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Monday, March 4, 2013

How to "Top Off" your inflation pressure

Hopefully all the readers of this blog understand the importance of having the correct inflation pressure in ALL their tires. Be they on a 45' Class-A, your toad, a tow-dolly, regular passenger car or anything in between. The question is how do you get a few more psi of air for your tires when you check in the morning.

There are a number of different situations and I can't possibly address them all here, but I think you can review these suggestions and find a plan that will work for your situation.

I do need to separate out the few folks that discover they have a flat tire or one that has lost more than 20% of the minimum required pressure. NOTE: Tires that have lost 20% of their air are considered "flat" by the tire industry. You have a problem. Maybe a puncture or a failed valve or a tire that has been damaged. You should not drive on your flat tire. You need to change it if you have a spare and the proper tools and experience to do the job safely, or have it changed by a tire service truck and technician.

Now the rest of you who just need a few psi to get back to your goal inflation that provides the inflation needed to carry the load plus a few psi "cushion", there is a way to handle your situation. The options depend on how much air pressure you need.

If you need 80 psi or less one option is to carry a small "tankless" or "pancake" compressor rated at 100 psi and 1 or 2 Cubic Feet per minute (CFM). These are available for $20 to $60 at discount tool supply companies or auto parts stores. Some are 120V and some are 12v and can run off your battery or on-board generator. Just be sure you have enough extension cord or air host to get to all your tires.

NOTE You will have a tough time ever inflating a tire to the pressure the compressor is "rated" for so don't buy a 100 psi compressor is you need 100 psi.

If you have a larger rig like a Class-A, you probably need 90 to 120 psi and a compressor rated at 125 to 150 psi and 2 CFM or higher. If you have air brakes you may have enough on-board capacity and just need the appropriate fittings and host. There are small compressors on sale at less than $100 that claim to be capable of 125 psi.

One other option for those only a few psi low. Drive to the nearest service station at slightly reduced speed (10 mph under the speed limit would be max) and follow these instructions on how to inflate a hot tire.

1. Record your cold inflation.
2. Calculate how many psi each tire would need to reach your goal cold inflation.
3. Drive at reduced speed, hopefully no more than 10 miles, to the service station with air available. You might want to call ahead to be sure they have enough space or long enough hose to reach your rig. Not all service stations can accommodate a Class-A with a toad.
4. Measure your now warm inflation pressure
5. Add the psi needed from step #2 above plus 3psi to learn your temporary "warm" tire inflation
6. Inflate your warm tires to the temporary goal inflation calculated in step 5.
7. Confirm you have the needed inflation the next morning after the tires are at ambient temperature and adjust accordingly.

If you follow these steps I think you will find that your tires have the proper inflation or 1 or 2 psi more so you can set the inflation at your exact goal cold inflation using your digital gauge.

If you have any concerns then have a service truck come out to top off your tires.
Remember DO NOT DRIVE on any tire that has lost 20% or more of its air.


  1. If my 80PSI tires are at 78 or 79 on a below 50 degree morning when its sunny and the high temp will be in the 70's do I need to add those 1-2 PSI? On a trip in TX in November with temps in the 70's and sunny the "Hot" Tire pressure check was 85 or 86 PSI.

  2. Is 80 psi the minimum that is needed to carry your load or is that the inflation shown on the tire placard of the motorhome or is it just the inflation molded on the sidewall of the tires?
    From the "hot" pressure of 85-6 it sounds like you may not need 80 psi cold inflation to carry the motorhome load.
    I think you need to review the post of July 17 2011.


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