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Old 10-28-2017, 11:01 PM   #1
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Sprinter Tire Pressure

I'm finding that I have to inflate tires every few days on all the tires, but especially the inner duallies. Pressure is dropping to 30 psi. I had them checked twice since we bought them in Feb. (Michelin Defenders), but it's still happening. Is this normal? What are you finding with your AI?
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Old 10-29-2017, 02:14 AM   #2
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The culprit on the inner tires is either the stock rubber valve stems, or the plastic stem extensions. One of the first things I did on my Interstate, back in 2012, was to replace the plastic valve extensions with aluminum ones. Haven't experienced a problem with leaks ever since.

For the other tires, I don't have an explanation. My tires hold 60psi indefinitely.
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Old 10-29-2017, 07:13 AM   #3
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I ran my original Continentals and 75-80 psi and never had to add air. (I found the higher pressure eliminated the edge wear on the front tires that I got at the recommended 60 psi.) I recently switched to Michelin Defenders and have not yet discovered what pressure they like - so I am running 75 - 80 on them too. I have no problem with them holding pressure - once I got rid of the flow through valve stem caps. I never had problems with the rubbers stems or plastic extensions leaking air - but switched to metal when I started running the higher pressure.
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Old 10-29-2017, 07:38 AM   #4
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My original Continentals held pressure well. I kept them at 65, after I found my tire gage was a POS and replaced it. Just replaced them with Michelin Defenders and had metal valve stems installed. I have the TST sensors to install later. Dealer put the new Defenders at 65 and I will be watching them closely. The ride improvement with the Defenders is dramatic!
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Old 10-29-2017, 08:13 AM   #5
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Quote:
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(I found the higher pressure eliminated the edge wear on the front tires that I got at the recommended 60 psi.)
If the edge wear is just on the outer edges or just on the inner edges, that's an indication of improper front end alignment. If the wear is on both outer and inner edges, it's an indication of low tire pressure.

One of the first things I did when I bought my Interstate was to get a front end alignment, because the van comes from Mercedes with an alignment suited to the curb weight of an empty cargo van. Then Airstream adds a huge amount of weight, but doesn't do another front end alignment. So when you buy your Interstate, the alignment is all wrong for its new curb weight. And I have never had a problem with edge wear on the front tires, despite having the same tires for 6 years without ever rotating them.

This sort of thing isn't usually a problem for a passenger car, because the cargo capacity is a small fraction of the car's total weight, so the difference between curb weight and loaded weight isn't enough to throw off the alignment by much. But a bare-bones Sprinter cargo van has a curb weight of about 6200 pounds, or just over half the gross weight. So increasing the curb weight by over a ton during Airstream's conversion makes a difference to the suspension, including the front end alignment.

Higher tire pressure to correct edge wear due to improper alignment is not exactly best practice. Over-inflation means less tread is in contact with the ground, and that can lead to poor traction, as well as greater tread wear in the center of the tire.

Your gross front axle weight is 4410 pounds, or 2205 pounds per tire. At the recommended maximum 61psi, that means at most 2205÷61=36.1 square inches of tire tread in contact with the ground, per front tire. Running at 75psi instead means that you only have at most 2205÷75=29.4 square inches of tread in contact with the ground per front tire. Your rubber-to-pavement contact— and thereby your traction— is reduced by 18.6 percent.

The real telling factor whether 61psi is too low for your Interstate is the rear tires. If you got both inner and outer edge wear on all four rear tires, then 61psi is too low. But I'd be willing to guess that you never saw any edge wear on the rear tires even when the front tires were being worn away on the edges.

