Why do my 31 inch tires measure 29 inches. - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 06-06-2006
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Why do my 31 inch tires measure 29 inches.

Alright so I was bored and I decided to measure how much room 33's will take up in the wheel well so after that I measured my tires from top to bottom and they are only 29inches and they are 31's so is this just because they arent fully inflated and have the trucks weight on them? This may be a stupid question.
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Old 06-06-2006
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the tire should measure 31 when its not on the wheel. when you put it on the wheel and put air in it, the side walls push out and the tire becomes shorter.
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Old 06-06-2006
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Most tires labeled as "31" measure about 30.5"~30.7" when new and installed/inflated on an average width rim. Similar discrepancies are common for other "inch" sizes like 33's and 35's.
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  #4  
Old 06-06-2006
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besides that a regular 33 only measures 32.2 i think. they're never what they've advertised at.
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  #5  
Old 06-06-2006
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You can go to summitracing and see what the actual diameter of the tire is before you put them on the truck...

Not that it really matters...

Just put 50psi in your tires and remount them....then they will be 31"...lol... DONT DO IT!!!!
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  #6  
Old 06-06-2006
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^ I run my tires at 50PSI for gas milage and then air down when i go off-roading... on a 65psi max tire whats the problem with 50?
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  #7  
Old 06-06-2006
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you will loose alot of contact area when you do that sean. but im sure you knew that.
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  #8  
Old 06-06-2006
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wow, i never run over 36 in mine. I cant imagine 50!!!!
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  #9  
Old 06-06-2006
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i was runnin 50 in mine for a while, but it got a little too stiff of a ride.
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Old 06-06-2006
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Yeah I think mine could use a little bit of air.
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  #11  
Old 06-06-2006
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Quote:
Originally Posted by Mr. Special
^ I run my tires at 50PSI for gas milage and then air down when i go off-roading... on a 65psi max tire whats the problem with 50?
Keep an eye on the center part of the tire it will start wearing quicker, best thing is to use the mfr ratings in the door panel.
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Old 06-06-2006
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anthony84_2003

I don't think you know what your talking about
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  #13  
Old 06-06-2006
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Quote:
Originally Posted by jay123
I don't think you know what your talking about

Why is that??
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Old 06-06-2006
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Quote:
Originally Posted by anthony84_2004
Keep an eye on the center part of the tire it will start wearing quicker, best thing is to use the mfr ratings in the door panel.
The MFR rating is for the stock tires, not our after market tires that require more.
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  #15  
Old 06-06-2006
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Quote:
Originally Posted by Trigger01
The MFR rating is for the stock tires, not our after market tires that require more.
It shouldnt make a difference might be a couple of psi dif, but u don't wanna run 50. I have seen it happen too many times at work, people want us to warranty tires for problems like this because they thought they were supposed to run what it says on the tire,
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  #16  
Old 06-06-2006
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Quote:
Originally Posted by zabeard
you will loose alot of contact area when you do that sean. but im sure you knew that.

what he said
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  #17  
Old 06-06-2006
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well the contact loss is obvious, but at an 11" wide tire thats not much (especially on the street). Plus the fact that 360 days of the year the roads are bone dry here, traction isnt a problem. I just run them at 50 to get the best MPG i can, since all my driving is the 240mile trip from home to school, and the occasional errand run up here.
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  #18  
Old 06-06-2006
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Quote:
Originally Posted by anthony84_2004
It shouldnt make a difference might be a couple of psi dif, but u don't wanna run 50. I have seen it happen too many times at work, people want us to warranty tires for problems like this because they thought they were supposed to run what it says on the tire,
Quote:
Originally Posted by anthony84_2004
Keep an eye on the center part of the tire it will start wearing quicker, best thing is to use the mfr ratings in the door panel.
BS...My B-pillar says 35psi, my tires say 65psi....Im runnin 285/75r16's and your telling me to run at 35psi....BS. That would be me running 30psi low...hmmm...that would be horrible on the sidewalls let alone the rim and everthing else.

I also think that if the tire place wont honor the warranty for tires that were inflated according to the tire manufacturer then I think Id get my shoes else where. Sounds like some BS scam.
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  #19  
Old 06-06-2006
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Max psi!! my tire says 60psi on it but im not gonna run that, my moms f-150 says 80 but not gonna run that either > any body else wanna back me up on this.
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  #20  
Old 06-06-2006
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Quote:
Originally Posted by anthony84_2004
Max psi!! my tire says 60psi on it but im not gonna run that, my moms f-150 says 80 but not gonna run that either > any body else wanna back me up on this.
yes maxing out your tire's PSI is retarded, but we are saying that on a Max 65psi, 50 is ok for good weather conditions. If i lived somewhere where it rained/snowed i would likely be running 45psi. And when off-roading i am down to 40 (12 at Pismo)
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  #21  
Old 06-06-2006
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Quote:
Originally Posted by anthony84_2004
Max psi!! my tire says 60psi on it but im not gonna run that, my moms f-150 says 80 but not gonna run that either > any body else wanna back me up on this.
So then what would your tire shop say if I brought in a tire that says MAX PSI 65 and I told them that I was running at my vehicles manufacturers reccomended 35psi? They would probably look at it and say WTF mate! What the duece is wrong with you!
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  #22  
Old 06-06-2006
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Quote:
Originally Posted by Mr. Special
yes maxing out your tire's PSI is retarded, but we are saying that on a Max 65psi, 50 is ok for good weather conditions. If i lived somewhere where it rained/snowed i would likely be running 45psi. And when off-roading i am down to 40 (12 at Pismo)
Summer I run 55, winter I run 45-50.
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  #23  
Old 06-06-2006
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****, my tires say 33 max... i run 28psi with equal wear
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  #24  
Old 06-06-2006
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Yeah there is a huge difference between LT radials with high ply counts and MTs and P series tires
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  #25  
Old 06-06-2006
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Quote:
Originally Posted by Kanoeking
So then what would your tire shop say if I brought in a tire that says MAX PSI 65 and I told them that I was running at my vehicles manufacturers reccomended 35psi? They would probably look at it and say WTF mate! What the duece is wrong with you!
umm...ur not running stock sizes tires (and neither is a lot of people, not isngling u out) so throw the manufactors spec out the window...BUT running them at max spec on the sidewall is silly. plus sidewall stiffness is a factor, 285s are a class d? tire (most are) and require more pressure than a class c? (normal tire)...

wanna know the best way to get good contact patch? mark 6" of ur tire on the tread with chalk and fill up to a desired PSI. then move the truck so the chalk leaves a mrk on ground and u can see how the contact patch is...adjust is nesseccary...
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