Instability at highway speeds.

JZChen – Yes, 52/51 “is really high” and “52 is definitely over...,” but it is not substantively “exceeding the limit on the sidewall” nor is it dangerously high. The Max Load embossed on the sidewall of my low-profile Toyo Proxes states “MAX LOAD 600 kg (1323 lbs) AT 350 kPa (51 PSI) MAX PRESS.” 52 PSI is a 2% nudge above the sidewall embossed 51 PSI number, and is at a 358.5 kPa Up-Pressure Level, which is well within the Maximum “Cold” Pressure Engineering Design Margin of these Toyo tires.

Your initial post that started this thread said you “…have the 17" wheels as a background” as well as you displaying in your JZChen sidebar information that you are driving a Prius v Five Petrol Warfighter. The Pv5 comes OEM fitted with 17-in. 10-spoke alloy wheels and P215/50R17 tires. Therefore, I would expect that the tires you are running on with those 17-inch wheels are the same Low-Profile tires I am running on, and are similarly marked with “…350 kPa (51 PSI) MAX PRESS.” If you are running at 33F/32R PSI on those Low-Profile tires, IMHO, you are driving a “Mush Mobile.” Those Toyota Door Post 33/32 PSI tire pressures you are pressuring your tires at and running on, are the likely source of that “somewhat lofty feeling” you are noticing when driving at high-speed on the Freeway.

The “maybe if you tried the factory recommended 33/32” you mentioned IS NOT the TIRE FACTORY RECOMMENDED 33/32 PSI, but rather the TOYOTA RECOMMENDED 33/32 “Cold” PSI pre-load number selected to deliver a softer-cushier (i.e. “Loftier”) ride where you feel the road less. Your Low-Profile P215/50R17s (i.e. Low-Sidewall dimension) would “Like” running at my “Solid” 51-ish PSI more than at the Toyota “Soft” 33/32 PSI you embrace, and at which you keep them pressured. Additionally, Up-Pressuring them would aid you in seeing your Pv5 deliver improved, higher Per Tank-Full MPG Averages to you.

FWIW FYI:

■ My tires are running cooler at my 52/51 PSI Up-Pressure Level than your tires are at their 33/32 PSI Air Pressure Level.
■ My Up-Pressured tires provide a more robust response to protect and prevent road damage to my 17-inch alloy wheels should I hit an errant “Pot Hole, Road Hazard” compared to that provided by your “Softer” pressured 33/32 PSI tire pre-load.
■ Last, but not least, I am more in tune with the EPA Tire Pressure related Fuel Economy “Rule-Of-Thumb” Guideline for tire inflation that states, “Every 1-PSI increase in “Cold” tire air pressure will deliver an incremental gain in fuel economy of from 0.3 to 0.4 MPG,” than are you.

As F8L said regarding excessive tire-wear from running at Up-Pressured PSI Levels, “Not likely. High tire pressure doesn't wear the center of the tire like it used to.” Take it from me, JZChen, F8L KNOWZ TIRES!!!

I am assuming you dislike buying gasoline, and love being able to drive by gas station after gas station because your v (vee) delivers High MPG. In the game of achieving and running your Pv5 at MAX MPG, every incremental “Tweaking” bit helps, from Pre-Operative set ups on oil type and viscosity selection, “Cold” Tire Pressure Preload, all the way to applying and using “Hybrid $mart” Operating-Driving Techniques on the road. Among the reasons I am able to run my 2ZR-FXE 1.8-Liter I4 powered Prius v Five Hybrid, which is rated at EPA MPG-FE 44 City/42 Combined/40 Highway with its Curb Weight = 3274 lbs and Coefficient of Drag (Cd) = 0.29 to have it achieve and maintain > 50 MPG Per Tank-Full Fuel Economy numbers, is partly because of my running on Up-Pressured tires.

My running at 52/51 PSI on my tires delivers increment MPG-FE gains that surpass those you are getting running your Prius v on P215/50R17s “Cold” PSI loaded to 33/32 PSI. If I had to make a guess on the additional amount of incremental MPG I am seeing from running my tires Up-Pressured to 52F/51R PSI, I would conservatively “guesstimate” it to be at around a 3± MPG Gain.

I invite you to join me in the War Against Petrol Terrori$m, One Gallon Of Gasoline Not Consumed At A Time.