My recommendation is to get a front end alignment, and then reduce the tire pressure to no more than the 61psi recommended by Mercedes Benz, and see if that solves your problem.
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Old 10-29-2017, 08:21 AM   #6
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My dealer, a Mercedes Sprinter dealer, probably set my new Defenders at 61. The pressure I read was after driving 35 miles, so my tires had warmed up a bit. Going to check the. Next time I go to the storage yard. Am going to have to find an alignment shop. Mercedes dealer wouldn’t touch the alignment for my Airstream, neither would the local Freightliner dealer. Mercedes gave me a local shop name to try......
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Old 10-29-2017, 11:50 AM   #7
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Sprinter alignment

Quote:
Originally Posted by toskeysam View Post
My dealer, a Mercedes Sprinter dealer, probably set my new Defenders at 61. The pressure I read was after driving 35 miles, so my tires had warmed up a bit. Going to check the. Next time I go to the storage yard. Am going to have to find an alignment shop. Mercedes dealer wouldn’t touch the alignment for my Airstream, neither would the local Freightliner dealer. Mercedes gave me a local shop name to try......
We have been on the road for about 3 weeks. Stopped in Indianapolis to visit our oldest son, formerly an ASE certified suspension and alignment tech before going back to school and changing careers. We were having some edge wear on the original Continentals, and at 40k miles we were nearing replacement time. Son looked at tires and recommended we have an alignment done based on the wear pattern he saw. He suggested camber might be out and maybe toe was a little off and we should have it looked at.

We took the Sprinter to Stoops Freightliner in Indianapolis. This is a huge dealership and truck service facility. The alignment tech at Stoops installed the camber bolts and conducted the alignment. I didn’t need to mention the camber bolts to the tech; he was already aware they were needed. Toe in was a tiny bit out of spec, and camber required adjustment. My local dealer doesn’t have an alignment machine in a space that will accommodate a Sprinter. Otherwise, I would have had that done before I left on this trip.

Subsequently, we had new Michelins installed at the Discount tire in Bryan, TX. We used Discount Tire because they have a store in our home city. Sales guy was great, but the tech was a little careless. He dragged the metal of the spare on the pavement while putting it under the van to hoist it, and I had to mention to him to turn it over. Not a huge deal, but I would like to avoid the rust that comes with scratches. Also I noticed scuffing in the bolt circle area on both rear Alcoas which may have been from the tire machine or balancer. I’m not sure the balance on the fronts is perfect, but I will deal with that when I am home in a week. I’m really fussy about that, and the Sprinter seems to be sensitive to perfect balance as well as feeling the road surface.

I might have waited until we got home until replacing the tires, but before we left Salt Lake City a couple of weeks ago, I was thump testing the tires at the campground and got a dull thud from the left rear inner. While tapping the tires with an object doesn’t tell you if the pressure is right, in my case, it kept me from leaving the campground with a flat and having an issue on the road.

I put the spare on, and we had been traveling without a spare for a couple of weeks. And I did not want to travel in the sparsely populated areas of the West, sans spare, on my way home. I could not find the cause of the flat. There was no obvious puncture cause in the tire. Based on the appearance of the the tire that went flat, there was no external evidence of sidewall flexing or degradation, and I felt it was likely that the tire had gone flat, or finished going flat in the KOA in Salt Lake City.

Now I will watch pressures, and monitor for wear patterns on the new tires.
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Old 10-29-2017, 01:28 PM   #8
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I went in for an alignment and the tire shop guy said that the front tire wear looked to be due to low pressure. Camber checked out near 0 and toe-in was very close to OK. The near-0 camber is what I see recommended for a heavy (motorhome conversion) Sprinter. Diesel, LPG, and fuel tanks were not completely full but total weight was probably near the upper end of what is typical for us. He said that Continentals 'liked' to be run at their maximum sidewall pressure. If there is truly a difference between what pressure different brands of tires 'like', then the 61 psi on the door plate would seem to be of little relevance.
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Old 10-29-2017, 02:15 PM   #9
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If there is truly a difference between what pressure different brands of tires 'like', then the 61 psi on the door plate would seem to be of little relevance.
It's of relevance. Tire pressure should be based on tire size, which determines tread width and tire diameter, and axle weight, which determines tire loading. Tire brand is of very little relevance in that regard. All tires of the same size designation, in this case LT215/85R 115/112Q, are almost the same in terms of tire diameter and tread width, within a fraction of an inch. That's what the 215/85 designation means.

