Unstable at higher speeds

Stock tires track "rain" grooves in the road. A lot! Move up to 195's over the stock 185's and there is a big difference.
Otherwise learn to relax and let it go and overall the car tracks pretty straight over the long haul. Its just kind of unusual to let a car float left and right 6" or so as it tracks the grooves.

 

You should have the alignment checked if you haven't done so already. My car felt unstable at highway speeds when I first got it. The toe in was out of spec on the right rear. The car had a tendency to turn one direction a lot easier than the other, giving it an unstable feeling because the correction was not the same in both directions. The worst conditions for feeling this was at highway speeds with a crosswind.

 

I think the Prius is in fact a little on the heavy side for a car of its length and width.

+1 on dogfriend's suggestion regarding the alignment. The 2nd Generation Prius has a history of being delivered out of alignment. That's why there was a separate TSB about it, and there's a separate, express, 1 year/20,000 mile warranty for it.

In any event, supplementing all of the above suggestions, you might consider getting the BT Tech front Strut Tower Brace and rear Stiffening Plate from the PriusChat Shop. IMO, they improve the car's tracking and handling a lot, especially the Strut Tower Brace.

 

I am also having the same problem.

 

ALL of the posts above are sound. These tires track rain grooves like water in a trough. Sanity check the front end alignment. If it's off, it will get corrected. If it's okay, then you purchased some very cost-effectie peace of mind. It's unclear what your mileage is. If your mileage is low and you haven't hit any curbs or potholes then it is probably okay.

 

I stayed with the 185 size tires, but swapped out the OEM Goodyear POS tires with some good ones. The difference is like night and day.

Tom

 

I have had nearly same problems. My suggestion is to prove the adjustment of stearance and chassis. They has often to much tolerance. After correction of only a little tick in stearance it has a much better handling. May be that better tires also has a positive effect for a better handling. In my opinion the Prius has no good straight running ability. All other cars I owned before has this better done. Sorry english is not my mothertounge.

 

One other issue is the question of what cars you are comparing it to.

The first car I drove up to 90 miles an hour was my father's 1968 Ford Mustang. I was lucky that I was on a divided highway with no other traffic near me. The thing was wandering back and forth over a substantial fraction of a lane.

Later I owned a 1975 BMW 2002 and a 1987 BMW 325i. When they were new, either one of those cars felt more stable at 90 mph than it did at 50 mph. On the other hand, somewhere up past 100,000 miles on the car I found the 325 felt unstable just doing a freeway past at 85. As people above have suggested, that was my cue for a little suspension work (I forget whether it was alignment or whether I actually needed to replace a part).

So the real question in your case is whether there really is anything specifically wrong with your Prius, or you are just accustomed to cars that track more stably at speed. Perhaps you could exchange cars for a day with another Prius owner who is happy with theirs.

 

i have had 2 Pri's and never had an issue described here in either one both using stock tires. have the vehicle checked out...

the BT brace helps but not in this situation. i will say, we have bridges here that run east-west across the straits of Puget Sound where the winds funnel between the Olympics and Cascade mountain ranges and on those bridges, the BT brace does help a lot with the north-south winds.

 

Don't be surprised if alignment is not the cause. Mine felt the same way when it was new and the alignment was spot-on. Not wanting to bother with new tires, after a few weeks I got used to the feel of it.

 

When I upped the air pressure to 42/40, the instability was reduced. When I bought GOOD tires to replace the Goodyear Integrity tires the instability disappeared completely (with no realignment, although that could hep as well). My first replacement tires were Michelin MXV4+ "energy saving" tires which were very good, but my present Nokian WR tires are great. Both improved MPG with the Michelin tires giving a small improvement (about 0.5 MPG) and the Nokian tires getting a 2 MPG improvement (averaged over a 12 month period) compared to the original tires.

JeffD

 

There are several possible causes for this. First, get the alignment checked, if for no other reason than to rule that one out. Apparently many Prius are delivered out of spec. Better tires are a good idea even if you're not having handling issues - the improvements in stability, braking, and traction make the car much safer. Chassis braces also help, though more with cornering. Another thing is to 'get used to it'. Not the wandering, I mean, but the car. When I first got mine, it was all over the place. After awhile, I realised it was my fault. I was used to a larger car with a fair bit of play in the steering, and was in the habit of gently moving the steering wheel back and forth. The Prius's steering lacks feel, but not precison. Every little movement of the steering wheel translates into movement of the front wheels.

 

I too had this on my new 2006 until this week. I replaced the OEMs with same size Michelin MXV4s. With new tires I decided to also have the front wheels aligned and checked as I never checked it since new. I think I just got use to the higher speed wandering in the freeway lanes.

Well I'm glad I checked the front alignment as the guy told me they were toed out 3 degrees! Our speed limits on the interstates are 75mph and the difference is night and day. The Prius is VERY stable with a proper alignment and good tires.

 

Incorrect toe in or toe out does not cause stability issue absolutely. It may cause over steer or under steer problem on high speed turns and of cause excessive tire wear.
Stability is usually caused by insufficient traction from the tires, light weight vehicles reduce the traction and tall vehicles aggravate the traction requirements.
A good tire with good traction will improve the stability.

 

In some of them the alignment is bad from Day 1, caused by the way the car was tied down on the ship.

 

Also note that the electrically assisted steering in the Prius has little dead band or feedback. It's very easy to over control until you get used to it.

Tom

 

Yes. Assume nothing about the alignment until it has been measured.

Let me suggest:

• early tire rotation - this gets them in front of a technician who can
• measure tread depth - normally they do just center and edges for each tire. If there has been an alignment problem, this will be 'the smoking gun.'
• wheel alignment - get a hard copy listing with all of the values:
  • toe - how much the tires try to roll towards each other. More toe, more stability but higher drag. Unequal toe tends to pull. Outside toe, the car becomes unstable and tries to dart to either side.
  • camber - how much the tops of the tires lean towards the car body. More camber, the better to take sharp turns at high speed. Less camber, less drag and more even wear.
• caster - how the steering linkages work so turns are smooth and the tires don't 'make smoke' in a turn. More of a linkages and suspension issue, it tends to go bad only after a bad accident or bad road hazard event ... very bad event ... like an accident type event.

I would recommend asking Mr.Google about wheel alignment but if you'll get your tires rotated, tread depth measured, and the alignment report brought here, we have a number of folks who can make practical recommendations.

GOOD LUCK!
Bob Wilson