Tire pressure when it's cold

Well here's the deal guys. You will see a noticeable decrease in your fuel economy going from 100+ to 85 or so psi. You might want to keep track of your economy before and after to decide whether it's worth it. You won't see much difference in overall tire wear. However at the price of fuel these days, you're better off concentrating on fuel economy than trying to cheap out on tires.

All other things being equal, the difference in fuel cost between using X-One Xline D Energy tires (Michelin's new fuel efficient wide single - rolling resistance = 89) and an XDN2 (rolling resistance = 133) is $3954 per 100,000 miles at a fuel price of $4.00 per gallon. That's about the price for a set of 4 Energy D or XDA Energy tires at my carrier. You can get the same results using Michelin's tire calculator. My own experience shows that using low inflation pressure is going to cost you another 0.3 to 0.5 mpg. Cheap out on the tires if you like, run low pressures and risk a blow-out as well as using more fuel than at higher inflation pressures if you like. There isn't enough profit margin in trucking to be foolin' around with decreased fuel economy by buying XDN2's, and running low pressures. The 800 pound gorilla in the profit/loss sheet room is the fuel bill... not the cost of tires.

If you run those XDN2's for 425,000 miles, that's over $16,000 you're going to pay the oil company's for the few days you might need a more aggressive tread. I've run X-One XDA Energy drives for over 4 years now, and needed to chain-up once. I don't shut down for snow if I have to move the truck, and I've never been stuck. That of course, is down here in the North American banana belt of the US. Our Canadian brothers as we all know actually have summer for 15 minutes on July 25th every year. Y'all might want to just never take the chains off, LOL!

As far as tire life is concerned, I've been running 120 psi in my tires - that's the maximum rated cold pressure in my steers (Michelin XZA3+) and drives (X-One XDA Energy) - with no ill effects. I've been getting 180,000 to 200,000 miles out of my steer tires, and 240,000 out of my drives. No weird tire wear, no tire failures. I get great fuel economy. The upshot is you can run the lower pressures if you like, but there really isn't any downside from running higher pressures and getting better fuel economy.

The CVSA criteria for putting you out of service for an under-inflated tire is a pressure below 50% of rated cold pressure - on any axle in any position. Interesting... I'd always "heard" it was 80 psi.

 

I disagree entirely. I'd always ran my tires at 100psi and they wear out in the centers before the tread on the edges comes close. My loaded weights are typically less than 10,000lbs in the box and lot of empty miles. The reason I asked you if you were sure 86psi was underinflated in all applications was because I learned I was overinflating my tires from a similar discussion down in the garage section.

I always thought 100psi and 105psi was where you set tires. I used to run heavy all the time and never did have 14ply tires to wear evenly. So I switched over to 16ply onm the steers and that problem went away. But the max psi on 16ply is 120... ....you most definitely DO NOT air up 16 ply tires to 120 psi or they will wear like crazy in the centers. I air those up to 105 and still tend to believe even that is too much air.

The old "air em up to 100psi" is just something fleets do because they're lazy and they don't even maintain their tires in the first place.

 

Ok guilty of not reading the entire post until I commented above. Are you running 16 ply tires?

 

Continental tire's inflation guide:

http://www.continental-truck.com/ww...index_en/download/load_infl_tables_pdf_en.pdf



Bridgestone's inflation guide (see page 5)

http://www.trucktires.com/bridgestone/us_eng/load/load_pdf/loadTables.pdf

And Yokohama's really nifty Mobile PSI/tire load calculator:

http://mobile.yokohamatire.com/air_pressure_calculator#


The verdict is in, 75-80 PSI is what they all recommend.
They must not be listening to Kevin Rutherford.

 

I imagine they aren't. OTOH, I'd rather keep more of the dead presidents in my pocket with lower fuel costs than pretending that running tires at low pressures is getting me anywhere. Been doing this long enough, and keeping track of the numbers to the point that I know that following those recommendations is costing you $$$.

Tires are load range H, 12,000-ish pounds on the steer axle when the GVW is just under 80,000 pounds.

 

This is an XZE3+ LRH with 117,000 miles, 15/32 right across the tread. Mounted on the trailer. All 8 tires look identical. When loaded, it's usually 32-34,000#.




I tried to take pics of the depth measurement but you wouldn't be able to see the numbers on the gauge.

 

Do you buy your own trailer tires? As I said in an earlier post, I suspect that the higher psi/ cupping and strange wear phenomenon is primarily a trailer issue. But I'm not taking any chances since what I'm doing is working.

A projected fuel savings of 2/10ths is about $2300/year. But if you're buying tires twice as often (based on what you're getting for miles) the savings is half of that. It's not insignificant, but I watched a set of Michelins die an early and needless death due to over inflation.

 

No, it's a power-only deal for me. Now we do have the inside diameter cupping issue on some of our trailers, but they were ordered with a lighter weight axle and 2" offsets. The combination causes the axle to bend under load.

You misunderstand. I run X-One XDA's that aren't going to get the length of wear than an XDN2 will. OTOH, an XDN2 has much higher rolling resistance. The net effect is that while I may buy two sets of tires to your one, the fuel savings between the tires and higher pressure operating point more than make up for any extra wear an XDN2 provides. It's also been shown that running XDN2's at that low pressure will result in much higher wear rates than an over-inflated tire suffers from.

 

No, I understand completely. I also calculate costs "Ad infinitum".

A bunch of us took some loads to a mine on the Steward- Cassiar Hyw. The guy with the X-Ones cut a tire right across the tread, destroying it. It could have happened to anyone.

However.... The closest X-One was 1000 miles away. What to do? Pull a wheel off the trailer, put it on the drive, chain up trailer axle.

Then BEND OVER THE FUEL TANK and pay full retail on two new drives and keep a spare. That was equal to one year's fuel savings.

As you said earlier, you run the US banana belt. Comparing your costs vs mine is pointless.

 

Show me. I need a link.