Wheel alignment in degrees

Hello all:

I had my new '09 Prius aligned yesterday, as the steering wheel was somewhat off center and I wanted to get it fixed (alignments are free for 1 year/12,000 miles).

In other threads on this topic, users have reported that many west coast dealerships and alignment shops seemed to only provide readouts in inches, rather than degrees. Also, not all provided "before and after" measurements.

I want to report that Kerry Toyota in Florence, Kentucky, seems to get it right. The report that they gave me was in degrees. The report also had "before and after" readings, which I really appreciated. The top half of the paper had all the "before" measurements for all 4 wheels, plus thrust angle, and some others that I forget. The bottom half of the report had the "after" results.

If an individual reading was "perfect" the result was displayed in a "green" block with the allowable range shown in the block. If just ok, but not failing, it would be in a "yellow" block, which would also show the range for this. If totally out of the any allowable range, the value would be in a "red" block.

I had two yellows ont the left rear. Right rear was perfect (green). As we know that the rear settings are not directly adjustable, there was no change for the rear between the before and after readings.

There were a few "reds" on the front end. I'm not home right now, so I can't tell you which ones were out (I'm pretty sure that the toe in was bad on both sides).




Results:

• before and after, no discernable pulling.
• After alignment, steering wheel properly centered.
• Driveability: it was a little windy coming home, but it seemed that maybe the car wanted to wander a little more?? I didn't seem to notice this as much previously. But again, it could have been the cross winds.

I know that "negative" caster will make the steering feel "light", and will cause a car to "wander", making it difficult to keep it in a straight line. So when I get home, I will check the printout again and see if the caster on the front wheels was actually adjusted. If so, and if they made the caster more negative, this could make the car feel less stable. Note: from what I've read in other threads, I don't think that the caster is actually adjustable on the Prius. But could that have been changed in the G2s for the later years of production?

When I get home I will upload a JPG of the report here, if anyone is interested

Best wishes,

 

Hello Fray:

I commented on Prius caster adjustment as pure speculation. I'm away for a few days, so I can't check the printout right now. I'm guessing that the Prius does not have adjustable caster, based on other posts in these forums.

Were it adjustable, however, it could be another tool to improve the stability of the car.

I saw a write up that said that years ago, when autos had bias ply tires,, they were often set up with a negative caster as a means of making the car feel more agile. When these same cars then had radial tires installed, they would be somewhat unstable. If the caster were then made slightly positive, the handling would improve. Hears a quote from that article (from familycar.com):

Caster

Positive caster improves straight line tracking because the caster line (the line drawn through the steering pivot when viewed from the side) intersects the ground ahead of the contact patch of the tire. Just like a shopping cart caster, the wheel is forced behind the pivot allowing the vehicle to track in a straight line.
If this is the case, then why did most cars have negative caster specs prior to 1975 ? There are a couple of reasons for this. In those days, people were looking for cars that steered as light as a feather, and cars back then were not equipped with radial tires. Non-radial tires had a tendency to distort at highway speed so that the contact patch moved back past the centerline of the tire (Picture a cartoon car speeding along, the tires are generally drawn as egg-shaped). The contact patch generally moves behind the caster line causing, in effect, a positive caster. This is why, when you put radial tires on this type of car, the car wanders from side to side and no longer tracks straight. To correct this condition, re-adjust the caster to positive and the car should steer like a new car.​

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And for further reading, here's the link to the article:

Wheel Alignment A Short Course​

I found this whole article to be very informative.