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Old 10-04-2007, 10:56 AM   #1
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1984 34.5' Airstream 345
Greenville , Ohio
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Classic Motorhome Tires

I was able to obtain from a friend new Michelin XZE 225/70R 19.5 Tires to replace my Goodyear G159 8R19.5. The Michelin are G rated tires with 110 lbs. max air pressure. I have the following questions:
Will the ride be firmer than the Goodyear.
What air pressure should be used with the Michelin.
Is there a clearance problem with the duals since they are a wider tire.
I realize I will loose approximately 2.5% speedometer accuracy and have to turn more RPM to arrive at the same speed as the Goodyear.
What additional information does anyone have that I haven't thought about.
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Old 10-04-2007, 11:12 AM   #2
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what is the difference in load rating?
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Old 10-04-2007, 11:48 AM   #3
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Speedway , Indiana
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If you check the temperature of each tire's tread, it will tell you the correct pressure. Check the temp on the inside tread, the center, and the outside. If it is hotter in the middle, it is over inflated for it's load. If the center is cooler then it is under inflated for it's load.
This way you can arrive at the optmum pressure for each location.
Start at about 90 psi at each tire, and work your way down from there.
My tires are as follows:
Fronts- 78# each
Duals- 78# left, 77# right
Tag- 70# each
This is for my normal loading.
This is well below the Maximum pressure on the sidewall.
Rob
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Old 10-04-2007, 11:49 AM   #4
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Quote:
Originally Posted by gunner
I was able to obtain from a friend new Michelin XZE 225/70R 19.5 Tires to replace my Goodyear G159 8R19.5. The Michelin are G rated tires with 110 lbs. max air pressure. I have the following questions:
Will the ride be firmer than the Goodyear.
What air pressure should be used with the Michelin.
Is there a clearance problem with the duals since they are a wider tire.
I realize I will loose approximately 2.5% speedometer accuracy and have to turn more RPM to arrive at the same speed as the Goodyear.
What additional information does anyone have that I haven't thought about.
Gunner,

Its my understand you shouldn't change from the recommended air pressure settings as listed by Airstream for the motorhome. Higher pressure rated tires should not be filled to the max rating.

On our 310 we filled the tires to the recommended pressures from the airstream manual. We had originally had higher pressures and the ride was horrible. After dropping back to the recommended pressures the ride improved considerably.

I believe it was Goodyear's tire rating chart that I used to compare their tires at various air pressure settings. With the air pressure set as recommended by Airstream the load ratings matched the original tires that came on the motorhome.

YMMV

Brad
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Old 10-04-2007, 01:21 PM   #5
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1985 34.5' Airstream 345
Frisco , Texas
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Just went the other way.

I've been on Michelins for fifteen years and just put a set of G670RV 225R70 19.5s on the front of my 345 yesterday. I always had two issues with the Michelins, the first being the quick rate of dry rot that always killed the tires. I'd put a new set on, drive 20K and have to replace them after two years due to side wall dry rot. The second was the incredibly rough ride I also had with Michelins up front. I'd adjust the airpressure up and down with no beneficial affect. In the first 15 miles with the Goodyears up front I feel like I'm driving a new rig. I've heard that the 225s will clear the dually requirements on the rears, but you are likely to "grab" road trash between the narrower gap. For the moment I'm staying on the originals in the rears, but staying on the goodyears up front.
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Old 10-04-2007, 02:02 PM   #6
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We have the Goodyear G670, 225's on our 345 all the way around.
I love 'em
Rob
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Old 10-04-2007, 03:32 PM   #7
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Tires manufactures recommend that you weight each wheel of your fully loaded rig and then adjust the pressure accordingly. Here are a couple of documents from Michelin on the topic.

RVTireGuide.pdf Michelin_Rv_Load_Inflation.pdf

I recently replaced all the tires on my rig. Based on recommendations from Henderson's Line Up (Supersteer) who said they would provide a softer ride, I went with Michelins. Based on weighing my rig I was running my old rear tires at 75 PSI and the fronts at 95 PSI.

I wanted wider tires in the front and wanted to be able to run them at lower pressure. So, I put 225 70/R 19.5 on the front, this allows me to run 80 PSI (actually I'm running 85). The difference in diameter between the 8R 19.5 and the 225 70R 19.5 means that the 8R requires 616 revolutions per mile and the 225 70R requires 646. This seemed too much of a gearing penalty since I don't have a Gear Vendors, so I stayed with 8R's on the back.

The difference in ride was dramatic and so far I'm happy with the change.
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Old 10-04-2007, 04:50 PM   #8
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Rob,

What would you recommend using for taking the temperatures of the tires? I have seen relatively inexpensive IR readers and wondered if they were reliable. I beleive you use a laser, but as a racer, you need the best.

Any advice would be appreciated.

Steve
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Old 10-04-2007, 05:10 PM   #9
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As a racer, the best tool for taking tire temps is a probe-type pyrometer, not a laser one. The probe will give you a more accurate temp. A laser would be okay if you have one, but it will not be as accurate. The main thing you are looking for is the temp range across the tire - outer, middle, inner - and to see what the variance is. This is a good diagnostic for tire wear, too - if the outers are hotter than the middle and inners, you may have toe-out, and vice versa. If both outer and inner temps are higher than the middle, you need air in your tire. And if the middle is hotter than the outer and inner, you need to deflate the tire a little.

You should ideally take the temps by doing regular driving and then pulling over to the side of the road as quickly (and safely!) as possible and check them immediately. This will give you the most accurate response.

Good luck!

Susan
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Old 10-05-2007, 08:33 AM   #10
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Steven,
What Susan said is spot on. I use the cheep IR unit. Since I am really not interested in an exact number, it works fine. You are looking at the relationship of the temps across the face of the tire.
The IR units are great for checking trailer hubs, headers, your fore-head, etc.
They can be found for less than $100.00
Rob
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Old 10-05-2007, 08:52 AM   #11
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Greenville , Ohio
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The tires I have are the Michelin Load Range G which take up to 110 lbs. air pressure instead of the standard F rating that take up to 95 lbs. the original Goodyear where also F rated. I thought that with the Load Range G they would be stiffer and give a firmer ride. I have new Bridgestone 12 ply 8R19.5 on the front and I have 7 new Michelin. My thoughts are to put the 6 on the rear and 1 on the spare. That way if I do get a flat I can place the spare on any axle. I don't believe it will affect the front drastically with the 1" difference in diameter unti I can get it fixed or replaced but at least it wouldn't affect my trip.
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Old 10-05-2007, 12:58 PM   #12
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Susan, Rob,

Thanks folks. I think I will spring for an IR for now.

Steve
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Old 10-08-2007, 05:17 PM   #13
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All,
Just a tip check the max PSI on your wheels them selves, Mine are 115 PSI
and someone was trying to sell me TOYO tires at 120 PSI max load
anyway- And I also love the G670, I put 6 new on this year, they had a 20 rebate per tire, and had wing foot put them on. I run them at 105 PSI, I'm not at max load on the MotoHome, they seem good, not too stiff
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