Of late, a number of readers have complained about vibrating steering wheels and wayward behavior of cars in experiences slightly similar but less terrifying to the one I described last week, so let us briefly delve into the kinds of adjustment that may occur to the wheels (particularly the front ones) either willingly or accidentally.
Wheel Alignment vs. Wheel Balancing: This is simply the correction done to wheels of a car so as to make them stand perpendicular to the ground and parallel to each other.
This is not to be confused with wheel balancing, which is something completely different, though they both affect the ride and handling of a motor vehicle.
Wheel balancing allows the tyres to spin without undue vibrations, and it is done by checking for heavy spots on the wheel/tyre combination and compensating for them with lead weights directly opposite, along the diameter of the wheel.
When in need of wheel balancing, the car will tend to vibrate the steering wheel (front wheels are the culprits), or even sometimes the seats and floorboards (rear wheels need attention), and you might experience some scuttle shake, all these at certain road speeds (most commonly between 80 and 130 km/h).
Wheel alignment maximises tyre life and optimises the predictability and linearity of a car’s steering. When the wheels go out of alignment, the tyre wear becomes uneven, the car wanders on a straight road and pulls to one side, meaning any permutation of three things could have happened: camber, caster and toe could have been adjusted from their default settings.
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Camber: This is the angle of a wheel, in degrees, when viewed from the front. If the top of the wheel leans outwards (or the bottom inwards, same difference) then this is called positive camber, and if the top leans inwards it is called negative camber.
Out-of-adjustment camber causes uneven tyre wear; for instance, too much positive camber causes more wear towards the outside of the tread pattern.
Also when driving, the car will tend to pull too much towards the wheel with positive camber. Camber can be adjusted, incidentally, but not on front-drive cars.
If your FWD car has its camber out, it may have had an accident and was not properly fixed. It would be easy to assume, then, that cars come out of the factory with zero camber, but this is not necessarily true.
For the longest time, camber was set by engineers towards slightly positive to compensate for vehicle loading.
This makes sense because when the car settles under load, the camber will settle itself out: zero camber tends towards the negative when a car is loaded.
It made even more sense when you consider a car in motion: when technicians set a car’s camber, they do it when the car is static and fail to consider what happens when it starts moving.
This, together with the search for straight-line stability and better handling through camber thrust which improves cornering grip, has seen the trend shift towards negative camber when the car leaves the factory, typically between -0.5 and -5.5 degrees.
At speed, the aerodynamic properties of most cars cause lift, as opposed to weight (or load), and the resultant change in ride height, which affects camber.
The quest for optimum stability and razor-sharp handling also sees many grease monkeys (DIY mechanics) adjust camber on their own cars — the most insanely tuned cars have outrageous negative camber at the back and a bit of positive camber at the front.
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Caster: When the steering wheel is turned, the front wheels turn on a pivot attached to the suspension. The angle of this steering pivot when viewed from the side of the car is called the caster angle.
If the top of the pivot is leaning towards the rear of the car, then the caster is positive; if it is leaning towards the front, it is negative.
If the caster is out of adjustment, it can cause problems in straight line driving. Inconsistent caster from one side to the other causes the vehicle to pull towards the side with the less positive caster.
With negative caster, the steering becomes light and the vehicle tends to wander, and maintaining a straight line becomes a major exercise.
Positive caster causes heavy steering and sometimes creates backlash when you hit a bump (the steering “kicks”). The best way to visualise caster is to picture a shopping cart.
Imagine yourself trying to push the cart and keep the front wheel ahead of the pivot. The wheel will continually try to turn from straight ahead.
That is also what happens when a car has the caster set too far negative. Like camber, caster is not adjustable on most front-drive cars.
Positive caster improves straight line tracking, we have established that. However, most cars had negative caster prior to 1975 because in those days power steering was unheard of, light steering was therefore a bragging point, and cars did not have radial tires.
Non-radial tires had a tendency to distort at highway speeds so the contact patch of the tyre moved back past its centerline (picture a cartoon car speeding, with the tires being egg-shaped) effectively creating a positive caster.
This is why, when radial tyres are installed on this type of car, the car wanders from side to side and no longer tracks straight. To remedy this, adjust the caster to positive and the car should steer like new.
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Toe: Also known as tracking, the easiest way to describe toe is to say whether a car is knock-kneed or bow-legged, but not like camber.
There are two types: toe in, also known as positive toe, where the front tyres both face inwards (as the feet of a knock-kneed person would), or toe out/ negative toe, where the front tyres both face outwards (as the feet of a bow-legged person would).
Toe is not as visually extreme as I may have described it there, but it is still present in almost all automotive front-wheel steer cars.
It is also factory-set, just like camber, and just like camber, it could go out of kilter or some enthusiasts somewhere will adjust them beyond any point within reason.
Increasing front toe in on a rear-drive car increases straight line stability, but dulls the turn-in bite (the cars is a bit more sluggish turning).
Increasing toe out on the other hand increases turn-in but it also drastically affects the linearity of the steering setup and makes the car dangerous to drive fast for those outside professional driving circles.
In fact, part of the reason drifting cars are banned from street use is because of the abnormal levels of toe out that tuners build into them.
When toe is combined with one form of camber or the other at the front wheels, as the vehicle turns the inside wheel will seem to turn in a conical curve (camber thrust), increasing the tyre wear.
A little toe (toe out for negative camber and toe in for positive camber) cancels this effect, reducing wear and rolling resistance.
From outside, it might look worrisome, but this toe-plus-camber effect can best be seen on most Mercedes saloon cars.
These effects are also used in go-kart racing where power caps mean the turning abilities of the race cars have a bigger role to play in determining the outright performance of the vehicles.
There are various forms of toe out which I will intentionally avoid to keep confusion away from my class, but what we have described here is actually static toe out.
Just so you know, Ackerman’s principle also causes a form of toe out, called toe out on turns, and splitting these different forms of toe from each other could be a headache, not just for me trying to describe them, but also for you reading about them.
Please note: do not perform any wheel alignment if the front suspension and steering components of the car are worn out or loose, first get them into top shape before performing the operation.