In my opinion, if a tire brand "likes" a pressure range that is above the range listed on the vehicle manufacturer's data plate by the driver's door frame or seat pedestal, then it's the wrong brand for the vehicle. Running the tires above the vehicle manufacturer's recommended pressure is detrimental in the long run. It degrades braking effort, which has just as much to do with rubber-to-pavement contact area as it does with caliper-to-disk or pad-to-drum contact area. And on the front, it also degrades steering effort, which can make a real difference if you're on rain-slicked pavement or other adverse conditions.

But you're all big boys and girls, and I'm not the tire inflation police. So you're free to do as you will and run with your tires 15 to 20 psi over what is recommended in your Sprinter owner's manual. Just don't expect to convince me that you're doing it right and I'm doing it wrong.
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Old 10-29-2017, 03:47 PM   #10
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Quote:
Originally Posted by Protagonist View Post
The culprit on the inner tires is either the stock rubber valve stems, or the plastic stem extensions. One of the first things I did on my Interstate, back in 2012, was to replace the plastic valve extensions with aluminum ones. Haven't experienced a problem with leaks ever since.

For the other tires, I don't have an explanation. My tires hold 60psi indefinitely.


I removed the extensions a while back and only use those for inflating. Do you think that some tire vendors don't know about aluminum valves? I'm disappointed in my vendor, as I just bought these in February and have only 6,000 miles on them. I think they should have inspected the valves and replaced or recommended aluminium. Do you think discount tire is a good source for fixing this?
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Old 10-29-2017, 04:38 PM   #11
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Not trying to convince anybody of anything - just relating my experience and that of the tire and alignment shop guy who knows more about tires then I ever will.

Regarding the Sprinter (Airstream?) numbers that are published:

The contact area analysis is interesting, but... I wonder what vehicle weight is assumed when they put the numbers on the doorframe? Our AI is in storage so I can't check it, but I think it has the same pressure for all four corners. Wonder what the chances are of that really being the case, versus trying to simplify things and settle on a single average number that is not exactly right for any corner.
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Old 10-30-2017, 10:03 AM   #12
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Tireman9 has several great posts regarding tires/ pressure and tire related matters.

http://www.airforums.com/forums/sear...archid=8036874

He also has a tire blog;

http://www.rvtiresafety.net/
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Old 10-30-2017, 02:29 PM   #13
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Quote:
Originally Posted by 3bcamper View Post
I'm finding that I have to inflate tires every few days on all the tires, but especially the inner duallies. Pressure is dropping to 30 psi. I had them checked twice since we bought them in Feb. (Michelin Defenders), but it's still happening. Is this normal? What are you finding with your AI?
I had the same issue with my '17 Interstate. It seems it took some time/miles to get them to finally stop leaking for whatever reason. I still have ONE pesky tire (driver side rear outer) that doesn't want to hold air so I'll take it to another shop and see if they can get it properly seated and yet another new metal stem put in.....
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Old 10-31-2017, 06:22 PM   #14
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Quote:
Originally Posted by Protagonist View Post
The culprit on the inner tires is either the stock rubber valve stems, or the plastic stem extensions. One of the first things I did on my Interstate, back in 2012, was to replace the plastic valve extensions with aluminum ones. Haven't experienced a problem with leaks ever since.

For the other tires, I don't have an explanation. My tires hold 60psi indefinitely.


It seems we may have found the problem. Took the AI to a commercial truck tire place (GCR in Lakeville, MN). They submersed the offending wheel in water and jostled the rubber valve stem. It allowed air to escape. They're replacing all six valve stems with steel. Will let you all know how well this works.
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