Straight line stability fixes

[sdcruiser]

I know there are lots of posts on this subject so I won't get into the debate over if some of us imagine our cars don't handle well, we own lemons, all the Prius are like this, they all handle great, etc. I just want to address some issues with my car finally after too exhausting drives from san diego to vegas with cross-winds. So here's my plan:

Since March 2005 all Prius have used the Touring Edition frt struts. So I ordered mine today.

In 2006 there was a change to the front underbody baffling/dam but that's about $150 and I'm going to hold off on changing that for now.

I also ordered the TE front anti-sway bar-15% stiffer and the rear TE anti-sway bar-about 48% stiffer.

I also moved the frt tire air dams right up to the front bumper (again). Another early adopter did this back in 2004 and I tried it then too. The theory is that while this isn't what you want to do for aero economy, the effect is to reduce the lift. I think there's too much lift making the tires and front end "light" and then any side force makes it move sideways easily. I'm pretty sure I feel a big difference now. Another early adopter found a way to hang 100-200 lbs out front to fix the lift issue.

The tires I'm running 195X60-15 really suck when it comes to gas mileage and catching those crappy wavey road grooves. I've tired Scion 17" wheels and tires, michelin hydroedge (both the std and slightly larger sizes) and now Falken 912's. I'm running 42/40 psig with them that too increased the stability a noticeable amount but these tires rival the stock tire in lack of stability with grooves. I just don't like them and will either go back to Hydroedge or X-Radial from Costco.

I have experiemented with stiffening the frt springs with those large rubber spring wedges. That worked really well. And I think it's because the side movements and wheel corrections did not exaggerate the nose dives like they do with the very soft front end. I've considered the B&G springs but I think the car is so low now that I'll do more damage than I have in parking lots and over speed bumps if it's another inch lower. So I plan to go back to the those wedges on the front once I evaluate the struts and anti-sway bars.

I've done some work with the alignment. I'm at max toe in now but once I do the suspension mods I'll back off just a bit. The camber is even on both frt wheels at -1.5 deg and will not go less than that per recommendations receive from others. I have not really looked at the back toe in yet.

Oh can't forget BT Technologies mid brace. I have that and I'm thinking I'll go with that frt strut tower brace too very soon, maybe even when I change the struts in a week or so.

So any thoughts suggestions or ideas. I'm also experimenting with a full air dam up front. I made a weak looking one back in 2004 that seemed to help too but it was too thin and weak and air just folded it back. The "Autospeed" site did some front end work with the gen I prius that looks promising and there's an article there that shows how to improve the underside. I can see an area in the frt middle of my car, underneath that acts like an air dam about a foot back and could be producing a lot of extra lift. Maybe that's what the 2006 change addressed.

[2maples49]

Hi SDCURISER,

I've only had my 2005 for 6 months, so I'm not expert. However, had several cars since my youth, the physics are all the same. I think you have at least three issues and one non-issue.

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.

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

3. Direction changes when the wind hits the side of the car.

4. Direction changes when the tires encounter grooves and ridges that are almost parallel to the direction of the car.

Regarding 2, body motions, be sure you are not steering with the wind and exaggerating the effect. I had an old Maxima, with bad shocks, that my daughter was learning to drive on a uneven two lane road. When she just held the steering straight while the body moved her course was much straighter. Shocks and springs and antisway bars help control body motions only on smooth roads. They do not help with straight line tracking. They could make body motions worse on uneven roads.

3. Direction changes in the wind are a hard one to fix on the Prius. It's tall, short, and narrow and it makes an excellent sail. The BT under car brace and strut tower brace my stiffen the chassis and suspension and may help if flex in either one is a problem. Generally, additional traction is the best aftermarket cure for this. Wide performance tires from the worlds top manufactures in H or higher speed ratings help, but they work against gas mileage. H rated stiffer side walls help. Higher tire pressures work up to a point of diminishing returns when the tire's contact patch starts to get smaller.

4. Grooves and ridges are another problem. The BT products may help if flex is a problem. The high performance tires that help fight cross wind direction changes may work against this. Tall flexible side walls and tires designed less for turning may have better straight line tracking. Higher tire pressures may make this worse.

Whatever you do, there are limitations of Toyota's design and there are tradeoffs. The best choice may be to keep the factory alloy wheels and install H speed rated tires, with 65 series side walls, and a narrow tread, fairly light tire weight (to keep the unsuspended weight down for compliance rough roads and reduce inertia for fuel mileage), and get a major tire brand with some of the best engineering and construction. Avoid cheap tires.

Have fun with your options, Dan

[dogfriend]

Originally Posted by sdcruiser

I have not really looked at the back toe in yet.

Rear toe was what made my car squirrely at freeway speeds. Once I got that fixed, it was much better.

[donee]

Hi All,

Due to the high profile of the Prius, its going to roll in strong side gusts. There is nothing that is going to change that. From my own experience, my guestmate is the aero design, stock, is just fine and is very neutral steering in side gusting condtions. That is, there is very little , similar to low-profile car, steering changes caused by high side-gust winds, as the car rolls a good deal.

That said, some owners have had all sorts of troubles, beyond just adding on a BT Tech rear chasis brace, as I have.

I think dogfriend is on the right track. The weldment construction of the rear axle, which is also a torsion beam spring, seems to be the issue. Variations in rear axle alignement have been satisfactorily fixed with shims. I am not fully knowledgable regarding this, but several on the board here are. The shims go between the hub(s) and the axle, and have to be hand-made. Which is some work, as you need to get them flat, after cutting. Cutting with a shearing tool leaves a raised edge, which needs to be ground flat. The material should be non-corrosive and hard, such as stainless-steel. Which is difficult to cut when more then about 30 mills thick with a shearing tool. In which case the shim needs to be cut out with a die-grinder and emory wheel.

