Straight line stability fixes

[Dobey]

Originally Posted by 2maples49

1. The possible non-issue is aero lift. With the streamlining of the Prius, the current legal speed limits and the 60%/40% front to back weight distribution, I don't think lift is an issue.

True - anyway, in conventional cars, the higher the speed, the greater the force pushing down on the front end of the car. The aerodynamics of most cars dictate that there is a greater surface area on top of the car which the oncoming air acts upon, than the undercarriage where limited air volume goes through. This is in fact one of the the biggest aerodynamics problem that land speed record vehicles face - busted front wheels due to massive forces downwards as speed increases.

Originally Posted by 2maples49

2. Body motions when the wind hits the side of the car.

One of the things that many people don't understand is the biggest steering stability factor - caster angle on the front wheels. Steering response is a delicate balance between snappy response and stable tracking. Large caster angle = stable, self-centering but heavy, less responsive steering. Small caster angle = snappy, light steering but less stable. Side forces like wind on the car body manifest themselves by either twitchy or stable tracking, depending on caster angle. Caster angle is unaffected by body stiffness (or lack of): the feeling of body roll is often times mistaken for steering stability.

Originally Posted by 2maples49

Generally, additional traction is the best aftermarket cure for this.

True, since caster angle changes aren't practical nor possible in most cases. Additional toe-in beyond specs can also add steering stability at the expense of tire wear.

[sdcruiser]

Yes castor angle is a key element in how different motorcyles are adapted to different sports. A trails bike for instance has a very step angle because it has to turn on a dime and doesn't need the high caster angle for stability. And so a trials bike is extremely twitchy in top gear, where a motocros bike isn't. Trail is the term used for bikes (probably appropriate for cars too but not used much) and it relates strongly to castor angle, triple clamp offset, and somewhat related to tire circumference and fork length. It really easy to feel the difference in various bikes but more difficult to feel in a car.

I have heard of few brave souls that know what they're doing modifying caster but that's pretty extreme. I think once I get the suspense just a bit tighter and less mushy I'm going to focus on these Falkens. At 20 lbs they are a bit heavy too but it's the tread pattern that's the biggest issue along with not being a symetric type and being a bit wider. I don't think they have a very low rolling resistance either based on my mileage.

[2maples49]

Hi SDCRUISER,

It sounds like tramlining is issue #4 that I mentioned, grooves or ridges running nearly parallel to the direction of travel of the vehicle. I think you are on the right track when you go after tires as the primary cause, especially now that you've said the Hydroedges are better than your Falkens.

I know a lot of people speak highly of Falkens, but I've had terrible luck with them. And my friend's son had high expectations on his Jetta, and now says he'll never buy Falkens again.

I don't think you can automatically consider directional tires as the problem. But I do think higher profile tires, as in 60 or 65 series may be generally better. I have Goodyear Eagle GT HR s on my 2001 Ford Escort. They are directional and they are 60 series. They are sweet. No tramlining at all. I know that the same tire is not always best for all cars, but I'd try a premium grade from a premium manufacturer. And I'd get more of a sporty tire rather than an all out corner apex chaser.

I'm sure you know this already. Also be sure to put exactly the same brand, size, and model of tires on the front and back.

Something else that has worked for me on front wheel drive cars is to run 10% to 15% less air pressure in the rear tires than the fronts, depending on how the car is loaded. With light loads, lower pressure in the rears approximates the same sidewall stiffness as the fronts and reduces rear end "steering" on ruts and ridges. It's worked for me, maybe you'll get lucky.

I may be putting the same Goodyears on my Pruis, but I have to wear out the cheap tires that were on my 2005 first. I should have a report by the Oregon rainy season, September or October.

Thanks, Dan

[sdcruiser]

Yes it is a combination of things of course but the general agreement is that the asymetrical tires are worse as are low profile and wider tires. Oh and higher pressures too. That's not my experience with the Falkens but it is with the hydroedge. And I'd be rich if I had a dollar for everyone here telling me that extremely high pressure cures the wandering. Not necessarily.

Also, tires with sharp side wall to tread transitions are more prone to this and that's why something like the Triple tred seems to be very good until it's very worn out and then I read about the owners complaining. Those edges get sharper....maybe??

The hydroedge tires are not very rounded off on the corners and obviously are directional. But they were far better than stock (just a better tire overall). Evans tire even let me try the 195X60-15 versions for 1000 miles and I lost a couple of Mpg and they were not better handling so I went with the stock size.

Yeah it's a bit frustrating finding a consensus on anything on the internet. Lots of opinions and few facts sometimes. It's expensive but you sometimes just have to experiment on your own until you find something that works. What I do know is that my car really doesnt go well in a straight line right now and any other Prius owner that's driven my car has agreed with me execpt for the factory reps..."normal" was their summary.

[sdcruiser]

I got my car back after my friend installed the touring edition struts (std after March 2005) and the touring edition anti-sway bars. And there is a big difference. I can feel the Falken twitching at the back, but I can virtually let go of the wheel and not have to constantly correct. Big difference and I think Toyota could have helped me enjoy my car more years ago. I'm not sure which change made the biggest difference but this is really motivating me to do more now. And I'm a little bit disappointed in Toyota for not offering us early adopters some deal on upgrading. I almost like my car again, lol. The Falkens are really bad with grooves but I bet with the Michelin Energy tires and maybe that new 2006 frt spoiler and underside shield my car might be decent. Toyota I really am disappointed in you now the more I think of the times your dealer and regional rep said my car was normal....NOT!

My gas tank is still only an 8 gal gas tank and the piece of *&*^% dash rattles like there's no tomorrow because the dealer has tried to fix the rattles so many times (with black putty mostly) and worn the snap fits out and made it worse to boot.

But I think there's some hope for my car. I think Toyota also did something to improve the dash rigidity too but I'll have to pay thru the nose for that too I bet. This is probably my last Toyota because of this but I guess I'm stuck with this car so I'm going to make the best of my $28K investment.

Moral, there's sometimes a steep price to pay for being an early adopter.

[200Volts]

SDCruiser,
For the dash rattles, go buy the speaker sound proofing material used for the inside of doors (like Dynamat). Stick it under every dash (and glove box) piece of plastic you can get at. It will help.
Also, put this on the doors and the inside of the door panels.

Tramlining is made worse with higher tire pressure, per a Regional Manager with Bridgestone.