Unstable at higher speeds

My car's much the same, though with less mileage, and I can report similar handling behaviour. Which is to say, vastly improved over stock. I did the plate first and then the tires, and noticed a definite improvement with each. I'm looking forward to more mods and even better handling.

 

heck i never did an alignment in either one of my Pri's. did do the BT brace on both, but that did not improve straight line driving that i noticed.

it did improve the feel on curves. as far as sidewinds, it handled about the same as any other car i drove. we have a few bridges that cross Puget Sound perpendicular to the prevailing winds. here sheer is a major issue. most bridges the MAXIMUM speed drops to 45 mph and i have seen it as low as 20 mph on the I-520 bridge.

i have taken several vehicles over the bridge and they all had issues to a a degree. the vehicle with the least issues was my 1987 Corolla. the one with the most was my 1990 Ford F-150 when empty. once i nearly lost it and was only doing around 30 mph....(sign said 20 but everyone else was doing 30-35...needless to say...after that, i was holding up traffic!)

the problem with stability issues can have many contributing causes.

alignment, steering wheel feel, tire integrity, pressures, etc.

 

And driver skill and experience. When I drove our Prius home from the dealer, it felt very skittish. It was a five hour drive on divided highway, with Goodyear Integrity tires, and the first section of highway was grooved. I white knuckled all of the way through that grooved section. Crosswinds had me twitching the car back and forth. Eventually I learned to relax my grip and not over-control.

Now, several years and many thousands of miles later, plus better tires, my Prius feels as docile as can be. I honestly like the way it drives on the highway.

Tom

 

me too Tom. when i got my 04; i took it from the dealer, jumped onto the 101, went about half a mile to the I-5 interchange which is a wide sweeping UNBANKED turn labeled at 45 mph...

well heck, the car was new, drove MUCH smoother than my Ford, and i basically hit the curve at a much higher than recommended speed and nearly wrecked it before i hit double digits on the odometer...

 

We had 30 mph crosswinds (essentially perpendicular) on Sunday and grooving on the interstate pavement. This demonstrated the worst of the Prius handling traits I've observed. The relatively high and narrow profile combined with its tendency toward body roll made the Prius dart and dodge like a welter weight prize fighter. It wasn't overcontrolling, it was that the wind would twist and roll the vehicle on its axes forcing me to countersteer to keep it in its lane. In this case, twitchiness isn't coming from steering input, but from the wind rapidly redistributing the weight on the tires, changing the thrust angle, and varying the aero forces and direction on the vehicle.

I've seen this to a lesser degree before in the Prius with lower windspeeds and less of an angle to the crosswind. I saw this same effect at placard tire pressures. In stock configuration (although I'm now running 42/40 on the tires) the Gen 2 Prius has stability issues in crosswinds unlike any other vehicle I've ever owned. Fortunately, this is an issue that some upgrades should mitigate.

 

Hi Shawn Clark,

Do you have a Stiffening Plate on your car ?

 

Not yet, but it is in the plans.

I generally upgrade various suspension components in vehicles anyway as I prefer a more precise ride, but I usually wait until it is time to do shocks/struts (36K-50K).

 

Much like Tom, I was concerned about the skittish nature of my Prius in windy areas, especially a short section of freeway near Cordelia, CA which is known for such high winds that all of the large trees grow at an angle!

After a few years of driving the car, a BT Stiffening plate and higher tire pressures I rarely notice the "skittish" behavior anymore unless it is really windy. In those cases I just deal with it. With my 17" wheels the car seems less affected by the wind BUT it tends to "track" more when you hit tire wear grooves in the freeway. So either way I notice some wandering. <shrug>

 

If you can afford it, try the front strut brace instead... you can get either the Tom's or C-One at sigmaauto.com. I have the Tom's and it really does make a big difference not just in crosswinds but in turns and tracking as well.

 

Its not just the Prius, its all small, light cars. I remember being moved over entire lanes in my first car, a Nissan Sentra by a strong wind.

 

After cycle touring through mountain passes, just about any car seems like a tank in the wind.

