My 2006 FEH has Conti's on it. I have run 48 psi from day one. I have 46,000 miles on the tires. I have 1mm more centerwear than edge wear.

Bias ply tires are far more susceptable to centerwear than steel belted radials are.

The manufacturers recommended pressure has many engineers input before it gets posted on the door. A large amount of the vote goes to those folks that want you to have a nice, cushy ride, thus this number tends to be at the very low end of the scale.

Law enforcement, cab drivers, and others who abuse their cars or rely on them to have crisp handling routinely run their tires at high inflation pressures.

In general, if one were to stick religiously to the mfg recommended tire pressures on the FEH, one would get inferior mileage and bunches of edgewear on their tires.

Evidence suggests that youd can save your tires from being destroyed by premature edgewear by running them at somewhere near "max sidewall".

Max sidewall is a legal term. Most light truck tires have either 35 or 44 psi "max sidewall" Odd and unlikely that they would all have exactly the same numbers no?

Burst tests by the re-tread industry suggest that the nominal burst pressure for a re-used steel belted radial carcass is in the 300 psi range.

Mark Mooney

 

I just changed my stock tires last month at 73,xxx miles.
I ran 44psi for most of those miles ( probably 60k+ ).

My tires did wear out the center faster, but only slightly so.
I had 2mm at the center and 3mm at the edges when I changed them out.

This is a switch, however, from every other tire I've own in the past.
( dozens ) Every other tire wore out the edges first, when set to the manufacturer's spec, usually 35psi.

 

I didn't say you religiously follow the door sticker for pressures.

If your outer edges wear faster, then the pressure is too low & if the center wears faster then the pressure is too high...

Escapes can't go fast enough to require higher than normal pressures because of high speed tire flex.

You adjust the pressure for even wear. If you stop & think about a tire, the face of the tire, the tread is designed to be flat against the road with a certain pressure. This is given as a cold pressure but the designers calculate the heat up for an extended run to get the pressure they want.

It is true that you can reduce the rolling resistance by running higher pressures in your tires, but with that comes decreased life from higher wear in the center of the tire.

Only at the design pressure will the tread be flat on the road. Steel belts do not influence this pressure since they have no lateral stiffness. If they did then the tire wouldn't flex with changes in the road surface.

At the design pressure you get maximum traction, braking capability, best water dispersion away from the tread and maximum tread life. If you set another pressure some element of that list will be reduced.

If you don't like the numbers on the door sticker experiment. When you find maximum tread life you've probably got the right pressure.

Despite the fact that the Japanese tire company took the fall for Ford's rollover mess, it should be noted that Ford set a pressure on the door sticker that was below the tire manufacturer's recommendation (as noted probably for better ride).

Get a tire gage, measure pressures, and adjust them where you want if you don't like or trust the door sticker (though it is a good starting point). The rule of thumb is simple: center wear = too high, outer edge wear = to low. And remember that your tire gage isn't accurate to 0.01 psi, it's probably closer to plus or minus 3-5 psi.

The remarks about steel belts is a canard for this issue.

 

I really don't think you have any experience or knowledge with high pressure in steel belted tires. GPSman had claimed he was running 48psi in his Eco Plus tires after driving with the great hypermiler Wayne Gerdes to a Ford program on the FEH. I also thought back then there was very little to gain with that much pressure but I was wrong. After doing some coasting and P&G testing for Wayne in my '05 FEH, I quickly found the benifits of better mileage, better handling, and longer ware. As GPSman noted, he had 73,000 miles on his Eco-Plus tires when he changed them. If what you claim about center tire ware was true, the center of Johns tires with all the highway driving he does would have not lasted near that long. I still have my rear Eco Plus tires at 60,000 miles and they are just fine and will most likely go another 20,000 miles if I can put up with the noise. I say this because the new Michelins make no noise on the front.

You must have not read the complete article I quoted and provided a link. Now, if others want the cushier ride and give up the other benifits that fine also. What John, Mark and I are saying is you do get a slight more wear in the center with high pressure, but overall the tire will go much more miles than lower pressures. Handling, even in the rain is much better because the contact patch of the tread stays flat even in hard turns. The tire does not colapes and allow sidewall contact or outer edge ware as bad. This may be why the tire center may show a little more ware than the outer edge.

GaryG

 

Back to the original topic of this thread.

