The King - a 2002 GMC Yukon XL... 496 CI of STILL not an LS!

[Supercharged111]

Nope. It's a freak occurrence that will never repeat itself.

 

[ck80]

Nope. It's a freak occurrence that will never repeat itself.

Whelp, on the old and improperly inflated tires I've consistently pulled down in the 14mpgs range on highway long hauls when not towing a trailer.

So the question, which I guess we'll see over time, is whether a fuel saving rubber compound plus proper tire inflation can gain another 2-2.5mpg on average, highway. Recall this is flat country, no hills of consequence to really be found.

At least on this 420 miles worth of trip the answer was yes. 200 miles highway and 10 or so off it that weren't measured - 100 miles because we werent topped off when leaving, and the other 100 miles back home from the truck stop we use in Dublin. It's been about 20 cents a gallon cheaper lately so we fill up there on our way. But that is all flat driving, and, I'd expect equal or better mileage.

Then again, I can hit lower 40s mpg in the v6 mustangs, and used to get high 20s mpg in the '18 f150 4x4 that has since been sold. Always been good at mpg driving - when I try

 

[Streetbu]

What you gain in MPG is lost in tire wear though. The middle of the tires will be bald before the edges. I don't care what brand of tire they are, it's a simple fact. Having sold tires for 22 years I've seen it before.

 

[ck80]

What you gain in MPG is lost in tire wear though. The middle of the tires will be bald before the edges. I don't care what brand of tire they are, it's a simple fact. Having sold tires for 22 years I've seen it before.

I've heard that too. What I was thinking before the trip was to try it *one time*, see how it drove. It was, as I said, much more squirrely because those hard tires in back didn't take to absorbing changes to the road through the sidewall, while the softer fronts did their normal thing.

My thoughts now are split. I don't know that we'll use the truck for much non-hauling duty. Yet it's nice on long trips though, closest thing to a limited/brougham/riviera seat gm has really ever made.

What I may do is lower the psi down around 45-50 and take advantage of the 'free' nitrogen top off service costco has the day before any heavy towing trips. It adds a step and inconvenience, but, also saves some tire wear in what are already short lived (50k?) rated tires...

 

[Streetbu]

I used to recommend to people with 3/4 & 1 tons to run them about 55psi if not hauling. Some vehicles you cannot get away with changing air pressures though. Ford Super Duty's are one. They get death wobbles if you lower the tire pressures. There was even a service bulletin about it.

 

[olds307 and 403]

So, The King went on a bit of a road trip today, first test of the new tire setup. Now old tires had a bit of a leak on the LR and tended to get soft over time, we're work, and most importantly getting old by my standards.

Those new tires with the nitrogen fill they set to the door placard (unfortunaately) meaning 45psi front and 80psi rear. What that mean? Rear is rock hard and feels like it wants to break loose a bit at high speeds (over 80) or with lots of rain/standing water over 70. Still, figured give it a try because we needed to get some things for the 77..

End results are an inexplicable new personal mileage record. I covered from southeast GA to Oxford Alabama. 80% of the trip was 75mph @ 2300 rpm. About 2.5% was 50-55mph @ just over 2000 rpm due to heavy rain. The remaining 17.5% was 65mph due to varied rain and seepage on the interstate.

Somehow, the trip on my end totalled 210 miles with 11.271 gallons of gas, filled all the way past pump shutoff. That's 18.6 mpg. Pump receipts and logged gauge mileage doesn't lie.

The wife, who isn't as good at powerband maintenance and tends to speed up and slow down more made the return trip, down hill, but surging between 60mph and 75mph. She did another 210 miles on 14.098 gallons of gas. That's 14.9 mpg. And it's for a wife who wasted fuel by speeding up and slowing down from not paying attention to speed, sometimes temporarily dropping as low as around 50 or getting as high as near 80...

Takeaway? I believe there MUST be some truth to the marketing claims on the tire compounds by michelin, and, being fully/properly inflated, no wind, and my ability to coast on large sections of interstate due to low traffic. I wonder what the max towing inflation of 80psi is doing as well? Even if you average driving styles you're at 16.75 mpg.... on a truck people claim is a 9-12mpg pig. AND..... the return trip was full of sheet metals and other goodies coming soon when unloaded in the other truck thread.

Very impressive for a big heavy truck with a huge V8.

 

[Supercharged111]

Question: have you ever verified your speedo against GPS? This of course assumes the odometer is perfectly tied to the speedo. I ask because my GMT400 trucks were off a couple at 70 and, once corrected, I lost 1mpg or thereabouts with it not overreporting. My goal isn't to crap on your numbers, rather, my 1500 has never seen 17mpg since.

 

[ck80]

Question: have you ever verified your speedo against GPS? This of course assumes the odometer is perfectly tied to the speedo. I ask because my GMT400 trucks were off a couple at 70 and, once corrected, I lost 1mpg or thereabouts with it not overreporting. My goal isn't to crap on your numbers, rather, my 1500 has never seen 17mpg since.

Good questions,, sort of, and wouldn't matter. If anything, real world mpg is higher than the lowest number, which is what I go by to account for the fact that "fillup" of the gas tank could conceivably be off by a fraction of a gallon, and the thermal expansion/contraction of fuel.

My speedometer reads lower than actual traveling speed. Tires are oversized from calibrated sizes and oem equipment.

GPS typically reads a couple mph faster than gauges when using various devices, including the less accurate version built into phone apps when it shows current speed next to posted limits on directions.

Verifying using a Spicer web calculator, axle ratio + 31.65" tire for the 265/75/16, rpm, and the 0.75 OD ratio in the 4l80/4l85 transmissions verifies speeds also running a couple miles than we aim for when seen as logged on odometer.

If taking just a map quest of route from gas station to destination, and back to gas station, and dividing that mileage traveled by gallons used to fill back up gives fractionally higher numbers. But again, there is error to account for as pump may stop a tenth or quarter gallon early. So I go with the smaller numbers.

Nice thing about the long haul calculations is we don't dally around, it's point a to b and then return.

 

[ck80]

Something something forgot pics...

So among other things for other projects, and for stashing, bought a pair of rockers for the yukon. Not sure if I'll cut em up and use em, or, just cut a donor, depends what I find first. But either way, for $30 I wasn't complaining and zero shipping damage or backorder times means a win for us

 

[ck80]

So, today was a day of long overdue maintenance, mixed with regular maintenance. I felt ambitious, and, had energy (or so I thought.)

I changed the cabin air filter and the engine air filter.

I also learned that although it says (ONE) cabin air filter in the truck, they put TWO in the package

You can clearly see Qty 1 in the bottom left corner. I don't *think* the rear air takes a separate one, but, ill be reading into that tonight just in case. My squarebody and gmt400 didn't have a separate rear I ever had to change.

I recharged the r134a for the first time this summer. Gave it a small shot of oil, and it took 5 cans r134a to get up to pressures.

Changed the oil, filter, filled the washer fluid with the good bug remover type, blah blah blah - normal oil change stuff.

Then, I was going to do 3 of the mustangs - two aged out, and one mileage out. I got through just two, the mileage out and one of the aged outs (I picked the one with the pilot sport 4s since it gets more spirited driven and the wife's DD with the Pirellis.

So, one mustang awaits, then I'm also gonna mess with the firebird and a regal once I get back from our trip. Of course I'll likely run out of energy after only two of those three, but, f●@k chemo.

Meanwhile I've got about 5 gallons of waste oil for the burn pit.