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Discussion Starter #1
31 psi feels a little less twitchy on the Interstate on some surfaces in two wheel drive. The warning lights come on if the pressure falls below 30 psi but goes off if raised above 30 without requiring a special bump. MPG actually increased by .1.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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Use the recommendation on the river's door sticker. "Cold" = ambient temps. NEVER check or adjust pressures with the tires hot - that's over 1 mile of driving.

The max inflation pressure on the tire sidewall is for Bonneville Salt Flats speed runs only.
 

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Discussion Starter #4
The car is brimming over with counter-functional devices to save infinitesimal amounts of gasoline in order to conform with the Corporate Average Fuel Economy requirement. Defeat stop-start, take some air out of the tires, I'd like to remove every other gear from the tranny, Just hope the direct injection (introed for mpg, of course) doesn't carbon up the valves big time like it did to the VWs and BMWs.

(Moderator edits to remove political references)
 

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My previous vehicle was an Isuzu Axiom, which had direct injection. Zero problems in the 13 years I owned it. Still would have it if new parts were hard to find. Hopefully the XT5's DI turns out to be just as good.

Agreed on CAFE.
 

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Discussion Starter #6
As to carbonized valves, the villain is crankcase fumes condensing on the backs of the intake valves without a port injector cleaning them off. The XT5 has a fancy PCV valve and I'm hoping for the best. Watching these forums, I see some older Cad owners vent to the atmosphere and hang drip cans to catch any condensed oil. If I had my druthers, I'd like a an additional port injector,Toyota style. So far, so good.
 

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For what its worth my XT6 was delivered with 40 psi in the 20's. I went with 36 psi as stated on the jam and it still rides harder than my XT5 with 18" tires. You think 31psi is the magic number? I'm ready to try it.
 

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Discussion Starter #10
There is no minimum pressure stated on the tire. The Cadillac warning light illuminates on the dash at 29 psi and below. Running 31 psi improves ride quality significantly with 18" tires. I would expect a dramatic improvement for XT5s with those low profile 20" rims. Actually, I had the idea of reducing pressures while driving my friend through the park over minor speed bumps. I thought, "Well that's the end of her being impressed by this Cad!" At 36 psi, it thumps over bumps like a truck on leaf springs. So said Consumer Reports.
 

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Imho, get a good digital air pressure gauge and go down in 1psi increments until you get to the pressure you can live with. Even a 2 psi change should be noticeable. However, as stated above, it's important to make sure the tires are cool before adjusting. I like to do it early morning while in the garage after the vehicle sat all night.

Also with a good gauge, you will find that the TMPS sensors are not particularly accurate. I have a very expensive calibrated electronic gauge I use for racing, and when I set all of the tires to the 10th, the DIC shows them all off up and down from each other by 1 psi. While most of these TMPS Mfrs tend to bury it, the accuracy of these are only spec'd at 3 to 4%, and in my experience, that's about right. The point being, trust a decent gauge over the DIC.

Regarding wear, that is a function of the footprint, and the ideal pressure will change from tire to tire, and vehicle to vehicle. Ultimately, the only way to know for sure is to do the chalk test to see if the entire width of the tread is evenly impacting the surface. If not, the tires will wear prematurely in direct proportion.

My .02 fwiw.
 

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For what its worth my XT6 was delivered with 40 psi in the 20's. I went with 36 psi as stated on the jam and it still rides harder than my XT5 with 18" tires. You think 31psi is the magic number? I'm ready to try it.
I think the low profile, vs. standard profile, accounts for most of the harder ride.

My wife’s $32K 2013 Hyundai Santa Fe sport with 18” standard profile tires rides smoother than my $65K 2017 XT5 platinum with 20” low profile tires.
 

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I think the low profile, vs. standard profile, accounts for most of the harder ride.

My wife’s $32K 2013 Hyundai Santa Fe sport with 18” standard profile tires rides smoother than my $65K 2017 XT5 platinum with 20” low profile tires.
Having more rubber on the sidewall will improve ride. Also it is much easier on suspension parts like shocks.

17" sidewall 7.3"
18" sidewall 6.8"
20" sidewall 6.0"
22" sidewall 4.9"
24" sidewall 3.9"
26" sidewall 2.7"

Example is for Escalade. I use 22's in the summer and change to 17's in the winter. Not hard to see what would give a better ride and easier on suspension.
Reducing air pressure is not recommended as the complaint for ride is equal to less sidewall. Less pressure would put the rim at risk. Also uneven tread wear.
 

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Keep in mind the TPMS alert is programmed to activate at 20% below the recommended pressure. That is why @Arminius said the TPMS light comes on at 29 PSI which is 20% lower than 36 psi. Any change in ambient temperature causes change in tire pressure. A drop of 10 degrees will change tire pressure by 1 psi. The tires running at 31 psi will turn on the TPMS light with any drop in pressure which could come about because of a 10 degree or greater drop in ambient temperature. As we head into Fall and then Winter, tires set at 31 psi now will alarm in the nest few weeks as the tempertures drop. That is why there is a 20% tolerance from recommended pressures so the driver does not need to constantly monitor and change tire pressures.
 

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Discussion Starter #16
If the low tire pressure text warning comes on, you press select and it is off except for an inconspicuous orange tire icon on right, Add air and the warning will go off after a couple start cycles. Just bring the pressure to the desired level of 30 psi or above and the light goes off. There is no need to bump the pressure up to a higher level to extinguish the light before starting back down. With all due respect, the 20% explanation seems very unlikely and I'd like to see the source document,
 

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Reminds me of the old Firestone/Ford Explorer thing way back when Ford told everyone to use XX Lbs which was under what Firestone recommended. Tires were blowing out on the highways as they got to hot from being under inflated. So be careful. Coming from Corvettes, Camaros, and trucks my Platinum rides like a dream at 35 lbs.
 

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@Arminius...You said it yourself. That is why @Arminius said the TPMS light comes on at 29 PSI which is 20% lower than 36 psi. Dropping your pressure to 31 psi will not change the reality that the TPMS warning will activate at 29 psi. A temperature drop of 20 degrees will activate the TPMS warning. While that orange tire icon is on, the driver will not be aware of further drop in tire pressure for any tire until action is taken to satisfy the warning.

As for source, the specific programming for GM vehicles was stated on a Saturday morning auto talk show hosted by an ASEP Instructor.
 

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There is no minimum pressure stated on the tire. The Cadillac warning light illuminates on the dash at 29 psi and below. Running 31 psi improves ride quality significantly with 18" tires. I would expect a dramatic improvement for XT5s with those low profile 20" rims. Actually, I had the idea of reducing pressures while driving my friend through the park over minor speed bumps. I thought, "Well that's the end of her being impressed by this Cad!" At 36 psi, it thumps over bumps like a truck on leaf springs. So said Consumer Reports.

You don't go by the inflation numbers molded into the tire. That is just the maximum pressure that the manufacturer warrants. Proper inflation numbers is posted on the sticker on the driver's door jamb. GM has determined that proper inflation for the XT5 is 36psi.
 
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