The impossible: 04 Yukon XL Denali AWD

[slowmover]

. . Air up the tires

OP, there is some work to be done here (reading for knowledge).

For pickups/suvs the tire pressure is critical to best handling & braking which trumps the very slight mpg change.

1] Pressure according to load

- It may be that your load is standardized, pretty much the same from trip to trip. I highly recommend you incorporate a stop at a certified public scale, such as the national chain, CAT Scale (online locator available) on your way out of town, with full fuel, all persons, critters and gear aboard.

2] Remain within factory guidelines

- The second reason for factory sizing of tires is to work within a very carefully established balance of factors. Remember the Ford Explorer fiasco? Since then the factory engineers have doubled down (or been listened to) in re tire specifications.

There is

A] An upper and lower set pressure limit
B] There is a FF/RR bias

Both of these are to be maintained. A scale ticket gives a per axle wheel position average (front axle, rear axle and total). One can "see" where one is. The minimum amount of pressure to support that load is very possibly below what the factory sets as a minimum. The maximum is lower than the sidewall marking. Stay within the limits, A & B.

But one can move up a few pounds (3-5 psi) if within the range, and likely not do much to upset the vehicle prematurely. The test (according to EM contributor and tire engineer CapriRacer) is that

after 1.5-hrs steady-state driving, the pressure rise should be no more than 3-5 psi.

The trick to all this is to find that best "lowest" psi number, and then adjust just barely upwards. Or, not. "Reading" tires with an infrared thermometer is what some of us do (pro drivers and RV'ers) to keep an eye on things; and we adjust according to season or condition as well.

Steering control, body roll, and braking are all predicated on tires being able to absorb a certain amount of road irregularities while maintaining a set course without steering corrections. Tires that are too "hard" cause a high COG vehicle like a pickup to lose traction or tire/road contact too soon.

Once you know the likely weights, and season-to-season changes, the range of pressure adjustments is quite small (the reason for records and scale tickets).

Frankly, long tire life trumps a few mpg. Best tires, and best EM practices for high mpg will mean long tire life. It is no mistake that on my pickup that it got 120k on the first set of tires before they were worn out from either time or miles . . . and I may not have to buy the second replacement set until the truck has a quarter-million miles on it.

Fuel economy is just a sub-set of ECONOMY where all dollars matter.

A set of CENTAMATIC wheel balancers (Alvarado, TX) and tires/rims done on a HUNTER GSP-9700 -- plus a TPMS system -- are all just good additions to keeping up with an expensive set of tires, and to the promulgation of best practice in keeping things in top shape.

In the same vein: polyurethane anti-roll bar bushing replacements and KONI shock absorbers (if available, if not, then BILSTEIN).

Best practice in going down the highway is not only near zero steering inputs, but to not have to change lanes, either. The smart speed (based on road, load, traffic, weather, driver condition, etc) is what one learns as skill improvement is taken seriously. Best mpg is just a part of that (at a generally, but only slightly, lower speed).

The vehicle that needs the least amount of corrections to remain lane-centered under all conditions will win any mpg contest over an otherwise identical vehicle (where driver skill is hypothetically the same).

So, from both the longest life and mpg perspective: do what is necessary to preserve tread life (past pressure). This means respecting exit ramp and flyover (overpass) limits for example. This is not a car. If it sez 30-mph, then drop it down to within 10-mph of that under perfect conditions and do that before you get there as using the brakes is an EM no-no. Keep perfectly centered in the lane, any lane you're ever in, under any and all conditions. No cutting the corner. Same for intersections as the law states that all turns must occur only within the intersection itself; one must enter the new lane of travel already in a straight line. (Re-reading the Texas Drivers Handbook is good EM practice).

Finally, anyone getting less than 70k out of a top set of tires needs remedial driver training (the vast majority of folks out there). Include ones self in this assessment of need.

It all pays, directly (mpg) and indirectly (tire life).

.

