Let's talk tire pressure...

Er......nothing.
Nothing at all!!

I buy tires at SAM's because I can usually get a fair price on good tires, and they rotate and balance them every 5-7k for me. Of course.....I have to wait in their STORE while this is done, but we usually limit our impulse purchases and so their scheme has limited success with us.
Costco takes this one step further by offering N100 (fully nitrogenated) tires in addition to the other standard install perks, and there is absolutely nothing wrong with N100! I simply wouldn't pay any extra for it.
Since you're already getting the N100 with the new tires, simply take the black valve stem covers off of your tires just before you walk into Costco, and replace the lime green ones that they (would have) replaced them with.
That way....you won't be confused with the the poor folks that are miss-led into thinking that there is a substantial difference between N78 and N100 in passenger tires.

 

The only issue with nitrogen if you need to inflate the tire you need to go to a shop that has nitrogen.. could be pretty inconvenient.

Increased tire pressure increases your braking distance especially on wet roads.. Not good..

 

Ha anyone else read the heading fo this thread as "Let stalk tire pressures" or is it my Aussie accent?

 

No, it does not make him an expert for determining maximum fuel mileage. Proper tire pressure is important for proper stability/handling, tire wear, tire structural stability, ride comfort and fuel economy. These are the factors that go into the vehicle manufacturer’s numbers printed on the tire inflation placard (found on the driver’s side door edge or adjacent body pillar). A tire that’s underinflated for conditions will run hot, wear excessively on the outer edges, decrease vehicle stability, waste fuel and is more likely to hydroplane during wet conditions. Safe load capacity decreases by roughly 100 pounds per tire for each 3 pounds of underinflation. An overinflated tire results in a hard ride, might wear excessively in the center of the tread and is more likely to skid during abrupt maneuvers.

 

I agree, except for one thing. In the case of the Prius it is heavy in the front and I have found after having two different Prius's for 8+ years. I ran 42 psi front and 40 psi rear in the tires. In both cases the tires ran perfect. No Excessive wear at all in the middle of tire! Nice and even all the way across the face of the tire. They do run a little harsher, I don't know about skidding, I do feel comfortable that the entire patch of tire is on the road for good handling at these psi's. Y MMV. Just my two cents.

P.S. Higher PSI does make for better MPG!

 

Yes, we're not debating these facts. We're talking about using a higher pressure within the tires maximum limits.
Adding 5 to 7 PSI to the "recommended" tire data, isn't gonna cause any of these conditions. I've been using
42 psi for years and never had a problem like anything you're describe in your reply.
All my tires wear evenly and I drive pretty hard. I ride a motorcycle and carry a lot of corner speed when in my car.

You're over reacting about 5 to 7 PSI. I know owners that run the MAX printed on the tires sidewall and haven't had any problems. That's adding about 15 PSI

 

Found this report at the Mythbusters site. After increasing the initial 5psi over recommended inflation pressures there seems to me to be a point of diminishing returns as the further increase of 20psi to 60psi only yields an additional increment of 1.4% in fuel savings. Still looking for Prius specific data:

Mini-Myth #2: Low tire pressure leads to lower gas mileage (and conversely, higher tire pressure improves gas mileage).

Mythbusters: Kari, Grant, and Tory

Procedure:

Lay out a driving course that simulates normal city driving with a series of stops, turns, etc.
Bypass the car’s gas tank and fit it with a fuel cell that can be removed and weighed in order to measure precisely the amount of gas used during each test.
Make sure tires are inflated to the recommended pressure of 35 psi for the control test.
Drive the course and calculate the gas mileage.
Repeat step 3 with tires extremely under-inflated (10 psi) and extremely over-inflated (60 psi).
Repeat step 3 with tires slightly under-inflated (30 psi — 15% lower than recommended pressure) and slightly over-inflated (40 psi — 15% higher than recommended pressure).
Analyze the results.


Results: With tires at 10 psi, the car used 3.7% more fuel than the control (tires at 35 psi). At 30 psi, the car used 1.2% more fuel than the control. At 40 psi, the car used 6.2% less fuel than the control and it used 7.6% less fuel with tires inflated to 60 psi.

