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Increase in Highway MPG from 22 - 26!!!

4K views 25 replies 7 participants last post by  Mark58 
#1 · (Edited)
I understand that this may not appear to believable, but here is the truth.

Brought my 2006 DTS to the dealer for service of the Tire Pressure Monitor System. The tech replaced 3 out of 4 TPM sensors, so tires were dismounted, sensors replaced and remounted/rebalanced. My dealer uses Nitrogen not straight air to fill the tires. The tech did NOT follow the 30 Psi guidelines listed on the door pillar for my vehicle W/ 17" wheels.

Prior to this repair I have always maintained exactly 30 psi all tires measured cold, no less than 60 degrees F ambient with the readings taken in the shade.

The best MPG Cleveland to NY previous to this repair had been 22. 5 MPG. During my latest trip from Cleveland to NY I had an avg of 26.7 MPG., conservative driving, 65 - 70 MPH used cruise the entire way. The TPM warning was active for the right front tire and was reading between 39 and 40 (Hot) Psi on the DIC. The other tires were reading 36 - 37. There was a slight decrease in ride quality, you could feel the road texture right up to the steering wheel just a little more than usual.

At my destination in NY I checked the cold Tire Pressure, approx 70 degrees F ambient temperature and in the shade. The cold Psi for all tires ranged from 33-36 Psi. I left all the tires overinflated. They are well in the safe inflation range, IMO there is no increased risk of thread separation or blowout at these inflation levels. The vehicle weight to tire rating ratio maintains a factor of safety.

The 3- 4 MPG improvement is still being maintained several weeks later in a mix of City/Hwy driving (more hwy than city). In city driving, the decreased rolling resistance is definitely noticeable

I don't plan on pushing the envelope by operating at 40 PSI hot for future highway extended trips. I plan on maintaining the hot tire pressure operating at 37 psi or less. BTW I am running Falken Ziex 502 tires.

Although its logical to attribute the major factor for the increase in gas mileage to the higher inflation, I am wondering if the nitrogen has enough of a positive impact on tire balance at highway speeds to be a minor contributor to the increase.

Any thoughts or similar experiences?
 
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#2 ·
I run my tires at 34 front 33 rear (cold pressure) almost all the time.
At highway speeds that gives me about 37/38 in the front and 36/37 in the rear.

I think the threshold for the TPMS coming on is 40PSI on the high side and 24 on the low side...
I never drive at 65 on the highway... our speed limit is 75 on the interstate with some interstates at 80 MPH.
Of course everyone goes a little faster than that... :) :)

Took this the other day cruising down the interstate...
.
.
 
#6 ·
Now Jim....thats too fast! reminds me of the first time I learned that the Northstar's have "Stones". I worked for GM and lived in Detroit in the mid 90's until mid 2000's. Once in the 90's I was tooling along at the speed limit on I75 and without much warning (vehicles travel at 2X your speed do appear to come out of no where!) was passed by a late 90's STS doing well in excess of 120. A couple of seconds later I was passed by a Red late 90's Trans AM. Not sure who eventually won the race, or if they both lived or died, but I never looked at the STS the same way again. I knew it was a true performance car, (at least it was in its time!)
 
#7 ·
Yep... there are "LOTS" of people who badly underestimate the NorthStar... :) :)
There are not many cars that you can drive between 80 and 90 and still get 20+ MPG.
I don't know what the top speed is on mine, I have had it to 144 mph and it was still pulling pretty good... but I ran out of room...
I was catching up to some traffic in front of me... REALLY FAST... LOL
I would estimate it at just a little over 150.
Not bad for a little 4.6 L engine in a 5000 pound car... LOL LOL

Texas Jim
 
#9 ·
Have it "TUNED"....
Mine was originally tuned by BlackBear Performance.

Mine has no speed limiter...no Torque Management, the timing has been advanced, the fuel slopes have been modified, injector pulse width has been increased, the transmission shift points and shift FIRMNESS have been modified, the speed that it will DOWNSHIFT back to another gear have been raised, the speed that it will shift to high gear has been lowered to 32, the speed that the torque converter will lock up was lowered from 41 to 36.
And a whole bunch of other things that I can't think of right now.... LOL

Check with some speed shops in your area...

Texas Jim
 
#13 ·
I had a guy put air into my tires after they had been filled with nitrogen and I can tell a difference. The tires I have were brand new when I got it a year ago. They are cheap Raptor (riken version) They never had any kind of vibration until the regular air was put in. But the vibration is only at 35-60 mph on the passengers side, Don't know why but thats my 2 cents. Any suggestions or....
 
#15 ·
PRESIDENT Obama joins a long list of Republican Presidents that recommended the same thing starting with Nixon back in 74 and the guy that replaced him so he could stay out of Jail (LOL) President Ford recommended the same. All our Presidents seem to recommend the same thing. Funny isnt it! LOL
 
#17 · (Edited)
Hey don't sweat it Marky, you didn't step on my toes, no drama! The current Pres knows what he is talking about though. Case in point.... The lowest resistance tires ever installed on a production vehicle were the Super-low-rolling resistance 50 psi Michelin tires on GM's EV1 with wheels that weighed only 8.5 pounds.

So if we adapt your humorous suggestion of 100 PSI tires we would likely not need all that that Iranian oil so much.

BTW if you want to find the all quotes from the former Presidents on "keepen yere tires eniflated"...just Do what George W Bush did....member???.... he said he had learned how to use the google! ..USE the google ta look at the ranch ..now thats funny! LOL LOL

di[flv http://video.thinkprogress.org/2006/10/bushgoogle.320.240.flv]

Digg It!
Transcript:

HOST: I’m curious, have you ever googled anybody? Do you use Google?

BUSH: Occasionally. One of the things I’ve used on the Google is to pull up maps. It’s very interesting to see — I’ve forgot the name of the program — but you get the satellite, and you can — like, I kinda like to look at the ranch. It remind me of where I wanna be sometimes.
 
#22 ·
Marky..... this thread originally references the MPG gains I experienced when the Cadillac Technician at the dealer increased the psi on all 4 tires on my vehicle, which I stated was clearly over what is suggested by GM on the B pillar label. Not sure how or why you ended up hijacking the thread to make it political, but .... I suggest that you keep it non political in the future.

BTW You indicate that President Obama might make gasoline from algae. Maybe Rick Sanatorium can do better and make more gasoline by instituting tighter control on women's reproductive systems. LOL LOL. Hows that chrome bright bar doing BTW?
 
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