Prime feels SCARY at 50mph with "big" load of heavy groceries.

What's your tire pressure, and what kind of tires do you have?

 

Never drove on highway, but I regularly put upto ~300lbs (either 6 bags of 50lb chicken feeds, or 8 bags of 40lb rock salt or in some combinations of other heavy items) on the back of my PRIME and never felt any instability on rural roads going up to 60mph.

 

I have carried that much weight... packed the car solid with grass/topsoil removed for our sunroom. I remember that drive to the compost, since I was racing just ahead of a thunderstorm. Finished unloading 10 minutes before the downpour.

Since that trip (12 miles each way on curvy & hilly suburb roads) was no big deal, I would take a close look at your tires.

 

I personally have never perceived any such concerns in this usage of our Prius Prime.

 

Sounds like he was driving 105mph In 120 degree weather with an almost flat tire <32 (or 2) On ridged cement with cross winds, his experience would occur in any normal car or truck.

If he is in the business of trying to get his license revoked driving 105mph on public roads he should consider aligning the front end with more toe And get sport tires.

 

Exactly! A tire's load rating increases with cold tire pressure, and max load only occurs at max cold pressure, usually 44 psi for these tires. Check your sidewall for the load statement. It should be something like this, "Max Load x,xxx lbs at xx psi"

 

Yes. I have certainly not driven large loads under those sorts of extremes, but I expect it would do as well as any other similar vehicle.

 

As has been said, check your tire pressure. I have had no trouble with two adults in the back seat and their luggage in the cargo area plus the wife in front with me. Car drove like normal.

This was our load last year for a 6,000+ mile trip. There was a spare tire buried in the back, too. Must have been way over 300 pounds. Car drove like it was on a rail. I keep my tires at 42 front and 40 rear.

 

The load capacity at the recommended pressure (35/36 psi) is adequate. No need to increase it if you're loading the car within the payload limit (which is on a sticker in the door jamb. I think it's something like 675 lbs for the passengers and cargo combined, at least for my 4 seater Prime). But increasing it could improve handling or efficiency, depending on the tires.

I asked about what kind of tires, because I just had new snow tires (Michelin X-Ice "Snow") put on, and it feels like the sidewalls are made of Jell-O. Not confidence inspiring, but they do have good traction. I'm going to experiment with higher pressure once they are broken in and the weather is a little colder.

 

Hmmm...My Michelin X-Ice Xi3 handle fine and feel fine. No jello sidewalls. I use the inflation pressures shown on the door jam placard.

 

Granted my only experience with hauling heavier loads was in a gen2, in which I had installed a slightly larger 'solid core' rear sway bar.

Once was with (13) five gallon pails of paint, and the other time with (8) five gallon pails of paint and 3 adults, including some larger sized pieces of airport luggage. Pretty sure in both instances the loaded capacity exceeded 1000 lbs, and though I never tried to hit 100+ in either of the over 5 hrs of travel time, there were numerous slow and tighter corners along the 101 corridor where the vehicle didn't really handle all that differently from a normal unloaded gen2. Tire inflation was generally kept around 44 psi front and rear, give or take.

Had a female 'race' driver at the Toyota World Record event in Alameda take me for a "ride" in a gen4, and was quite impressed

 

Well, Mr. Sleaze, three people have asked you what your tire pressure is and you have chosen not to reply. Just because the dealer has rotated your tires you cannot assume that they checked that they were at the correct pressure.

 

Recent tire rotation, are the lug nuts tight?

+1 on tire pressure.