My FEH has been at the dealer since last Friday. They have been waiting for Ford to tell them what to do. Just found out they are going to replace the exhaust manifold and the other o2 sensor. They won't have the manifold until tomorrow so I won't get it back until then.

Does this sound too extreme? The service rep did say that the welds on the manifold were a little less well done than they could be.

Thanks,

Rick

 

Over the years I have learned that those who only use anecdotal information and pontificate (eg lets put to rest....) have a high probability of not knowing what they are talking about.

The math:
Assume an FEH weighs 2000 lbs and its weight is distributed evenly to all four wheels.

Thus each wheel supports 500 lbs and 500 lbs/50 lbs/in2 =10 in2

With a tire pressure of 50 psi the tire footprint will be 10 square inches.
With a tire pressure of 40 psi the tire footprint will be 12.5 square inches.
And with a tire pressure of 30 psi the footprint will be 16.7 square inches.

You cannot change the fundamental physics of this.

At the tires design pressure the footprint will be roughly rectangular with the width being the design tread width. If you raise the pressure the footprint gets smaller as the edges and corners lift off the road surface.

In order for earlier discussions about mileage improvement without additional tire wear to be true, the face of the tread would have to remain rectangular against the road. It doesn't, it becomes more and more "ovalled" at higher pressures with the center of the tread bulging slightly.

The discussion about steel belts is similarly wrong. Drive a tire over small stone, say one inch diameter and see if the tire lifts off the road or if it envelopes the stone. If the steel belts did what has been said, the tire would lift off the road. It doesn't.

Steel belts stabilize the tread face against the road but do not add rigidity to the face of the tread. Thus they do not perform as set forth in the pontification beginning "lets put to rest..."

In the end there are many who read these sites to learn. I normally would not continue such a discussion given the anecdotal stuff unsupported by principle and the pontifications. But for those who may actually be seeking to learn something I have added this info.

 

So, you have 41,000 on your FEH. Are you still on the original Conti's?
I assume you've been a good scout and run the mfg recommended pressure during this time.

I've got 46,000, or maybe 47,000 on mine. Original tires.

Let's share some photos of the tread wear on each vehicle, and send in some edge and center wear measurements.

Empirical results, instead of misunderstood math.

Ready?

 

Ok. I gotta try this one more time.

The reason that edge wear is reduced with higher inflation is that sidewall flex is greatly reduced.

At a lower inflation pressure, the inside tread edge of the tire is more prone to being lifted away from the contact patch as the tire squirms.

Edge wear is higher at lower inflation pressures because as one turns, the vehicle runs on the outside sidewall to a higher degree, and lifts the inside portion of the tread and concentrating the wear on the edges of the tires.

With higher pressures, the rims stay over the tire to a higher degree; edge wear is reduced because one doesn't have the inside edge of the tread lifting under hard cornering. This is why law enforcement, cabbies, autocrossers and such run higher pressures.

You can verify this with chalk and your air compressor.

Put 30 lbs in your fronts. Chalk the sidewall from the tread edge up the sidewal for a couple of inches.

Run the car in circles in the parking lot, or go run it through the local traffic circle or what have you. Note how much chalk is worn off the sidewall.

Put 45 lbs in your fronts. Re-chalk the sidewall and repeat. You will easily be able to measure the difference.

Your contact patch math is true, but your contact patch visualization is faulty. Radials will have a shorter contact patch front to back with increased tire pressure, but very little difference in their contact patch from left to right. In other words, the length of the patch changes, but the width, not so much.

Again, while the vehicle has 30 lbs in the tires, drive it through a puddle or make one with the hose in your driveway. Check out the tread pattern that the tire leaves on the way out of the puddle.

Put 45 or 50 lbs pressure in the same tires and re-run the expirement.
You will not have lifted the edges off the pavement whatsoever.

On the fuel mileage side of things:

The consensus is that hysterisis is a big contributor to tire wear and a big factor in fuel mileage. The flection of the tire in general causes heat. Heat increases wear, energy is required to generate heat.

Higher inflation pressures produce less hysteresis, less heat, more mileage and lower tire wear. It's a fact, not conjecture.

The new michelins that are coming on the 2009 FEH are designed to have less hysteresis loss, AND they weigh 2lbs less than the Conti's (if I have my numbers right) That's like switching from clincher tires to sew-ups on your bicycle! I'm hearing reports of nearly 2mpg on tires alone.

 

How's the saying go?
Never wrestle with a...