The Mystery of the SAI (Steering Axis Inclination)
11-21-2010, 01:25 PM
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The Mystery of the SAI (Steering Axis Inclination)
After having a total of three alignments performed now on my car, the SAI has always been out of spec each of those times. The first two alignments were done after swapping out springs, and the third time was done after coilovers install. I'll admit that after numerous google searches, I'm still puzzled as to what this SAI really means. Each of my alignments yield different SAI measurements. You'll notice that on the 2nd alignment, the passenger side SAI was way off, and on the last alignment, the driver said SAI is way off. This leads me to believe that my suspension components aren't bent (the usual explanation for bad SAI). But now I'm even more puzzled after comparing my previous alignments.
All suspension components have been stock with the exception for springs, and now coilovers. The car drives fine, no crazy pulling or anything. Yes, I know my compression arm bushings are probably shot, since caster is off. Does this have anything to do with SAI? Do I really have anything to worry about with the SAI, anything I can look into?
Here are the specs from each alignment:
First one (Hotchkis springs)
Second (GF210)
Most recent (KW V1)
All suspension components have been stock with the exception for springs, and now coilovers. The car drives fine, no crazy pulling or anything. Yes, I know my compression arm bushings are probably shot, since caster is off. Does this have anything to do with SAI? Do I really have anything to worry about with the SAI, anything I can look into?
Here are the specs from each alignment:
First one (Hotchkis springs)
Second (GF210)
Most recent (KW V1)
11-22-2010, 07:30 AM
#2
SAI is the angle from vertical on a line drawn through the upper and lower ball joints. Where that line intersects the ground compared to the vertical centerline of the contact patch is the scrub radius. SAI affects steering feel and does not affect tire wear.
In your case the SAI numbers appear to be random so I would suspect alignment operator error. Most likely they haven't calibrated their machine because SAI isn't that big a deal for 99.9% of the numb hands street drivers. They could also use the bogus numbers as an upsell point.
Talk to local racers and find out where they take their cars to get aligned. Go there and be prepared to pay more then the $29.95 lifetime alignment special.
In your case the SAI numbers appear to be random so I would suspect alignment operator error. Most likely they haven't calibrated their machine because SAI isn't that big a deal for 99.9% of the numb hands street drivers. They could also use the bogus numbers as an upsell point.
Talk to local racers and find out where they take their cars to get aligned. Go there and be prepared to pay more then the $29.95 lifetime alignment special.
11-22-2010, 06:54 PM
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SAI is the angle from vertical on a line drawn through the upper and lower ball joints. Where that line intersects the ground compared to the vertical centerline of the contact patch is the scrub radius. SAI affects steering feel and does not affect tire wear.
In your case the SAI numbers appear to be random so I would suspect alignment operator error. Most likely they haven't calibrated their machine because SAI isn't that big a deal for 99.9% of the numb hands street drivers. They could also use the bogus numbers as an upsell point.
Talk to local racers and find out where they take their cars to get aligned. Go there and be prepared to pay more then the $29.95 lifetime alignment special.
In your case the SAI numbers appear to be random so I would suspect alignment operator error. Most likely they haven't calibrated their machine because SAI isn't that big a deal for 99.9% of the numb hands street drivers. They could also use the bogus numbers as an upsell point.
Talk to local racers and find out where they take their cars to get aligned. Go there and be prepared to pay more then the $29.95 lifetime alignment special.
11-23-2010, 06:51 AM
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