Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 09, 2025 ...

Using an Infrared Thermometer

September 20, 2010, 08:50:19 pm

Had my first opportunity to use the IF gun today and figured out I really had no understanding of how to use it and what the temps mean. 

First,  How to use it.

Do I point it at the sidewall or at the treads?

Next, interpreting the numbers.

Front tires were at about 127 degrees after four hours, but rear tires were around 145 degrees (both Fahrenheit).  Is this good or bad?  Why the difference?

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Re: Using an Infrared Thermometer

Reply #1 – September 20, 2010, 09:30:24 pm

George,
I found this information from a Bridgestone Commercial Tire website.  I would assume the front tires would run a little hotter than the rears because of the load per tire.  Maybe someone in the group knows for sure why the difference.


Dear Tire Doctor,

With air pressure and tire temp sensors installed in aluminum wheels, what kind of temperatures should be observed while driving in 90- to 100-degree temperatures?

What air temperature reading would be too high? I am using the Smart Tire system.

Thank you, Tom

^ back to top   Dear Tom,

Thank you for the opportunity to be of assistance.

The answer to your question depends on a number of factors, and quite frankly, there is no hard and fast rule.

There are basically three types of tire temperature measurements:

Probes inserted into the tire
Contained air temperature (which your system uses)
Tread (surface) temperature
A probe inserted into the tire - into either the belt edge or the bead area - the hottest points of the tire - is the most accurate method; however, it can only be performed under controlled conditions.

The contained air temperature method is the next most accurate, however, it is affected by the mounting system of the sensor - if the sensor is attached to the wheel, it will pick up heat from the wheel (which is picking up heat from the brake drum); and if it is attached to the tire interior, it will pick up heat from the casing.

Tread (surface) temperature is the least accurate; since measurement is normally performed by a hand-held unit, thus hampering repeatability, plus the question of where do you measure? The ribs will be cooler than the grooves, and the center will be cooler than the shoulders, etc. So, while all this has so far done little to answer your question, we hope it has shed some light as to why we are being a bit reserved in our answer.

Now, what can I say to try to address your question?

While this is not set in stone: A very general rule of thumb is that a properly inflated/loaded tire, when up to operating temperature - one hour or more of operation - will typically run about 60 degrees F hotter than the ambient temperature. Anything above 200 degrees F could lead to tire degradation and you need to investigate for a problem.

Best regards, Tire Doctor




Brad
2000 U320 4000

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Re: Using an Infrared Thermometer

Reply #2 – September 20, 2010, 09:34:22 pm

I started using the IR gun a couple of trips back. I measure the treads. I expect the two front tires to be similar, and I expect the four rear tires to be similar. If the sun is shining brightly, the bright side will be hotter. If the wind is blowing hard across the road, the downwind side will be higher because of the load transferred across the coach because of the cross wind. Given those differences, watch out for any tire that is "high temperature" compared to what you find to be normal. That would be a sign of low tire pressure relative to "normal."

My temperatures have never been that high. I generally run under 130F on the hottest tire, even in hot weather. I run 95 psi front, 85 psi rear on load range G tires on a U295 with no slides. According to a Michelin chart I downloaded recently, that will support 11,020# front, and 18,160# rear. Our measured weight after fills of water and fuel were 10,700# front and 17,400 rear.

I also check tires on the toad. For it, the front tires on the toad are usually near the temperature of the rear tires on the coach. The rear tires on the toad are closer to the temperature of the front tires on the coach. The toad presents a heavier load on the front tires, that there may be additional scrubbing because of steering forces.

Measure consistently, find what is normal, and look for abnormalities. Check and set cold pressures based on your tires, weight, and manufacturers recommendations. Use the IR gun as another tool to check for anomalies.

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Re: Using an Infrared Thermometer

Reply #3 – September 20, 2010, 09:38:59 pm

Based on Brad's post, the temperatures I measure may be relatively low because I usually check the center of the tread. Perhaps a check of the sidewalls might be a better indication of low pressure.

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Re: Using an Infrared Thermometer

Reply #4 – September 20, 2010, 10:03:54 pm

Tire temperatures also depend on how fast you were driving and how long before you took the temperature.  Best chance to get an accurate idea of highway temps is to pull into a rest stop, pick a location close to where you entered and then take the temps.  One set of readings will not necessarily tell you what you will normally expect, I would suggest keeping a log of miles driven, speed and weather conditions.  It is obvious from other replies that the temps will vary within a range and anything out out that range requires looking into.

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Other uses for an IR thermometer

Reply #5 – September 20, 2010, 11:40:31 pm

I find the IR thermometer great for checking trailer wheel hub temps to make sure wheel bearings and trailer brakes are working correctly (you can burn your hand if they are running hot).  I also sometimes use it to get an idea of outside temps when it is cold since my indoor/outdoor thermometer broke.

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Re: Using an Infrared Thermometer

Reply #6 – September 21, 2010, 06:47:10 am

I measure temp on the side right at the base of the tread consistently. The sun side can easily run 20 degrees hotter.  Again, consistency is the key.  If your rear tires on both sides continue to run this much hotter, suspect under-inflation for the load those tires are carrying.

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