What mods to stop freeway drifting?

Replace the OEM tires with real tires, lower your tire pressure, and get some toe-in if the other two don't do the job. I would start with good tires first.

Tom

 

You're going to get responses ranging from "I've never experienced that, you must be imagining it or suck as a driver" to "I have the exact same problem and never found a solution so I had to sell my Prius".

My experience: High (but still within mfgr recommended) tire pressures tend to make a car feel darty, or in the worse case, like it's skating on ice. Couple that with crappy, narrow OEM tires, and a large flat side-profile to cross-winds, and some will find their car jumping half a lane when a semi passes. It wasn't that bad for me, but I did have to remain alert in those conditions.

Switching tires (Goodyear TripleTred in 195mm width) made the most difference. Crosswinds and semis don't upset the car, even when running 42/40 psi. If you're intent on keeping the OEM tires (I'm assuming you've got the Goodyear Integrity, not the 16" Bridgestones on the Touring model), try lowering tire pressure to the pressures listed on the door frame. Running tire pressures towards the lower end of the mfgr recommended range tends to help damp things out a bit and might make it more comfortable to drive.

 

If you got and installed the BT Tech stiffening plate already, next mod is tires. The OEM tires, IMHO, are poor.

 

I tend to agree with your thinking, but when you switched to the Goodyears, did you take a hit in MPG, and if so how much???

I am going to have to cross this bridge someday, I like to plan ahead!!

Thanks

73 de Pat KK6PD

 

The cheapest remedy is time. After driving it for a couple months my reflexes adjusted, and now it feels normal.

 

Hi ZC1,

I did the BT Tech plate. And it solved the dartyness altogether. But if you have negative toe-in (toe-out) the impact wont be as great.

After a few months, I switched to Michelin Hydroedges, due to the greasy morning commutes here. Slid around a little too much for my liking. Those are great tires in a rainy fall morning, after a long dry spell.

There is a fuel economy hit, but as the tires wear in, its less and less. The Hydroedges use Silica in the tire coumpound, which is hydrscopic, and helps the wet traction. But you will see allot of Low Rolling Resistance tires use Silica as well.

There is no yaw action in my car at all when semis go by when I am hypermiling down the road at 55, and the semi goes by at 75 mph. When a 40 mph side gust hits the car, there is a very small amount of yaw even though it rolls a good deal.

I think the problem is related to a rear end oscilation the Prius has, which is probably related to the high strength (springy) steel used in the car. This allows less steel to be used, and the steel that is there has good energy restitution. If you do not sync up with the rear end oscilation, in your control inputs, the car will jump all over. But even if you just hold the wheel perfectly still, the car will jump a good deal and yaw half a lane in a good cross wind gust. Staying in touch with what the rear end of the car is doing, with your rear end, requires allot of attention.

With the BT Tech plate, the rear end oscilation period and duration from impulse side load exitation are both decreased by 5 times. This makes the car dramatically more controlable on the highway.

 

Yes, I did take an mpg hit, somewhere in the 2-3mpg range. I switched out the Integrities with only 10k miles on the car, now I have about 33k, so thats 23k miles on the TripleTreds. I used to get 46-48mpg, but since the tire change I've been in the 43-45mpg range (most trips are short and widely spaced in time, not conducive to high mpg). They also aligned my wheels at the same time, even though my read of the sheet said it was within spec and I really didn't have any issues with it. Not sure if that had any affect on mpg.

 

Probably the easiest, although not likely the cheapest, is to just trade the Prius in for a 997 C4S Porsche - Just kidding- I have the TRD suspension, a heavier rear sway bar, 17x7.5 wheels, strut tower brace and under frame brace- car handles well. I am going to add the BT Tech front sway bar as soon as I can get my hands on one. But seriously, the Prius handles well and I blow the minds of several people on canyon roads.

 

I switched to Micheline MXV4+ Energy tires in the stock size with no mpg hit. They are LRR tires.

Tom

 

Hi ZC1,

Cannot stress the plate more. The BT Tech is probalby better for the winter weather (its anodized), but there is also an cheepie for sale on EBay too, which is just bare aluminum (you could paint it).

And with the weather here today (gusts to 50 mph), I expect we will have a bunch more of these threads this week.

 

ZC1, cheers. i am also learning a bit more about my prius here and there, but something doesn't make sense in the earlier posts.

if we're pumping the tires to 42/40 or 44/42, doesn't that take away most f the sidewall flex already? it might make the car a little more responsive, but i dont think that's what we're talking about here, we're talking about the car wandering or being effected by winds.....................am i making sense?

 

thanks ZC1. i dont dare to bring the TP higher than 44/42.

good luck and when you fix this, please post or send me a message. i am curious to find out what solved your problem.

 

How does the stiffening plate differ from the stock plate? It seems like the stock plate does its job.

 

Huh? My passengers aren't wild-eyed. The unconscious steering corrections I make are continuous and small. Maybe I misunderstand you?