Are you sure it's the wheels leaking air?  Have you put the entire wheel into a water bath to determine where the air is leaking from?

I don't like putting "Slime" into your tires or other type of sealant.  It's messy when it is time to change the tire.  Sounds like your tire rims are porous.  I would demount the tires and seal the wheels with a coat of polyurathane.

You can always put an innertube in your tires.  Worked for me!

Marla

Just how much and how fast are you losing air?

Do you have metal valve stems?

If its alot and quickly...fill the tire to operational numbers and drop the tire in a horse tank and look for bubbles...

If its a little and over a long time...you may be the victim of temperature swings...

Finally the last suggestion of corrosion can be ruled out as described by previous poster...

How old are they and what make and size are they? Valve stems or valve cores leaking?

My Michelins LTX-M/S's were mounted on my truck last fall, checked them yesterday, still 80psi. Set of Uniroyal Laredo AWP's mounted on a stock trailer September of 2006, inflated to 65psi, they're now about 62psi with no adjustments since mounting. G614's mounted in December of 2007, 110psi, they're still 110 psi. These were checked at about 05:30 in the morning, outside temp 65 degrees and the sun wasn't up quite yet.

Take off the valve stem caps, apply soapy water to the valve stems and cores and around the tire bead areas. Any bubbles will indicate a loss of air pressure.

Are you loosing equal amounts of pressure in every tire? It's unusual that all your tires would have the same malady. If they are all involved, a total immersion in a tank will quickly reveal the source of the problem, which maybe common to all.

Sealants can be applied to the inner surfaces of wheels. Generally, it's not advisable to put a tube inside a radial tubeless tire unless it's your last resort to save the tire. It will add to a larger amount of heat build up and may lead to a possible failure. If you do have to attempt this fix, use that tire for a spare.

Gard

As another posters said, do not put tubes in them except as a last measure and then do it only temporarlily. Heat is the enemy of all tires. The reason radila last longer than bias is because they have less rolling resistance, thus less friction and heat. If you put a tube in one, you are just asing for heat build up and there will be a problem.

 (quote) Do remember there are varying degrees of quality in aluminum wheels. I've seen some cheap imports that seeped air through a semi-porous casting. So don't rule out the dunk tank idea. Holding the inflated tire/wheel underwater can be entertaining though. Been there, done that.

Yes siree buddy! A helmet with a functioning face shield would be advisable.... Just in case it were to slip out of your hands and defy gravity!!

We tried all the fixes listed above. nothing worked.   We regularly haul 15 to 18 thousand pounds of cattle to the sale barn, which is over 100 miles away.  The manager of the local tire shop recommended the tubes, and in the three years since we have never had a problem with overheating tires.  We have also not had to stop and air  tires on a trailer loaded with cattle!

Marla

I am out on the nitrogen... http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=9545&start=1 , but...I don't have a trailer on the place that doesn't lose 3-4 pounds per month from the tire when not being used. For those of you that dont check your pressures regularly, check your spares. That can be entertaining when you realize how low some of them will be.

I would fill the tire with Nitrogen instead of air. It will keep the tires cooler and the Nitrogen has a larger molecule which will assist huge in keeping the tire inflated. I would also make sure there is no corrosion around the rim where the tire meets the rim. Sometimes the tire doesn't seat completely. Also check to make sure there are no obvious cracks or fractures in the rim or that it is not warped. I don't know if all your tires are leaking, but if it is 1 or 2, maybe you just have a bad tire. If all else fails, you could always by new. I use a place online called trailer parts supply. They carry several Tire and Rim Assemblies, and they are awesome for working with you on price when you buy more than one of something. I buy all my trailer parts there.

I would not suggest adding a sealant to your tires. That just covers up the problem and it really stinks when you have to clean that stuff out of the tire and rim, when it ends up not working.

Rick