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Discussion Starter · #1 ·
I have a technical question about tire pressure and load capacity. Is the PSI and Load rating a 1 to 1 ratio. In other words if the max load at 50 psi is 1000 lbs does it reduce to 500 lbs if psi is 25? The reason I ask is my TPMS light came on a couple days ago and when I checked my pressure they were at about 31 and the decal in the door says to run at 33. I thought it odd the TPMS would have such a narrow range. I read the tire and it has the max pressure at 51 psi with a load rating of 1168 lbs. After some quick math I calculated at 33 psi I'm running at 65% of capacity or 759 lbs per tire. Total of 3036 lb which is barely over the curb weight of 2864 lbs. Certainly not enough to carry me and the weight of the car. Not counting full tank of gas and my stuff and when I carry my family. I know there is a safety margin in load ratings but it seems odd to have it so close. I put in 45 psi until I get some clarification. Can anybody shine some light for me? Thanks. :-\ 8)
 

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If I'm not mistaken, the maximum pressure takes heat into account. As you drive, tire pressure increases due to friction. 51 is the most your tire can handle in a Vegas heatwave with you peeling out - not what the tire can be set to when cold.
 

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Discussion Starter · #3 ·
none said:
If I'm not mistaken, the maximum pressure takes heat into account. As you drive, tire pressure increases due to friction. 51 is the most your tire can handle in a Vegas heatwave with you peeling out - not what the tire can be set to when cold.
I got that part and understand the thermal expansion thing. It will vary a couple psi or so with the heat. But the psi also determines how much load (weight) you can put on the tire(s). If you read the tire it will have the max load along with the max pressure. As you reduce the psi you also reduce load capacity. Therein lies the problem. Reducing the psi to 33 from a max of 51 also reduces the load capacity from a max of 1168 lbs to 759 lbs if it is a direct 1 to 1 ratio. Running at 33 psi only has enough load capacity for the curb weight of the QB and a driver much slimmer than me.
I'll keep researching. I did talk to a tire guy and he told me the ratio is 1 to 1. When I put forth the scenario he said to run it at 33 and see what happens. What???? :eek: So have a blow out and if you don't kill yourself then put more air in. Great idea. :no: I'll post up more if I find anything. 8)
 

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Discussion Starter · #5 ·
fotomoto said:
More than I care to know:

Warm up your calculator.
??? :sick: Thanks for that :no: After I get my 13 year old to figure it out I'll let you know. :D 8)
 

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Sorry I did not answer your question... just didn't want to see you have a blowout due to over-inflation.

Other than that I am not much help. I just know that I've never had a problem with tires & loads (and I have overloaded cars many times cross country).
 

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Discussion Starter · #7 ·
My wife and I haul a lot for our business and after a couple blow outs I pay attention to the tires, capacities and pressures. Might esplain my discomfort with the oem psi. :yes: Usually you just see premature wear from over or under inflation. Probably much ado about nothing on my part. 8)
 
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