37" Tires and PSI
05-29-2016, 07:55 AM
#21
JK Super Freak
Join Date: Apr 2008
Location: Thunder Bay, Ontario
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Proper tire inflation for oversized tires must be calculated with a formula where vehicle weight and tire max capacity are taken into consideration... I your tire man doesn't know this then either educate him or move on to another tire shop.
Doing the base calculation as your starting point then back up with a chalk test is the best method. I have found the calculation to be spot on.
formula as follows:
5000lbs GVWR vehicle is 1250lbs per corner (tire)
If load range on tire says 4080lbs @65psi the math is.
4080 (lbs) a 1250 = 2830 (reduction of weight)
2830 / 4080 = 0.6936 (% reduction in weight)
65(psi) X .6936 = 45.08 (45psi)
65 - 45 = 20psi at 1250lbs load to maintain PSI ratio in balance for sidewalls for proper temperature dissipation..
So your starting point would be 20 psi for this tire.
Doing the base calculation as your starting point then back up with a chalk test is the best method. I have found the calculation to be spot on.
formula as follows:
5000lbs GVWR vehicle is 1250lbs per corner (tire)
If load range on tire says 4080lbs @65psi the math is.
4080 (lbs) a 1250 = 2830 (reduction of weight)
2830 / 4080 = 0.6936 (% reduction in weight)
65(psi) X .6936 = 45.08 (45psi)
65 - 45 = 20psi at 1250lbs load to maintain PSI ratio in balance for sidewalls for proper temperature dissipation..
So your starting point would be 20 psi for this tire.
05-29-2016, 09:09 AM
#22
JK Super Freak
That's the stupidest thing I ever heard. These guys should know what's printed in the tire is max pressure. Also if they want to go by a "number" they should be going on the tire pressure number inside the door jam. Even so that number is recommended for stock size tires. How does a tire shop not know that tire pressure should be based on both tire size and vehicle weight
05-29-2016, 10:24 AM
#23
JK Junkie
Join Date: Jan 2013
Location: CT
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That's the stupidest thing I ever heard. These guys should know what's printed in the tire is max pressure. Also if they want to go by a "number" they should be going on the tire pressure number inside the door jam. Even so that number is recommended for stock size tires. How does a tire shop not know that tire pressure should be based on both tire size and vehicle weight