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Vague Handling at Highway Speeds

When I first bought my Prius Plug-In Hybrid in 2014, handling was fine in the city but was awful at highway speeds. If I held the steering wheel still, the car would start to wander out of its lane within seconds. There was no pattern or “pull” to the left or right; it just didn’t stay straight and therefore needed constant steering corrections to stay in its lane. At 70 mph, I felt like I was constantly driving on slick roads even when they were bone dry. I took it back to the dealer who checked and adjusted the alignment and toe-in.

Fast-forward 4 years: The same problem has been slowly returning. I now feel as if I am driving on wet or even snowy roads when the highway is perfectly dry and clear. I find myself slowing down much more than other cars (and more than even the yellow recommended speed signs) on highway turns. I just got it aligned again, but the mechanic said that the alignment was already nearly perfect. He also said that the tires are in fine shape with no damage or uneven wear. So, I’m at a loss.

Has anyone else had this issue? Suggestions / Advice?

Tires inflated to the sticker amount? How many miles on the tires?

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Tires inflated to sticker level with nitrogen. Garage just checked and said they were just right so they didn’t add any.

Tires have about 20K on them. (I don’t know exactly because I switch between all-season radials and snow tires each winter/spring.) (The car only has 30K on it.)

Have they been road force balanced recently? Since you switch between sets, I suppose a weight could have fallen off or shifted…

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I have the tires re-balanced each time I rotate them.

The other reasons I doubt it is a balance issue is that (1) there is no vibration like I associated with out-of-balance tires and (2) the problem has been developing very slowly over time – not a sudden change.

Virtually everything in regard to tire design involves trade-offs from one quality to another, and if–as I suspect–this car has ultra-low rolling resistance tires, then it almost surely has less traction than if it was equipped with tires with a higher rolling resistance. And, as the tread wears, whatever traction the tires originally had would have been significantly decreased by tread wear.

I strongly suggest that the OP surf the tire offerings for his car on the Tire Rack website, and then prepare to purchase new tires–even if those tires have a higher rolling resistance. Excellent fuel economy is nice, but a lack of traction can kill you.
:thinking:

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A possibility is that there are grooves or ruts in the road and the car is trying to follow those.

Try a different road where you can get the speed in the same range and see if it is still there.

Also - No - tire rolling resistant has nothing to do with this. Put in technical terms, (assuming this is a tire issue, which I doubt) this would be a force and moment issue, not a traction issue.

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My 1990 Mazda RX7 had 2.25/50/16 Toyo tires that liked to follow the cracks that had been temporarily patched with tar. I didn’t consider it a problem since I enjoy cars that I actually have to drive. When the highways were properly resurfaced they were less fun.

The car needs to be re-aligned, I believe. It is possible that the toe-in has changed a bit due the the car “settling” a bit. Plus the tires are a bit more worn. The addition of a little toe-in (looking from above the tires are turned in a little bit towards the front of the car) will help settle this down.

While the wandering on the highway is annoying and tiring, this has little affect on the car’s cornering traction and ultimate handling. It just feels like it does.

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Like @Mustangman said, a good alignment shop is needed. There’s always a range of acceptable values for each specification, and your shop needs to push each towards the ‘stable’ end of the range.

@CapriRacer - what would those be, besides toe in, as already mentioned?

p.s. - google “Prius alignment adjustments” if you want to learn about this, both for your front and rear axles (bother are important).

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Thank you. I believe you may have hit it on the head.

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My 2012 Corolla did that when it was new and still does it. The electric power assist is highly sensitive at highway speed but I got use to it.

There are some other possibilities for this. First that comes to mind is that the steering rack may have been left loose at the factory. Next would be a defective tie rod end. You could also have a defective control arm bushing that was defective from the factory. Most of these would cause some excessive wear on the inside edges of the front tires, but if you are rotating them religiously, that may mask the problem.

You may also have a defective strut if you have a sense that the car is floating at freeway speeds and is harder to control after hitting a bump. The dealer mechanics seem to have more trouble with suspension issues because there isn’t an “check suspension light” with corresponding codes.

If I had that problem I’d experiment rotating the tire positions, and if that didn’t have any effect I’d have the toe adjusted in a little more “in” than it currently is, toward the range of the spec that has more toe in. Beyond that you’re looking at

  • suspension system problems
  • steering & steering rack problems
  • could be the way it is supposed to drive, and for some reason you are just now noticing it. Have you noticed any recent change to your mobility, balance, eyesight, etc?

I might also do a temporary experiment where I’d re-mount the two front tires on the wheels so they roll the other way around, and see if that had any effect.

Texases,

When I mentioned Force and Moment, I am talking strictly about the tire. Toe in is vehicle.

But F&M is one area where I just don’t have the expertise. I know there is a tire force (or moment) that translates into “On Center Feel”, but I don’t know much about it.

“On Center Feel” is a tire property that describes the vagueness (or lack of vagueness) when the steering wheel is pointed straight ahead - that is: How positive does the car feel when it is driven straight ahead. Does the steering wheel feel “centered”? Does it take a bit of force to get the car to deviate from the straight path. Does the car want to return to the straight ahead path?

But in this case, I think the fact that the problem is gradually returning points to something other than the tire. I suspect the vehicle is gradually developing toe-out, and toe-out is basically unstable.

post #1 said they aligned it and it was fixed.
did they provide a readout of before/after specs?
it has slowly started to wander again.
usually slowly means something did not break and is gradually occuring
i had a 2012 prius. rock solid driving. straight ahead. no wandering
had a nail in front tire at 8k miles got a cheapo non matching new tire
zero difference in tracking.

Thanks to all who offered advice. I have now figured out the problem: tires.

My particular Prius Plug-In came with Yokohama tires rather than the Bridgestones that come on most. The root of my problem is that the particular set of Yokohamas that came on my car are essentially garbage. While Yokohama does seem to make some good tires, I checked on Tire Rack and other sites for reviews of the exact model that came on the Prius. They rank at or near the bottom of every ranking. A typical comment from a user said something like “I should have throw those tires away the day I bought the car.”

With less than 25K, the Yokohamas on my car had roughly half their tread left but handled as if they were completely bald.

I’ve now switched to Michelin energy star eco tires and the car handles just great.

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Always good to get a final response.

Yes, I also appreciate the OP’s response on the resolution of his problem, but before he becomes too confident about Yokohama’s supposed inferiority to Bridgestone’s tires, I have to point out that Bridgestone also manufactures some garbage tires. If he doesn’t believe me, he can ask anyone who ever owned a car that came from the factory with Bridgestone’s incredibly crappy RE-92 tires.

I have never had a really good tire on a new car. The best I had were the ones that came on my 2012 Camry. They were Michelin Energy Savers, OK handling and ride, great gas mileage, but they were worn out by 30,000 miles. The Goodyears I have now ride and handle better, have a 90,000 mile rating but get slightly less gas mileage and much better winter traction. They are slightly larger in circumference which could account for the measured mileage but I was comparing worn out tires to new ones.

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