2008 Ford Expedition.
I would like 43 psi back, 44 in front.
What should I put in?
Thank you.
Robert
Robert, we just can take much more of this…
The correct tire pressure for any vehicle is in the owner’s manual and on the plate inside the driver’s door pillar.
Twotone
This is the guy who does blood delivery runs at 100 mph up and down I-25 and I-70 in Colorado…But he can’t figure out how much air to put in his tires…
Hey Bob, not more than 47 PSI !!
Ford’s post placcard reads 35 psi for the P255/70R 18 tires
and the spare P265/70R 17
35 psi seems way too low and soft. The tires even look too low with sidewalls bulging out.
Why does the snow tire read 47 max psi?
If possible, I would like to obtain less rolling resistance/better fuel mileage with a higher psi but which is under the max psi.
Robert,
First, since you are using the Expedition outside the range this vehicle was intended for, your situation is one of those rare ones where the placard inflation pressure might not be appropriate. More pressure decreases the heat buildup caused by the higher speed you occasionally run.
Yes, higher pressures decrease rolling resistance, but that also results in a smaller contact patch, which has traction implications.
So why do your winter tires say 47 psi max?
Long version: http://www.barrystiretech.com/loadtables.html
Short version: What pressure is displayed on the sidewall is not well connected to anything concerning the tire itself, while the pressure displayed on the vehicle tire placard is directly connected to the vehicle.
In your case, higher operating speeds would suggest a higher inflation pressure - but you don’t want to over do it because of the traction implications. I would suggest you start at 40 psi (+5 psi), and after one of your high speed runs measure the pressure build up. If you get 2 or 3 psi buildup - that’s good. If you get more buildup, then add more pressure until you get buildups in the 2 to 3 psi range - but don’t exceed the maximum listed on the sidewall.
Short version: What pressure is displayed on the sidewall is not well connected to anything concerning the tire itself, while the pressure displayed on the vehicle tire placard is directly connected to the vehicle.
The pressure on the sidewall IS connected to the tyre and is NOT a recommended pressure.
The pressure listed on the car is a recommended pressure, but only for normal conditions. Note: The car should also have specifications for the speed range for tyres on that car. Make sure YOUR tyre's speed range meets or exceeds your usage.
The car manufacturer test the tyres on your car under a number of different conditions and test for safety under emergency conditions before recommending tyre pressure.
The pressure on the side of the tyre has not been tested with your car or any car. It is only a measure of the amount of pressure that particular tyre can be safely run at, assuming that the pressure is safe for the car.
The only real use of that number on the side of the tyre is to tell you that if it is less than the car manufacturer calls for, you can't safely use those tyres on your car.
None of the above proves that it would be unsafe to use the 85-90% of the max on the tyre. It only proves that it has not been tested. I prefer to have my tyres (and the other guy's as well) inflated to a pressure that has been tested and found safe for handling under emergency conditions that I hope I never have.
References:
This is sponsored by a tyre manufacturer Bridgstone - Firestone and instructs the reader to check the owner’s manual for the correct tyre pressure.
Here is another from the Goodyear site.
Check Your Air Pressure
Keep your tires properly inflated and you could improve gas mileage by more than $1.50 every time you fill your tank. The recommended tire pressure for your vehicle is located on a sticker inside your driver-side door or noted in your owner’s manual.
You might also try the US Department of transportation.
http://www.nhtsa.gov/cars/problems/E...intenances.htm
They say:
You can find the correct tire pressure for your tow vehicle in the owner?s manual or on the tire information placard.
The vehicle manufacturer’s recommended tire inflation pressure is the proper psi when a tire is cold. The term cold does not relate to the outside temperature. Rather, a cold tire is one that has not been driven on for at least three hours. When you drive, your tires get warmer, causing the air pressure within them to increase. Your tires can get warm after just 1 mile of driving.
Thank you so much, Capri. (Also Joseph - saw your post after I posted this.)
By far, most of the miles are below the speed limit.
To save fuel, pollution and vehicle wear and tear, I’m usually 50 mph in 55 Zones and 58 in 65 and 75 Zones - always in the right lane.
After the next emergentransport I’ll check tire pressure.
Some long transports are at 95 mph, (on dry roads) well below the 118mph tire “T” speed rating.
Wish I could do a footprint at 35, 40, 45 psi.
When I inflated the tires, I looked but noticed no change in footprint.
All of the roads we use are dry, now, which is usual for Colorado.
In snowy weather, should I lower the pressure to 35 psi?
47 psi is the max that the tire hold safely. That is a tire specification, not a vehicle specification.
Your vehicle spec for psi is on the car and in the owner’s manual and you say it is 35 psi, but you don’t like that number. It must be too soft.
Are you loading the vehicle at capacity, over capacity, hauling a trailer? If you are just driving with a minimal load the 35 psi as per Ford is the best number for ride, safety, and handling.
If you exceed the 35 psi number you could reduce the “contact patch” which is the amount of rubber on the pavement. Radial tires are supposed to have sideway flex, which is why they look “soft” to you. Forget looks, a tire with 20 psi can look OK so you need to check pressures with a guage.
If you want to run 43 in back and 44 in front go ahead. You must have some logic for the extra 1 lb in front. So you’ve thought this out, do what you want. Who cares what Ford says they only have the ability of engineers, computer modelling programs, test tracks, and so on. You’ve got you and your opinion is all that matters anyway.
FWIW, the MAX inflation pressure is the absolute limit the carcass was built to withstand. Driving above that pressure can cause the body plies to separate from the bead or the inner liner to push through the sidewall radial plies. Most light duty automotive wheels are designed to the 45 psi pressure limit and can also fail when over inflated.
You’re driving an Expedition and you’re concerned about fuel mileage and being green? Really?
Minimal weight. I even removed the rear seat which is never used.
Front of vehicle is heavier than rear due to engine and transmission.
Ford dealer affirms my assumption that Ford wants the owner to be pleased with the softer ride at 35 psi - at the expense of poorer mileage.
Also, when I am driving at 80 mph and above, harder tire has less flexion so less heat produced by the flexion.
The only way to know the affects of different tire pressures is to take a 12 volt air compressor, a tire guage, and stop watch and go to your local race track. Change the pressures and run a couple of laps full bore around the track and get your lap times. Change the pressures and do a few more laps. Then do it again, and again.
Then you’ll know, otherwise you are guessing. Maybe guessing right, maybe wrong, but guessing just the same.
Yes. I try to be as efficient as possible: gentle accelerations, anticipating and coasting up to red signals and stopped or slowed traffic, traveling at lower speeds (wish I could know the ideal speed.)
Removing all weight I can. Unfortunately must keep the fuel tank full.
Being as aerodynamically smooth as possible (Wish I could remove the light bar when not in use.)
According to the digital readout, I once attained a whole 20 mpg!