4x4 alignment

[Sal Lubrano]

If a 4x4 has two solid axles and it went in for an alignment. How does the alignment machines read caster? I know caster is the amount of roll the axle has. Positive would be when the upper ball joint is rearward of the lower. Negative would be opposite. I was trying to set the caster myself with an angle finder. First time I set the angle finder on the machined face of the
axle right next to the cover. That did not work out so well. Then I tried to put the finder on top of the upper ball joint with a socket. I think it worked correct. I was only trying to ballpark the caster temporally. Would any of these methods be correct?

 

[DailyDrifter]

You are correct. Positive caster will have the upper ball joint behind the lower ball joint. Positive caster is good for high speed stability, and makes the steering wheel a little harder to turn, it also wears out the tires a little faster. Negative is just the opposite. FWIW they arent going to do anything with the caster more than likely. They might change the camber and definatly the toe. If your trying to get in the ballpark you set it up in this order, caster, camber, toe.

 

[TURBOTWIN2]

"If a 4x4 has two solid axles and it went in for an alignment. How does the alignment machines read caster?"

Caster is an inferred reading similar to horsepower is an inferred reading from torque.
Alignment machines read the change in camber when turning the the front wheels right to left at turning angles of 10* to 20*, depending on the particular alignment machine.
There are magnetic camber/caster gauges available similar to this for DIY'ers:

JOES Racing Products designs items to meet the demands of the racing market. Check out our full line of high quality items and browse our website to find great products that track tested and simple to use. - JOES Racing Products

Caster is NOT a tire wearing angle.
HTH.

 

[DailyDrifter]

Straight from TireRack
"What's the downside to positive caster? If thevehicle doesn't have power steering, a noticeable increase in steering effort will be felt as positive caster is increased. Other than that, the effects of positive caster are pretty much "positive," especially increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead."


Basically it wears the outside of the tire.

 

[TURBOTWIN2]

If you have negative caster, will it wear the insides of the tires when turning?

 

[DailyDrifter]

If you have negative caster, will it wear the insides of the tires when turning?

I dont think it will, you might experience random wear patterns of the tire. If you have negative caster you car or truck will basically drive like a shopping cart. At my old shop we swapped out coil-overs on a 02 Porsche 996, That car had a redicoulous amount of negative caster. When I was driving behind my boss to get it aligned the car was darting all over the place (we only hit 35mph tops) and was incrediably unstable.

 

[gnxtc2]

My truck has a solid front axle (Dana 60). The 4wd shop aligned the truck so it has 0* caster, truck had positive caster. They drilled new holes in the front leaf rear mounts to tilt the axle forward. Truck handles so much better. There is a lot of math involved to correctly drill the holes. Makes a big difference towing.

Billy T.
gnxtc2@aol.com

 

[charlief1]

Straight from TireRack
"What's the downside to positive caster? If thevehicle doesn't have power steering, a noticeable increase in steering effort will be felt as positive caster is increased. Other than that, the effects of positive caster are pretty much "positive," especially increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead."


Basically it wears the outside of the tire.

It actually wears out the inside and the outside DD. It has to do with the angle the tire is at when in a turned position. The biggest benefit of caster is that it helps the vehicle go straight if the steering wheel is let go of. It doesn't matter whether it's positive or negative, it all works the same. The measurement is taken at different angles per side. IE" 20 degrees on one side and 30 on the other when the wheels are turned each direction. (not the actual measurement angle, my memory is fuzzy on this) The measurement is the angle between the upper and lower ball joint in relation to the position of the wheel.

If you set caster to 0 degrees you have one of the most unstable steering situations out there so the fact that someone did this is not only a shock to me but a liability to the shop. I has a Samari years ago and when I lifted it, it was very unstable. I had to add shims in between the springs and the axle to add caster so it would drive right. I'm suprised that a shop did this for you Billy.