 

JZChen – If it is good enough for the exotic Bugatti Veyrons to roll on, it is good enough for my humble Pv5ATP Petrol Warfighter to roll on, too.

The firmer sidewall with less flexing that comes with Up-Pressuring (i.e. Not Over-Pressuring) Low-Profile tires provides an extra bit of robust resilience margin when a pothole, drop off or curb edge is hit that helps keep the edge of the 17-inch alloy wheel(s) from “Bottoming Out” impacting the potential damaging object, edge, hole, etcetera.

While Low-Profile Tires On Alloy Wheels may be de rigueur, their “Dirty Little Secret” is that they are especially susceptible to being damaged, as compared to Standard Profile Tires On Alloy Wheels. This and the vulnerability of Low-Profile Tires On Alloy Wheels to being damaged has spawn new small businesses specializing in “We Repair Damaged Alloy Wheels.” Just today, I followed in a “Mobile Repair Of Alloy Wheels” Truck being given access through the gate of my community to perform such a repair service for a neighbor. This Box Truck had signage all over the Cargo Box advertizing this Mobile Alloy Wheel Damage Repair Service. Such Alloy Wheel Repair Businesses would not be able to earn a living and stay in business if Low-Profile Tires On Alloy Wheel were not regularly being damaged in large numbers… Just Saying…

NOTE: My Brother drives a Porsche Boster S w/ 20-Inch Carrera S Alloy Wheels. He was cruising along one of CALTRANS “excellently maintained” (cough, choke, gag…) roadways at Interstate/Freeway speeds, when the road “jumped up” and bit both Low-Profile Tires On 20-Inch Alloys putting a “Chunk” dent into the edge of both front wheels. No, the tires did not “Blow Out” Moral of the story, younger Brothers should always take the advice of their older, wiser Brothers.

Fearing a “Blow Out” from P215/50R17 tires running at “Cold” Air Pressure Pre-Loads of 51± PSI, assuming the tires have no hidden internal flaws, is an unreasonable fear. At the chance of appearing to be “The Old Man On The Mountain Top,” in my lifetime I drove my various personal automobiles with “Balloon Tires” and Radial Tires. All these tires were safely “Cold” PSI Up-Pressured to provide me a “Firmer, Good Road Feel” ride, and optimal handling. Balloon Tires-To-Radial Tires is a long time. Over these scores of my driving years, I have never had a tire fail strictly from riding with “Firmer” air pressure levels.

There is nothing wrong with you electing to use Toyota’s 33F/32R PSI Recommended Door Post Air Pressures. They work fine, and will give you a “Toyota Corporation-Selected Ride.” I just prefer the ride selected by Ol’ Watakushi-wa, me, which is one designed to help me achieve and continue to achieve “$tellar Miles-Per-Gallon Fuel Economy.”

The proof of the superiority of my tire air pressure preference is in the Fuel Consumption Log for my v (vee), along with the extended number of miles I get out of my tires before they need replacing. The MPG-FE for my v (vee) has been and is tracking at 125% of Official EPA MPG “Combined” Fuel Economy from Tank Full-To-Tank Full over the nearly 12-months I have owned it.

Have Fun!!!

 

JZChen – For What It Is Worth ---You “…putting winter pressures on my parents' '91 420SEL and driving to Lancaster in less than winter weather” DID NOT “cause the OE Pirellis in the rear to have bubbles on the tread.” It was the flawed Pirellis, NOT THE “Winter Pressures” or you driving them “in less than Winter Weather (i.e. ‘Warm Weather’'.” Your parents blaming you for their failure, those many years back, was a “Bum Rap.” Pirelli Tires International is to blame for your parents having to paying $150 per new tire to replaced the failed OEM Pirelli tires.

I remember that particular Major “Latent Defect ‘Bubble’ Flaw Failures” Recall for the OEM, V-Rated Pirellis, which came installed on some new Mercedes-Benz and BMW cars sold in that Late ‘80s/Early ‘90s timeframe. Fortunately, the OEM tires that came on my now vintage 560 SL were Continental Tires, not Pirellis.

The Recall was similar in the kind of defect and failure mode, and the magnitude of the recall to that of the major Firestone Radial Tires “Latent Defect ‘Bubble’ Flaw Failures” Safety Recall of the Firestone OEM Radials supplied on new “Big Three” American cars sold in the mid-1970s)

RE: UP-PRESSURING ON MY V (VEE) - “I don't think I could handle the bumpiness.”

