Same size trailer tire, different psi rating?
I've got three 20.5x8x10 tires for my trailer (used to haul atv's); one tire is suspect (would make a good spare) and the other has a different psi rating.
Of the two good tires, one tire is load range C and 50 psi rated and the other is load range C and 90 psi rated. One is new (90 psi) the other has two years use, but is in great shape. Can I run them both a 50 and 90 psi tire on the trailer problem-free, even with different psi ratings? They're different brands but are the same size and tread pattern.
Oops. The 90 psi tire is Load Range E, not load range C? Any difference?
Load range E tires are designed for a larger load capacity. They are not the same tire. I wouldn't run either with different air pressure other than what they are designed for and I would check the load capacity on the load range C tire to insure that it is actually suitable for your load requirements. See the info below.
Load Range Ply Rating
There is a common misconception that there is a specific equivalence between a tire's Load Range (or ply rating) and its inflation pressure at which it achieves its maximum load. In reality, tires of the same Load Index may require dramatically different pressures to achieve their published load ratings.
This can be seen by consulting the standards published every year by the industry standards group, the Tire and Rim Association. As an example, their 2010 Year Book shows that Load Range C tires may require 35 PSI or 55 PSI, Load Range D tires may require 50 PSI or 65 PSI, and Load Range E tires may require 65 PSI or 80 PSI to achieve their Load Index and Maximum Loads. This is also the case in the tables published by major tire makers, who do follow these TRA standards and have multiple inflation pressures for the same Load Range in the tires they sell. 
It is essential to consult the guides like those just mentioned when making tire substitutions, and to read exactly what is imprinted on the sidewalls of tires. A different size of tire with the same Load Range may require a higher inflation pressure, and may fail in use if under-inflated.
Wow. These snowmachine trailer tires suck. I blew out two of them on the Denali. 30 miles; bang! Blew out both sides. Another 40 miles; bang! Blew straight out the TOP. Made it to the Su Bridge and back and that's about it. Time to upgrade to a better trailer or somehow modify mine for bigger 13 or 14 inch rims/tires.
Get load range E tires and one of those 12v air pumps. When you get to a dirt road like Denali Hwy, let some air out of the tires. They are harder to puncture when they are softer. When you get back to pavement, pump them back up. I do this going to McCarthy and get far fewer flats.
You can run a tire at less than it's max pressure listed on the sidewall IF you are also loading it up at less than the max weight listed on the side wall. Don't believe me? Look at the owner's manual for your car/truck and see what psi it says the tires should be at. Then look at the tires and see what the max pressure is. I bet they are different.
How much air should I let out? The load range E's are rated at 90 psi and I'm loading about 1500 lbs and I believe the axle is 2200 or 2500 lbs axle.
My method is highly scientific - I guess. Actually there is a little more thought but I'm not claiming it is right, just that it works for me. It also assumes that you are not traveling at high speeds - 45 mph or so with occasional higher and lower speeds.
Look at your tires and see what the max load is for the tire at the max psi. I bet you will find it is more than the total weight of your trailer and load. Since you have two tires you are only loading them to somewhere around 1/2 their total capacity. That is a typical load for me, and I'll air down to 50 or 60 psi, which is a bit more than half the max psi. Also, make sure they don't look flat and bulge too much where they touch the ground, otherwise the sidewalls will get hot which is no good.
I air back up when getting back on the highway where I might be doing 65-70 mph, but with that load I still wouldn't go all the way to 90 psi. Probably 75-80 psi. People may claim that this is wrong, but I have experienced far fewer flats doing this then running them at the max psi.
Has issues with my tires this weekend..4 identical trailer tires and one went bald.
The pressures had dropped since my last check. 50psi load rated tires sitting at 22,33, 25 and 32...Sure doesn't take may miles to rub a new tire down. Twas the 22 BTW. --Yes..My screw up.
Should write a country song about this..........:-)
I usually run the load range c's and e's at max inflation (kinda need to on the c's) on the highway and I haven't had any problems; one flat since '05. On gravel I'll try deflating like you said NR, can't hurt. At this point I have three mounted spares.
On my trip to Eureka my starboard side tire (load range C) was hotter on the sidewall than my port side tire. Don't know why, but didn't have any flats.
Yeah, I guess I should be clear. If your load is approaching the max rating on the tire, you should be inflating them to the max psi. That's likely the case with the lower load range rated tires.