Michael,

I'm curious why you have ruled out the internal systems? The obvious issue with the internal system is that it costs a bit more. However, personally I think the advantages outweigh the dis-advantages.

The Smartire system monitors accurately both pressure and temperature. There is some interesting reading on their website regarding heat and equalization temperature that tires should reach when driven.

Once mounted, the monitors are done. You don't worry about sensors being stolen, being too heavy for the valve stems and actually causing failure (although alerting you at the same time), or clogging up due to use of equal or other type of balancer.

The Smartire system is highly programmable, so you can set things like the base pressure for each axle, the alarm limits (when should the alarm go off), low pressure limits etc.

The Smartire system also makes a guage that is designed to mount in your dash, which makes it look better than the big plastic monitors, which I've generally seen hooked up via velcro.

I'm really happy with my system. Now that it's installed, I don't worry about it, other than to check my pressures before driving off. I also have it setup that if my toad is with me, the system will also monitor the toad tires. I did use a 3 antenna setup, which catches all monitors, up to probably 30 feet behind the bus!

Anyway, I'm delighted with my system. I am sure the other systems work fine, but personally, I didn't want to have an external sensor. Main reasons were that the smaller ones which put less load on the valve stem couldn't be filled without removing. And the ones that were fillable through the sensor, were quite large and a bit heavy. Obviously you can support them through grommets and stuff, but I personally worry about valve stem breakage. We've had that happen to several parties on this forum. I also removed the extended stems from my inner dualies. Maybe overkill, but that was my concern.

Ray