 

Neither my 240 nor my Accord had much of a problem with cross winds. The Prius is definitely more sensitive to them and more inclined to follow highway grooves with the stock tires.

 

I am so happy to find this forum. I have been very unhappy with my new 2009 Prius. I have about 1500 miles on it and it is wandering all over the place, especially at higher speeds over 40 mph. I don't seem to feel the wandering in cruise control but otherwise I literally feel out of control in this car. It makes driving it very unpleasant and tense. I am getting good mileage on and off the highway - 45- 47 mpg but so far I am not happy. Do I have to add all of these braces etc and get it aligned to get rid of this feeling?

 

I would start with alignment first. You should be able to get an alignment under warranty for the first 12 mo/ 20 k miles. Make sure to tell the service manager what the symptoms are and the conditions when it occurs, so they have the best chance of reproducing the problem.

If alignment doesn't correct the problem to your satisfaction, then I would look at adding the brace(s) and upgrading the tires. The original GY Integrity tires are mediocre at best.

 

Good tires will help a lot. The dealer will do a free alignment on a new Prius, so it makes sense to check that sooner than later.

Tom

 

i have OEM's, i do have the BT brace which i installed right away, but it doesnt do anything for straight line driving and i didnt install it on my 04 for close to a year and i had no issues with either.

i would check tire pressures (make sure front is at least 2 PSI higher) and alignment first. i dont have the tower struts, but as i understand, they are also mostly for stability in turns, etc.

 

I have Tom's front strut tower brace and it does make a difference in turns done at speed, but it doesn't do much for crosswinds. I really don't think anything can help with crosswinds, short of changing the side aerodynamic shape of the car. When there is a force trying to push the car sideways, the car will give where it can - including the front wheels.

I think a good analogy is when travelling on a road with a high tilt/camber... gravity is pulling the car straight down, but since the car is tilted, it acts like a sideways force, and the driver has to turn the steering wheel against the tilt to counter the drift and keep the car travelling in a straight path. Obviously grippy tires and good alignment will help in holding the car to the road, but the sideways force will still have to be countered by the moveable front wheels.

 

It doesn't follow that the strut tower brace and stiffening plate would have no effect in wind. Wind is still going to apply a twisting moment to the structure, as does cornering, braking etc. Stiffen up the structure and you will have less deflection of the structure itself, leaving the suspension do what it is designed to do.

Having said that, I don't expect any single change like that to work wonders either. But incremental improvements do add up.

Dave, I'm pretty sure you would be able to detect the handling differences in the cross winds around here. 40 mph gusts perpendicular to the highway have a serious effect on the Prius' heading, but lower wind speeds were noticeable as well, at least in the two 2008's and the one 2009 I have driven.

 

I don't think any amount of stiffening for the frame or body will ever address the caster angle and trail of your front wheels. These parameters are what makes the car turn in crosswinds.

Think of an extreme case like a shopping cart - front wheels have plenty of trail, little to no caster angle. Increasing caster angle will increase the stability of the cart wheels to track a straight line, but having trail means that a sideways force on the cart will always make the cart wheels turn in the direction of the force (and this is easily demonstrable!)

Likewise in a car, the trail of the front wheels means that a sideways force on the car body will always make the front wheels turn in the direction of the force (crosswind). In my mind there are only a few things you can do to reduce a car's crosswind instability, none of them related to frame or body stiffening - increase the mass of the car, increase camber angle and/or eliminate trail (not advisable!), or lock the steering linkages in place while driving in a straight line (also not advisable!).

But maybe there's a complex dynamics interaction I'm not seeing....

 

I'm pleased to state that my '07 has always tracked straight as an arrow, no modifications, never had an allignment, on oem tires with 40 front and 38 rear. I have 30k miles on the oems but almost ready for new tires. Yesterday I was impressed I could go straight for a whole block without correcting the steering wheel. And right now I have 61 mpg after 150 miles on this tank. Dreading getting new tires as I know my mpg will go down, at least initially. My Prius tracks straighter and is less affected by wind than my last car, a Sienna, ever did. So I'm