Let's talk tire pressure...

Well, tire pressure is definitely a topic of concern since every dealer that I have ever taken my previous 2005 or now new 2013 Prius into has always set the tire pressures to 32lbs all around! So, the mechanics at Toyota are apparently just pushing buttons and not performing the maintenance on the Prius in accordance with Toyota's published specifications. What does that say about these mechanics if they cannot get something as simple as tire pressure correct??? I even told the guy who took the keys from me that they always get it wrong, and he said he would correct it. BUT, when I got my Prius back after the maintenance, I had him check it and he appeared to be shocked since again it was 32lbs all around! So, I still had to wait longer for them to correct their mistake.

 

I have obtained my first data points for the mpg effects of changing tire pressures (I am using a paired data points method, so both drives were roughly 1000 mile summer drives from southeast Wisconsin to northern Virginia using toll roads at speeds of maximum 67 mph or 5 miles over the posted limit if that was less.)
Pressure 35 psi front, 33 psi rear: 958 miles, 18.5 US gallons, 51.7 mpg
Pressure 39 psi front, 37 psi rear, 1002 miles, 17.9 US gallons, 55.9 mpg
I was trying to be exceedingly careful to refuel in exactly the same manner at all times, but obviously some refueling inaccuracy could occur. The apparent gain is about 4 mpg or about 8% for the 4psi increase.
Does this jive with the effects on measured mpg that other folks are finding?

(Ride is noticeably firmer or harsher at the higher tire pressures , but my spouse and i are fine with that.)

 

Looks like 8% to me, not 2%.

 

My mileage dropped into the mid 40's. Checked my tires. They were 29 to 31. Changed to 38 and 35. Mileage back to 51.

SCH-I535 ? 2

 

Sigh. I double checked all the other figures and ran them with a calculator, but estimated the percent in my head and obviously halved rather than doubled. You are right and it should be slightly less than an 8% gain. Will continue to gather comparative data.

Thanks for info! Were those refueling estimates or the display estimates? Exact numbers?
I decided to collect comparative data after the dealer at the 10000 mile check apparently reduced the tire pressures and I watched my mpg consumption estimates steadily decline as I drove home from the dealership! I suppose they thought they were doing the right thing but it gave me a jolt.

 

Display right now. Waiting to finish this tank of gas. Yea I am surprise how this air preasure thing works. I had put nitrogen in the tires so I was surprised they went down. Now I will just stick with air.

 

Accu-Gage Tire Gauges

Accu-Gage, accept no substitutes.

 

I use good quality dial-type gauges that I check against each other. Keep one in each vehicle. But checking with tires cold is important as they warm up rapidly and even a few miles of driving raises the pressure by several psi. My experience with digital gauges is that they were surprisingly inaccurate and the batteries failed at inconvenient times. Dropping the dial gauges can ruin their accuracy, though.

 

No need to really. As long as it shows "0" with no pressure applied, a dial gauge is likely to be accurate. Nothing really changes inside one over time as long as its not allowed to remain pressurized.

 

I bought my 2014 Prius Three in November, but I never checked the tire pressure until yesterday, and I was blown to see that all the tires had ~63 PSI on them! But even with this high pressure and hot weather, my MPG is still abysmal at 38MPG average. Should I lower the tire pressure? They feel "ok" to me as-is..

 

I would check the pressure somewhere else as 63 is crazy high and most likely a lot more than max psi!

Reduce to 40s and enjoy the comfort in comparison

 

Lower your tire pressure to Toyota specifications that are on a label inside of the driver's side door. You are way too high. Adjust the pressure in the morning before you drive your car.

 

Sounds like the tire pressure was never lowered after it came off the boat. The tires are kept at high pressure for the sea voyage, why I don't know, but my 98 Camry was delivered with over 50lbs pressure per tire, and it took me 3 or 4 days of hard riding to discover it.

 

If you are ok as is, I wouldn't bother messing with them.

I've never really gone much above mid-50's myself, but even at your current level you are nowhere near the true bursting point of the tire.

That said, for customers I never set them that high unless they ask.

 

Double-check pressure with another gauge as first step as that is way off the pressure it should have from dealer. If confirmed high, the dealer prep was faulty and you might want to switch dealers and have it checked over just in case.
But very odd your mpg is also so low. Is there an experienced Prius driver in your area who could analyze your driving style? Or he/she could test drive your car with a reset trip odometer to see what mpg can be achieved. If they cannot get 50-ish mpg in normal traffic and moderate speed conditions, you really should have all systems thoroughly checked.

 

63 PSI is dangerously high! I second the motion that you check your tires with a known accurate gauge.

How do you keep you dentures from falling out with the tire ballooned up like that? The ride has to be exceptionally harsh.

 

S California, after driving, in the sun, bet cold in the am, shade, they would be 40-45ish?

The tag inside the door might say 35-32, most like 39-37 ymmv