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Old 03-27-2007, 06:59 AM   #1
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There seem to be a lot of opinions about maintaining tire pressure in a motor home.

My new 07 Itasca Meridian came from the dealer with the tires inflated at the Michelin recommended max for the capacity of the tires.

The Michelin owners guide spends a lot of time talking about getting the tire pressure right for the actual fully loaded and towing weight of the coach.

I have yet to meet up with A Weigh We Go to get my rig weighed on all 4 corners.

Does any one have any good ideas about the best rules of thumb for ride, handling, fuel economy, and wear?
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Old 03-27-2007, 06:59 AM   #2
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There seem to be a lot of opinions about maintaining tire pressure in a motor home.

My new 07 Itasca Meridian came from the dealer with the tires inflated at the Michelin recommended max for the capacity of the tires.

The Michelin owners guide spends a lot of time talking about getting the tire pressure right for the actual fully loaded and towing weight of the coach.

I have yet to meet up with A Weigh We Go to get my rig weighed on all 4 corners.

Does any one have any good ideas about the best rules of thumb for ride, handling, fuel economy, and wear?
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Old 03-27-2007, 07:39 AM   #3
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what is the lenght of your new rig
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Old 03-27-2007, 08:05 AM   #4
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">good ideas about the best rules of thumb for ride, handling, fuel economy, and wear? </div></BLOCKQUOTE>
Best rule of thumb for handling, fuel economy and wear is to inflate the tires to the loaded weight according to the tire mfg chart for your specific tire

If you don't know the loaded weight, a good rule of thumb for handling, fuel economy and wear is to inflate to the tire mfg recommended maximum weight for the specific tire. Assuming your are not grossly overloaded, you should then be at least assured your tires will not be damaged by excessive heat from being under-inflated for the load.

My personal rule of thumb for "best ride" is buy a vehicle that gives me that when the tires are properly inflated for the loaded weight. I will not run tires low to get a "better ride feel."

If you won't have a chance sometime reasonably soon to get a four corner weight, I would see if I could at least get axle weights at a mover's warehouse, grain elevator, etc.
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Old 03-27-2007, 08:13 AM   #5
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The Itasca Meridian is a model 34H it's 34'9" long and has a wheelbase of 208"
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Old 03-27-2007, 08:17 AM   #6
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Sounds right to me Paul:

We're just finishing moving in. Will be heading out tomorrow, for a trip to FL. Will weigh the rig and toad at the first gas stop, and set tire pressure Thursday Morning before we pull out.

Thanks for the input.

If the CAT scales at the Pilot truck stops gave me enough room, I'd just weigh twice, once with just one side on the scale.
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Old 03-27-2007, 08:43 AM   #7
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I'd just weigh twice, once with just one side on the scale </div></BLOCKQUOTE>
Good plan. You'll want two weights at a minumum ...front axle only, then rear axle only. If you can get four individual wheel weights, go for it!
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Old 03-27-2007, 08:55 AM   #8
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The CAT scales at the truck stops are segmented.
with one weighing, I get front axle, rear axle, toad, and gvw

They just have a narrow aisle, with curbs on both sides so I don't have room to get one side off the scale.
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Old 03-28-2007, 03:19 PM   #9
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Ok so I weighed the rig today.

Front Axle 7780 divided by 2 = 3890 per front wheel
Rear Axle 16,500 divided by 2 = 8250 for each rear dual
Toad 3300

GCW 27580
GCWR 37510
GAWR Front 10410
GAWR REAR 17500

Coach is well within the weight range on all counts.

As delivered the tires are inflated to support the GAWR on each axle 110 on the front, and 95 on the rear.

If I'm reading the michelin tables correctly,
for the 255/80R22.5 XRV then 3890 translates up to 4070 which = 75 pounds on the front and 8250 translates to 8410 which = 90 pounds for the rear.

That's a big difference in pressure. I wish someone could tell me if that's correct.
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Old 03-28-2007, 03:53 PM   #10
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You're reading the chart right if your tires are Load Range G, which they probably are.

