Wobble/swaying issue

Is the freeway pavement grooved. Often some tires will follow the grooves.

Did you try to put more air in the tires? I think 38 front and 36 in the back.

 

I also think it's the grooves in the pavement. With new tires, they dig into those grooves much more than used tires that are worn. That's why you don't always notice it when you're driving and also you didn't notice it before you changed your tires.

If the mechanic checked your alignment, suspension, balance, steering column, there really is nothing left that can cause an issue. You can always go in for a second opinion at another shop but I feel it's what xpcman mentioned, the grooves or uneven pavement in the road.

 

Despite the potential cost of doing so, I think I would want a second opinion and evaluation from the dealership.

You say "The Mechanics" but is this a tire shop? An independent repair facility? Or a dealership?

I think you need an opinion from a qualified technician with no vested interest or connection to the installing of the tires.

I hate to say it, but who knows about the training level if this is just a tire shop? And sometimes if you are in a position to be blamed for something being wrong, you consciously or subconsciously might not be looking too hard to find something wrong.

In short? I'd want a second independent opinion. It might just be money out of your pocket, but stability and suspension can be so important that I'd want one.

If the feedback from both entities is that nothing mechanically can be found wrong? Then I'd assume it is just the breaking in of the new tires and I might just give it time.

 

Try going 65 on a brand new like smooth highway and see if it occurs. That can help eliminate the grooving and suspension issues aspect for the differential diagnosis. I had a very serious wobble, heavy shaking up to the steering wheel in my Lexus LS430 after getting it. I had just put on new tires, Michelin Primacy MXV4's. The issue was my front suspension which I had anticipated as needing to replace @ 120k miles.

I would agree to having your car looked at my an independent Toyota mechanic. The best ones don;t charge you an arm and a leg for just checking out the car without doing a service procedure. I am accustomed to the SoCal roads and environment with the Santa Ana winds and can tell you that occasionally I have felt the car sway due to a tractor trailer buzzing me along the next lane. The Santa Ana winds haven't appeared since I got the car in late June but I imagine they'll sway this car quite a bit. It it sways my LS430 on occasion which is a behemoth. Also if you have stock 185/65R15's they are pretty thin. Perhaps look into 195/65R15's since they're also the largest 15 inch size for Energy Saver A/S's and are the std size for 2010+ priuses. I bought some recently for my 05 prius.

 

Generation II is 2004-2009 model years. Generation III is 2010-2015 model years. Prius C is the tiny Prius (1st Generation, 2012- likely 2017). Prius V is the Wagon (1st Generation, 2012-likely 2017).

How many miles have you put on the new tires since installation?
Michelin says a few hundred miles are required to break the tires in. LINK
Perhaps a road trip to San Fran or Vegas, putting 600+ miles round trip, on nice smooth asphalt?

Out of balance tires would be consistently noticeable, esp at speed (>40MPH). The wobble would be proportional to speed. LINK

Are the other suspension components in good shape: tie rods, ball joints, struts, bushings?
Once the "sway" gets resolved, consider replacing the 4 struts, if they have never been changed and you have 50,000+ miles.

As others have pointed out, spend the diagnosis fee at another shop (independent or Dealer) to get the suspension checked out. Assuming alignment is w/in specs (what does the pre and post alignment sheet show?) and tires have been properly balanced, might turn out to be some suspension component(s).

Good luck, let us know what the diagnosis is.

 

Pictures of all Pri generations from Edmunds. Your 2007 should look like the Gen2 pictured below, unless you mistyped your model year.

Gen 1 (2001-2003)

Gen 2 (2004-2009)

Gen 3 (2010-2015)

Prius C (2012-TBD)

Prius V (2012-TBD)

 

There's a recall notice re: the steering column. May not be the cause of the wobbling but a good reason for you to have the dealership look at the car.
Yours may qualify for other recall work.
While the car is there, maybe mention the wobbling. They'll most likely check it out for free in the hope of getting future repair $$$$.

Good luck.

 

This is a very common complaint with people who just buy the car. There are many many posts about this.
I posted myself about this back in 07 when I bought the car new.

The G2 Prius has very tight steering and zero deadband. A little deadband allows you to relax a little with your hand on the wheel and the car will track just fine. The G2 does not do this well. It likes to track every little anomaly in the raod. It's extremely irritating.
This sometimes even increases with new tires. I had a Crown Vic and that car would go done the road a long way without me touching the wheel.
Don't try that with a G2 Prius.

This car is all about tire and tire pressure. If you buy new tires and run the tire pressure at door placard pressure (very low at 28-32) the car will track every little groove in the road and will require constant steering wheel input. Its really my only compliant about the G2. That and the seats suck.

To really help mitigate this issue increase the tire pressure to 42 front 40 rear. This will improve this issue but the car may hit hard over bumps. But at this pressure your gas mileage will improve immensely.

If you bounce between different cars all the time you will notice this issue. if the prius is your only car you'll get used to it pretty quick.
You have alot of reading to do about this great but twerky car.

 

It isn't a prius, but my work van was getting tires one by one. By the time it had all four changed it became unstable at speeds over 45 mph. Basically all over the road and hard to keep in its lane. Felt very dangerous.
The fleet mechanic was out troubleshooting it when we came upon him. He said he couldn't figure it out. I mentioned to him that it felt like it does when the tires are low on air. I checked the tires multiple times and they were aired up correctly. Van was returned to us later in the day with four new different tires on it. Apparently the ones being put on it didn't meet the requirement for load rating and the sidewalls were too weak. New heavy duty tires fixed the issue.