Search the Community

I attended a tire seminar in Redmond. OR this year and I remember it being stressed to get a tire pressure monitor for the coach and toad. I did so before leaving the reunion and was quite disturbed by the operation of them. These have sensors that screws on the end of the valve stems and transmit to a receiver kept in the coach. I didn't have the toad with me at the time so I only installed the sensors on the coach. Tire are Michelin 275/70R22.5 XZA2 Energy with about 7,000 miles on them and less than a year old. The first thing I noticed is that reading from all the senors on the monitor itself is reading 5 lbs too high. I verified it with two known good tire gauges. The second thing I noticed is the temperature started out normal but didn't raise much while driving. When I stopped at a rest stop in Washington then the temperature raised about 10 degrees in about five minutes. I wonder how in the world are these sensors supposed to get internal tire temperature if it is spinning around on the stem on the outside of the rim? Maybe there should be a seminar on tire monitors so it could be explained what a misfit add on are. Nothing like the tire monitors that comes with the vehicles today. Hopefully for me it's not $410.00 wasted. TireMinder monitor, charger, 10 sensors, booster and 10 extra batteries. http://www.minderresearch.com/tireminder/tireminder-tpms-with-6-sensors-and-a-signal-booster-tmg400c-6/

<p>On this and other RV forums, I see mention of tire temperature and the use of IR "guns" to keep track of tire temperature.</p> <p> </p> <p>Using hand held "guns" on conductive metal objects such as wheels, hubs, brakes and engine components is OK but using them to learn what the critical temperature is, on tires, just a waste of time. The main reason this is not a good idea is that rubber is really a good insulator so the hot zone of tires which is buried internal to the structure as the heat is generated internal to cords and at the high strain (movement) locations between the steel at the belt edges. IR guns can only measure the surface temperature of the tire so you are not getting accurate reading of the critical location.</p> <p> </p> <p>The other problem with using the guns is repeatability. Locating the precise point of measurement if you are going to do a comparison of the same tire at two different times is critical. Even the angle you hold the gun can affect the reading.</p> <p> </p> <p>There is also the problem of why heat is bad for tires. A tire does not fail because of the average temperature of the tire but because of the hottest temperature at a specific location internal to the tire structure.</p> <p> </p> <p>Here is a sample graphic from Finite Element computer model showing the hottest area in red and coolest in blue.</p> <p> </p> <p><img alt="o5rr6t.jpg" src="http://i42.tinypic.com/o5rr6t.jpg" /></p> <p> </p> <p>If you look near the shoulder (just to the left of the red zone) you see very high changes in temperature with minor changes in location of temperature measurement. Since this is a computer simulation it is basic in that it does not introduce the variations in rubber thickness ( insulation) due to sidewall decoration or tread pattern. These variations simply add to the difficulty in getting accurate measurement in real tires.</p> <p> </p> <p>When I used laboratory quality IR thermograph equipment costing tens of thousands I was able to measure significant temperature differences over distances as small as 0.10" this is smaller than to normal target area offered by the Harbor Freight IR gun. This means that unless you measure at the identical location on a tire at +/- 0.05" location you will not get repeatable temperatures.</p> <p> </p> <p>The other variable is time and distance traveled since you were driving at your controlled speed. Based on my real life experience I would suggest that you need to drop from your constant highway speed of 60mph to 0 within 20 seconds and then take the tire temperature at the same time from stop (say 20 seconds +/- 5) or the temperature reading would not be providing you the information you would need to make a valid A-B comparison for load or inflation adjustment.</p> <p>When I was working Indy Car tire tests we would shoot for collecting the 12 tread temperatures using a needle probe always in the same sequence at 3 to 5 second intervals (less than 60 seconds total with 45 seconds the goal for all 12 measurements starting from the second the car stopped moving.)</p> <p> </p> <p>You might as well just use your hand to judge if the tire is hot or really hot.</p> <p> </p> <p>I have two posts on my blog on the topic of IR guns</p> <p><a href="http://www.rvtiresafety.com/2012/05/what-do-you-think-about-temperature.html">This one</a> has additional temperature pictures.</p> <p> </p> <p><a href="http://www.rvtiresafety.com/2012/05/what-do-you-think-of-ir-guns-part-2.html">This post</a> has data showing a direct comparison between internal TPMS, IR gun and a professional racing pyrometer as used by a major tire company race tire engineer.</p> <p> </p> <p><a href="http://www.rvtiresafety.com/2011/05/tire-temperature-pressure-hot-topic.html">This post </a>covers "Gas Law" and the mathimatical relationship between temperature and pressure and has a picture of my race car.</p> <p> </p> <p> </p> <p><strong>Bottom Line</strong></p> <p>Does this mean you can't use your HF $29 IR gun? Not at all. Just keep in mind that we are talking about trying to improve the safety of your travels. I am not sure if it a good practice to use a "toy" when making safety related decisions.</p> <p> </p> <p> </p>