Caster adjustment...not possible?

Caster affects turn in response. I wouldn't worry about it unless you're concerned about lap times.

 

Absolute caster is not as important as having equal caster right and left.

 

I agree with the above responses, it's not likely to cause any kind of abnormal tire wear. Generally a tenth of a degree out of spec isn't enough to do much even if it was toe or camber.

 

Wheel alignment is as much an art as a science. We used to set up cars with the drag link in front of the control arms closer to the positive end of the spec and if it was behind, to the negative end. The best alignment guy we had was as good with a carpenters square and measuring tape as the machine. He built a limited sportsman class local half mile track race car every year and never once brought it in to be alighned. He did it in his garage at home. Guy was a real master at it. I drove it around his neighborhood once. Let go of the wheel and it would go hard left. If it bothers you take it to a frame shop. Just don't watch when they wrap the chains airing it and start bending. This is how you used to have to alighn the old Ford twin I beam suspension pickups. If you were smart you did this they day you bought it. Tire wear was horrible right off the lot.

 

(1 No, Caster is not adjustable.
This is due in respect that when your car was assembled from the factory, the accepted castor was within specs. Not every car that comes from the factory is in perfect specs, so Toyota uses a degree of error for each measuring point of alignment.
(2 The number one killer of tire wear is Toe. Caster only affects your steering output.
(3 If your car has been in any major accident, your alignment would be off the accepted numbers within the range Toyota recommends.

Hopefully, I answered your questions!

What is your Toe numbers?

 

Very good! 0.10 is within the range of specs but if your mechanic took more time he can get it closer to 0.00. It all depends on the amount of time your mechanic wants to spend on your car. Time is money!

 

I'm not understanding the above. A "spec" typically is an ideal and an acceptable deviation, for example:

5.1 degrees plus or minus 0.1 (or 0.2 or 0.3) degrees.

Addendum: checked the repair manual, think you're good:

 

You don't necessarily want 0.00 toe - this results in a car will tend to wander on uneven roads. A slight toe-in is preferred over slight toe-out and Zero toe for stability.

 

I know from karting, negative toe makes the car darty. We ALWAYS ran toe out

 

Yes. Toe out increases turn-in response, but it sacrifices straight line stability. It's amazing how much an alignment transforms a car for track duty - even if it's a show room stock car.

To clarify, you do know that negative toe is "out" right?

 

Note that someone pulling up to a curb who misjudges and bumps it -can- change the castor. The Prius is NOT a truck. It bends on impact.
Further, while like most vehicles there is no built-in castor adjustment, it -can- be adjusted. You have to bend things to do so. For example, a solid rear axle vehicle rear castor is adjusted with a tool that bolts onto the axle and bends it. Very high tech -NOT- !

 

I adjusted caster on a gm by filing the holes in the front strut towers into slots. The hunter alignment rack computer told me to file the holes I'm not making this up!
I wonder why that wouldn't work on a Toyota too.


iPhone ?

 

One problem with any slotted connection, it's relying 100% on the bolts ability to clamp the two surfaces. If the clamping action is overstressed the bolt could end up at the end of the slot, way out of alignment.

Also a slot in a plate is inherently weaker, more prone to opening/tearing. In structural slotted connections oversized plate washers are mandated, to bridge the slot. When post-slotting an automotive connection if you were to add plate washers you might be exceeding the bolt's length.

That said, it might still work, lol.

 

Caster is determined by the relative position of the upper strut mount and the ball joint, and these are about 25" apart in the Prius. Thus, a change of 0.75 deg is equivalent to a change in position of the strut mount or ball joint of about 0.32 inches, and the spec is +/- 0.75 deg. This is why it's not adjustable -- it would take serious body or control arm damage to move the strut mount or ball joint by 0.32 inches. If this were to happen, the vehicle would be in a frame shop if not totaled. Wear is another factor, but obviously a ball joint with anywhere near this much wear would separate.

 

Sounds like my old 1964 Ford F150. it kind of went straight down the road.... It had a big steering wheel, bench seats and a PTO. bored her out to a 312. ran great, sounded like a sewing machine until i blew the head gasket. errrr.