Why is Prius unstable in windy conditions?

[nickfromny]

Car looks very aero but gets moved around in high wind. Will downforce wings on front and rear improve stability. Any ideas on how to improve stability in windy conditions appriciated. I don't want to hear stay home or slow down.

[ForTheGlory]

We probably need more information to answer your question. In a crosswind, I'd wager that the relatively large cross-sectional area of the side of the car causes it to catch the wind. Downforce won't do much to change that.

I suppose you could mount a vertical stabilizer on the aft end of the car, but that would just get you pushed around more while adding some marginal directional stability.

[aaf709]

Well, although I don't have that problem, I've heard that the BT Tech Stiffening Brace (available on the Priuschat shop) has helped that.

[edthefox5]

Car is rather slim and stock suspension is not real tight with some free no extra charge body roll. Lots of people here add Toms suspension parts that seem to help. The car is excellent for what it is except for that crosswind problem. You get used to it though and you'll be forced to slow down. I drive across a thin peninsula between 2 Bays everyday and its crosswind city.Gotta hang on tight!! Scared me a few times. Sorry, just gotta slow down or start working on the suspension. Search: Tom's. Oh and the front end is so low now I'm clipping some driveways so don't think a front dam would work.

[qbee42]

The Prius is fairly high and narrow, with a large cross sectional area. It may be aerodynamic from the front, but not from the side. The power steering system on the Prius has very little dead band (feels like zero dead band to me), which tends to cause operator induced oscillations with new Prius drivers. It has to be driven with a light hand. The crappy OEM tires are a third factor. We swapped ours for good Micheline tires and the difference is like night and day, especially at highway speeds. The suspension is also fairly soft. To summarize:

1) Height, side area, and aerodynamics - Nothing you can do with this.

2) Steering - It works well, but you need to get used to it. Don't correct every little gust of wind. Give the Prius its head and it will track fairly well. Over control and you will be all over the road.

3) Tires - Give them away and get real tires.

4) Suspension - I like the soft ride. If you don't like it, you can add new suspension components for a stiffer ride.

Tom

[Rae Vynn]

When we first got ours, it was a bit bouncy in the wind.

After better tires and a BT stiffening plate, I no longer feel the wind.

[BIGGDOGG]

I was having the same problem when I drove on highways and I thought it was my alignment. (NJ has the most pot holes especially after winter).
I will be getting better tires once I wear through these OEM's. Other than that I guess I will have to get used to it... Boo

[donee]

Hi All,

It is typical for cars with low Cd (Coeficient of Drag) , like the Prius does, to have poor cross-wind maners due to their aero shape. But this is not the case with the Prius. It was designed for a low Cd and a small, but negative coeficienct of rear lift.

But, the stock Prii can be very unwieldy in cross wind gusting conditions.

This issue has been tracked down to allignment, and chasis stiffening, primarily, and improved tires (as well as higher pressures) help as well here on Prius Chat.

First thing to do is go get an the free alignment offered during the first year of ownership at your dealer. Ask them to insure that the front toe-in is positive. The specification spans 0, and sometimes the cars are negative which is a problem.

Second thing is to get a rear stiffening plate. BT Tech is popular, but there are other vendors too.

PIO (pilot induced oscillations) can make it seem worse than it is, but even if you deliberabately hold the wheel perfectly still during a sideways gust, the response of the stock car with one or both front wheels at negative toe-in, is scarey. Do the two things above, and you wont believe your driving the same car it will be so stable. The stock car is very hard to drive by the seat-of-your-pants, due to the back end wiggle in cross winds. The stiffening plate will damp down the rear-end wiggle to that typical of other cars, and the car becomes easy to cross wind counter steer.

[priusenvy]

Originally Posted by donee

This issue has been tracked down to allignment, and chasis stiffening, primarily, and improved tires (as well as higher pressures) help as well here on Prius Chat.

That is the opposite of my experience, as well as the opposite of what my engineering education tells me should happen.

Higher tire pressures make the problem worse. With higher tire pressures, the tire sidewalls are stiffer, and the contact patch is reduced, making it easier to change direction. The car feels "darty". Running the front tires at 35psi tends to help dampen things out, eliminates the "darty" feel, and actually helps the car feel more stable in crosswinds.

Assuming the alignment is within spec, I believe a tire change and running at mfgr's recommended pressures offer the most benefit in reducing the sensitivity to crosswinds.

[eestlane]

This is food for thought for all you "over inflaters" out there in Priusland:

Lets see now, the Toyota engineers were smart enough to design a very complicated and efficient car. Remember, the main goal for them was to design a fuel efficient car, and that includes the tire pressures. But from what I read on this forum, they were totally stupid when, after running hundreds of hours of tests of tires at various pressures, they decided to "arbitrarily" recommend 35 and 33 psi for the Prius. Come on now, folks, there is a lot of wrongheaded thinking going around. Sure, you want the best gas mileage, but there are other things to consider that the Toyota engineers probably figured in. For example, the extra wear and detuning effects on the suspension components and the rest of the car. As a fellow engineer, I resent the second-quessing by many untrained people in this matter. If the tire pressures are so totally wrong, the rest of the car must also be quite poorly designed and therefore you should not have bought it.