Weird Marathon Picture - what happened?

[Rocinante]

Be that as it may, the previous Michelin tire is rated at 108T and the new Defender is rated at 109T. Don't know what that means for "durability", but it does mean the new Michelin Defender tire is rated to carry slightly more weight. Right?

[CapriRacer]

Originally Posted by Rocinante

Be that as it may, the previous Michelin tire is rated at 108T and the new Defender is rated at 109T. Don't know what that means for "durability", but it does mean the new Michelin Defender tire is rated to carry slightly more weight. Right?

Sort of.

What's being encountered here is the difference between the American way of calculating load carrying capacity (ala The Tire and Rim Association - TRA) versus the European way (ala European Tyre and Rim Technical Organization - ETRTO). Not only is there a difference because of the measuring systems (English vs Metric), but there is a slight difference in the formula. For practical purposes, it isn't a difference at all. In other words, that alone does NOT have an effect on durability as the tire design would be the same in both cases.

[xrvr]

But the weight safety margin would be greater.

[SSquared]

Originally Posted by CapriRacer

Sort of.

What's being encountered here is the difference between the American way of calculating load carrying capacity (ala The Tire and Rim Association - TRA) versus the European way (ala European Tyre and Rim Technical Organization - ETRTO). Not only is there a difference because of the measuring systems (English vs Metric), but there is a slight difference in the formula. For practical purposes, it isn't a difference at all. In other words, that alone does NOT have an effect on durability as the tire design would be the same in both cases.

Interesting! So you are saying that for a given tire design, if the manufacturer labels it with a "P" they have to use the TRA formula and units, and if they label it without a "P" (or LT or ST) they have to use the ETRTO formula and units. AND they can come up with a different load rating, higher for an ETRTO tire?

[TheDuke]

Luckily, looks like that one is still "unexploded!" I'll tell you what happened....all ST tires are made in Asia now days. They are all JUNK! The best money that you will ever spend, if you are planning on towing, will be to replace all your ST tires with 16" LT tires, preferably USA made. Then if you run the max pressure listed on the sidewall, you will never have to worry about your trailer tires again. It's just that simple! Everyone tries to explain this with some "educated guess." Really, it's just not that hard. Look around at all the other "great" products we get from China..... lol.

[CapriRacer]

Originally Posted by avionstream

But the weight safety margin would be greater.

Not exactly. Remember the construction of the tire is exactly the same - so when the tire is applied to a vehicle, it doesn't matter what which standard was applied - the tire behaves the same.

Put a different way, when a tire is properly designed, the tire engineer can apply either standard and label the tire accordingly. It will pass the tests regardless.

Originally Posted by SSquared

Interesting! So you are saying that for a given tire design, if the manufacturer labels it with a "P" they have to use the TRA formula and units, and if they label it without a "P" (or LT or ST) they have to use the ETRTO formula and units. AND they can come up with a different load rating, higher for an ETRTO tire?

Not exactly. LT and ST standards are TRA. ETRTO uses a "C" (for Commercial) after the numbers in place of LT and doesn't have an equivalent of an "ST" designation. Plus there is another standardizing organization JATMA (Japanese Automobile Tire Manufacturers Association) that also doesn't use the letters for passenger car type tires (and they have a third different formula).

[CapriRacer]

Woopsy! Posted in the wrong thread.

[Rich Jenkins]

Originally Posted by Andrew T

"Andy - For the avoidance of doubt as they say, you are talking about this tire?

http://www.tirerack.com/tires/tires....TR5LTXMS2OWLXL"


Sorry I did not get back to this thread sooner. To answer your question, this is the tire we use on most Airstreams.

The Defender looks to be a slightly different tire, it weighs 2 pounds more on its spec. This can mean it is even more durable as there is more structure in it. Also though there is more unsprung weight though not very much.

Once they are available I will put a set on a high mileage unit to test but in the mean time it might be better to stay with the one that is proven.

Interesting we had a customer on the Newfoundland Caravan last summer. His Michelins were 4 or 5 years old on his 30' Classic with plenty of miles on them. He mentioned other tires were dropping like flies but not a problem with his.

Andrew T
__________________

Thanks very much Andy.

I'm sorely tempted to dial up Tirerack and order up a set of these for my 2016 27 FC FB.

As a retired, risk averse Systems Engineer, I see the benefit of doing this sooner rather than later, at least before we get on the road for the big trip next spring.

My plan would be to get the four Michelins, and have them mounted and balanced with short metal stems on my 15" wheels here in Tampa. I'd replace the dual chrome lugs with the McGuard one piece nuts.

I just have to go look one more time at the weight specs of my trailer, in order to make sure I don't need to go to the 16" wheels. (I don't think so?).

All I need then is to ask Santa for a special xmas delivery.

If anyone sees a flaw in that plan, please let me know.

Much obliged for all the comments in the thread, as a newbie, I find it very interesting.

