preferred since it will counteract the geometric tendency for the suspension to lift the contact patch as the body rolls during cornering. This setting can have the most dramatic impact on the cars ability to hold front end traction in a corner. It also can cause the most uneven tire wear over time. That is because the inside edge of both tires are loaded higher than the outside causing them to
I m pr oved handling and cor ner ing per f or m ance. Caster has a direct relationship to negative camber, which is fundamental to maximizing the tire?s contact patch when cornering, and therefore key to maximizing the available grip.
Specifically, positive caster helps to create increased negative camber on the outside wheel during cornering. When cornering, the vehicle weight shift is met with a maximization of the tire contact patch on the outside front wheel that ?s under maximum cornering load. In performance driving circles a caster increase ? sometimes to the maximum available setting? is credited with wear more. Often, factory specifications opt for zero to positive camber to keep the car in an understeer condtion, making the front end tend to ?push? in a corner, which is an inherently safer condition for most drivers.T Negative camber is the characteristic generally desired in performance driving. When we use the term, we?re referring to static negative camber. That is, the wheel and tire should exhibit some negative camber while sitting. When you barrel OE
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