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Tuesday, April 30, 2013

Gauge Accuracy - I was wrong.

Previously in my post on gauge accuracy I suggested that you could get your pressure gauge checked by visiting a tire store from a tire manufacturer or very large dealer. Well after doing more investigations it turns out I was expecting more from dealers than they actually provide.

Tire dealers are primarily in the business of selling tires and vehicle service. They use gauges every day to inflate hundreds of tires but they do not have ISO calibrated gauges as this would be very expensive and the difference between the gauges they use every day and a calibrated gauge might be measurable but is not really meaningful.

Now this doesn't mean you should not make an effort to confirm your gauge is reasonable accurate the question is "How accurate is accurate enough"? If your gauge is +/- five percent of the inflation pressure you're measuring then you are probably okay, especially if you're running at least five percent above the minimum inflation needed to carry your load as measured in individual tire load scales.

Still, I would suggest you get a digital gauge for your personal "master gauge." They cost as less than $15. Then use that master gauge to check your everyday gauge. Keep your master packed away and not rattling around the bottom of your tool box under the hammer and wrenches where it will get dirty and damaged.

If you check a front tire with the digital master and then your every day gauge and note the difference then when you compare them again maybe a month later you should see the same difference. It is very unlikely for both gauges to go bad the same amount in the same direction at the same time.

If both gauges are within two to three percent when you first get the new digital master you are probably okay. If there is more than a three percent difference then I would check both against some other gauge to learn which is wrong.

Hope this clears things up and sorry if I mislead anyone.

Tuesday, April 23, 2013

Have you read a tire lately? Tire Marking

Have you read the information provided to you by the tire manufacturer? If you have, did you bother to record the important numbers in your log book so you only need to do this job once in the life of a tire?

There is a lot of information molded into the sidewall of your tires. Most of this is required by law. Most of this is important for you to know so you can look up the correct inflation for your tires or if buying new tires be sure to get replacements that can carry at least the same as the original tires.
Here is some information from one tire.

First the SIZE
This tire is a "Passenger" type as it starts with the letter "P" other types might be "LT" for Light Truck, or "ST" for Special Trailer. Small tires intended for passenger cars migth not have the "P" if made to European specs. Large tires like 19.5 or 22.5 rim dia have no letter and are "TBR" of Truck Bus radials and are found on Class-A RV. The "114S" is the Service Description which is a Load Index (from a published table but using the actual Max Load is better). The "S" is the Speed Rating or max operating speed. Like the Red Line on your engine. Not all tires have this description.

The DOT Serial
This has important information used in determining the tire age. Other information such as the location of the tire plant that made the tire is part of this code ( first two characters  8X in this example). If there is a recall, this code is used to identify which tires are covered by the recall. NOTE that the last portion, the 4 digit date code, 3908 in this example is only molded on one side of most tires. Every tire sold for use on the highway in the USA must have a full DOT serial including the date code molded on at least one side. This tire was made the 39th week of 2008.

The Load & Inflation information
This is the maximum load capacity for the tire when the cold inflation is set to this pressure. In this example (2601 lbs) when the inflation is set to( 44 psi max press) when the tire is at ambient temperature. NOTE for LT and TBR type tires there is a second lower load limit for dual application (tires side by side on the same axle as on the rears). If you have two axles and ST type tires I personally suggest you not exceed the "dual" tire load as you need a safety factor in your tire loading due to extreme side loading unique to tandem axle trailers.

Tire Materials
This is really just FYI and is more like truth in advertising to let you know the materials used in the sidewall and center of the tread of your tires. In this case there are two ply of Polyester in the sidewall and in the tread there are two ply of polyester + 2 ply of Steel + 1 ply of Nylon. Most TBR tires will only have 1 ply of steel in the sidewall.

Safety Warning
This is for the person mounting and inflating the tires for the first time. Do not confuse the inflation number here ( 40 psi) with the inflation number associated with the load (44 psi). This is the max inflation to seat the bead. If you have ever watched a tire being inflated it is the "Pop" or "Bang" first heard. If the tire doesn't seat by this inflation then it should be deflated, re-lubed, re-centered and re-inflated. People can die if they ignore this warning.

Bottom line
If you get new tires and they match the Size and Load & Inflation information you are good to go. If ANY of these numbers are different you need to be sure you completely understand why and that you are not getting a tire with lower load capacity.




Thursday, April 11, 2013

Morning Vibration. Why do you have it? Why does it go away? How do you minimize it?

So you get up and after a nice hot cup of coffee you finish packing the motorhome. You have enjoyed the last couple of weeks at a real nice campground and were glad you had that nice concrete pad to park on but now it's time to hit the road.
You say your goodbyes and then pull out. The interstate is only a couple miles down the road, so soon you are on that nice smooth ribbon of asphalt. Then it hits you. Just as it does almost every time you start out on a days drive you feel that vibration.

What is wrong with the RV? You had the tire tread trued just a month ago and an alignment a month before that and you even had the tire tread trued the month before that, but you still get that d....m vibration almost every time you leave a campground. There must be something wrong with the new tires as you didn't have the vibration on the old worn out tires last year.
The biggest problem is that after driving for 30 minutes to an hour the vibration goes away so when you go the the RV center or tire shop you can't show the service manager the problem.

Does this sound like you?   Do you have a "ghost" vibration that is real bothersome but almost always bothers you in the mornings. It that what's troubling you bunky?
Well I have news for you, there is a good chance what you are experiencing is tire "flatspotting".

When rubber,  Nylon or Polyester are warm and you place them under load or deform them as happens when you park and the portion of the tire in contact with the ground is flat not round, these materials take a "set" and when they cool down and the longer they are deformed the firmer that "set" becomes. Later when you start up it takes a combination of heat and flexing to work the "set" out of the tire. New tires with heavier tread rubber will need more exercising that a worn out tire. High Performance tires with Nylon cap ply will need more exercising than a tire with no Nylon in the tread area. Passenger or LT tires with Polyester body ply will need a bit more flexing that a steel body tire does. Other major contributors to the level of flatspotting the the length of time the vehicle is parked, the temperature of the tire when parked and the amount of deflection the tire takes when loaded.

There really are very few things you can do to completely eliminate this flatspotting but I can provide some suggestions on how to decrease it.

1. Ensure you have at least the minimum inflation needed to carry the load. More deflection due to overload will generate more heat. More heat means the "set" will be more pronounced with the warmer materials.

2. Give your tires as much time as possible to cool off before parking. Coolers tires take less of a "set" than warn tires. Maybe move to your campsite but park a couple feet forward of your final spot then after a couple hours move back that last couple of feet.

3. Decrease the load on the tires. Get rid of the extra load of that bowling ball collection you are hauling around in the basement storage. Less load means less deflection which means less flatspoting.

4. If you are going to park for an extended time you can inflate your tires to the max inflation they are rated for. More inflation means less deflection....see #1 above. This is something I do when I am parking for the Winter.

5. Consider running 5 or 10 or maybe even 15% more inflation than the minimum needed to carry the load but do not exceed the tire or wheel max cold inflation.

6. Cover your tires with a White tire cover. This will help keep them from heating up while parked.

7. If you have an older coach and it is on it's 2nd or 3rd set of tires you should probably consider a new set of shocks. They will help control the vibration due to flatspotting.