Rich

[Tireman9]

All the concern about the Load Index ov 108 vs 109 when in reality this translates to 3%.
How many are confident that their pressure gauge is accurate to better than 3%?
Have you confirmed the individual load on each tire is within 3% of a 50/50 side to side load balance or 3% axle to axle variation?
If not then why are you worrying about 3% more load capacity?

[Rocinante]

Speaking of tire pressure gauges, I'd love to know of a good one. I'm not actually happy with any of the gauges I've seen so far. Each one returns a different value for the same tire. Not happy. I want a gauge that's precise, accurate, and easy to use. I have yet to see one that fits all three requirements.

[xrvr]

Originally Posted by Tireman9

All the concern about the Load Index ov 108 vs 109 when in reality this translates to 3%.
How many are confident that their pressure gauge is accurate to better than 3%?
Have you confirmed the individual load on each tire is within 3% of a 50/50 side to side load balance or 3% axle to axle variation?
If not then why are you worrying about 3% more load capacity?

If you use the same gauge for each tire, the difference will show. As far as the three percent goes, then why are we worrying about ten percent. If the gauge is inaccurate then it will have the same error for each tire, to be used for comparison.

[switz]

I use this LongAcre racing products digital tire gage (0-125 psi) and these folks often have special sale prices on their units. It reads in 0.5 psi increments and is accurate to 0.5 psi or 0.3%. There are more elaborate models listed.

Longacre Pro Digital Tire Pressure Gauge 53028

[Rich Jenkins]

Originally Posted by Rocinante

Speaking of tire pressure gauges, I'd love to know of a good one. I'm not actually happy with any of the gauges I've seen so far. Each one returns a different value for the same tire. Not happy. I want a gauge that's precise, accurate, and easy to use. I have yet to see one that fits all three requirements.

The last few years, I've been replacing my tire pressure gauges annually.

What I do is to write "January 2016" (for example) using a Sharpie on the body of the gauge. This gives me a reminder to get it replaced.

I've been looking over options for 2016, and I've had this one in my cart on Amazon, based on its features and good reviews:

http://www.amazon.com/TEKTON-5941-Di...cm_wl_huc_item

[kscherzi]

Originally Posted by Llando88

The last few years, I've been replacing my tire pressure gauges annually.[/url]

Please explain why? This practice seems wasteful. The digital unit you reference seems very accurate. I bought the two pack. One for my truck and one for my wife's car. I tested both together on the same tires and read identical, to 0.5 psi. They say the battery lasts 3 years.

[Tireman9]

Originally Posted by Rocinante

Speaking of tire pressure gauges, I'd love to know of a good one. I'm not actually happy with any of the gauges I've seen so far. Each one returns a different value for the same tire. Not happy. I want a gauge that's precise, accurate, and easy to use. I have yet to see one that fits all three requirements.

Here is what I have used and recommended for years. Have tested them myself against ISO standard laboratory gauges and found them to be withing 0.5 psi.
An excellent tire pressure gauge
The Accutire MS-4021B digital tire pressure gauge has an easy-to-read LCD display that provides pressure readings from 5-150 PSI. It’s ergonomically designed with an angled head and a rubber-coated easy-grip handle. If you forget to turn off the gauge, don't worry, it will automatically shut off. The included lithium battery never needs to be recharged or replaced. And all this for about than $13! Learn more or order from Amazon.

Note. I do not work for or get a commission on any sales of the Accutire gauge.

I have also written on gauges a number of times on my blog. Simply check the list of labels

You don't have to spend $50 or $100 to get a good gauge.

[Rich Jenkins]

Originally Posted by kscherzi

Please explain why? This practice seems wasteful. The digital unit you reference seems very accurate. I bought the two pack. One for my truck and one for my wife's car. I tested both together on the same tires and read identical, to 0.5 psi. They say the battery lasts 3 years.

The same reason I switch out the battery on the smoke detectors annually.

I really don't want to be checking my tires in the middle of nowhere, and think, gee, I could have saved $10, but my gauge isn't working.

I forgot to add, I keep the old gauge around for the year, also, because "Two is one, one is none."

Your mileage may vary, of course.

[TheCabin]

I use the Accutire and really like it. Glad to hear it is actually accurate. I find that the TPS system I use registers 2 psi less so I go by the Accurate.

[kscherzi]

I have the Accutire too. Also noticed the same 2 or 3 psi difference in the TPMS reading. Also still have Marathons, thus the extra diligence.

[Tireman9]

Originally Posted by avionstream

If you use the same gauge for each tire, the difference will show. As far as the three percent goes, then why are we worrying about ten percent. If the gauge is inaccurate then it will have the same error for each tire, to be used for comparison.

and if the gauge is reading 5 or 10 psi high you will think you have more load capacity that you need so will be in fact overloading your tires.

[Tireman9]

People seem to forget that TPMS is primarily to warn of a pressure loss and may not be accurate enough if you are within 3% of your tire load limits.

I would go with the PSI reading from the Accutire for knowing the pressure but rely on my TPMS for warning if there is a pressure loss.