 

[DailyDrifter]

It actually wears out the inside and the outside DD. It has to do with the angle the tire is at when in a turned position. The biggest benefit of caster is that it helps the vehicle go straight if the steering wheel is let go of. It doesn't matter whether it's positive or negative, it all works the same. The measurement is taken at different angles per side. IE" 20 degrees on one side and 30 on the other when the wheels are turned each direction. (not the actual measurement angle, my memory is fuzzy on this) The measurement is the angle between the upper and lower ball joint in relation to the position of the wheel.

If you set caster to 0 degrees you have one of the most unstable steering situations out there so the fact that someone did this is not only a shock to me but a liability to the shop. I has a Samari years ago and when I lifted it, it was very unstable. I had to add shims in between the springs and the axle to add caster so it would drive right. I'm suprised that a shop did this for you Billy.

Charlie I pulled that quote from tire rack, but I do agree with it wearing the outside of the tires. I am aware the caster makes the steering more stable at high speeds, and also "snaps" the steering wheel back when you let it go. I assume that in Billy case it makes positive caster due to the back being pushed down, therefore making the caster positive and better handling.

 

[charlief1]

Charlie I pulled that quote from tire rack, but I do agree with it wearing the outside of the tires. I am aware the caster makes the steering more stable at high speeds, and also "snaps" the steering wheel back when you let it go. I assume that in Billy case it makes positive caster due to the back being pushed down, therefore making the caster positive and better handling.

The old RWD Impalla SS were one of the worst I've ever seen about wearing the inside and outside of the tires DD. Every one I worked on got set for the lowest specs so it wouldn't eat the tires off of it. You have to work on them long enough to see what the tires will do. If you don't know what the settings will do in the long run you can screw the customer over in a heart beat. My boss always wanted me to set the caster as high as I could so he'd get the repeat business. Sad to say, but true.:frown:

 

[TURBOTWIN2]

Guys, my point is about caster not being a tire wearing angle.

Drifter, you say pos. caster can cause tire wear but neg. caster won't?
1. If you have excessive caster (pos. or neg.) and NEVER turn the wheels, it's impossible to have tire wear from caster alone.
2. If you have excessive camber (pos. or neg.) and NEVER turn the wheels, you WILL have tire wear.
3. If you have excessive toe setting (in or out) and NEVER turn the wheels, you WILL have tire wear.
All 3 scenarios assume the other alignment settings are in spec.

Caster is simply the angle of the top to the bottom going straight ahead. It provides directional stability if within specs side to side.
You need to take into account the included angle and toe out on turns. If you have a bent spindle on one side but have correct camber straight ahead, it CAN affect tire wear. If you have a bent steering arm or tie rod but have correct toe setting staight ahead, you CAN have tire wear when turning.

There are actually 6 alignment angles, but most people only think about 3, caster, camber and toe. Add steering axis inclination (SAI: camber and the included angle), toe out on turns (inside tire must turn at a tighter radius than the outside tire) and the Thrust angle (relationship of the rear axis to the front).
Not trying to bust anybody's chops.

To the OP, Sal Lubrano, just let your front end man handle it. (You do have a good alignment man, right?) I can't tell you how many mechanics I've seen who think just because they "set the toe and let it go", they did an alignment. Quite few wouldn't even take a thrust angle reading because they didn't want to have to compensate the rear heads for the machine. They had to hang the heads anyway, but didn't want to take 60 seconds to compensate them. Reading the SAI also takes about an extra 60 seconds to perform.

Sal, get the toe setting close enough to drive it to your front end man and let him do his thing. Incorrect toe in or out will wear the tires quicker than anything else. HTH.

 

[gnsrule]

The biggest benefit of caster is that it helps the vehicle go straight if the steering wheel is let go of. It doesn't matter whether it's positive or negative, it all works the same.

