Quote:
Originally Posted by Fred M
Any advice on what tire pressure to use on my fifth wheeler. The sticker says maximum 80 cold but the service technician at dealer said 65. I these tires are from China Bomb Company Lionshead but I just completed a 900 mile trip with out issues. They’re rated E 10ply on 16 rims. I felt 65 was too little so I put it up to 74. I have a TPS and they did stay consistent and increased to a little over 80 or less. Temperature was typical Florida in October and the tires were less than 105•. Weight of the rig is 9700 dry and 11500 gross.
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The IDEAL way to determine the cold inflation pressure would be to first weigh your trailer when loaded for a trip. Take that weight and divide by four which will give you a general weight per tire. Then consult a Load/Inflation table for that size tire's cold inflation pressure for that tire weight.
To be safe, due to how most trailer tires unevenly loaded, add 10% (a commonly used "rule of thumb") as long as it doesn't exceed the max inflation pressure molded on the side of the tire.
Another method that's been used for years to determine a good tire pressure for one's specific use/conditions is called "the chalk test".
First start with the pressure shown on the manufacturer's "sticker" (on side of trailer or door post of motorhome).
Using a piece of blackboard chalk or sidewalk chalk, mark across the tire face and an inch or so over the shoulder onto the sidewall. Only need an inch wide chalk mark max.
Once tires are marked drive down the road a few miles and stop. Look at the remaining chalk marks.
If the chalk mark still remains on part of the tread, and doesn't end on a fairly clean line at the shoulder, the tire is overinflated for the load.
If the chalk mark is missing on the sidewall side of the shoulder edge, the tire is under-inflated.
Ideally the chalk will be erased from all of the tread face, remain on the sidewall, and a clear line of demarcation will be exactly on the edge where tread and sidewall separate.
Here's a Youtube video showing a chalk test. It's on a different type tire than used on trailers but the method is pretty much the same.
As for tire pressures rising while driving, one should disregard this when inflating tires. Tire pressures are spec'd as COLD inflation pressures which mean just when the vehicle hasn't been driven a while and are at ambient temps. It's a MINIMUM pressure for the load and trying to compensate for any temp rise will often lead to one driving with a tire underinflated for the load. Tire design engineers have taken into consideration the increase while driving and the tire will handle the increase. It's important to know that a properly inflated tire will not heat up as much as an underinflated tire so just check before driving and forget trying to compensate for temp rise. It's far more important to have enough air in the tire.
PS: a TPMS is also very helpful as it checks tire pressures continuously, not just once at the beginning of the day and can warn of any pressure loss due to puncture or failure causing pressure loss.
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