2010 Prius "floaty" and poor directional stability at highway speeds

Same here , I have an early 2010 liftback. No problems wandering, running the original 15 inch Yoko Avids, replaced with Goodyear Fuel max. Both run at 40-44 psi. 40,000 + miles Might be different traffic or road conditions ???

 

I had a 2010 III and it was very unsteady at freeway speeds. I now have a Persona with the 17 inchers and the difference is remarkable... very stable at all speeds, handles much better, corners well. It made all the difference. Yes, I do take a hit on mileage but well worth it to me.

 

Probably about 3-4 mpg.

 

My Prius is similar. While I would classify its handling as "safe", I do fine the lack of precise tracking annoying. To me, what the vehicle needs is independent rear suspension with an appropriate amount of passive rear steer. I'm also wondering if the electric power steering is actually less precise on-center than traditional servo-hydraulic. I think that electric has to potential to be as good or better than servo hydraulic, but the latter has been around so much longer and has had the opportunity to become very refined.

 

some quick thoughts?
1. Does the problem of vague steering and road feel persist with no load in the cargo area?
2. The Michelin Energy Saver a/s have a tendency to wander until they break in (read it somewhere in a review) - did the problem exist prior.
3. what happens at the same speed with an extra passenger in the front? Slower speed 50-55mph?
4. have you tried putting the 150lb of cargo in another Prius to see if the problem persists. POE (process of elimination) would tell you if the cargo is the issue.
5. The max tongue weight load (trailer hitch) is 200 lbs. so i am thinking the extra 150 weight in the back is lifting the front of the car up enough to substantially effect the handling. Perhaps the way the car is sitting could be putting extra downforce of air at speed under the frame. etc. In Motorcycles we have Preload adjustments that changes the spring tension with the rider on the bike. So if the preload is soft then the bike will settle down further with the rider weight, thereby lifting the front up. It essentially changes the geometry of the bike and lightens the front end. Conversely, adding 2-3 clicks of preload to a motorcycle will stiffen the rear thereby lifting the rear of the bike with the addition Pillion, luggage, etc. So a thought is that with your weight and the extra 150 of weight in the rear it is changing the CG (center of gravity) and altering the WB (weight and balance) of the car. Not quite sure of the weight distribution of the Prius, but it is not neutral 50/50?

The point of this above dissertation is too examine the inherent issue of the car: the suspension of the car quite possibly could be causing your issues??? When i went into the dealer to ask about pulling a trailer the service tech - first words of advice was "suspension - rear suspension" to support the extra load. He implied that was the weak link, not the torque of the motor or the CVT?

6. have you tried putting a known good set of wheels and tires on your prius and driving with and without a load.
7. Alternatively, have someone swap Priuss and drivers see if it the problem still persists? Don't know if it is your driving inputs or expectations?

8. if the problem persists i would bring the car to a frame and body shop and have them look the car over... If you have any buddies in the body shop business they can use a micrometer and check the paint thickness over each of the panels in various quadrants to see if there is any statistical difference in the paint thickness - which would tell you if a side or a panel was repainted. The body is a unibody construction so it is difficult to fix without the proper french Celette jig. It is not a cheap jig and you need someone that knows how to work on unibody frames. When i was much younger i worked at a salvage yard, major collision shop that worked on Porsches. I quit after i found out the guy was a crook and stealing Porsches and changing vins, etc...

FWIW - it kind of sounds like how a Prius drives with 15" wheel, Vague, save for the fact of the car launching right or left. In all due respect the Lexus is CT200H is a prius (a sheep in wolf's clothing, hoofed with 17" wheels) and i don't think it suffers from any anomalies you mentioned.

 

How many seconds can you go at freeway speeds with no steering input? Straight road, before it wanders out of the lane.

 

I wish the steering angles where more adjustable on the Prius.
I know what you are describing with the gen 3 road manors.
I switched to 17" rims with summer tires and changed the struts on my 2010 Prius. It helped a lot.

 

Chassis braces are simple and easy to install. Over the past two years, I have made and developed many of them.

They are simple "bolt on" installs that take about 20 minutes.

While I was a skeptic at first, I am sold on them.

Just search "chassis brace" in the search function on the menu.

The Cusco strut tower brace, although harder to install, also helps.

 

To me a non-Plus Performance feels like it has huge amounts of rear steer making the car a handful to drive in heavy cross winds, rutted Interstates, and having to pass big trucks or having one blow past you. My Plus Performance tracks well bone stock. Toyota should include the rear swaybar as stock equipment.

Mike

Somewhere on my phone ;-)

 

Why would I be so foolish as to take my hands off the steering wheel when I'm driving??? All I can tell you is that I don't seem to have to correct with the steering wheel any more than with any other car I've driven.

 

Could be the Plus equipment, could be the Plus setup/suspension alignment.

 

Is the TRD rear sway bar a good upgrade for a 2012 II or should I save my money?