Caster is the front or rearward tilt of the ball joint. A bicycle is set with alot of positive caster. You can ride w/ no hands. Turn the wheel 180* and you'll crash before your hands are off the wheel.Anything less than positive is unstable.Caster also helps the wheel return to streight after a turn.Caster also pulls/pushes twice as much as camber as a rule of thumb

You can lay out 20*in/center/20*out on the floor and get pretty close w/ a protractor. Turn in 20*, zero the protractor. Turn out 20* and mesure caster.
Dont forget to set toe acuratly. Toe out decreases stability too. Toe out helps turn in for you dirt track guys.1/8 in is all you need.
All measurement need to be done w/ the weight on the suspension.

Good Luck

Craig

 

[gnxtc2]

There are actually 6 alignment angles, but most people only think about 3, caster, camber and toe. Add steering axis inclination (SAI: camber and the included angle), toe out on turns (inside tire must turn at a tighter radius than the outside tire) and the Thrust angle (relationship of the rear axis to the front).

The guy that did my alignment was telling the same stuff to me to which I was clueless. I told him do whatever you need to do. The end results was a better driving truck. I could let go of the steering wheel and the truck would go straight and not wander.

Big difference between a lifted Sideflip and Ford Powerstroke F-250HD X-tra Cab Longbed.:tongue:

Billy T.
gnxtc2@aol.com

 

[charlief1]

Caster is the front or rearward tilt of the ball joint. A bicycle is set with alot of positive caster. You can ride w/ no hands. Turn the wheel 180* and you'll crash before your hands are off the wheel.Anything less than positive is unstable.Caster also helps the wheel return to streight after a turn.Caster also pulls/pushes twice as much as camber as a rule of thumb

You can lay out 20*in/center/20*out on the floor and get pretty close w/ a protractor. Turn in 20*, zero the protractor. Turn out 20* and mesure caster.
Dont forget to set toe acuratly. Toe out decreases stability too. Toe out helps turn in for you dirt track guys.1/8 in is all you need.
All measurement need to be done w/ the weight on the suspension.

Good Luck

Craig

I agree that positive caster is more stable but when using a 4 wheeled vehicle caster will behave in the same manor. Most of the "muscle cars" from the late 60's and early 70's had negative caster. The reason for changing to positive is better control at higher speeds. The reason negative was chosen was for ride quality. Negative caster cars go over bumps a little smother but don't handle as well as a car with positive caster.

 

[TURBOTWIN2]

A few cars without power steering liked negative caster, but we won't talk about that.
We also won't talk about front wheel drive cars likeing toe out, rather than toe in or about toe in on deflection.:biggrin:
Also, how can you measure caster on cars that don't have upper balljoints, ie, front struts with coil springs on the strut, like many cars today?
(Answer, measured the same).
Everybody confused now?

 

[DailyDrifter]

1. If you have excessive caster (pos. or neg.) and NEVER turn the wheels, it's impossible to have tire wear from caster alone.

Its impossible to drive a car and not turn , getting on and off onramps at 70mph, turning into a parking spot............its impossible not to turn. Caster IS a wear angle because you cant drive in a straight line everywhere. When the car is going straight its not going to wear, but when you start taking corners it will wear, and I dont know about you, but I do have to make an occasional turn when I drive. I'm not a rocket scientist, but on the other hand, this ain't my first time at a aligment rodeo :biggrin:


As far as measuring caster on cars with struts, thats no different than a ball joint. Wearever the top of the strut sits in relations to the lower ball joint will determine caster. Its all the same

 

[TURBOTWIN2]

OK, Drifter. Caster is now considered a tire wearing angle.

So, what settings should I put my caster at to prevent "caster tire wear"?

 

[charlief1]

This should help you some.

http://www.turbobuick.com/forums/threads/g-body-drag-car-alignment-settings.290592

Lots of info for you to read.

 

[DailyDrifter]

OK, Drifter. Caster is now considered a tire wearing angle.

So, what settings should I put my caster at to prevent "caster tire wear"?

Ahh, sometimes I hate the internet

I knew you would see it my way . All manufactures have there specs, for example Benz's have high caster, but they were designed for autobahn speeds. For all around driving I would go for +2 degrees, you wont feel to much in the steering wheel and the car will still be stable at higher speeds (within reason). .02