Gen 4 Alignment - How good is good enough for top mileage / handling / tire wear?

Was it a TOYOTA Dealer?

You could ask them - they can only say "NO" or "Pay more and we'll get it exact".

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

You could also find out TOYOTA Specifications and see if they're within the +/-. You might find them on-line.

I'm not sure how much adjustment is available with castor or camber - sometimes only adjustable with changed parts - ie extra $$$$.

 

Indeed. Rear camber is not adjustable, and front camber adjustment can require new bolts.

If the alignment meets all of the published specifications, and you don’t notice any objectionable driving characteristics, such as pulling or wandering, I wouldn’t pursue further adjustments now. Drive the car for a few thousand miles, and then check the tires for uneven wear.

 

I just now had an alignment done on my 2017Prius at a non-dealer shop and the front caster reading is 5.7 (left) and 5.8 (right) whereas the spec is 6.51 (+/- 0.45) per Toyota. The shop says Caster is NOT adjustable. Wondering if this is true and if so if I should take it to a frame shop or something.

 

The Repair Manual (more info) gives the front caster inclination specifications in degrees and minutes of arc and in decimal degrees, which the shop or their source of alignment data seems to have confused. For model year 2016–2018 Prius cars with tire size 195/65R15, the specifications are 6°51′ ± 0°45′ (6.85° ± 0.75°), and the right-left difference should be 0°45′ (0.75°) or less.

That’s correct; at least, the Repair Manual doesn’t include a procedure to adjust caster, as it does for front camber and toe-in, for example.

Assuming the measurements you gave are in decimal degrees, the right-left difference (cross camber) is well within limits, and the left and right measurements aren’t all that far outside the specifications. If the car hasn’t been in a collision or had other known damage, and the shop has made other adjustments, I’d see how those work out, and invest in further diagnosis only if you notice unacceptable handling or tire wear.

 

You are right; I was the one confused between the degrees/minutes of arc and decimal degress. The sheet the shop provided gave everything in decimal degrees. I meant to mention the spec from Caster from the Toyota manual as 6.85 +/- 0.75 decimal degrees. Whereas the left side read 5.7 degrees and the right 5.8.

I happened to accelerate over a significant/wide bump a couple of months back in the dark and in a hurry and I could feel the front struts/shocks pressed in to the limits and the entire car go up in the air a little bit and land. The car always had a slight wandering on the highway and that happened to increase after this incident. I thought perhaps the worn tires had suffered some damage internally and so replaced them with Michelin CrossClimate2's recently and took it in for alignment. Attached is the sheet.

 

Rear camber/toe is adjustable with using Godspeed kit. Here's the link https://www.ebay.com/itm/384735773718?fits=Year%3A2020&hash=item59940a0416:g:RCoAAOSwWnViCz~0&amdata=enc%3AAQAIAAAA4Oyy8CV6oVY2zueAdZ4KCs3vvt6tIj5U32499uplcCO0qidPuTBZqlwS4Z2UjbpXCQ%2FQYBVYFNC%2FInZo9jnaOhaMDwcsBi7B0QgMP1%2BSfPvs2KF%2B%2FRywrN4FKRHHhgW%2FisxRCYp5%2B2pa02Dmq890kg%2FfKSPrayZJg3Q42%2F7W3m6RGTaxe5zWKo%2F5kb1V2gvsHhcKsy92Wtw2bpri4%2Fs7Bx0U86DBzxje7fOxncPDOCiOkaKQ6UlF2Yo9LLtOFegs%2B1AtFxGFIwl7GIBrBWg%2BYpqDpoa5kcgUETanFuUF1l%2FG%7Ctkp%3ABFBM-qj7g45i