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Old 06-22-2014, 07:56 AM   #99
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Graysailor: I'm not sure if you are driving an interstate but when we took delivery the dealer told us to disregard the tire pressure placard in the driver's door jamb and fill all tires to 60 psi. So if you're at 40, you may decrease your tire life.
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Old 06-22-2014, 07:59 AM   #100
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A fun fact... The tire minder system turns off when you're not in the vehicle and turns on upon your return. I presume that it senses the change in weight (and pressure) when you climb aboard.
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Old 06-22-2014, 06:55 PM   #101
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TireMinder seems to be working. The problem I am having now is that the Minder tells me I have 36.5lbs of pressure but I checked the tires and all four have 40lbs. of pressure. I changed the batteries with the same results. The trailer tire pressures are still accurate. Just not sure how to adjust the TV so that it will be more accurate. Difficult system to set up and adjust.
I wouldn't be too concerned about a 3.5 psi difference. Is your hand gauge a digital 0.5 reading gauge that you have checked against a certified calibrated gauge?
I did a post on gauge accuracy Oct 26 2012 on my blog and had 36% of the group of gauges fail.
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Old 06-22-2014, 06:56 PM   #102
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Don't forget "TireMinder" is the trade name of one brand of aftermarket TPMS and not all TPMS are the same.
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Old 06-22-2014, 06:59 PM   #103
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Graysailor: I'm not sure if you are driving an interstate but when we took delivery the dealer told us to disregard the tire pressure placard in the driver's door jamb and fill all tires to 60 psi. So if you're at 40, you may decrease your tire life.

Interesting. Have to wonder what information the dealer had that justifies him giving you that info. Did he have the motorhome weighed and did he do the calculations?
Did he mention the Interply shear forces in trailer applications and the decrease in cornering force generated?

Is he willing to put his advice to ignore the placard in writing?
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Old 06-22-2014, 07:49 PM   #104
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TireMinder seems to be working. The problem I am having now is that the Minder tells me I have 36.5lbs of pressure but I checked the tires and all four have 40lbs. of pressure. I changed the batteries with the same results. The trailer tire pressures are still accurate. Just not sure how to adjust the TV so that it will be more accurate. Difficult system to set up and adjust.
I am curious what gauge you are checking the Tire sensors against. 3.5 Psi out of 40 is less than a ten percent error. 10 percent error would be considered a good external tire gauge. Since the tire sensors are four separate sensors being compared (I assume) to a single external tire gauge, I would say, if as I understand it all the tire sensors are in showing the same difference from the external guage, that they are giving the most accurate readings. Unless you pay much more for an external gauge than most people do, it is not going to be a particularly accurate tool. Not to mention that you only need to drop one once and its accuracy becomes a big unknown. I imagine that the Interstate's sensors are probably calibrated accurately before they leave the factory. Trust me: Trust them before you trust your external gauge.

Ken
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Old 06-23-2014, 05:25 AM   #105
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Originally Posted by paullovern View Post
Graysailor: I'm not sure if you are driving an interstate but when we took delivery the dealer told us to disregard the tire pressure placard in the driver's door jamb and fill all tires to 60 psi. So if you're at 40, you may decrease your tire life.
Interesting. Have to wonder what information the dealer had that justifies him giving you that info. Did he have the motorhome weighed and did he do the calculations?
Did he mention the Interply shear forces in trailer applications and the decrease in cornering force generated?

Is he willing to put his advice to ignore the placard in writing?
I'm with Roger on this. A dealer verbally suggesting that a Federally mandated label is incorrect and should not be followed is like ignoring the prescription your doctor wrote out and using something the clerk at the pharmacy told you about.

I'm continually amazed at what people will offer as advice and continually amazed at how many people will listen.
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Old 06-23-2014, 08:11 AM   #106
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I have a Flying Cloud 25. I maintain 65lbs. on the trailer tires. TV is a Ford F150 which I maintain 40lbs. I double check with two external gauges. They both read about the same.
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Old 06-23-2014, 08:49 AM   #107
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The door sticker may be for a stock Sprinter, not an AI. For an Interstate you need close to the max tire pressure because you are close to the max weight. You do not have to weigh an Interstate, they are all close to maxed out weight wise for the Sprinter chassis or close enough that it does not matter. Jim
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Old 06-23-2014, 10:22 AM   #108
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FWIW the door sticker in my 2013 AI, the MB Owner's Manual, the Airstream manual, my dealer's recommendation, and the tire shop that put on the extended valve stems all concur the tire pressure should be 61 pounds.

I tried a TPMS with valve stem sensors, but they were not passthrough and I had to remove the sensor to adjust the pressure in the tires. Removing the sensors was a total pain in the nether regions of my anatomy so that one went back to the dealer for a refund.

