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Suspension Changes - Handling vs. Tire wear

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Written by: Matt Woomer
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Suspension changes-- Handling vs. Tire wear and how to find your camber angle.

Without a doubt, changing from a stock suspension set-up can dramatically improve a car?s handling.  As with every change, however, there are some trade offs.  When it comes to suspension, the two major trade offs are, ride quality and tire wear characteristics.  Most show cars are not driven enough to really worry about either one of these.  That is why you see some extreme camber angles on show cars and trailer queens.  I myself am all about drivability, however, I am by no means against lowering a car to improve handling ability.  However, there is a limit to what helps and what hinders, and even what is safe, for that matter.  The main problem with lowering a stock suspension by way of shorter springs and shocks is the tendency to increase negative camber.  This is not always a bad thing, as some negative camber, even in a daily driven street car can dramatically improve road handling while still providing acceptable tire life.

To understand why camber angle affects tire wear and handling, you first have to understand exactly what camber is.  Camber angle is the angle in which the wheel sits on its Y-axis.  There are two flavors of camber.  Negative camber, where the top of the wheel is set in from the bottom (the wheel leans into the car) and positive camber, where the top of the wheel is set out from the bottom (the wheel leans away from the car).

 

If you were to drive your car in a straight line 100% of the time, then a zero degree camber angle would be ideal.  When you corner, however, the car wants to push the tire off the wheel.  This pushing causes more weight to be put on the outside of the tire and the inside to want to life off the road.  To counter this effect and keep and even pressure across the entire contact patch you would want to add some negative camber to the mix.  What this does is put more weight to the inside of the tire so that when the car is cornering and starts to push the tire sideways an even pressure exists across the contact patch, in some special cases positive camber may want to be used.  The camber angle is measured while the car is at rest.  A car that is built for speed and is going around an oval track may exhibit some positive camber at rest, but negative camber once the car is up to speed and the air is pushing down on the car squatting the suspension.  The downside to too much positive or negative camber is the loss of traction during straight driving because the weight of the car is not evenly distributed across the entire tire.  There is also the fact of uneven tire wear in which the part of the tire that has the most weight on it wears first.

This picture shows a tire with uneven wear from either too much negative or too much positive camber.  On a racecar in which the tires get changed after every race this is fine.  On a daily driven car, however, this can become the deciding factor.  Usually it is the toe of the car that causes the most tire wear, though camber does have some effect as well.  When a car with stock suspension components is lowered using springs, negative camber will exist.  How much negative camber depends on how much the car is lowered.  Generally a 1 ? 2? drop will not produce any more then 1 ? 1.5 degrees of negative camber using stock suspension components.  Most of the time this is an acceptable angle and no action is needed to correct it.  In fact the car will handle slightly better in corners in this condition.  I myself am not a fan of dropping a car any lower then 1 ? 2? but if you feel it?s a must to put your tires through your inner fenders then a camber kit is probably for you.

On some suspensions the toe of the front wheels is also affected when the suspension is lowered.  Excessive toe-in or toe-out can cause major tire wear.  Generally a small amount of toe-out on a front wheel drive car is wanted.  This is because when the wheels spin to drive the car forward, they pull themselves in a tiny bit, thus making the wheels in line with the driving direction.  In opposition to this, on a rear wheel drive car the front wheels should have a small amount of toe-in.  When the rear wheels push the car forward, the driving force on the front wheels contacting the road pushes the wheels out making them in line with the driving direction.

Finding your toe angle is rather difficult without the use of precise tools.  However, finding your current camber angle is relatively simple with the use of basic mathematics.  With the car on a level surface, use a plum bob (weight on a string) or a large angle to produce a 0 degree vertical line beside your wheel.  Measure from the top of the wheel (not tire) out to the string or angle, and then from the bottom of the wheel out.  With the use of these two measurements and a vertical line you can form a triangle, and then from that formulate your camber angle as shown below.