Why is Prius unstable in windy conditions?

Anyone of you remember how the VW bug handled in a side-wind? It was very tricky to maintain a straight course in any significant side-wind at speed, because in the case of the rear-engined bug the C.G. was significantly behind the aerodynamic center of the side profile, through which the side-wind forces act. So any side-wind had a tendency to rotate the car around the C.G., with the aero force increasing with the disturbance. In aircraft terminology it is the difference between positive stability (C.G. behind the Center of Pressure (C.P.); coincident with it (neutral stability) or the C.P. ahead of the C.G., which is negative stability.

While wheel alignment and tire pressures will obviously have an effect (especially the latter, front to rear and side to side differential especially), has anyone tried to determine the C.P. position of the Prius lateral area, and compared it to the car C.G. position fore-and-aft?

If there is a significant difference, this too could affect the car's lateral handling qualities in gusty conditions.

ron.

 

Hilarious!!!!!:lol:

 

You had a roof box? Jeez louise! That'll really harsh Prius fuel economy at highway speed by ruining the carefully designed aerodynamics.

 

Seriously? You complained about crosswind instability and failed to mention that you were using snow tires and had a roof box?

 

I just had a very bad experience going from Kingston, NY to Rochester , NY in high winds. I was blown all over the place and my gas mileage dropped from av. 47 to 39. So far that has been my only complaint about my "07 Prius package 6. If that is the worst of my complaints, I guess I'll learn to live with it and slow down.

 

Hi Ron,

While I have not done this for the Prius, I was doing it at 15 years old for model rockets. Between Estes Rocket handbooks, and my dad's teaching (he's an PHD ME and worked on rockets at one time), I was graphically calculating the odd-shaped parts CG's/CP's and combining the whole rocket to find out. My dad figured he better teach me this, after I had a divergent launch of a standard Estes model (Apogee?).

With the stiffening plate alone, on my car, in 0 to 40 mph gusting winds at 65 mph, my Prius still rolls, and the counter steer to keep a straight line is about 2 or 3 inches of steering wheel circumference movement, into the wind. This is with one driver in the driver seat and no passengers, and the wind perpendicular to the car approaching from the drivers side. Which is not bad at all.

So, I would hazard to guess that the CP is very near, the CG. From the reaction to the wind, it would seem that the CP might be a little forward of the CG. But I think that is unlikely, do to other effects that would cause the front of the car to vere with the wind, rather than into it.

 

Is it worth a childs life?

I was very happy with my 07 Prius up until I took it out of town with my family. I got caught in some high winds between Houston and San Antonio and the car was all over the place. I’ve owned the car for 6 months and now I don’t feel comfortable taking it out of town with my family in it. I traded in my Chrysler Town and Country for the Prius. I drove the van across many storms with high winds, hail and never had a handling problem. This high wind handling problem is not something you should get used to, change stiffening plates for or have to change tires. This is something that Toyota should have addressed before the car was released. This design has been around since 05 and I’m sure Toyota know it is dangerous. Slowing down can be just as dangerous specially on a single lane highway with and 18 wheeler riding your bumper. I don’t know about you but the mileage is not worth the life of a child.

 

The new Scion XB is supposed to be pretty bad in cross-winds too. Anyone here driven both and want to share your opinion?

 

I'm driving an '08 with touring suspension and Nokian WRs. I've had no tracking issues at all with crosswinds up to 45 mph. Minor corrective steering required as on any car, but very nice behaviour for it's class.

 

Re: Is it worth a childs life?

Improved air quality, driving a little slower, and no wars-for-oil will save many lives.

 

Re: Is it worth a childs life?

Rant on\
GOD how I wish that were true. No matter who tells you- wars are never about commodoties like oil. They always have been; and always will be about political power only. Oil is just the excuse we hear presently.

I drive like I do now in a Pri because it is less expensive to me. Much less cost of ownership on a monthly basis. Sorry for the rant.

\Rant off

 

I believe part of the cross wind problem is from our low coefficient of drag, which Toyota aimed for. On other cars the body is designed to have a downforce to give the car stability at high speeds. This of course creates drag which raises the coefficient. With the Prius, Toyota tried to minimize drag (I believe the Prius has a lower coefficient of drag than any other production car) and the bi-product of this was a loss of downward force at high speed, result..... unstable car. That said I believe adding a spoiler would improve the condition, though you'd look like a dork.

 

I was curious about what the Tech Strut Tower Brace looked like and after seeing it I was surprised that any discussion about the BT TECH Strut Tower Brace's effect on frontal crash worthiness was seemingly absent from the forum. To me it doesn't seem like a good thing to insert a crossmember of steel in close proximity to the passenger cage at chest level to the driver and passenger and at a distance as close as the firewall ??? I wouldn't risk changing the crash characteristics of this vehicle for what already seems to be acceptable stock handling characteristics ... but admittedly I worry about things others don't even consider.

 

I realize now the discussions were referencing the rear stiffening plate which doesn't look like it adds any safety issues but that strut tower product looks scary to install and to have if car is ever in a frontal accident.

 

But the Prius has a spoiler on the rear hatch!

I believe it is there to generate a down force on the rear of the car to alleviate the lifting force that would otherwise exist. The latter arises from the negative pressures generated from the airflow over the rear of the car at speed.

I believe Toyota spent considerable effort in coming up with a shape that would minimize aerodynamic drag, in addition to providing good handling characteristics. I find my 2008 Prius handles just fine in sidewinds, based on a recent trek through the San Gorgonio pass here in Southern California. The windmills were churning and the sand was blowing; but the car at 60mph was manageable. Most car manufacturers pay little or no attention to minimizing aero drag - just look at any typical SUV! That is changing as gas prices continue to rise.

ron.

 

Sorry, this is a pet peeve of mine. A spoiler doesn't "generate a down force". It spoils the air as it goes over and reduces lift. On the other hand a wing on a car does generate a down force. So to sum it up, a spoiler reduces lift and a wing generates down force.

With that being said I've often considered if the Touring model has any measurable fuel economy deficit due to the slightly larger spoiler reducing lift (and there fore in a way causing more drag) in higher speeds. Yeah I know the EPA rating isn't any different but I'm wondering if they just assume they're both the same since it's the same car/drive train. I could be trying to fool myself here but I swear I typically find a lower combined MPG on people I come across with Touring models. I was very surprised last weekend when I got into my cousin's brand new Touring and he was getting a full 10mpg less than I am. Granted he has a slightly higher percent of freeway driving and he gets to work much earlier (lighter traffic which lowers the economy of the Prius). He also only has about 1k miles on it while I'm about to turn 8k. Furthermore I'm running full synthetic and 42/40 air pressure....

Mike

Mike

 

To add to the above discussion about spoilers, the spoiler is there to "spoil" the airflow over the back of the car. If you look at the back of the Prius you can easily see that it is anything but sleekly streamlined. In fact, it is cut off short, or truncated. This style is referred to as a Kammback, named for the designer who originated the concept. The Kammback design works by inducing an area of turbulent airflow behind the car body. This turbulent mass acts as an extension of the car body, allowing smooth airflow around it. You get much of the benefit of a long streamlined body without making it long. The spoiler helps induce the turbulence.

Tom

 

I don't have a spoiler on my car. Is that available in a certain package? Maybe that's why your car is more stable than mine?