Running at Max “Cold” Sidewall PSI on my v (vee) definitely lets me “Feel The Road” more, but in a good way. However, the quality of the road surfaces on the streets / highways / roads I drive on here in Florida are very good (i.e. “smooth”). Additionally, the suspension on the v (vee) [on my v (vee), anyway] does an excellent job of absorbing and ameliorating transmission of the road “Shock ‘Bump’ Pulse” input from the Tires / Wheels / Suspension into the v (vee)’s chassis, and ultimately to me sitting in the Driver’s Seat.

Have a Happy Holiday Season.

 

You bring up a very good point there. High tire pressure should not be used on rough road surfaces. The higher pressure causes the tire to skip over these surfaces rather than conform to them. This reduces forward traction and wastes energy both in terms of momentum and suspension movement. Safety can also be compromised because the tire has more difficulty "grabbing" surface irregularities.

On smooth roads high pressure is fine IMO.

 

Thanks Catgic for the info, and quite interesting. Given that information, wouldn't you also expect Lexus CT200h will have that same "problem"? I assume that the Prius Gen2 uses similar design in Gen3, thus carry over the same instability feel, however, I hope this is something that can be remedied. I'm looking into finding stiffer bushing... but first I want to understand how this steering system works. Any suggestion? Anyone have "fixed" this "problem"? I mean I still consider it a "problem" because driving long trips, and I mean from LA to SF type of trip, adjusting the freaking steering every second for 8 hours is going to be crazy. I've driven a Ford Van that had an alignment problem before on a road trip, I couldn't even relax. I really hope this is a fixable "problem". thanks folks.

oh, just found this on another site:
Poor stability and handling at highway speeds. - Toyota Prius Forum : Prius Online Toyota Forums

I guess this has been in the design and not everyone has it. kind of like the FR-S/BRZ idle chirp.

ahh... !@!@#$%^ This thing is all controlled by some CPU logic. Yaw, sensors, calibrations... VSC? WT...

Tire Review - 2001-09 Toyota Prius Alignment & Suspension Specs

 

SamuriaSD – Thanks for the e-link to the Prius Online Toyota Forums "Poor Stability And Handling At Highway Speeds" (Circa 2004) discussion on this “Problem/Quirk.”

The e-babblings there align with my observational take on what I have experienced and conjecturized from doing High-Speed Open-Road Driving in my 2G, and now in my v (vee).

My tolerance level is such that I do not characterize this “Quirk” as a “Problem”….but that is just me. My extended 70-ish MPH, High-Speed Open-Road Driving “Interstate/Freeway” driving is infrequent, with most of my driving being “Around Town/City” traveling in 30, 35, 40, 45,& 50 MPH speed limit zones. This “Quirk/Problem” is negligibly noticeable or nonexistent at these slower travel speeds.

Have Fun!

 

When I first bought my 2006 Prius it drove pretty well until I hit the highway and accelerated to about 70 MPH. at that point the car felt like it was swaying in the front and that the rear of the car was going to spin out from under me. So I drove the car over a specified road at specific speeds and noted how it handled. I then bought the Brace offered here. Its much thicker and more solid than the original. Once I installed it (took 15 minutes) I again drove over the same terrain I had before and the car handled much better. I've had it up to over 85 now and there is no sway, just a good solid feel.

We have over 130,000 miles now on the car, we still have the original 12 volt battery, original Brakes, I am on my third set of tires. Other than that No Issues! I change the oil every 5,000 miles and the plugs every 60,000 - 70,000. I just had the PCV valves changes for the first time.

 

The v has a larger sail area (side profile) than most sedans so if there is wind from the side, you will feel it. I find the v stable up to 80 in normal conditions and I just slow down if the conditions are bad.

I've delaminated 3 tires in overloaded, high speed driving without checking the inflation pressure. Akron Ohio and Germany. I carry a gauge in every car and check before any high speed extended driving trip. But I also pay a price in comfort when I overinflate and they don't handle in rain or snow as well.

I laugh when I think of the Boxster with 20" wheels. Mine had 17"s and I thought that enough. Every time I see an expensive wheel with about 1" - 2" of tire between it and the road I recall a visit to a wheel repair shop in Md and how many seemingly beautiful wheels were in for very expensive repairs.