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Old 05-30-2016, 11:03 PM   #1
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The best free suspension mod ever

How many times have you seen click bait like that? Well, folks, it ain't click bait.

When I picked up my coach it was inflated to 90 PSI. The steering was extremely squirrelly, requiring a ton of steering input to go straight. I could barely take my eyes off the road to check a mirror before it would dangerously veer off course. It also rode quite hard, especially over expansion joints.

I weighed my rig and consulted the Michelin load and inflation table for my 235/80R22.5 G tires.

I deflated my tires to the recommended 80 PSI and drove home. I could hardly believe I was driving the same coach. The ride was soft and compliant, the steering, straight as an arrow. My stress completely disappeared and I am looking forward to my next 2,000 mile trip.

I have read many pundits recommendations to fill to maximum pressure. That information is simply wrong. A coach is not a trailer and the manufacturer knows best. Extend the life of your tire and enjoy the ride by using the correct inflation pressure.

Overinflation will cost you more in tires and stress than you save in gas.
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Old 05-31-2016, 06:52 AM   #2
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think most coach manufactures simply go with the max tire pressure.

The placard on mine calls for 100 psi in all six tires. After I weighed the coach and looked at the tire pressure table, I discovered I could run the minimum pressure of 70 psi.

I decided to run the tires at 80 psi. Like you, there is a big difference in ride and handling.
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Old 05-31-2016, 08:47 AM   #3
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I think this is a case of looking at the tables and running the correct pressure. Michelin does not use the word minimum. I imagine if you fall in the middle of the range you could extrapolate.

The point is to make sure that your tire has the contact patch the manufacturer intended to get optimal wear and performance.

The tables uses ranges which can be a little imprecise so I plan to use the tire chalk method as soon as I have a chance. There are many variations on this test so be sure to google 'tire chalk test' for more information. Here is a recap:
  1. Find a nice flat surface, concrete is best but asphalt works too. Keep in mind that roads are crowned and it can throw off the test. Parking lots are probably best
  2. Use tire chalk (or large kid's chalk for sidewalks) to mark a wide line across each tire.
  3. Now drive in a straight line, allowing the tires to turn several revolutions
  4. Analyze the wear pattern on the tire and ground, if the chalk is worn out in the centre, reduce the tire pressure. Keep doing this until it wears evenely.
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Old 05-31-2016, 09:14 AM   #4
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You may want your tires to be up to temperature before adjusting pressures to the "footprint". My tire pressure monitors show about a 18psi difference from cold to highway temperature. Not sure how accurate the sensors are tho.
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Old 05-31-2016, 09:54 AM   #5
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Good point, Goodyear and Michelin recommend all tire pressures be taken cold. Goodyear goes so far as to say that air should only be released from cold tires but that would affect the contact patch.
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Old 05-31-2016, 10:03 AM   #6
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Max pressure is good for a TT but not for a class A motorhome where the weight can very by 100 of lbs. Adjust your tire pressure based on the weight of the coach at that time that is what I have always done on the winne with good luck.
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Old 05-31-2016, 10:05 AM   #7
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Quote:
Originally Posted by SeaDog View Post
Max pressure is good for a TT but not for a class A motorhome...
Said that in my first post
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Old 05-31-2016, 10:23 AM   #8
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Ya I saw what you posted, but added the information about the variation in weight that some may not understand happens with a class A.
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Old 05-31-2016, 10:26 AM   #9
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It's an excellent point and bears repeating for those, like myself, that come from TTs.
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Old 05-31-2016, 11:13 AM   #10
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I totally agree that knowing your weights are critical and matching the weight to the specific tire brand/size chart is important.

I just installed Toyo tires 245/78/22.5 and this is what I have found.
See my thread on my new Toyo tires psi testing.
http://www.forestriverforums.com/forums/f16/toyo-tires-108612-2.html


Great information and works for me.
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