[MTrenk]

I want to be helpful and tell you all about how a flat underbody is actually no good at reducing drag, and that there are all sorts of other things that people on this forum have assumed that are not correct, but no one wants to hear it.
I made the comment about 'being right' because I have read much of what many of you have done to your cars, and while it's mildly helpful, you could gain drastically better results with more insight into how aero really works.
Also, you aren't very nice. I hear BS everyday all day. I simply just tell people what I know and if they choose not to believe it, I don't get all butthurt about it and start shoving crap down their throats.
I would appreciate it if you would try to be effectively helpful, instead of just another guy who likes being 'right'.
Since you care so much about being right, why don't you go spend some money learning from people who know what they are talking about, instead of just putting down everyone who puts out info that doesn't agree with yours.
This attitude is chronic among many of you ecomodders.

[maczo]

Originally Posted by MTrenk

I want to be helpful and tell you all about how a flat underbody is actually no good at reducing drag

Please do.

[MetroMPG]

Originally Posted by MTrenk

I want to be helpful and tell you all about how a flat underbody is actually no good at reducing drag

Originally Posted by maczo

Please do.

A new thread on the subject would be a good idea. Please post the link here if you do.

[scivicblu83]

WOW, a new guy shows up with some crazy ideas looking for advice and the thread turns into to a denali roast and a mess of quotes with lawyer-istic responses. Good job. I hope this is not who we really are.

[hoover]

A little research on the web will show that many 4 wd vehicles can be lowered. Google mcgaughy's and review their site on lowering trucks, including 4 wd. Just had to put my 2 cents in.

[Cy-Gor]

You can thank the rappers for this. there are several kits to lower the yukon/tahoe platform.

2-3 inches can be done with out anything crazy with the AWD system.

$500-1000 for parts.

Might take a while to recoup that costs.

I am not against lowering the vehicle some since it does look good with nice wheels, but to save gas i am not sure how much return on investment i will get.

[non-prophet]

I would like to revive this thread if possible. I've been searching the last few weeks for a vehicle within my price range that can carry a payload of 1500 pounds and 4 adults on long distance trips so I can take my band on a few 10 day tours around Ontario, Quebec, New York, Ohio, etc.

IT's brutal, I can only afford 7000 MAX with all mods all in. I've been trying to find an adequate pickup truck, but it's very hard in that price range. The possibility that popped up was a very well maintained 2004 Yukon XL... remember, I can't buy a rust box and hope for the best after spending a year fixing it up.

I have a small car for getting around the city otherwise, and this is primarily for long trips. I have managed to get some excellent tanks out of my corolla, the best being a 800km tank on a trip to montreal and Ottawa.

I expect to put 20,000 km on the truck i get this coming year. 20,000km at 13L/100km is looking like 3300 dollars in gas at 1.30 a litre here. I'm really stuck. I test drove the yukon extensively when it came up as an option, and I couldn't get it to act reasonably on gas (going by feeling, and rpm read out at various speeds - no scan gauge or anything in test drive).

First question.... can the AWD in the yukon be disconnected in some way to make it 2wd?

Seriously, the thing feels like it's eating gas. I test drove a diesel f250 and it seemed to be doing far better... way out of my price range though.

[non-prophet]

Oh yes, note the Yukon XL was a 2500 as well....

[Cy-Gor]

the 2500 is a 4x4 not an AWD, so the system should be purely mechanical to remove, maybe a couple of sensors.

Its a pretty old school system so it should be as simple as removing the transfer case and front drive shaft and replacing the rear drive shaft with a longer one.

I say simple but its likely a big pain and may or may not be worth it.

It also depends on your driving, if its all highway the weight and drag of 4x4 will be less noticeable than if its all city.

The 6.0L is also a beast so you have to be pretty easy on the throttle to make sure its not just sucking down gas.

Another option for a band which i think would be easier, is a trailer.

You can leave your gear in if you wanted to and you have a ton of options that can tow 2000lbs and get good mileage.