[sdcruiser]

Originally Posted by dogfriend

Rear toe was what made my car squirrely at freeway speeds. Once I got that fixed, it was much better.

Ok so let's talk specifics on the rear toe in then. I can't find my latest alignment report, but assuming this older one is right, I have 0.23 deg on the left rear and 0.19 deg toe on the right rear. The spec was listed as 0.05 to 0.55 deg and nominal is 0.30 deg. So I'm close. I know the front is right at the max toe in of 0.2 deg. I'd really like to reduce the amt of toe in on the front but the car was pretty wild then. when the tire dealer set it to zero. I now have a friend that has a modern alignment system so I try lots of thing.

And please, I'll try to set the record straight on this. I'm not causing this. I can use a death grip or barely touch the steering wheel or anything in between and the car will literally jump to where I feel it and my wife, who really doesn't notice much when driving, feels it too. I think I've mastered the art of slight correction with this car and if you're doing that constantly it can really wear you out on long trips.

I've been driving since my I got my first car, a '55 chevy back in 1967 and have owned anything from a 65 corvair, 64 GTO, Fiat X-19, 2003 RSX, 94 RX-7, vans, mini-pickups etc. I'm not new driving a car and had a few that exhibited characteristics similar to my Prius, but not as bad. The Fiat X-19 did it when I put new Michelin tires on it and it badly needed a rear alignment. The RX-7 did it with some brand new Yokahama tires that were on it when I bought the car new. That one, because it was so quick and fast, scared the crap out of me but new bridgestone tires on it were like night and day.

Sadly the Prius has been that easy to fix. I have driven a few others and while they share similar characteristics, they all were noticeably more stable.

I'm going to have to disagree on the aero lift not being an issue for a couple of reasons. Some of you will remember the real spoiler that Brian from BT tech made a few yrs ago (I just learned he died and still trying to assimilate thas). It was made for a BMW and Brian in talking with an Aero engineer came up with using it on the Prius. As small as it was, it did work and everyone that tried it noticed a difference. But we could not make it stick to the back glass. I kept mine on for overa year by usingan glass etching adhesive but it finally popped loose. And I know the front end under treatment I just did has made the car more stable (but probably hurts gas mileage). So I'll probably try tweaking that some more today.

Yeah all of this is a bit subjective but having almost hit an SUV recently, that drifteded into my lane at 75 mph at the same time the Prius chose to "jump" that way has motivated to improve my car in the interest of self-preservation. And yes it will never "feel" as stable as my wife's RSX but I think there are some additional improvements to be had. The trick is to not buy and try everything that's available but try to sort thru all the opinions, beliefs, experiments, etc. of others. My tire dealer swears the P4 Pirelli is what I need for instance but my experience was that the Hydroedge was pretty good. Is the P4 enough better to risk $4-500? Thanks for the feedback everyone.

[dogfriend]

When I got my car, LR toe was .15°, RR toe was .40°. It had a weird feeling at the rear that reminded me of a towing a trailer. After getting the alignment readings, I realized that it did not take the same effort to turn in each direction because of the extra toe on the RR. So I was constantly over steering to one side and then would have to correct.

I was able to shim the RR to .15° with some custom made shims from Galaxee and her DH. Stability is much better. It will still move a bit in crosswinds but it is predictable now.

[donee]

Hi SD...,

I think I remember Toyota publishing a negative but very small Cl for the rear of the 2nd gen Prius. The best way to get a negative rear Cl and low drag is to get the air from under the car to be accellerated upward. I think they call the devices "difusers".

I have hydroedges on my car, but had OK cross wind performance with the original integrity's and the BT Tech rear chasis stiffener plate.

[sdcruiser]

I did some work today with the front dam and I confess it's so windy that I can't tell the difference. So I did some searching on a term you may be familar with, tramlining. That's really what I'm feeling exaggerated by soft suspension, tall narrow car with lots of side area, numb electronic steering with no real centering feel, and from what I've read directional tires (wider is worse, I have 195's and directional).

Here's a good article of a guy on the cadilac site that took 2 yrs until he fixed his tramlined and then it was ALL about the tires.

Severe Tramlining Follow-up—Problem Resolved - Cadillac Owners Group

And his orginal reports of tramlining (sounds like me, lol)
Tramlining, aka The (Un)Happy Wanderer - Cadillac Owners Group

And here's a pretty good description of the why:

http://homepage.ntlworld.com/robert....tramlining.pdf

So maybe if I really want to effect a change I should try the x-radials and not the hydroedge tires again.

[ETP]

Originally Posted by dogfriend

Rear toe was what made my car squirrely at freeway speeds. Once I got that fixed, it was much better.

I will get this checked before the 12/12 runs out. The dealer said they would cover alignment and balance. Then I will than take it to my local shop and we will make some alignment 30% contact plates if that will work for the rear. You can see the neg camber and toe standing behind the vehicle.

[dogfriend]

Originally Posted by sdcruiser

So maybe if I really want to effect a change I should try the x-radials and not the hydroedge tires again.

Coincidentally, I just replaced the last two GY Integrity tires with Michelin X-radials (Michelin Destiny sold by Americas Tire). Having run the X-radials on the rear since 15k, I think they do help compared to the awful GY tires. I have almost 30k now, so I replaced the other 2 tires this weekend.