The best free suspension mod ever

[Modmike]

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.

[waiter21]

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.

[Modmike]

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.

[Grumpy Guy]

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.

[Modmike]

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.

[SeaDog]

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.

[Modmike]

Originally Posted by SeaDog

Max pressure is good for a TT but not for a class A motorhome...

Said that in my first post

[SeaDog]

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.

[Modmike]

It's an excellent point and bears repeating for those, like myself, that come from TTs.

[Iggy]

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.

[Modmike]

Originally Posted by Grumpy Guy

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.

This kind of threw because every piece of literature says to measure cold tire pressure, but it makes sense. I had to get a nail pulled and patched and the tire guy agreed, chalk test needs to be done when at operating temp.

Make sure to take a cold pressure reading after the test so you know what to shoot for. By the way, make sure you get a good pressure gauge, I have 3 and they vary by up to 5 PSI when dealing with high pressure!

[sherman12]

I used to run 100 lbs in my tires until I saw the recommended tire pressure sticker from Forest River inside the rig, on the wall behind the drivers seat stating all six should be run at 90 lbs. which is what I've been going by since.

[RVnut]

Originally Posted by sherman12

I used to run 100 lbs in my tires until I saw the recommended tire pressure sticker from Forest River inside the rig, on the wall behind the drivers seat stating all six should be run at 90 lbs. which is what I've been going by since.

X2

[Kevin M.]

Just got back from a trip with new tire pressure monitors, all tires set at 90 when cold.
While driving the inner rear tires got up to 108 while outer rears were at 98, fronts stayed at about 94-97 range.

I will be lowering mine to 80-85

[Modmike]

The sticker is misleading in that it assumes maximum weight.

Weigh your coach and follow the load tables for a more enjoyable experience.

[Iggy]

Originally Posted by Modmike

The sticker is misleading in that it assumes maximum weight.

Weigh your coach and follow the load tables for a more enjoyable experience.

You are 100% that's why we tell everyone they need to get weighed.

[SimoRandy]

After reading this maybe I don't need to upgrade my shocks to get a better ride! My sticker in the coach says 100 PSI so that's what I've been keeping them at! I was looking for an excuse to head somewhere! Now, where is this chart?...


Randy & the Dogs
RV'rs as of 2015
G-town XL 369 w/ wrangler hanging on the back!

[waiter21]

Randy, head to the scales and get weighted. Although weights for each tire would be nice, I think its an overkill.

Weight for each axle is ok, (front and rear). Then use the table that comes from your tire manufacture. It will give the minimum pressure for each tire when used as a single or dual configuration.

My placard from Coachman says to run 100psi in each tire, after weighing, the tire manufacture says the minimum I could run is 70 psi.

[sherman12]

When I think of the lay out and storage areas of my rig I just wonder how much difference there could be from tire to tire. I would assume that the main weight of the front is from the engine and set up while the rear wheels carry more of the house and storage. I would guess that when our F53 chassis' are used in a commercial application they don't weigh their trucks and adjust tire pressure daily to reflect how the load of the day is placed in the trucks, it would take to much time. which we all know is money. My guess is they use a set pressure and roll with it. Sometimes reading these forums some of us RV'ers are looking to get the performance and ride from our rigs that one may get in a BMW instead of a boxed house on wheels.

[Modmike]

Originally Posted by SimoRandy

After reading this maybe I don't need to upgrade my shocks to get a better ride! My sticker in the coach says 100 PSI so that's what I've been keeping them at! I was looking for an excuse to head somewhere! Now, where is this chart?...


Randy & the Dogs
RV'rs as of 2015
G-town XL 369 w/ wrangler hanging on the back!

Click on the hyperlink in the first thread.