"Topping Off" Tires To Correct PSI When Hot/ After Driving

[tireman9]

Here is a post from my blog in March 2013 for those that haven't scanned the various topics.

 

"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' DP or 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 but aren't parked next to a supply of high pressure air?
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"

[manholt]

I understand what your saying, but to me and where I live...it's a tad nit picky and over kill.  One thing don't fit all.  From May to November in the South and particularly in Texas, I can check mine in the morning and be 5 to 7 psi low, get on the road and check again after driving 10-15 miles and be the same amount or more over!  There are a dozen or more reasons why that is and half again as many mathematical formulas as why! 

Back in the era of non radial or steel belted tires, we did not have the Technology of TPM's and yes, I had blow outs a lot.  Since Radials and Steel belted came about, I have only had one, same reason, no TPM technology !  My opinion is that #1 thru 7 is more of a concern in cooler parts of the Country.  Just my 2 cents!

Carl

[dickandlois]

Good information regarding inflation point when the tires are on the warm side and Carl, tires do tend to run a little high pressure wise when traveling in the Southwest midday when the road surface is hot enough to fry and egg, but standing on the road surface to cook them will make one do a dance routine. LOL

An yes many of the diesel powered coaches have connivance air ports, but many of them are set at 65 psi. max. and will work fine for most tires, but come up a little short when adding air to Class A or AD coaches. A quick check with a pressure Gage will answer that question and yes the Air pressure set point for coaches with air brakes is 120 lbs. but I'm not a fan of installing a second high pressure point in the high side of the air system.

Rich.

[manholt]

I use my coach air to fill up my Jeep tires, 45 psi when towing and 35 in the woods...sometimes 25, I do carry a air tank in jeep.

[tireman9]

On 5/13/2017 at 6:56 AM, manholt said:

I understand what your saying, but to me and where I live...it's a tad nit picky and over kill.  One thing don't fit all.  From May to November in the South and particularly in Texas, I can check mine in the morning and be 5 to 7 psi low, get on the road and check again after driving 10-15 miles and be the same amount or more over!  There are a dozen or more reasons why that is and half again as many mathematical formulas as why! 

Back in the era of non radial or steel belted tires, we did not have the Technology of TPM's and yes, I had blow outs a lot.  Since Radials and Steel belted came about, I have only had one, same reason, no TPM technology !  My opinion is that #1 thru 7 is more of a concern in cooler parts of the Country.  Just my 2 cents!

Carl

Carl,   I suggest people select a CIP to be +10% of the minimum needed to support the measured load. I hope that when you discover your tires are "5 to 7 psi low"  you are still above the minimum required to support the load. IMO any level below the minimum needed to support the load is not a good thing.

 

If your minimum inflation needed was 90.  Your CIP should be 99 but you are discovering your morning inflation is 92 to 94.  All that means is you are not running a +10% margin to address side wind, cornering etc.