SmarTire®
Tire Pressure Monitoring System

Overview of Tire Pressures

Having the proper air pressure in your RV's tires is critical. Tire pressures are as important to your RV as blood pressure is to your heart. The air in a tire is what enables it to carry a given amount of load. As that load goes up, so does the air pressure required to carry it. Every tire has a contact patch, a small number of square inches where the tire actually meets the road. If you divide the weight that the tire needs to carry by the tire patch area you will get the amount of air pressure required to carry that load. If you increase the load, you need to either increase the air pressure in that tire or go to a larger tire with a greater contact area. Every tire has a given limit to how much air it can contain. This is referred to as the maximum inflation level. Different tires come in different degrees of load capacity, even within the same size. They are described by load ratings, which roughly equate to the ply ratings of years past. For example, a load range H tire can carry more weight than a load range G tire.

It's important to refer to the tire manufacturer's tire pressure tables when setting tire pressures for your tires. First, weigh your RV to determine how much weight is being carried at each corner, then check the inflation table for your particular tire to determine how much air you need to run in that tire to keep it properly inflated. Detailed instructions on tire inflation and weighing procedures are better described in the RV Tech Library and I highly recommend you look over that information.

If a tire is run at a lower pressure than is designed to safely carry that weight the tire will be overworked. It will overheat and most generally you will develop a sidewall failure. A blowout on the steer axle can be deadly, or at the least give you a pretty wild ride, so it's important to keep your tire pressures at or above the required levels and check them often. This is a great reason to have a tire pressure monitoring system.

Tire Pressure Monitoring Systems

Tire pressure monitoring systems (TPMS) are gradually becoming mandated at various levels by the DOT. They not only offer you the advantage of not having to physically check each tire's pressure every day but they also give you instantaneous warning should you pick up a nail or develop any kind of leak while driving. The idea is to warn you before things get out of hand so that you have time to pull over and rectify the situation before it gets costly or dangerous.

With the extensive use of tow vehicles behind motorhomes, a TPMS gives you the additional benefit of being able to monitor your toad's tires from the RV while driving. If something were to happen on your toad while you were towing chances are you would not see it until it was too late and the damage was done. A TPMS will prevent that from happening.

Tire pressure monitoring systems come in two flavors - internal sensors and external sensors. External sensor replace the valve caps on your tire's valve stems. They require depressing the valve stem in order to read the tire pressure. They incorporate small radio transmitters that communicate to the RV's display unit and receiver. Internal sensors offer several advantages. For one, they can't be stolen. Secondly, they do not require depressing the valve stems, which can be an issue on inner duals sometimes. Thirdly, they can also measure temperature as well as pressure.

As a tire deflates, its rolling resistance increases and its operating temperature goes up. As it's temperature increases, the air inside the tire expands so the tire appears to be operating at correct inflation. When measured using a non-temperature compensated gauge, a tire can be 30% under-inflated and still appear to be normal. The SmartTire system measures a tire's temperature in addition to pressure in order to do a temperature compensation calculation. The system provides deviation numbers in its on-demand tire information and first level alert showing exactly how many PSI under or over inflated a tire is at its operating temperature. The following chart illustrates what kind of pressures you can expect as your tire temperatures increase. This chart doesn't go up high enough to reflect actual on-the-road temps but you can see the general idea of where this is going and how temperature will affect your true tire pressure needs. For even more information on how SmarTire accompishes this temperature compensation check out This Link.

I personally feel that SmarTire is the best system available on the market. My initial foray into a TPMS was with Tire Sentry back on my 2003 Suncruiser. When we got our 2004 Allegro Bus, I tried the Doran Pressure Pro system, which I played with briefly and got rid of after having too many reliability issues. I then selected the SmarTire system, which I ordered from Bob Dickman Tires in Junction City, Oregon. They were very knowledgeable and helpful. I installed this system on my 2004 Allegro Bus 40DP and was very happy with it's performance and reliability so when I upgraded to the 2007 42QRP I immediately ordered another system from them. Following is the installation procedure on my 2004 Allegro Bus, which is pretty much identical to my 2007.

Feel free to download or save any of this text or images if you want. If you repost any or part of it to any other website just be sure you don't change any of my wording and please mention where it came from.

Mark Quasius - "Cruzer"

The Installation

After previously having the Doran Pressure Pro and Tire Sentry tire pressure monitoring systems on my RVs, I recently completed a conversion to the SmarTire system. Whereas Tire Sentry and Pressure Pro use external sensors, the SmarTire system uses internal sensors. Not only are these sensors theft proof, but they also afford the ability to report tire temperature as well as pressure. Internal sensors also made it easier to add air to the tires because I was able to return to the small valve caps that the chassis originally came with. So, after having some level of success with the Tire Sentry I decided to make the move to the SmarTire system.

The SmarTire system is a bit more pricey and it does require professional help in order to dismount and remount the tires when installing the sensors, but otherwise is a very clean install. The basic system consists of 6 sensors for every wheel on the RV, a receiver unit, a remote display, and a three antenna arrangement.

In addition, I also ordered a complete set for the Wrangler which consisted of 4 sensors, a receiver unit, and a remote display.

The toad kit did not require an external antenna because the receiver was easily capable of picking up the signals from the Jeep. Now, I didn't have to get this entire setup. I could have just ordered the 4 sensors if I wanted to monitor the Jeep while towing. However, when using my Tire Sentry I did have a blowout on the Grand Cherokee that destroyed the tire. Unfortunately, while driving the toad I was 15 miles away from the RV so I didn't know I had cut the tire on a rock and has a leaking tire until it was too late and the tire was destroyed. I also had to remember to remove them from the Wrangler when off-roading or else risk knocking them off on rocks.

