Caster, Camber, Toe-in???
Senior Member
Joined: Feb 2000
Posts: 1,544
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From: Kalamazoo, MI, USA
Front Axle 101:
Toe in is the term given to the amount that the tires point away from parallel to one-another. If left on their own they would roll forward and converge upon each other they are known as towed in /--\. If like this \--/ (with forward toward the top of the page) they're toe out.
Reason for toe in: The rolling resistance of the tires causes them to toe out -- so they are intentionally set to toe in so that when rolling down the road they look like |--|. Front-drive cars are actually set up \--/ so that under the drive of the engine, they look like |--|.
Let's assume that you wanted your tires to be flat against the road and the road is crowned. You'd tip your tires outward at the top (positive camber) so that the tires fit the road. There is no reason for positive camber any more, since roads are not highly crowned.
Caster is a neat one. By adjusting caster, you can make your car pull left or right. Actually, it makes the truck 'climb' left or right. Your bicycle has a small amount of caster on the front wheel -- it is the angle made by a line drawn from the wheel's axle thru the steering hub that the handle bar connects thru. Motorcycles have more caster than do bicycles -- and they want to go in a straight line more -- since the angle resists wheel left-right turning.
Choppers with huge angles (called rake) want to keep the wheel pointing straight -- which makes them hard to steer -- which gives the CHP heartburn (and is why they record every darned accident with a raked chopper).
Now, imagine that severely raked caster angle on your truck as you'd turn the wheel left or right, you'd be lifting the truck ever so minutely on the tires -- and the effort of the lift would cause the tires to return to forward when you let go of the steering wheel. By changing the caster angle and playing with the toe-in, you can make the truck climb left or right.
A good front end man can 'tune' your front end for the roads you intend to ride -- such that if all of your driving is on crowned roads, he can make it so that when you let go of the wheel, it will stay straight and not creep off the road.
That's not usually done, since you're undoubtedly going to be on the freeway on the left side of the slight crown -- and then it would really 'drive' left off the road.
Toe in is the biggest reason for tire wear. It also causes wierd driving. If excessive toe in /--\, when you are on the right side of a crowned road your truck will want to lean right but it will steer left. When you go over the 'whoops', whichever wheel has the most weight will steer the vehicle in the direction of that wheel -- causing the truck to seem to have overly-sensitive reaction to steering input by the driver.
Excessive toe out \--/ causes the truck to wallow like the steering is 'loose' or non-responsive -- and the truck will tend to follow the direction of lean.
So...
If you're setting up your truck with lift kits, just set your camber at zero degrees plus or minus zero -- so that the tire sits flat against the road (assuming a flat road). If you're '****' about it, lean it top-out (positive) camber just a teenie bit so that they squash perpindicular to the road when the truck is loaded.
You won't need to dink with caster unless you've raised your truck's rear end up so much that it looks like a bitch in heat.
Pay close attention to your toe-in. It should be ever-so-slightly toe-in so that the tires roll parallel to each other when rolling down the road.
For a primer on how to 'read' tire wear, see one of the tire mfr sites.
Good thing you didn't ask about kingpin inclination angle.
End of Front Axle 101
------------------
Y2K™
Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"
Toe in is the term given to the amount that the tires point away from parallel to one-another. If left on their own they would roll forward and converge upon each other they are known as towed in /--\. If like this \--/ (with forward toward the top of the page) they're toe out.
Reason for toe in: The rolling resistance of the tires causes them to toe out -- so they are intentionally set to toe in so that when rolling down the road they look like |--|. Front-drive cars are actually set up \--/ so that under the drive of the engine, they look like |--|.
Let's assume that you wanted your tires to be flat against the road and the road is crowned. You'd tip your tires outward at the top (positive camber) so that the tires fit the road. There is no reason for positive camber any more, since roads are not highly crowned.
Caster is a neat one. By adjusting caster, you can make your car pull left or right. Actually, it makes the truck 'climb' left or right. Your bicycle has a small amount of caster on the front wheel -- it is the angle made by a line drawn from the wheel's axle thru the steering hub that the handle bar connects thru. Motorcycles have more caster than do bicycles -- and they want to go in a straight line more -- since the angle resists wheel left-right turning.
Choppers with huge angles (called rake) want to keep the wheel pointing straight -- which makes them hard to steer -- which gives the CHP heartburn (and is why they record every darned accident with a raked chopper).
Now, imagine that severely raked caster angle on your truck as you'd turn the wheel left or right, you'd be lifting the truck ever so minutely on the tires -- and the effort of the lift would cause the tires to return to forward when you let go of the steering wheel. By changing the caster angle and playing with the toe-in, you can make the truck climb left or right.
A good front end man can 'tune' your front end for the roads you intend to ride -- such that if all of your driving is on crowned roads, he can make it so that when you let go of the wheel, it will stay straight and not creep off the road.
That's not usually done, since you're undoubtedly going to be on the freeway on the left side of the slight crown -- and then it would really 'drive' left off the road.
Toe in is the biggest reason for tire wear. It also causes wierd driving. If excessive toe in /--\, when you are on the right side of a crowned road your truck will want to lean right but it will steer left. When you go over the 'whoops', whichever wheel has the most weight will steer the vehicle in the direction of that wheel -- causing the truck to seem to have overly-sensitive reaction to steering input by the driver.
Excessive toe out \--/ causes the truck to wallow like the steering is 'loose' or non-responsive -- and the truck will tend to follow the direction of lean.
So...
If you're setting up your truck with lift kits, just set your camber at zero degrees plus or minus zero -- so that the tire sits flat against the road (assuming a flat road). If you're '****' about it, lean it top-out (positive) camber just a teenie bit so that they squash perpindicular to the road when the truck is loaded.
You won't need to dink with caster unless you've raised your truck's rear end up so much that it looks like a bitch in heat.
Pay close attention to your toe-in. It should be ever-so-slightly toe-in so that the tires roll parallel to each other when rolling down the road.
For a primer on how to 'read' tire wear, see one of the tire mfr sites.
Good thing you didn't ask about kingpin inclination angle.
End of Front Axle 101
------------------
Y2K™
Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"