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Friday, October 26, 2012

Gauge accuracy

If you are reading this blog you know that along with others, I constantly complain that people do not always maintain their tire pressure.

One part of the process is using a sufficiently accurate gauge. I consider +/- 2 to 3 percent or +/- 1psi when measuring passenger tires to be sufficiently accurate.

Over the past few years I have checked more than 40 different gauges and have observed a 14 to 18 percent failure rate in two groups of 20 or so gauges.

I have two digital "Master " gauges as seen to the right, which read to 0.5psi increment. Both have been checked against ISO certified laboratory gauges and one reads 0.5 psi high and the other 0.5 low. I compare these gauges to each other to confirm they have not gone out of calibration before I conduct my gauge test. I figure the chance of both going out of calibration the same amount and same direction at the same time is very unlikely.

This year while at the Gypsy Journal Rally in Celina, OH, at my Tire Basics seminar, I offered to check gauges. Here are the results.

Actual         Indicated      Type Gauge             Error
82.0                81                Dial                       -1%
70.0                69                Dial                       -1%
77.0                75                Stick                     -2.6%
76.0                81                Dial                       +6.6%   Fail
77.0                92                Short Stick            +19.5%  Fail
74.5                81                Long Stick             +8.2%    Fail
79.5                78                Long Stick             -1.8%
77.5                78                Long Stick             +0.6%
68.5                72                Long Stick             +5.1%   Fail
68.0                68                Dial                         =
68.5                74                Long Stick              +8%   Fail

As you can see we observed a 45 percent failure rate with all the "fail" gauges giving a high reading which could result in the operator unknowingly operating their tires in an under-inflated state yet thinking the tires were properly inflated.  Given the general tendency for RVs to be overloaded in the first place or to be operated right at the limit of the load capability for the specified inflation this is definitely not the better way for a gauge to be wrong.

Having your own accurate "master gauge" is not unreasonable given the low cost of good quality digital gauges. You don't even need a special dual foot master gauge.

Do your own "calibration check" by using the "master single head gauge to check a front tire. Then use your "truck" dual foot gauge (as seen on the left in the top picture above ) to get a reading on the same tire to confirm the reading. If the readings match you can be confident all your readings will be sufficiently accurate when you use your dual foot gauge on the rear tires.

I would suggest you get a digital gauge and then visit the tire store from one of the major tire companies and ask if they would check your digital against their master certified gauge. You could also ask when their master was last calibrated. A competent certification includes affixing a dated calibration sticker to a master gauge. If they cant tell you when it was calibrated just say "thank you" and go to a more competent  tire dealer.

Finally don't just throw your master gauge in the bottom of your tool box. I suggest you keep it in a box of some type. Even a Tupperwear type container can protect your master gauge.

Also don't forget to always use a cap or screw on TPM sensor to keep dirt out of the valve core area of your valves. If you don't understand why you need a cap on the valve I suggest you subscribe to this blog as I will be posting a story showing exactly why you should always protect the valve core.

Edit:   I have conducted similar evaluations at FMCA Conventions in Perry, GA  in 2016 and Madison WI in 2015. At those events I tested about 50 gauges and found between 10% and 16%  were off by more than 5 psi.

Tuesday, October 16, 2012

Tire Warranties

Recently saw a post where someone stated emphatically, and incorrectly, that tire company ABC only covered their tires from date of a manufacture. So in an effort to set the record straight I decided to pull together some information. I am providing links and only a brief summary of the length of time a tire may be covered. As you see the time does vary and in many cases the clock doesn't start ticking until the date of sale BUT you will need to keep your proof or purchase.

You may recall that in my post on The Best Tire, I suggested that one measure is the warranty.

I strongly suggest you read the warranty information for your brand and type of tire. In some cases the coverage for a Light Truck Radial, LTR is different than a Truck Bus Radial, TBR. DO NOT use what I say here as the final say or as the complete statement of warranty.

In alphabetical order...

Bridgestone  TBR
Upon examination by Bridgestone, before wearing down to 2/32 inch (1.6 mm) remaining original tread depth (i.e. worn down to the top of the built-in indicators in the original tread grooves) and within six years (seven years for certain tires, see the section entitled “Enhanced Casing Limited Warranty”) from the date of tire manufacture, any eligible tire that becomes unusable for any reason (see exclusions in the section entitled What This Limited Warranty Does Not Cover”) within the manufacturer’s control will either be repaired or replaced with an equivalent new Bridgestone brand truck tire on the basis set forth in this Limited Warranty. occurs first. At that time, all warranties, expressed or implied, expire."

Bridgestone LTR
"5 years from the date of purchase—proof of purchase date required, or (b) 6 years from the date of tire manufacture without proof of purchase date"

Cooper LTR
"Worn to 2/32” (1.6mm) or more than 72 months old (based on date of purchase) whichever comes first. Proof of  purchase is required. Without proof of purchase the manufacturer date will be used to determine eligibility."

Firestone  TBR
"What This Warranty Covers And For How Long
If before wearing down to 2/32nds of an inch of original tread depth (i.e., worn down to the top of the built-in indicators in the tread grooves) or 6-years from the date of manufacture (referenced by the last three or four digits of the DOT number), whichever occurs first, an examination by Firestone shows that any tire covered by this warranty has become unusable for any reason within the manufacturer’s control, such tire will either be repaired at no charge or replaced with an equivalent new Firestone tire on the basis set forth below...."

Firestone LTR
"3 years from the date of purchase – proof of purchase date required, or (b) 4 years from the date of tire manufacture without proof of purchase date. "

Goodwear TBR RV service
"The new tire coverage of this warranty ends when the treadwear indicators become visible or five (5) years from the date of purchase, whichever occurs first. The only exception is weather cracking, which carries a seven (7) year warranty from the date of purchase or when the treadwear indicators become visible, whichever occurs first. Without proof of purchase, date of manufacture will be used to determine eligibility."

Goodyear LTR
"6 years from the date of original tire manufacture, or new tire purchase date (whichever comes first). (Without proof of  purchase, the date of manufacture will be used to determine eligibility.) "

Michelin  TBR
"MICHELIN® truck tires bearing the MICHELIN® name and complete serial and identification numbers, used in consumer service, such as on a motorhome, according to the instructions contained in this Operator’s Manual, are covered by this limited warranty against defects in workmanship and materials for the life of the original tread or five years from the date of purchase, whichever comes first"

Michelin LTR
"If there is a defect in workmanship and materials during the life of the original usable tread, or six years from date of purchase (whichever comes first), a replacement"

Toyo Truck Tires
• Within the first 2/32nds inch of tread wear
• Used in the service it was designed
• Within 66 months from the date of manufacture

Bottom Line
I provided some links. Use them and read the contract. It is your responsibility to get clarification from your tire dealer.