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Sunday, November 24, 2013

Save money at the fuel pump

Tire Pressure.
 Ya, we tire engineers are like a broken record when it comes to tire pressure.Tire Pressure Monitor System. If you don't have a TPMS then we tell you to check your pressure every morning you are traveling.
We tell you you need to monitor it all the time by using a
We also want you to get your RV weighed then to consult some confusing tables to learn how much pressure is needed for your motorhome.
To make things worse we expect you to have an accurate gauge but then we don't tell you how to check your gauge to be sure it is accurate, or even why its important to have an accurate gauge.

Is that what's bothering you bunkie??

Well this post is going to help answer your questions, solve the problem of how to be sure your gauge is sufficiently accurate and to top it off tell you that its possible that many of you will end up saving more money than the "fix" costs.

To start off lets take a look at accuracy of gauges many RV owners are using today.
In a previous post I showed the results of a series of gauge tests conducted at an RV Rally Sept 2012 on 11 gauges, we saw that there was a 45% failure rate. This was higher than the failure rate seen on a similar sample from 2011 when 11% failed. This year my test sample was 24 gauges and we had a 12.5% failure rate. Failure is defined as more than 5% off when compared to a certified digital gauge that reads to the nearest 0.5 psi. For all these tests the test pressure was between 77 and 95 psi.

According to sources there is a range of fuel economy savings possible from keeping your tires properly inflated because tires are only one of the contributors to fuel consumption. Also different tires have different affects on fuel economy based on a number of variables. Some of these include different rubber compounds, basic tire construction features, tread design and tread depth. Without getting technical we learn that the impact of lower inflation on mpg ranges from  0.05% to 0.3% per psi. Now you may say this isn't much but lets look at how this hits you in your pocketbook

Assume fuel is $4.00 a gal when you do a fill-up. Lets look at the range of savings at -2psi and -10psi from our goal of 100psi (our cold inflation to carry the load with a built in +5psi safety factor). With a 30 gal fill-up the range of "extra cost" for being low on inflation is between $0.12 to $3.60. If you do a 70 gal fill-up running low on air is costing you an extra $0.28 to $8.40 for that fill-up. Remember this is from just being 10 psi low on your tires. A number of the gauges we tested had the owners running from 9 to 18 psi low so they were wasting some real cash.

With this much potential loss from your pocket each fill-up you certainly do not want your pressure gauge to be giving you wrong readings. Having an accurate gauge is easy and based on the above calculations you might save enough in a few tanks of fuel to pay for what you need.

A quick search for "Digital tire gauges" at Amazon. shows you could spend well over $300 for a digital gauge but that really isn't necessary. You can get a good digital gauge for less than $10. This becomes your "Master Gauge" Then you get a second gauge for every day use. When the gauges are new you compare them and they should give the same reading. If you notice a sudden change in tire inflation pressure you can dig out your master gauge and confirm. You should also do a comparison at least a few times a year. The chances of both gauges going bad the same amount at the same time is vanishingly small.

Finally don't just throw your master gauge in the bottom of your tool box. I suggest you keep it in a safe place that offers some type for protection.


  1. Roger,
    So you suggest to buy two of the same type gauge? How would one know if both are reading low? Will you be at the FMCA Indio rally and testing gauges?

    1. While it is possible to get two bad gauges it is unlikely. BUT simply comparing the reading to your new digital gauges against a fellow camper's gauge reading or check with a tire dealer. Again the chance of three gauges all being off the exact same amount is very unlikely. If buying two gauges be sure you can get to both dual tires. FYI Amazon has digitals at less than $7 right now.

  2. Roger,
    I have a question about my tag axle tire pressure. Should I run the same PSI in the tag tires as I do in the drive axle. The tag is rated at 2,500 lbs, the drive is rated at 11,000 lbs. When I had the MH weighed the tag weight was 2350 lbs.

    1. The tires on the tag are not the same as on your dual tire drive axle. I would select the tire pressure appropriate to the higher side load on the TAG.
      Maybe you could send me your exact weights I can work through the suggested inflation. Check my email under the video on the right.


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