Need 620 long bed loaded and unloaded tire pressure for

[620crumudgeon]

I've done the Beebani disk brake conversion and have 195/65-R15 tires. I'm trying to calculate the tire inflation pressure for my 1976 620 long bed using front and rear axle weights. I would like to find a calculator for the tire pressure, a tire pressure chart that shows inflation pressure for a 750 pound load and up on a tire, a formula to calculate the inflation pressure, or the Ratsun forum members' knowledge.

 

The 1977 service manual says the payload is 1100#. The metal plate on the driver's door frame says  loaded front GVWR is 1690 pounds (42%) and the rear loaded GVWR is 2325 (58%) pounds for a total GVWR of 4015 pounds. Datsuntrucks.com says the unloaded vehicle weight is 2286 pounds (short bed?) and the payload is 1441 pounds resulting in a GVWR of 3727 pounds. There are discrepancies.

 

I'm assuming the long bed weighs about 2500 pounds with a full tank of gas and driver with weight distribution of 55% (1500 #) front and 45% (1000 #) rear. The tire pressure, from the service manual, for the OEM 6.00-14 6PRLT (6 ply light truck) tires is 21 psi front and 25 psi rear unloaded and 21 psi front and 42 psi rear loaded. The load rating for the 195/65-R15 tires on the truck for a given inflation pressure is:

 

26 psi --> 1035 # max load

29 psi --> 1130 # max load

32 psi --> 1222 # max load

35 psi --> 1313 # max load

38 psi --> 1403 # max load 

 

Assuming an occasional 150# passenger and a 400# load, what would the F&R tire pressure be? What would the tire pressure be for a max GVWR 620?

 

Thanks,

John

 

[datzenmike]

Read what the max and min pressures on the sidewall of your tire says and use them.  NEVER go lower than the min pressure. A rule of thumb is... too high a pressure is better than too low. Higher pressures give better rolling resistance and better MPG but an increasingly harsher ride. Low tire pressure or heavy loads forces the tire to bulge and appear low on air. When driving, this constant flexing generates heat and heat is what destroys a tire. Speed and distance are factors. Tires can produce less and dissipate more heat if driving at slower speeds. If on the highway and carrying a heavier load than normal always get out and feel them for heat. Too low a pressure for the load also causes instability and wandering.

 

I had 207/60R15 on my 620 and ran 32 PSI front and back. If I had to carry 500 pounds I would air up the rears to 35. Short trips of only a couple of miles I didn't bother, but if any distance on the highways at highway speeds I would air them up and stop and feel them after a few miles. Warm is OK but hot needs more air to take the bulge out of them. Always carry a gauge, don't guess or set visually on a radial tire and air them back down when done. If your tires remain neutral temperature you're ok.

 

My 620 was a long wheelbase king cab GVW 2750 and with maximum load of 1,100 pounds this is under 3,900 pounds.