I'm new to owning an '06 Gen 2 Prius Base (82k miles), so I don't know if there are certain unique driving characteristics. On a 65 mph highway, I am noticing at speed a feeling of slight porpoising (up/down). This is in dry conditions, no wind, brand new pavement not damaged by tractor / trailer rigs that can cause surfaces of concrete to become uneven between slabs. (This particular surface i am driving is brand new blacktop). I've not had the suspension looked at yet as on other vehicles a failed strut would be a likely suspect. It passes the simple "bounce" test. The tires from the prior owner are <5k miles with no noted cupping. Based on the prior owner always taking it to a dealer who also replaced the tires over the entire service life and performed an alignment when the tires were recently replaced, I have all the records), it seems doubtful that they would miss out on a sale for new struts. (The owner was very diligent in keeping this Prius well serviced). I will have it checked out and report back here, but I'm wanting to hear from others if the suspension, wheelbase, etc. of these cars could contribute to such characteristics. iPhone ?
If you can test drive a different Prius of similar age and miles on same stretch of road that'd give some perspective. Or at least try that patch of road next time your car is full of people... These cars aren't design for speed or handling, but for mpg... Likewise, new road paving standards are designed for heavier vehicles, which are more common. Over the years I've seen posts that might be similar to yours, such as people that are used to their big heavy truck and gravity accelerating them down a long hill on the highway getg in their new lightweight Prius and think its slowing down in comparison. Also experiment with tire pressure... Max reccomended tire pressure is a legal liability pressure not a high mpg or better handling pressure. I've comfortably gone up to as high as 48 psi in certain ideal driving conditions.
What you are reporting is not usual. 65 mph is not "speed" and the car is designed to handle this speed. I have taken a Prius to max speed on the autobahns in Germany and it handles quite ok at 117 mph. There is no need to excessively air the tires – they only wear out sooner. 37 PSI front and 35 PSI rear is more than enough to get good economy without prematurely wearing out tires.
I would be surprised if what you feel isn't anything more than a poor job of getting the road surface level and having slight waves in the road that harmonize with your wheelbase and suspension. Harmonics are amazing.
There's plenty of threads on here that argue the exact opposite about tire wear being less severe at higher pressure. What's more the car rolls further while coasting and has a much less sluggish handling response... Mostly, of all the low-cost modifications to improve gas mileage this is #1... As for wearing out soon, many on Prius chat argue the opposite and I have more than 80K miles on a pair of Bridgestone Ecopias on the rear wheels and there's still a surprising amount of tread. I bought a brand new set of 4 ecopias last November on black friday online via Simple Tire for ridiculous price of $70 each and have yet to be at the end of life on the last two. Is that due to them being kept at 45-48 PSI all their lives? Hard to say without tests, but did they wear out early? Nope, not even close, quite the opposite. But it has a lot to do with the roads you drive. My experience with previous cars has taught me that driving too fast on gravel roads are not for high PSI tires and creates flat tires... But if you're primarily driving in the slow lane of major freeways most of the time you'll be please with the results...
I can only go by my first hand (and documented) experience. Running higher pressure wore out the tires at least a year earlier than they should have, due to the tread wearing out in the middle. There was still 3, or so, mm of tread on the outsides, but the centres were at minimum and would not have passed inspection, so the tires had to be replaced. There is a lot of variability and the only "correct" pressure is the one that gives even tread wear over the whole width of the tire. Only the individual car owner can monitor and adjust accordingly. I have read most of the arguments for and against "on here" and most all posts contain no empirical evidence for their claims. Whilst it is hard to tell who actually knows about what they are talking, I take most all of those "reports" with a grain of salt against what I have proved to and for myself. One addition point I will make, that I have categorically proved to myself, the benefits of increasing pressures over and above the placarded values decreases exponentially for every 1 PSI increase. I am convinced that most people who claim to see huge increases in MPG after increasing their pressures north of 37 PSI Front and 35 PSI rear, have in fact unknowingly been running their tire at less than the placarded 35F/33R in the first place, because they never check their tires. So, their conclusion is that the high pressure was the reason, rather than just bringing the tire up from being under-inflated. I just add my point of view for some balance.
Great feedback from all on this thread thus far! Tire pressures are at 36 PSI currently. I took the car to a regional chain (Les Schwab) to have the struts inspected. They did find that there is a small bit of "evidence" of leakage on the left front strut. Unfortunately I wasn't on the shop floor to see the extent. The quote for all 4 struts replaced by them came out at $903, including alignment. Toyota quoted $2000 for the same job, not including alignment. Front only from Toyota was $1056. (Les Schwab is typically not considered inexpensive, so.... )
$903 seems like a really good price. I have a mechanic that works for himself (and is therefore always cheaper than a shop) that it would have cost me $1000, even if I were to buy my own parts. I ended up just doing it all on my own. And saved $500-$600 or so.
Your point make me wonder if there's some validity to tire wear patterns as related to tire pressure when the tire is first installed and broken in? Perhaps boosting tire pressure 10-15 psi on tires that already have wear patterns at 35psi foor tens of thousands of miles is more problematic than boosting pressure on brand new tires soon as you put them on the car? Because I'm 20K miles above the 60K warranty and there's still tread on the tire that is the same depth everywhere. And while the thought of uneven tread wear from an over inflated tire makes sense in theory, my tires demonstrate that in some case that's just not true in practice.
Agreed! Great work at doing it all on your own, too. How many miles/years were on your Prius when you did the work?
I had 130,000 miles, and the Prius was 9 years old at the time. I went ahead and replaced the rear coil springs while I was at it, and I was surprised at how much higher the rear end stood after that. The rear end “sag” was apparently pretty bad on mine and I didn’t even know it.
Nothing to add... Just posting to follow the thread that uses "Porpoising" to describe an automotive condition. You don't get that adjective used very often. Good descriptor. Pretty accurate.
I lost a strut just before 100,000 miles and the car did bounce a lot. I just changed both fronts and the first check should be for leaking oil coming out of the strut, my whole front wheel well was wet but it could be a partial leak. I bought the complete assemblies ready to install and it was an easy job.
What brand of pre-assembled shocks and struts did you buy? I made the mistake of buying Oready on ebay for my rear assemblies and they didn't fit and had to return them and it happened in a way that I couldn't realize until after I took everything apart. That was a bad day!
