Tire Pressure Calculation for Toads

July 15, 2004, 09:10:49 pm

Hi Folks,

We coach owners have tire pressure charts and weighing procedures and there has been many discussions on this subject in our group - we all have become very savy.

However, the discussion has not come up on our towed vehicles and trailers. I would like to present a similiar approach to weighing our toads and calculating the required tire pressure.
Some vehicles have the front and rear vehicles weights placarded on the left front door. Some have this and the OEMs recommended tire pressures. Some have nothing and would need to get the front and rear weighed. Getting your vehicle or trailer weighted empty and loaded would be the most accurate approach.
2. Obtain the tire load carrying weight and tire maximum pressure off the side of the tire.
3. Divide this number by the tire pressure. e.g. 1400/44 = 31.82 #/psi
5. Now make a table with 2 columns - psi and #. e.g. 44,1400, 40, 1272.8, etc - this is not a requirement but helps to visualize and compare what is provided in the Toyo tire charts for example.
6. The front measured (preferred) or placarded weight (be sure to add weight to this for the hitch, and anything else you load in your car) is divided by 2. e.g. F2180/2 = 1090#
7. Now divide the tire carried weight by the value from step 3. e.g.
1090/31.82 = 34.26# which can be rounded up to 35# for the front tires. (I would be curious what the OEM recommends - remember the Ford Exployer problem.)

Note: When reverse engineering the Toyo tire pressure charts, one notes that for lower pressures, more weight can be carried and as the pressure is increased, the loading is reduced. Therefore, using the above linear approach, the results error on the side of safety.
Note: Front and rear placarded weights may not include a full tank of gas - I don't know.
Fred Kovol

2000 Allure 30593

Re: Tire Pressure Calculation for Toads

Reply #1 – July 19, 2004, 02:48:42 pm

Yahoo Message Number: 10707

Hi Fred,

This was one of the best posts I have read. I always wondered how to use the tire pressure and weight loading provided on the side of the tire.

After I did the calculations, I got good matches for two vehicles when comparing to the recommended tire pressures. My Toyota pickup was dead on. The Jeep was the farthest out but I have oversize tires so the pressures came out lower. For my trailer, I weighed it unloaded and came up with pressures that matched the placard. With the trailer loaded, I had it weighted and increased the the tire pressures accordingly. I intend to weigh the car I pull just before my next trip with the stuff in I normally take and set the tire pressures accordingly.
Thanks again.
Joe

2001 Magna

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