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Discussion Starter #1 (Edited)
This is my steering and alignment post.
I do not know everything, but I will at least tell you what I do know and maybe it might help someone.
To start I would like to say that the dealership has all the correct alignment equipment to do wheel alignments the proper way. This includes weights, ride height measurement tools, etc. If your vehicle was in an accident then a BMW certified body shop could check it on their frame machine. The outside shops that do alignment have machines with adjusted specifications in order to do the alignment. This is within approximately 1% of measured angles so your alignment will come out just about the same. There are some shops that do alignment for body shops. Usually these guys know what they are doing. If your vehicle was modified then you may want to find a shop that does lowered / raised vehicles.
If you want to have tire longevity and even wear, then an alignment will correct bad tire conditions.


Tires should be the same size per axle front axle / rear axle. Different tread patterns will have an effect on driving conditions as the contact patch between the tire and the road are different. Before any adjustments are to be done on the vehicle. The most important thing to do is to make sure that your tires are properly inflated. Conditions caused by under inflated tires is that both outer and inner edges are worn and the middle has more tread. This also has an effect on fuel economy and will cause the vehicle to drift / pull to the side with the lowest pressure. Conditions caused by over inflated tires is that both outer and inner edges have more tread than the middle of the tire.

Suspension components that are worn, bent or damaged will have an effect on the outcome of your alignment. If you know something is defective then change it. Also the technician working on your vehicle should have checked your front end and suspension before they do the alignment. If not then ask them to do so.


The 3 most common angles / adjustments used in alignment is Toe , Camber , and Caster. Afterwards there is SAI Steering Axis Inclination , Included Angle , Thrust Angle , etc.

The most adjusted angle to correct an off centered steering wheel is called "TOE". Not the one on your foot but you can also use that for reference. Toe alignment is the measured difference between the front of the tire and the rear of the tire. This is the same for the front and rear wheels. An even Toe alignment will straighten your steering wheel for you.


Toe adjustments that are out of alignment will cause "feathering" of the tires and increase tread wear. Also if extremely out of adjustment will cause tire noise while driving and steering stability problems.
"Toe In" or "Positive Toe" is the front of the tire pointing in towards the center line of the vehicle. See below illustration.


Slightly increased Toe-in will reduce over steer, steady the vehicle and improve handling at higher speeds.

"Toe out" or "Negative Toe" is the front of the tire pointing out away from the center line of the vehicle. See below illustration.


Slightly increased Toe-out will reduce under steer during initial turn in or while entering a corner at higher speeds.
 

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Discussion Starter #2 (Edited)
Camber is the inwards or outwards tilt of the wheel. Out of adjustment camber will cause uneven tire wear on either the inside treads of the tire or the outside treads of the tire. There are camber adjustments on the front and rear of our vehicles.


Excessive camber can cause the vehicle to pull to one side. Also if extremely out of adjustment will cause tire noise while driving and steering stability problems. Your Camber adjustment also directly affects Toe. If no other adjustment is touched then Positive Camber will give you Toe-in and Negative Camber would give you Toe-out. This is because our vehicles have the steering ahead of the front axle. If our rack and pinion was behind the front axle the opposite would be true. If no other adjustment is touched then Positive Camber will give you Toe-out and Negative Camber would give you Toe-in.

Positive Camber is the the top of the wheel pointed away from the vehicle center line. Excessive Camber will cause accelerated tire wear on the outside tread area of the tire. See below illustration.


Negative Camber is the top of the wheel pointed towards the vehicle center line. Excessive Camber will cause accelerated tire wear on the inside tread area of the tire. See below illustration.


Caster angle is for the front of the vehicle only. Caster helps with tracking and allows the steering wheel to come back to center when coming out of turns. Caster directly affects Camber while turning. While turning the steering wheel you will see Camber gain. The outside wheel will go Negative Camber and the inside wheel will go Positive Camber. Caster is the forwards or rearwards tilt of the steering knuckle. In our cars we have struts. So the angle of center strut bolt in relation to the lower ball joint. On vehicles with SLA (Short/Long Arm) suspension, the relationship between the upper and lower ball joint is where the measurements / adjustments will be taken.


Positive Caster would be the strut top leaning more towards the rear of the vehicle. This would cause the vehicle to pull / drift to the side with the least amount of Positive Caster. Positive Caster also allows the wheels to come back to center out of turns and improves directional stability. See below illustration.


Negative Caster would be the strut leaning more towards the front of the vehicle. This would cause steering instability at higher speeds especially with wider wheels / tires. There will be more of a tendency for the vehicle to track the road that is grooved. See below illustration.
 

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Discussion Starter #3 (Edited)
SAI (Steering Axis Inclination) is the distance from the center strut nut to the tires true vertical center line. SAI is the strut top tilt inwards or outwards to the vehicle center line. It is always a positive measurement. Increased SAI would give you better steering stability. SAI is a front end measurement *non-adjustable only.


Increased SAI directly affects Camber. Positive SAI in turns will cause the Camber to go positive on the outside wheel and negative on the inside wheel. This is not good for cornering at higher speeds and will cause the outer treads of the tire to wear out faster. SAI will usually be the same amount on the left front and the right front. If the numbers are off by more than a 1.5 degrees then most likely something is worn damaged or bent in the front end.


Notice in above picture how the Tire is straight but the strut is facing more inwards even though the tires are vertical.

Included Angle is the combination of SAI and Camber. If the Camber angle is negative then the Included Angle will be less than the SAI. If the Camber angle is positive then the Included Angle will be more than the SAI. See below illustration.


 

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Discussion Starter #4 (Edited)
Thrust Angle measures the direction that the rear of the vehicle wants to go. When aligning the rear of the vehicle the rear Toe numbers should be the same amount positive or the same amount negative.


If the rear Toe is out on one side, it will cause the vehicle to want to travel in the direction of the highest Toe angle.




Well that's it.
THE END.
 

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Hi! So how do you do the adjustments for caster, camber and toe? Does it have to be in following order? And what's a good specs or settings for each? And also how do you align your steering wheel? Cause mines pointing to the left when the wheels are straight. Thank you
 
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