I know, I know, "caster doesn't affect tire wear" I've heard it before, BUT I am going to explain how it does affect tire wear.

No car ever only goes in a straight line.

For example, lets take a car with excessive pos ( <- corrected 9/27/13) caster on the front wheels.

When the steering wheel is turned to the right, btw right turns are much sharper than left turns in LHD vehicles, alot more force/momentum/weight is applied to the left front wheel when making a right turn.

With excessive caster, this force is applied mostly to the outside of the tire during the turn.

To demonstrate what I'm trying to convey, take an ink pen (the kind with a pocket clip) place the pen 90 degrees vertical and imagine the clip as the outside of the tire. at 90 degree (0 caster) the clip turns horizontal to the ground. At 10 degree neg caster (top more forward than bottom) swivel the pen and you'll notice the clip has now move closer to the horizontal plane. Increase the negative caster and the quicker the clip approaches the ground.

So if the caster is off (too negative) the toe and camber will be mal-adjusted to compensate for too much caster, which throws off the entire thoroughly German engineered XYZ Axis wheel alignment design.

Forgot to mention this rant is over a 1987 300SDL (why I posted in the diesel thread,,, sorry mods, feel free to move)
Before alignment LF Neg caster 12.1 after alignment neg 13.0

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You're saying that excessive wear is over .9 degrees of caster?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Maybe not to clear,,, before the alignment, caster was measured as 12.1 degrees. After the alignment caster increased to 13.0 degrees.

The company "aligned" my 300SDL. but never adjusted the caster first, the tech, assumed that caster would fix itself when camber was set. After the reading, he probably said, oh well, best I can do,,,

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What you have is positive caster. I'm pretty sure it's physically impossible to produce ten or more degrees of negative caster in a 126 front suspension without severely bending some components. I see a starting value of 1.5 deg negative camber on the LF, which is enough to cause the tire wear we see in the picture.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

the neg 1.5 camber on the LF was a "Before"

I believe caster is supposed to be 10 degrees, I'm also under the impression that negative caster is top ball joint forward of lower ball joint, and vice versa.

With the steering wheel turned all the way to the right, the tire isn't as tilted (top inward) as it should be, putting more surface pressure on the outside of the tire during turns.

NOTE: I should look at the ball joints up side down,,, it is positive caster,,, what was I thinking???

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how did the tech force a W126 to have 12 degrees of caster? were the wheels actually touching the bumpers?

I was thinking that aligning my W124 would be hard, I talked to a few shops and one agreed to do it like the book. I gave them a print out of the values and procedure.

The first thing that MB wants you to perform is to center the steering wheel and dial in zero toe with slip plates under the wheels, first thing is to check and adjust caster (align toe to zero as required - this is done constantly). Then the camber is set (align to zero again and again during these procedures).

Finally toe is set, use a scissor jack and 2x4 to act as spreader bar just to verify work. - very important in MB as it can cause outer tire wear due to the caster angle design which will tilt the wheels if they are not straight.

To imagine the caster, look at a motorcycle front wheel when its parked, the wheel slopes to one side even if the bike is upright on paddocks when the handle bars are turned.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I would imagine that as the brake bearing bracket gets old, the ball inside gets out of round and the LCA moves to the rear of the vehicle.

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I had a tech chase his tail all over the place when aligning the 84SD. He ended up giving the car back with the wheels tilted to the passenger side. Both adjustments were maxed out and he said there was no adjustment left.

A change in either caster or toe causes the other to change in the same direction. I forget the details but it is in the FSM. I think a change in caster causes a lesser change in toe. A toe change causes a 1 to 1 change in caster.

This means adjustments need to be done in increments. You also have to anticipate and allow for changes caused by the next setting adjustment.

It helps if the tech will set caster close to specs and the same side to side. He should then 0 toe and then go back through the process. Large adjustments cause problems.

My take is they claimed competency and agreed to align. The old rule "you shot it, you eat it applies." It is also to get the $10/hr grease monkeys to understand that the owner likes to wrench and just might know something about his car.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Well I sent them an email yesterday, haven't heard back. I think my next step is to take it to the Benz dealer, get a before and after printout, and if the before from the dealer is the sarne (or close) as the after from the tire shop they WILL be buying me a couple of tires.

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Now I got to rethink this,,, it is pos caster, don't know how I looked at it wrong. But either way, it's out of spec and I need more than 5,000 miles out of my front tires.

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