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Discussion Starter #1
I'm running 265/70/17 big horns on the XK pretty aggressive tread. My question is on the amount of tire pressure I should be running at. They were installed with about 37PSI but the tire says 60PSI. I know what pressure to run for sand and off roading mud and rocks. But what are you guys running on the street with these type tires. I know more PSI better gas mileage I think but would like some feed back on what you guys are doing. 60PSI just seems Like a lot to me any feedback would be great thanks.
 

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Sal?
That 60 psi is max mounting/operating pressure to achieve the per tire weight rating that is molded into the sidewall.
Obviously, your vehicle doesn't weigh near what the combined weight the tires can safely support so 60 psi would not be needed.
I suspect at that pressure with your weight, they would hardly conform to the terrain.
If they were on my vehicle I would be operating in the 35 to 40 psi range......much more than that and I think you would be able to call heads or tails if you ran over a dime.

My thoughts,
Rob
 

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The 60 psi is probably the max pressure for max load. I run a similar size tire and just keep it above the point where I get the low tire warning. At 60 psi the tire will be hard and will not give you as comfortable of a ride as it will at lower tire pressure. You might get a little better mpg but the trade off is a stiffer ride. You can safely run at lower pressure as long as you are not overloaded. Many tire failures occur because of running a tire at too low of pressure and it getting hot and failing. I do not think there is much danger of this at 37 to 40 psi

edit: I just saw that Robby said pretty much the same thing as I was posting. You can't get better advice than from Rob.
 

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A general rule of thumb is to check your tire pressure cold then get the tire up to operating temperature (30 minutes on the highway). Pull over and check the tire pressure it should have risen 4psi. If it has risen higher the cold pressure was too low if the pressure rise is lower than 4psi then the starting pressure was too high. It is pretty easy to do then you have the optimum pressure for the tire type/ vehicle weight. Anyway thats the way i do it when I get new tires on the car or trailer.
 

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I run my Cooper STT's at 50 PSI, and they are 10 ply with a 80 PSI max pressure. If I start to notice that the center of the tire is wearing quicker, I will back it down to 40 PSI or so but no problems yet.
 

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Discussion Starter #7
Sal,
Did you keep your TPMS after you installed the new tires?
What effect will the higher pressures have on the system?
Ya I kept it. I know 60PSI is way to much but was thinking 37PSI was to low. Probably going to try 44PSI and see how the tires are sitting at the pressure.
 

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I set my tires at 40 ( all 4) for a trip a couple years ago and the tpms lights kept blinking until i reduce pressure. Maybe because the spare was still set at 37
 

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if you wanted to get really technical about it you can do the chalk test.

find a smooth and level conrete surface (like a long driveway) and coat it with sidewalk chalk, enough so that you will see a full rotation of the tire across it. drive across it slowly then stop and get out. take a look at the pattern left on the concrete and also the chalk that's on the tire. it should be even all the way across.

if it's not then you need to correct your pressure. if the center shows more than the edges of the tread you have too much air, if the edges show more than the center of the tread you too little air.

for optimal offroad traction you should air it down to about 12lbs and continue to lower it until the tire starts to burp air from the bead, or starts to spin on the rim, then bump it up 2 lbs.
 

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Sal, where did you buy your tires ? I got mine from Discount Tire and I called them , gave them the vehicle / tire info and they gave me proper inflation.
 

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Discussion Starter #14 (Edited)
Ok I probably should of done one step at a time but oh well. I pumped up the tires to 40PSI cold and disconnected the battery and turned the key to on for five minuets as posted by Robby in another thread. I started out at 11.5PMG confirmed by mileage divided by gallons. I took my normal route to work 19 miles one way. By the time I got to work I had increased to 14.1MPG putting around there driving threw some lights and parking lots it dropped to 13.8MPG I drove home running the AC half way because of the rain pulled in my drive way at 14.0 MPG. I did previously hit the reset on the MPG with no luck after 10mn it dropped back to 12MPG and under. I replaced my plugs last week and my MPG plummeted from 15MPG to 12 and under. So I have been confused what happen. I thought maybe I messed up the gapping or had bad plugs or something. I was ready to pull all the plugs and throw them out but thought I would try this first. Hopefully this helps. Oh I am guessing that all these reading are slightly off as well because of my bigger tires and I have not had the speedometer recalibrate. I am running 3mph off what the computer thinks I am so at 60 I'm really at 63 this is consistent threw out the speed range confirmed by GPS. But even with this 11.5MPG is not cool. Hopefully this works and thoughts or ideas on the subject.

Oh tires hot measured 40.5PSI in back and 41PSI up front.
 

