So it is pretty well known that higher tire pressures lead to (much) higher FE in the FEH. However, how high have people on here gone? I see reports that say running the tire pressure at the max listed on the tire's sidewall is fine. (44 psi on the stock 08 tires)

I have also seen that 15-20% over the sidewall max might be fine as well and this (say 52 psi) really improves FE. Anyone have any experiences with running high tire pressures? Are you worried about safety?

Thoughts?

The stock FEH Continental tires wear really slow, so minor changes in tire pressure do not affect wear greatly. Safety can be compromised when overinflating the Contis above 44psi, especially in hot climates or high speed driving where pressures may greatly exceed the tire's limits. There are heavy duty truck tires (load range 'E') which will fit FEHs and handle up to 80psi if you're not afraid of a rough ride.

Over inflated tires will flex less and should run cooler, reducing wear and grip. How much of either is pure speculation without running some serious testing.

My own experience with motorcycle tires has been that grip falls off much faster than tire life increases. However, my bike actually comes with a guide for how much to increase tire pressure based on various conditions (cold weather, passenger, etc.). There is an expectation that the rider will be proactive and understand that a single tire pressure can't address every situation.

Just throwing in my 2cents.....

Example vehicle: 2004 Hyundai Santa Fe AWD
Hyundai spec 32psi
(Bridgestone)Tire Manufacturer spec 36psi

Hyundai says that 32psi is optimum based upon a formula balancing ride quality, handling and fuel economy in that order.
Bridgestone recomends 36psi for tire longevity.
Each vehicle is a little different depending on steering and suspention tuning but I have found that 50 to 70% of the difference is a perfect balance, i.e.:
36 - 32 = 4 x .7 = 2.8psi 34.8psi
I keep the Santa Fe's tires inflated to 34.5psi and have gained a .3 MPG increase to our anuall average.

Also consider replacing the air in your tires with Nitrogen. Nitrogen does not cause the tire presure to fluxuate in hot or cold weather the way air will and it reduces the amount of moisture trapped in a tire that can cause oxidation and premature tire wear. It will also reduce rolling resistance due to it weighing slightly less than regular air. Filling your tires with nitrogen should only cost $4 - $8 per tire and will save much more than that in the long run.

getnitrogen.org has a savings calculator and based upon my santa fe's specs our savings is:
Your Savings
Reduction in fuel costs by improved mileage: $143.66Savings by increased tire life: $44.44Total savings per year: $188.11** Based on maintaining proper tire pressure, according to your vehicle manufacturer's recommendations




Our future FEH should be:
Your Savings
Reduction in fuel costs by improved mileage: $87.50Savings by increased tire life: $44.44Total savings per year: $131.94** Based on maintaining proper tire pressure, according to your vehicle manufacturer's recommendations


once again...just my 2 pennies

Sincerely,
Blind Mike & Michelle
TwoLostMinds

I this article there is a pretty good write up in the "Steady State speed FE" section - the guy has his tries at 52 psi. I get no where near thoes MPGs with my tires at 34psi. I would say it isn't speculation at all.

Actually, I wouldn't spend 2 cents for nitrogen. Nitrogen is MAYBE useful in high performance racetrack vehicles whose tires might face extreme temperature changes. Street cars....not so much. Weight savings? Seriously?

Remember, our air is already 78% nitrogen.

1. The leaks in our tires are usually in the valve stem...and these leaks are larger than either molecule. Nitrogen won't help.

2. The amount of water vapor or oxygen in a tire is not going to rot your tires prematurely. In fact, I've never heard of anyone suffering from that problem. Tire treads wear out long before the insides ever have a chance to "rot".

3. Unless you are inflating your tires in a vacuum, there is no way to remove all the air from your tires before introducing the nitrogen so there is going to be some "air" in your tires anyway.

4. The reactions to temperature changes are so minor....like less than 1%. As in, immeasurable on your tire.

5. Weight? Seriously. I would bet you that putting a penny in your pocket adds more weight than 4 tires of Air vs. Nitrogen. I think N's weight is about 88% of Oxygen's. And then consider what % of the weight in a wheel is actually the gas inside it.

This is snake oil.....don't pay for it.

-Tim

2006 Mercury Mariner Hybrid AWD
Black with Pebble interior
Premium Package with Nav & Moonroof



Current ODO: 26,152
Typical Drive: 20 min crosstown in heavy traffic (3.5mi there and back twice a day)


532 Gallons of gas saved
That's 10,642 lbs less CO2 emitted

We had a previous thread on nitrogen. Consumers Reports actually did a long term test on nitrogen. They found it would reduce air loss but it would only be of noticeable value for people who only check the tire pressure once every few years.

That's a great link. Note, I didn't say that it was speculation if increased tire pressure would help, but how much. Clearly, Gary G.'s driving habits aren't the same as mine, but it would be interesting to know what percentage of his FE is due to the increase in tire pressure.

I'd also like to get him out on a skid plate and see what effect the tire pressure changes have.

footnote: I write testing software for a living. The occupational hazard being that I don't believe anything until I get the numbers to back it up.

GaryG's posted fuel efficiency results sparkle and I have not read or heard of anyone posting higher MPG on a regular basis. This hypermiler use to post frequently here and I can remember when he actually "limited" his tire psi to 44 because that was the "rated max psi stated on the tire". When his tires were at 44 psi, he still posted mid-40 mpg figures. Could this be the point of diminishing returns?

2005 AWD Escape Hybrid
Best Interstate tank trip MPG 39.02 (scangauge II) for 402 miles on I-70, 10.3 gallons used over mostly flat terrain. Aug. 2007

Best Interstate tank trip E30 MPG 34.6 for 271 miles along I-80 in Indiana and Ohio. May 2008

Best multiple road tank trip E30 MPG 36.2 for 202 miles in Southwestern Pa. July 2008.