Poor centering of steering wheel after slight movement

I would suspect alignment since it has the same behavior with two different sets of tires. Normally I would suspect tires

 

First step is a 4 wheel alignment, that usually solves the problem. If your warranty is similar to ours you should get it free. The cars sometimes are banged around pretty badly during loading and unloading, it's not to uncommon to find alignment problems in new cars that have been transported by ship.

 

What exactly is our warranty with a free alignment? Heard several people mention it but is that in writing somewhere? I have experience "tramlining" since I got the car and it continues with my new wheel/tire combo and would love to score a free alignment. I just figure they will try to not give me a free one once they see aftermarket stuff on my car.

 

I bet this is the first non-European car you drive, Toyota's are not know for steering input and tight response. The behavior you describe is normal. This is not like European cars that have strong self-centering and the car will go straight for mile with your hands off the steering wheels. I always have to keep my hands on the steering wheel to keep it going straight or it will drift slowly to either side and this have nothing to do with alignment. It is design that way.

 

It's not in writing in the warranty booklet so I guess it's more of a Toyota policy. I was told by two service managers that if there is an alignment problem, such as tracking, stability, tire wear, etc, and the car was from the Japanese factory they would align it free for the first year. I had some pretty serious alignment issues with my gen2 and actually ended up getting 3 or 4 free alignments before I finally fixed the problem with shims.

I think when you take it in you need to tell them it has a problem such as pulling to one side, steering not centered, drifting all over the road (which my Gen2 did), etc.

Thankfully my Gen3 has very good highway manners so I'm not going to have it done unless there is excessive tire wear.

 

Actually this model Prius should be very good if everything is aligned correctly. My previous car was a BMW 3 series and this Prius is just as good on the highway as the BMW was, although it doesn't corner nearly as well of course. It will indeed go down the road for a very long distance without corrections. I have the V model with the new type steering motor and wider tires which may help.

 

Yea I also had a Z4 which I just got ride of but my Prius IV is all over the place on the highway even with 17x7's. I guess I will call to see if they will agree to take care of me when I make an appointment.

 

Although mine is only a Prius III, this sounds pretty much like what I experience, except for me it doesn't favor either direction. If I had to describe it, I'd say it felt like the steering column was packed in heavy grease -- you'd increase your hand's pressure on the wheel and suddenly it would turn, sometimes just slightly more than you wanted. Relax your hold on the wheel and it does not return automatically, forcing you to manually turn it back.

Many describe this as "numb" steering, and I believe it to be an artifact of the electric power steering assist. I found that the effect can be reduced (but not eliminated) by increasing the tire pressure above the recommended settings.

Earlier on in the year, there was talk of Toyota reprogramming the power steering to change this behavior, but I haven't seen any followup on this yet.

 

It has nothing to do with the EPS, self centering force comes from the caster angle of the front wheels. If you have ridden a bike or bicycle, you know what I mean.
Toyota cars are mostly using McPherson strut suspension like in the Prius, which limits the amount of caster can be dial in without sacrificing cornering force. This is why for good handling cars they always have double wishbone suspension.
I suspect the Toyota you claim to have good centering may have double wishbone suspension (some European version may have a different suspension setup then the US version) or it is a Lexus.

 

Prius steering does feel different to most cars. You get used to it.
As others have said, check your wheel alignment.