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I'm glad to see everyone here recommending a good tire pressure range (35-40)... on most of the truck forums im on there are way too many people that dont understand what you guys just posted about tire pressures; everyone focuses on the "Max" pressure posted on the sidewall :eek3:

I just wanted to add something to what has already been said about over-inflated tires. Not only does the ride suffer, but there are inherent safety concerns when doing this as well. Simply put, when you're over-inflated you reduce the surface area of the tire making contact with the ground (hence why some people do this for sliiiiiiightly better mpg) and also make the tire more rigid (less likely to squish/deform). The problem with this is if you are faced with the need to STOP really fast or employ an evasive maneuver; that decreased surface area also equates to increased stopping distance. Same thing when making a quick turn (like to avoid a deer or someone running a stop sign).... the lateral load that the tire will hold before sliding has been reduced.

Just some food for thought. I'm a big advocate of proper tire pressures.... keep the ride smooth and safe. I'll take ride comfort and safety anyday over saving ~1mpg with over inflation and a harsher ride. :icon_cheers:
 

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Ok I probably should of done one step at a time but oh well. I pumped up the tires to 40PSI cold and disconnected the battery and turned the key to on for five minuets as posted by Robby in another thread. I started out at 11.5PMG confirmed by mileage divided by gallons. I took my normal route to work 19 miles one way. By the time I got to work I had increased to 14.1MPG putting around there driving threw some lights and parking lots it dropped to 13.8MPG I drove home running the AC half way because of the rain pulled in my drive way at 14.0 MPG. I did previously hit the reset on the MPG with no luck after 10mn it dropped back to 12MPG and under. I replaced my plugs last week and my MPG plummeted from 15MPG to 12 and under. So I have been confused what happen. I thought maybe I messed up the gapping or had bad plugs or something. I was ready to pull all the plugs and throw them out but thought I would try this first. Hopefully this helps. Oh I am guessing that all these reading are slightly off as well because of my bigger tires and I have not had the speedometer recalibrate. I am running 3mph off what the computer thinks I am so at 60 I'm really at 63 this is consistent threw out the speed range confirmed by GPS. But even with this 11.5MPG is not cool. Hopefully this works and thoughts or ideas on the subject.

Oh tires hot measured 40.5PSI in back and 41PSI up front.
it is incorrect to say you are off by 3mph all the time... you are actually off by 5%. before you calculate your MPG you need to multiply you indicated mileage on the odometer 1.05 then devide by how many gallons it took to fill the tank.

example 1

my speedo is off by 6% but it indicates faster than my actual speed.

indicated mileage on odometer - 300
gallons at fill - 15

the simple math would show that i'm at 20 MPG

the truth is

300 * .94 = 282 true mileage
282 / 15 = 18.8 mpg

exampe #2

your jeep off by 5%

indicated mileage on odometer - 300
gallons at fill - 15

the simple math would show that you're at 20 MPG

the truth is

300 * 1.05 = 315 true mileage
315 / 15 = 21 mpg

and for what it's worth the computer that calculates MPG will only be accurate if you reset at fill up and don't touch it until you fill again. every time you reset it you ruin your average. fwiw if you reset it on the freeway at a moderate cruising speed you will see numbers approaching 20mpg... if you reset it at full throttle you will see numbers as low as 3mpg...
 

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it is incorrect to say you are off by 3mph all the time... you are actually off by 5%. before you calculate your MPG you need to multiply you indicated mileage on the odometer 1.05 then devide by how many gallons it took to fill the tank.

example 1

my speedo is off by 6% but it indicates faster than my actual speed.

indicated mileage on odometer - 300
gallons at fill - 15

the simple math would show that i'm at 20 MPG

the truth is

300 * .94 = 282 true mileage
282 / 15 = 18.8 mpg

exampe #2

your jeep off by 5%

indicated mileage on odometer - 300
gallons at fill - 15

the simple math would show that you're at 20 MPG

the truth is

300 * 1.05 = 315 true mileage
315 / 15 = 21 mpg

and for what it's worth the computer that calculates MPG will only be accurate if you reset at fill up and don't touch it until you fill again. every time you reset it you ruin your average. fwiw if you reset it on the freeway at a moderate cruising speed you will see numbers approaching 20mpg... if you reset it at full throttle you will see numbers as low as 3mpg...
Uh, yeah. I just use my gps. :)
 

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I just bought a set of Goodyear Duratracs and will have them installed tomorrow, hopefully. I have the Load range C (50 max psi on the sidewall). Underneath the truck I still have a brand new Goodyear "regular" Wrangler 265-70-17, that I belive the max psi is lower than that of the Duratracs. Is there something I need to do to or restet anything in regards to the tpms? Someone mentioned Robby spoke of this in another thread...any links? Where would you guys keep the pressure set to in the Duratracs? Is the higher pressure in them going to throw something off because the pressure in my spare is lower? (I will be buying a matching spare in a few months when I get a tire carrier)
Thanks guys
 
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