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2010 Prius "floaty" and poor directional stability at highway speeds

Discussion in 'Gen 3 Prius Main Forum' started by Technigogo, Feb 14, 2014.

  1. Technigogo

    Technigogo Member

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    2010 Prius
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    This seems to be a common issue. Same complaint as many others.

    I bought a used 2010 Prius with 37K miles. It is a very clean car and never been wrecked. When I test drove it from the individual, I never got it out on the highway much. My first road trip was 400 miles each way on I-10 here in Texas. I did not feel the instability for most of the first couple of hours. I then got behind a semi and "drafted" for a bit till I got tired of all the buffeting. It was shortly afterwards that I noticed the similar feeling with the car when driving straight stretches. I tried gripping light to see if I was imagining things but after a second or so, the car felt like it was floating and would slightly "launch" to the left or right. If I had enough lanes and no cars around me, I could keep the wheel still at the same exact direction and in a bit the car would launch in the other direction. The front tires were coming up on needing replacement so I thought a new set of tires and an alignment would fix the problem.

    I now have the new set of tires and have had two alignments done at the Toyota Dealer and the problem still persists. I have played with tire pressures, weight distribution, differing wind speeds and wind direction (different days) and it is still there. The service tech foreman is very nice and willing to help even though I am not in warranty.

    Bottom line and disclaimer: I REALLY love this car; except on the interstate. I used to be a Sales Manager at a very large Ford store for 10 years so I know cars pretty well; I have owned 37 of them both new and used. I'm now a computer engineer so try hard to look at things logically. As I said, I really like this car and I planned on keeping this thing till the wheels fall off. I am desperate to get this problem solved so I can enjoy a road trip. As it is now, I'm worn out after 100 miles on the interstate with this.

    My last alignment was two days ago when, because of my research on Priuschat, I asked the dealer to set my Toe in to the maximum acceptable. I have attached the report. This alignment did not help.

    I have about 500 miles on new Michelin Energy Saver A/S tires. I have tried varying PSI settings for the tires and no significant difference. No other drive-train modifications have been done to the car. I weigh about 215 and I carry about 150 pounds of tools and computer parts in the cargo area. I have tried to place the heaviest of these items at the front of the cargo area.
     

    Attached Files:

  2. priusually

    priusually Junior Member

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    People here may say get a rear away bar and/or under chassis bracing but a simple swap to 17's will cure the floatiness. It was my main concern after driving on the freeways (especially on the grooved portions).

    Yes, there will be an effect on in-town city mileage due to the heavier wheels/wider tires but to me it's worth it. The car just feels safer in the freeway (like all my other vehicles).
     
  3. Feri

    Feri Active Member

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    I never had problems as severe as you describe but I did notice a little tendency to shimmy at highway speed. I did install a mid chassis brace and the shimmy disappeared.
     
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  4. vtwin_pilot

    vtwin_pilot Junior Member

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    I noticed the effect you describe for the first few months after I bought my 2010 last summer. It seemed "twitchy" at highway speeds and it seemed I had to correct the steering way too often.

    Some research I did turned up info such as the fact that with a very low drag coefficient - which of course helps to attain the MPG it does - the downside is that there isn't as much designed in downforce on the rear as with most cars, and the result can be this "floating" feeling you describe.

    I too played with several factors, mostly tire PSI and I rotated the tires, and it seemed to have helped a bit. I don't notice the twitchiness anymore so I'm not sure if the changes I made effected a real change, or if I've simply gotten a bit used to it. My guess is it's a bit of both. I have fairly new Kumho Ecowings and run them slightly overinflated at 38/36 psi front/back.

    In the end, you'll get used to this feeling. It's a small price to pay for the car's other benefits.
     
  5. Technigogo

    Technigogo Member

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    Vtwin, thank you. I really like the other benefits so you may be right.

    SCH-I545 ?
     
  6. bisco

    bisco cookie crumbler

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    i haven't noticed any problems upto 65 mph, how fast are 'highway speeds'?
     
  7. Technigogo

    Technigogo Member

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    60-75 although we have a couple of 85 mph toll roads here. I-10 and I-35 are 75 mph.

    SCH-I545 ?
     
  8. ForestBeekeeper

    ForestBeekeeper Active Member

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    The interstate here is 75MPH. The normal flow of traffic is around 80MPH.

    I do notice that cross-winds knock our Prius around a lot at those speeds.

    We have had our Prius since it was 'new' and it now has 60,000 miles on it.
     
  9. BZzap!

    BZzap! Senior Member

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    If I'm not mistaken, the early Prius Gen III models did not come with the mid-chassis brace. In the later production runs the brace was added to minimize body deflection. It may be advisable to install an after market brace. They are readily available. Also, I understand that the after market rear sway bars do wonders for stability issues.
     
  10. car compulsive

    car compulsive Active Member

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    I had my dealer install the TRD rear sway bar - problem solved. (BTW I run 15" wheels with winter or summer tires.)
     
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  11. Technigogo

    Technigogo Member

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    Car compulsive, is yours a gen 3? My car is at the dealer for the next several days for assessment and for the recall. I could have them install that while it is there. How much did it run?

    SCH-I545 ?
     
  12. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    Under $300 at my dealership, parts & labor.
     
  13. car compulsive

    car compulsive Active Member

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    Yes, my car is a 2011. IIRC, the sway bar plus install was under $250. I ordered the bar from my dealer and was going to have a local shop install it, but they declined. I had the dealer install it on my next service visit.
     
  14. Feri

    Feri Active Member

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    They did come with the mid chassis brace but it was improved (stiffened) from 2012 on.
     
  15. Technigogo

    Technigogo Member

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    My dealer is quoting me $500 installed. Should I look elsewhere? Are you sure this will fix this problem?

    SCH-I545 ?
     
  16. burstaneurysm

    burstaneurysm Active Member

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    If you're even moderately mechanically inclined, the rear sway bar is an easy diy job.
     
  17. xpcman

    xpcman Senior Member

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    It's best done with a floor jack and two jack stands. Plus standard auto tools.
     
  18. Technigogo

    Technigogo Member

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    I have all that; tools and mad skillz. I ordered the sway bar from Amazon and I will install on Saturday!

    SCH-I545 ?
     
  19. DtEW

    DtEW Active Member

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    Also consider adding the RAV4 FSB. The reduction of roll resistance with a sway bar on a given end of the car usually comes with a reduction of grip on that end. I might be in the minority among people who would slap hop-up parts on a non-sporty car... but I do not think neutrality (read: increased rear-looseness) is desirable for this genre of vehicle in which you can't really steer with the throttle.

    I've been running the TRD RSB + RAV4 FSB combo for the last 4-months or so, and it has been great after the bushings wore-in. It ran a little harsh initially, but now it's great. We even went and endured some brake-rutted dirt roads this last weekend. This mod was pursued because I glide (from pulse-and-glide) down mountain passes at 90-ish mph.

    Also AFAIK, downforce is pretty much non-existent on "normal" cars without some special factory attention that is almost always trumped-up in ad-copy when they bother. However, body-shape-induced-lift is quite real (see the issues with the 1st-gen Audi TT), and I would not be surprised if the Prius was subject to this (I would almost be shocked if it wasn't).
     
  20. southjerseycraig

    southjerseycraig Active Member

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    I must say that I've never had this problem with my 2010 Prius. I wonder what's unusual about the OP's.