Conclusion: Myth confirmed, although extreme measures are not recommended. Keeping tires inflated to their recommended pressure is definitely a good idea, since the car gets better gas mileage than with under-inflated tires. However, although the car got even better gas mileage when the tires were over-inflated, this is not a good idea for safety reasons and because it causes the tires to wear unevenly.

 

Information from NHTSA Tire Fuel Efficiency Consumer Information Program Development: Phase 2 – Effects of Tire Rolling Resistance Levels on Traction, Treadwear, and Vehicle Fuel Economy suggests a MPG increase of 0.3% for an inflation increase of 1 psi. This result should be relative vehicle-independent as long and the powerplant's fuel consumption is linear with output for these small differences. Of course the Prius will experience an actual MPG increase about twice that of other vehicles for the same tire pressure increase because it gets twice the mileage to begin with. On the other hand, rolling resistance can vary by as much as 20%, comparing a conventional tire to a LRR tire, so choosing the right tire may be more beneficial than increasing inflation. Of course you can do both.

Polling users here will give you a rather complex data set to analyze because of variations other than pressure and tire type:
-- tread wear (tread depth) leads to slight mis-clocking of miles
-- energy loss in flexing the tread also changes with tread depth
-- tire age affects the properties of the tread compound, primarily hysteresis

 

We are also able to detect the increase in mileage with the Prius systems. Not like the myth busters inaccurate methods
with old cars that can't give proper data feedback. I've proven it to myself over a 90 mile commute with two different vehicles. Both the 08 Prius and the 2013 Prius C have shown increased MPG's from bumping the tires up 5 to 7 PSI. YMMV

 

I clearly think as owners of our own vehicles we can do what we want to do. (As long as it's safe).

But I have to wonder if there isn't a degree of psychological back-lash here.

As in "Whatever the manufacturer recommends, can't possibly actually be the best recommendation".

I kind of think Toyota wants the best for their own vehicles. So there is good reason to believe the recommendation is a good one. If everything was significantly better at 5 PSI, 10 PSI or even 15 PSI higher, what benefit to Toyota is there in denying this reality?

That being said, I myself have been running 3-5 PSI higher than the recommendation.

You guys talked me into it.

 

Not really. Toyota is held hostage by the tire maker, the legal system (liability), comfort expectations of the customer and a range of other factors. Lowering recommended pressure satisfies several of those requirements while not necessarily offering optimum mileage or even safety. For example, lowing pressure reduces roll-over risk and increases comfort but hurts performance and mileage as well as tire wear.

I don't think I've ever seen recommended tire pressures that were not too low for best mileage and performance. The disparity will vary from vehicle to vehicle, and even from one tire to another on the same vehicle. But there are ALWAYS tradeoffs being made that effect performance.

 

That's fine. Like I said, I do run my pressure above the recommendation.

But I just wonder if there isn't a degree of stubborn consternation.

Like if Toyota suddenly changed the door jamb recommendation to 42/40, then everyone would start lowering or raising from that point.

I keep mine 3-5 psi higher, I can then imagine possible benefit but also have plausible deniability when the dealership checks my tire pressure.

 

1

 

195.65.15 is a very popular tire size. It is normal for most small cars. That means it will work on those cars. You may not get a 3mpg increase on a 2004 Jetta as you would for a 2012 Prius. Each car works differently. LRR tire on a Prius will be different on a full size BMW. Its just the way it is. Not all tires get the same mpg nor do all cars with the same tire get the same results. I got 45k on my stock Yoko's, and will be changing them soon. I can be just as happy with the stocks again or with the Energy Savers.

 

Running 44 max sidewall on our 2010 OEM tires with 57,000 and even wear.

Ride is harsh, but handling and wear and mpg trump comfort for us.

 

+1

 

Untrue.

The Mythbusters use a far more accurate method of measuring fuel usage than the overly optimistic Prius's on board system. I'll trust the science guys.

 

Your long commute would be better for gathering comparative mpg data than the miscellaneous driving I typically do. I was going to run a time-series design in which tire pressures would be systematically changed after each refueling to obtain the data to construct the graph showing measured mpg vs inflation pressures. Unfortunately the changing mix of driving I do will add more error to each data point than would be found on a stable long-distance commute. I just increased tires to 40 psi front and 35 back and will start collecting data, but I would certainly be interested in seeing the results from others.