found at
http://www.mrtrally.com.au/performance/howctc.htm
Camber, Toe & Castor - the difference
Most people hear these words but rarely have the opportunity to understand what they mean and do.
TOE
This is the amount that the wheels are pointed in or out EG often called "total toe in or out". On rear independant suspension cars this is also adjustable, Subaru, Daihatsu etc. NOT live axle cars though. Fords, Holdens etc. Often measured in mm this little change makes huge differences in handling. As a car moves forward the suspension often moves back reducing toe in, so cars are often set with 1 - 3 mm toe IN. If the car has toe out it often tends to wander on the road more.
On all our rally cars we run about 1 - 2 mm on the front and BACK.
Rear is less important as it tends to be less likely to be affected by knocks, pot holes and kerbs. BUT it is important to be correct
CAMBER
Think of the angle of most roads, look along it and it slopes to the side to make the water drain or is banked on fast freeway corners. This is camber, the angle your wheel sits in relation to vertical when pointed ahead and you look straight at the car from front or rear. Measured in degrees, most common road cars have 0 - .5 degree std. some more. Too much NEGATIVE camber will wear out tyres on the inside. POSITIVE wears out the outside. Look at really old cars they often have POSITIVE camber. (I do not know why).
The correct amount varies depending on CASTOR, (see follows) and how you drive your car. If you have little castor and you love driving fast through corners then you need more NEGATIVE camber, if you do heaps of freeway driving then less is better.
THE REASON? When you turn a corner the outside tyre tends to roll under the rim, causing it to wear on its outer edge. By laying it on its side you reduce this effect. Too much and it will wear on the inside, too little and wear on the outside.
NOTE this is often used to stop wide tyres rubbing on wheel arches or suspension points, this case tyres wear is not a focus! REMEMBER too much neg camber and you will lose traction in straight ahead driving as the tyre is not flat on the road.
CASTOR
This is the best of both! BUT is often not adjustable on modern cars.
Camber stays the same if the pivot (vertically) of the car suspension is zero. EG if you turn the wheel about its axis (steer not spin) it stays the same. BUT if the axis is at an angle (for and aft) then the more you steer the car, the more camber you get!
Its hard to relate, but if you imagine looking at the LHS of the cars wheel, with front to your left, if you grabbed the top of the axis and moved it back (to horizontal) with the wheel position staying still then this is castor, then imagine, if you turned the wheel to the right 90 degrees then the wheel will lay flat, this is obviously an extreme example but best explained.
SO, the more castor the more the wheel will increase negative camber the more you turn the wheel. BUT too much castor and the car will want to wander as it has less tendency to want to point straight ahead.
REMEMBER
Check your tyre pressures, over 80% of cars have UNDER inflated tyres AND most companies, TYRES AND CARS, suggest low, for better ride. On most Subaru's, Hyundai's Daihatsu's etc try 35 PSI it will steer better, ride a bit harder, but go HEAPS better!
On most cars these days we can supply camber kits to increase and allow adjustable camber, most Subarus have some adjustable limits. Castor well thats hard, but possible!
Remember that you pay for what you get, a cheap wheel alignment means just that!
Posted: Wed Oct 31, 2007 10:53 am