I replaced it with the TireSafeGuard TPMS ($279 for six wheels) with passthrough valve stem sensors. It has simple automatic initialization feature that takes with the average pressure in all six tires and uses that as the standard pressure. When I compare the monitor readings with a calibrated manual pressure gauge the TPMS readings are within + or - a few pounds. Certainly close enough for government work. The monitor can handle up to 18 wheels and different tire pressures on the trailer or toad using manual setup because of the varying base pressures. When you are stopped for an extended period the TPMS goes to sleep to conserve battery life and the batteries in the sensors are replaceable. On the road, the faster you are moving the more frequent the sampling rate. The system comes with a range extending antenna, but it is unnecessary to read the AI tire pressures and temperatures. however I may need to for the toad.

So far the only complaint I have is the glue used on the furnished mounting bracket won't stand up to the heat of a North Texas summer day and the darn thing falls off. Some industrial strength Velcro should fix that. The planned permanent mounting point is the CB radio knock out panel in the overhead and tapping into the wiring that is already there for power. It works well enough that I am going to get additional sensors for the tow dolly and the toad vehicles.

A final note. IMHO metal extended valve stems are essential for valve stem sensors and be sure to get the ones designed to work with the aluminum and steel wheels used on the AI.
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Old 06-23-2014, 01:34 PM   #109
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Originally Posted by joemikeb View Post
FWIW the door sticker in my 2013 AI, the MB Owner's Manual, the Airstream manual, my dealer's recommendation, and the tire shop that put on the extended valve stems all concur the tire pressure should be 61 pounds.

I tried a TPMS with valve stem sensors, but they were not passthrough and I had to remove the sensor to adjust the pressure in the tires. Removing the sensors was a total pain in the nether regions of my anatomy so that one went back to the dealer for a refund.

I replaced it with the TireSafeGuard TPMS ($279 for six wheels) with passthrough valve stem sensors. It has simple automatic initialization feature that takes with the average pressure in all six tires and uses that as the standard pressure. When I compare the monitor readings with a calibrated manual pressure gauge the TPMS readings are within + or - a few pounds. Certainly close enough for government work. The monitor can handle up to 18 wheels and different tire pressures on the trailer or toad using manual setup because of the varying base pressures. When you are stopped for an extended period the TPMS goes to sleep to conserve battery life and the batteries in the sensors are replaceable. On the road, the faster you are moving the more frequent the sampling rate. The system comes with a range extending antenna, but it is unnecessary to read the AI tire pressures and temperatures. however I may need to for the toad.

So far the only complaint I have is the glue used on the furnished mounting bracket won't stand up to the heat of a North Texas summer day and the darn thing falls off. Some industrial strength Velcro should fix that. The planned permanent mounting point is the CB radio knock out panel in the overhead and tapping into the wiring that is already there for power. It works well enough that I am going to get additional sensors for the tow dolly and the toad vehicles.

A final note. IMHO metal extended valve stems are essential for valve stem sensors and be sure to get the ones designed to work with the aluminum and steel wheels used on the AI.
Great information, joemikeb - thanks.

Regarding tire pressures, I cannot imagine Mercedes Benz would issue a door sticker that couldn't take into account anything other than the vehicle being fully loaded. Without that, owners would be left guessing. And we know RV upfitters pretty much load up the chassis towards the limit.

Regarding the passthrough sensors, they look pretty hefty. Do they affect wheel balancing?
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Old 06-23-2014, 04:09 PM   #110
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Old 06-23-2014, 08:06 PM   #111
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Regarding the passthrough sensors, they look pretty hefty. Do they affect wheel balancing?
Actually the sensors are pretty light weight in fact probably lighter than the non-passthrough sensors they replaced. In any case, I installed the sensors before I had the tires balanced.
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Old 06-24-2014, 06:34 AM   #112
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The door sticker may be for a stock Sprinter, not an AI. For an Interstate you need close to the max tire pressure because you are close to the max weight. You do not have to weigh an Interstate, they are all close to maxed out weight wise for the Sprinter chassis or close enough that it does not matter. Jim
Jim,

Federal law mandates that when a vehicle modifier (and Airstream would count in this case) modifies a vehicle, they become responsible for the vehicle tire placard and must alter it appropriately, if needed.

I imagine that Airstream is large enough and has done vehicle modifications for so long, that they are not only aware of the federal regulation, had conversations with both the Feds and MB on the subject, but also have taken more than just a superficial look into what is written there - like doing some handling studies. If they haven't replaced the vehicle tire placard with one of their own, it is because they are convinced it is appropriate.

This is not to say that your argument doesn't have merit for other vehicle modifiers, but I think Airstream is just not in the same category as the rest. But just so you are aware, what you are arguing is that not only is Airstream derelict in its responsibility to the law, but also to its customers. I would be very careful with that accusation.
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