2010 Prius feels unsettled on the highway

Some amount of wandering is noticeable on mine as well. I think it is due to the tires, since it has been more prevalent with my current set of Energy Saver A/S tires than other tires.

 

Coming from a first gen 2008 Honda Fit to a 2012 prius v i too noticed this "floaty" unstable feeling on the highway at speed. I quickly adjusted after a couple of trips on the highway and i do not notice it anymore.
The honda fit despite having the same suspension layout(struts in the front/beam in the rear) felt very tight even at highway speeds. Surprising considering the Honda has a 12.9" shorter wheelbase! I attribute the difference in the handling to taller sidewall tires on the prius as well as it being a much larger car but not much heavier than the smaller fit=lots more chassis flex, as well as lighter steering feel.

 

I have Energy Saver A/S tires on my SUV and it is very stable running well over 100 mph on the Interstate

Mike

Mobile on my SGH-i717

 

Different car, different platform, different size, etc.

 

Just sayin those tires handle at speed well even on a SUV which in no way would handle as well as a stock Prius.

Mike

Mobile on my SGH-i717

 

Sorry WEOH, that makes about as much sense as saying that just because an 8-yr old will be very satisfied with MCDonalds, does not mean that a 35-yr old with good culinary tastes....will also be very satisfied with McDonalds.

 

^^^ LOL you guys are killing me.

The Prius is designed to be fuel efficient which means that the aerodynamics are not designed for extra downforce at speed. My guess is that at higher speeds, lift is increased which will exacerbate the floaty feeling. Combined with higher profile tires with soft sidewalls and you have a twitchy car at high speed.

 

To fix the problem you would want to do what everyone else does to increase handling at high speed. Lower the car with a slight rake, add larger wheels with lower profile tires, air up the tires to max sidewall pressure, add chassis stiffening devices including rear sway bar.

 

Speaking for myself, not complaining about the Prius handling, just stating my observations. If I wanted a race car I would've bought one.
Love my Prius as is, and unless someone comes up with a car that can beat its combination of mpg, comfort, utility and price, I'll just have to replace it with another when this one wears out.

 

I have the same problem on my 2013 Prius. Last night I installed mikes Box Beam and notice most of the floating feeling went away. But I think I still need to get it check out.

 

Chassis stiffeners have been discussed and discredited by some. Some say they are fantastic.
Some think it is just a placebo effect.

There needs to be some Blind A - B Testing. Identical cars with and without all those bolt-on stiffeners.
The Big Prius Hoe Down would be a good place to do Blind Testing to see if anyone can feel the difference.

Different tire/wheel sizes and anti-sway bars do make measurable improvement to a car's handling.

Stiffeners are all about feelings ( placebo effects). Save your money. Do some research.
I agree that the large tolerance considered "Normal Range" for wheel alignment leaves a lot to be desired.
I'd get another shop to take a measurement. They always vary...

 

It's NOT a "placebo." It offsets a designed in "signal" built in by the manufacturer.

On Gen III Prii, it has to do with the front and mid-section that causes a feeling of instability.

The chassis of the Prius, beginning with the Gen II, has been subject to a bit of "flutter." This issue has been discussed extensively over the years.

In mid-2012, Toyota quietly introduced a new stiffer mid-chassis underbrace to address this matter. I noticed the same thing, when my then NEW 2012 Prius"v" had the "flutter" characteristic. It was an earlier model with the thin "hourglass" shaped brace like the one on your 2010.

When I started driving in the late 1960's, nearly all cars available were rear wheel drive.

The only US made car that could be had in the early 1960's was the Chevrolet Corvair.

Rear wheel drive vehicles have a self tracking "return" to going forward in a straight line direction. It took a definite decision from the driver to force the vehicle into a turn. The harder the driver turned the steering wheel; the more resistance the driver felt the feedback resistance. This phenomenon is called "understeer." It was simple and intuitive to control.

Then came the Corvair and the military jeep replacement called the Vietnam Era M-151 or "Mutt."

These "independent" suspension vehicles, when driven, had understeer. But, at one point, when driven to a hard turn at speed, quickly transition from understeer to oversteer. At this transition, instead of resisting the turn, the car forced itself into the turn. This alarmed the driver and caused these vehicles to "flip" and overturn in turns.

Front wheel drive car, by nature, are subject to oversteer. The suspension design and alignment is set to create understeer.

At some point, the designed understeer will switch to an oversteer condition like the Corvair.

To alert the driver to the impending change, Toyota, as other manufacturer, build in a degree of flex that provides a "flutter" or physical feedback of instability for the driver to alert him or her to slow down.

The car is NOT losing its control. All Prii have electronic stability control.

The effect of the stiffer mid chassis and front bars delay the onset of the flutter to make it closer to the real loss of stability.

As a historical note in aircraft design. The British Spitfire was designed with a "flutter" near the point of where the designed top speed and turns to warn the pilot. The Messerschmitt BF-109, its competitor did NOT have this designed in "flutter." The pilot had to rely on his instruments and had to constantly monitor the speed of his aircraft. Consequently, in the heat of battle, a lot of Messersmitts went down due to pilot error

This is the "why" and "how" of OEM and aftermarket chassis braces.

 

So much wrong there, hard to say where to start.

The Corvair had handling problems due to a swing axle rear suspension and no front sway bar.

Modern front wheel drive cars are stable and are designed to understeer for safety reasons. They have virtually nothing in common with the inherently flawed swing axle rear suspension of an early Corvair.

The Prius wanders because of narrow tires, slippery aerodynamics, and alignment specs designed to reduce drag.

The Prius chassis is not designed to flutter like the aileron of a WWII Spitfire. That is just preposterous.

A chassis brace alone is not going to stop the Prius from wandering.

 

Mike,

Funny you should bring up aircraft. You don't see aircraft stiffened. That flex is part of the structural design for a reason. Aerodynamic flutter is a totally different subject. It is not designed into an aircraft. It is to be avoided at all cost.

Stiffeners don't control understeer/oversteer. Anti-sway bars, suspension design/geometry and tire size/inflation control those aspects of handling. It is not a "phenomenon". It is totally understood.

If a car's structure has flex, or is stiff, that is hard to quantify. Sure, you see Cusco's site come up with some insignificant numbers for how much flex is there and how their bolt-on stiffeners FEEL BETTER. They have a product to sell.

I repeat, Blind A - B Testing of identical cars (with and without bolt-on stiffeners) around an autocross track would tell if there is anything to bolt-on stiffeners. The test would be measured with a time clock and most importantly,, The Feel. Drivers could fill out a question form after driving each car.

This is a scientific way of measuring phenomenal claims.

How else could they be quantified? Ideas????

 

Bill and evpv, thanks for bringing some rational thought to this topic.

 

No further explanation needed....You guys act like you know everything............

 

So, back to the OP, rmani,

You could try running tire pressures at max rated (per the sidewalls), at stock recommendation and at 10 psi above recommendations. See if you can feel any differences. Your fuel mileage will feel the differences!

Also, you know how old roads get 'Crowned'? New asphalt is SO nice! Concrete is nice,but noisy if grooved.
See if you can tell any differences.

And then,, lots of tire shops offer free alignment checks. If you have the time, get a few of those. Average the measurements??? If you wanted to spend the dollars, you could get the alignment set to the center of specs.

Or,,, could you borrow a friend's wheel set for an afternoon, just to narrow the search for what you are feeling?

Or,,,, sell that old Jetta and get the most high-tech, fuel efficient car on the road !!
Hey, why the misleading title to this thread????

Good luck, B