Unstable at higher speeds

[Shawn Clark]

Higher tire pressures will somewhat improve stiffness, but the car still wanders more than others I've owned in wind and follows road grooves more. I expect changing tires eventually will change the tendency, but I also intend to do the brace and stiffening plate to reduce body roll of the narrow/tall design.

Ironically, other than the Prius, every new car I've ever bought needed an alignment when it was delivered. They either pulled a little or I noticed the thrust angle was off while following them with my wife driving.

Originally Posted by GreenRepublican09

Thanks for all the input. I think when I have the oil changed I'll ask them to check the alignment.

Make sure they don't overfill the oil. This is one of the primary chronic issues in maintaining the Prius. Mine was shipped from Toyota with an extra 1/4" on the dipstick. Don't let them put in over 3.5 quarts (Toyota spec says 3.9, but is wrong, 3.5 will result in it being about 1/4" below overfull) and let them know you will check it before you leave the dealership. I'm not suggesting being confrontational about it, just specifying what you want so that they have adequate instructions.

[jorgeez]

Or maybe installing a strut tower braces can help you with the car's stability...

[pattom]

I had the same problem, my 2008 was unstable at highway speeds. Going 60 to 70 mph. Took into dealer and had it aligned, that took care of my problem. Didn't cost me anything. The car had about 6000 miles.

[Porsche998]

Just bought some snow tires from Tire Rack - was concerned that since snow tires frequesntly wonder more than regular tires, the Tire Rack Rep. pointed out that the Goodyear Integrity was very poorly rated for stability. Almost all tires were rated better.

[ceric]

Check alignment first.
W/o proper toe-in, the vehicle will wander.
If OK, check the tires.
My Prius is no BMW, but it does OK at high speed (before any mods I did to it).

[rvndave]

I would check all tire pressures first.

[edthefox5]

Tires are hunting. Underinflated tires. Its tracking every little groove. Our OEM tires are the worst. If your still running at the tire pressure the dealer delivered the car to you (like 30/28) that's alot of it. Try inflating to 40 front 38 rear to start. There's alot of trial an error on tire pressure on these pos's for a give and take on liveable road noise, harsh ride, handling, and mpg gain.
Max tire pressure for good mpg gain is like 44/42 but ride is very harsh and road noise is high. At least imo. Alot of posters here pump much higher which you may get away with as these tires are Low Rolling Resistance tires which mean they have a much strengthened sidewall but extreme inflation way above sidewall warning level makes little sense to me just to gain 1 or 2 mpg.

Once you've had a side wall blow out at speed you will try real hard to avoid that in the future.

But at much higher inflation steering hunt is much improved. I'm at 38/38 and road noise is ok...mpg is not to bad at 46-47......and hunting is almost gone. Run lower psi and the tire is very quiet...poor mpg..and it will hunt bad.
I got 17k on my pos's. At about 30K I'll buy new. Can't wait.
Good luck.

[donee]

Hi All,

I do not find any dead spot in the middle of my Prius steering. And that is probably part of the problem for some people used to the dead spot in the middle of hydraulic power steering. Without the BT Tech plate, a side gust will provide such a long time variation in required steering input, that PIO (Pilot Induced Oscillation) can be a problem.

I really liked the improvement the BT Tech plate provided in variable side load tracking performance and controllability of my Prius. Although, its no panacea for high speed understeer. It helps allot with side wind gusting tracking, and left turn oversteer over reverse camber surfaces. The difference was noticable and dramatic, even with the GY Integrity tires. I had the luck(?) of having nearly identical extreme conditions before and after installing the BT Tech plate, and made identical test before and after.

But, I agree that better tires are certainly worth it too! Hydroedges are great around here with the slick surfaces during rain after a dry spell.

I never had an calm weather straight line problems with my car even at 70 mph in dense air conditions with trucks flying by at 85.

[donee]

Hi Shawn Clark,

At first I thought this too. And aerodynamic cars are notorious for side wind pressure induced tracking problems. But this is definately not the case with the Prius. The problem is almost for sure due to body flex induced steering. With the BT Tech plate on my car, at 65 mph, and a 40 mph side gust (0-40 mph in about a second), my car tracks nearly straight and is easy to counter steer to a straight course. And that evaluation was done with the stock Integrities. It does really roll a bunch though. That takes getting used too.

[tools]

i have the same problem i changed tires and still have the same problem. i delt with it thinking it was just me. then i bought a second used prius and it has more miles on it and the same tires and it drives great no wander. is there anone that has fixed this problem.