The hardest part was removing the tires and taking them to a truck tire center to install the sensors. The Bus did look strange sitting in my driveway on jack stands without any wheels during that day. The sensors attach to a worm drive hose clamp which goes around the wheel rim. Once the tires are off it's a simple install.

I ordered the SmarTire system from Bob Dickman Tire Center in Junction City, Oregon. They are located right across the street from Country Coach in Junction City and are the largest distributor of SmarTire systems and I received excellent service from them. I was able to talk to 3 different persons on 3 separate occasions and everyone was very knowledgeable and more than willing to assist. Country Coach, as well as a number of other high end brands use the SmarTire system as OEM equipment.

I found that the SmarTire setup was really a class act. In order to conserve battery life, the sensors only report data when the tire is turning. These new generation II sensors are purported to last 7 years until needing service. At that time, I'm assuming that you have to send them in for exchange or whatever, similar to the Doran sensors. The only drawback to that is that you have to pay to have the tires dismounted/mounted. Although, with a 6 year life expectancy on RV tires, maybe that could coincide with a tire replacement anyway. The new sensors will report a seriously low tire as soon as the ignition is turned on but normal reading occur within a few revolutions of the wheel. I found the construction quality to be far superior to that of the Doran or Tire Sentry sensors.

The temperature feature was also helpful. You may have equal tire pressures but you might find that one wheel is running hot. This could happen from a number of conditions. You may have a brake dragging, a wheel bearing starting to go, or you might just be a bit overloaded on that one wheel. The system will warn if the temperatures get too high in the same manner as it warns for low tire pressures. Another advantage of monitoring temperature is that the pressure warnings are temperature compensated. This means it won't give false alerts based upon temperature changes. If you want to know more about this check out the Dickman Tire site, who has more information on this.

The SmarTire system has the ability to display this information in a number of ways. The most popular is the remote display adapter but if you have a Silverleaf VMS system, or a TripTek in-dash computer you can utilize them to display the tire pressure information. This has the benefit of eliminating an additional display but it also ties your tire pressure information to these monitors. If you decide to go this way, Dickman Tires can provide a "JIB", which is a J1709 Interface Breakout box to interface your SmarTire reciever with your computer system. Country Coach and Marathon Coach choose to utilize the Sliverleaf VMS system in their coachges. It's also possible to interface the SmarTire system with the VMS/PC laptop based software with the proper interface. Again, Dickman Tires has all of the details on that.

I chose to install this remote display unit in the Wrangler. You can use it to program your tire pressure as well as temperature thresholds and also handle any tire rotations. By far this is the most popular adapter. For the RV, I chose to use the new round in-dash gauge display unit.

The round Inspuire guage is back lit with a white light that is controlled by the dash lights dimming circuit. It will flash amber and an alert will sound in the event of a pressure or temperature alert. A separate keypad is included that can be placed anywher in the coach where it's easy to access. The buttons on this keypad are also illuminated by the dash lighting and control the various functions of the SmarTire system.

The gauge fits into a standard 2" gauge hole and was an excellent match with the Freightliner white faced gages with chrome bezels.

I placed the separate switch pod on the side console within easy reach and view while driving.

Getting signals to the receiver was easy. It came with three coax cables and antennae - one 20' antenna cable went near the front axle while a 40' antenna assembly went just ahead of the rear axle. Yet a third 60' antenna setup went to the rear bumper area to pick up the toad. This 3 antenna system gave perfect reception with good strong signals that never once blinked.

I do have the Silverleaf System on my 2007 Allegro Bus and I did have the Triptek on my 2004 Allegro Bus. However, chose the 2" round gauge because it looked the most OEM. I also prefer to have separate devices display separate information. That way I don't have to toggle through menus to access what I'm looking for or have my rear vision monitor all junked up with data overlaid on the screen. But, that's just my personal preference. Your's may vary. Besides, I already had a 2" hole in the dash of my 2004 Bus where the Tire Sentry used to be so it had to be filled with something and a guy only needs so many clocks.

The helpful folks at Dickman Tire preprogrammed everything to my exact tire pressures for both the Jeep and the Allegro Bus. When the package arrived (same day shipping - even with the programming) I immediately wired up the receiver and ran the antenna cables. The next day I had the tires mounted and by the time I left the driveway I was reading pressures and temps.

The display will alternate between the RV and toad. Under normal conditions it'll just sit there quietly until either a low pressure or high temperature warning is given. If you want, you can cycle through the tires displaying each wheel's pressure or temperature. You can also cycle through in a pressure differential mode. This mode will tell you how much that tire's air pressure varies from the normal pressure and will read in plus or minus PSI. The same holds true for the Jeep. When not towing, the RV's system will ignore the fact that the toad is not there. As soon as it's in range it'll automatically add it to the system. You can have two toads programmed if you want and it'll replace the one with the other should you switch toads. All with no operator intervention. All in all I really like this system and am very glad that I made the switch.

For more information you can check out the SmarTire or Bob Dickman Tires website (he has lots of installation "PDF" docs you can print or download). Also, Camping World is now selling and installing the SmarTire system, although their expertise will vary from store to store. It's not a hard installation so any RV dealer should be able to handle it. In that event, simply call Dickman Tires, order your SmarTire system, and have a local dealer install it.

Summary

This system does an awesome job of monitoring tires on both the RV and the toad. It has the benefit of temperature compensated readings as well as the ability to monitor the toad's tire pressures when driving away from the RV. The system intergrates well into the dash and is an attractive display rather than an add-on item plugged into yet another power receptacle. It's very popular with Country Coach as an OEM item as well as many other high end coach builders. For complete information, including installation and owners manuals be sure to check out the RV Tech Library for more details.

This review written 4/2/07