Toe is an alignment parameter that describes how the front wheels are oriented with respect to each other and how the rear wheels are oriented with respect to each other. With the steering wheel centered, if the front wheels are pointing toward each other (from a top view), they have "toe-in" or are ?toed-in?. If they are pointing away from each other, they are said to have "toe-out" or be ?toed-out?. The same definitions apply for the rear wheels. Toe can be measured as an angle between the perfectly straight position of a wheel and its position after toe is adjusted. Toe can also be determined by finding the difference between the distance separating the front edges of the wheels and the distance separating the rear edges of the wheels. More distance between the front edges than the rear edges is toe-out. More distance between the rear edges than the front edges is toe-in.
Toe is used to change the way a car behaves on corner entry. The more toe-in you have on a pair of wheels, the harder it is to make those wheels turn into a corner. The more toe-out you use, the easier it is to get that pair of wheels to turn into a corner.
Why does this happen? Let's take an example where a car with toe-in on the front wheels is about to enter a left turn. The driver begins to turn the wheel left. Now, the left-front tire is pointing only slightly to the left while the right-front tire is pointing much more to the left. The problem with this is that the left-front tire needs to turn with a greater angle than the right-front tire because the left-front tire is on the inside of the corner and, therefore, must trace an arc with a smaller radius than the outside tire. However, with toe-in, the left-front tire is actually trying to trace a larger radius arc than the right-front tire. It is difficult to make the car turn because the left-front tire is fighting the right-front. When the car is already in the turn, weight transfers to the right-front tire and diminishes the effect of the left-front tire. Because of this weight transfer, toe mainly affects corner entry.
With toe-out, the inside tire in a corner turns with a greater angle than the outside tire (as it should). This improves the grip of the front tires on corner entry.
In addition to corner-entry handling, toe affects straight-line stability. Toe-in improves stability while toe-out worsens stability. This can be explained through the same reasoning as was used to describe corner-entry handling. Toe-out encourages turn-in since the inside tire turns at a greater angle than the outside. Hence, the car is sensitive to the slightest steering input. Toe-out will make the car wander on the straightaways requiring corrective steering. The car will always be turning unless the steering is perfectly centered. With toe-in, the inside tire fights the outside since the inside is trying to trace a larger radius arc than the outside. As a result, toe-in discourages turn-in and makes the car less sensitive to steering input. In other words, it is more stable.
Let's consider an example of the straight-line stability concept. Assume you have toe-out on the rear wheels. You are traveling in a straight line when your right-rear tire hits a small bump. It gets pushed back slightly by the impact, and it is now pointing more to the right than the left-rear tire. Therefore, the back of the car turns to the right until the right rear suspension comes back to its original position. The same thing can occur with the front wheels. In fact, the effect on the front suspension is even worse because the right-front wheel getting pushed back, for instance, will also turn the left-front wheel to the right.
Rear toe is usually only adjusted on front-wheel drive cars or rear wheel drive cars with independent rear suspensions. I wanted to include this example just to show that rear toe can be adjusted just like front toe on many cars. With a front-wheel drive car, it is sometimes helpful to add some rear toe-out to decrease the stability of the rear tires and counter the understeer inherent in front-wheel drive cars. For a rear-wheel drive car with independent rear suspension, the torque produced on the rear suspension when you step on the throttle tends to pull the rear wheels forward on the suspension pivots. This creates toe-in. To counter this effect, you can toe-out the rear wheels so they will become straight when you step on the throttle. I do not recommend this since rear toe-out in a rear-wheel drive car can cause severe oversteer. Instead of using toe-out, install aftermarket bushings and suspension links to keep the suspension from getting pulled forward under hard acceleration.
As you may have expected, toe increases tire wear because the tires are fighting each other and, therefore, scrubbing along the ground. Toe-in tends to increase tire wear on the outside edges of the tires. Toe-out tends to increase tire wear on the inside edges of the tires. Make sure that you consider your camber setting when adding toe-out. If you are using negative camber, you are already wearing the inside of the tires more than normal. The combination of excessive negative camber and toe-out can quickly wear the inside of a tire and cause it to fail.
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I have been an automotive enthusiast throughout my life and have participated successfully in various amateur racing series. I specialize in tuning the Nissan S platform cars, particularly the US domestic market Nissan 240SX. Visit my website www.240edge.com, which focuses on Nissan 240SX modifications, to get information about suspension setup, quality upgrades, and general 240SX tuning.
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