As you've already noticed in the forum, there is an opinion for everything. My opinion and preference is to run 10% over the listed air pressure for the weight. Using your numbers, that would mean 80psi in the front and 100 in the rears. Give or take a pound.

The reason we do that is to allow for variations in our weight and in the scales.

Happy trails
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Old 03-29-2007, 10:12 AM   #11
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I dropped the front pressure from 110 to 90 this morning. Still reluctant to take it down further, but we drove 250 miles today, and the ride and handling were much better.

didn't change the rear. 96 is close enough to be good for now.

I may try 80 in the front on the way home after Easter just to see what happens.

It seems that taking care of the tires is one of the more important tasks to pay attention to.
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Old 03-29-2007, 06:05 PM   #12
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Please remember even though you have axel weights you will not have a weight per tire unless your coach is loaded equally on each side. That is why a four corner weight is recommended.

Rather than adjust air pressure for the side to side differences you may discover, it may be better to adjust the loading.

Just a thought...
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Old 03-30-2007, 03:55 AM   #13
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Thanks for the reminder Steve.

This is kind of a work in progress.

I haven't found a scale that will let me get on with only one side of the coach, and I haven't been any place to meet up with A Weigh we Go. So this is a first best effort.

I think it's probably ok for starters since we're so far below the GAWR for the front and rear axles.

The Service Rep at Lazy Days said they're not allowed to set tire pressures at anything other than the max on the vehicle tag.

That bothers me since there's such a large difference between the max, and actual load on the front axle on the Meridian. With only an average of 3300 per wheel on the front and 110 lbs in the front tires, I believe that the handling characteristics could be dangerous if you weren't aware of the situation.
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Old 03-30-2007, 05:54 PM   #14
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RC,

I had a similar experience w/ my new Journey. The front tires were factory set at 110 psi. The handling on this coach was not good; I attributed it to 2 issues: 1) front tires being out of round, and 2) the front tire inflation pressure.

I replaced the 2 front tires, had the coach weighed, and now run 90 psi all around. What a difference in handling!

I agree with your conclusion -- the max tire pressure, especially on a 34' DP, has a significant impact on the handling of the coach.

With the pressures set at 90 psi (plenty of margin since my weights are similar to yours) it has significantly improved handling.
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Old 03-30-2007, 06:11 PM   #15
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Hi Don, I know this doesn't pertain to RC's topic and I hate to get too far off his topic but I just took delivery of a 34H, same color as RCs.

On my voyage back from the dealer (approximately 1200 miles), I noticed that the coach will stray to the right. When I take my hands off the wheel, it starts going to the right so I constantly have to apply a slight bit of steering presure to the left to keep it in a straight line. Is this the problem you initially had?

I know I had a car that did this and after many alignments and different tire pressures, it was finally determined to be an out of round tire.

Were your two front tires replaced under waranty?

I'm thinking of an add-on like Tru-steer or something but would like to see if I can correct it without doing that.

Sorry to hijack this thread but I couldn't quite figure out the PM system here or I would've PM'd you. I can give you my email address if you'd be willing to give me some advice on what to do. It sounds as if you initially had steering problems so I'd like to hear exactly what they were and how you solved them.

Thanks!
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Old 03-30-2007, 06:23 PM   #16
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'rocco--

I had significant handling problems with my new coach, and posted them here in this forum. I had it in the alignment shop 2 times, once when new and not loaded, and the second, after loading with all my stuff, water , fuel, etc. Both times the alignment was dead-on.

The problems I had were wandering on the road, vibrations, and when I took my hands off the wheel, the steering wheel would oscillate left-to-right.

Here is what I did to correct, from most significant to less significant:

1) Replaced 2 front tires (under warranty) as they were out of round (found when balancing wheels and tires on-coach).

2) After weighing coach (loaded) adjusted tire pressure from 110 psi (as shipped from factory) to 90 psi.

3) Balanced 2 front wheels -- this did not have a significant effect on handling.

The out of round tires and tire pressures had the most significant effect on handling.

I do not have any significant pulling to the right, other than following the crown of the road.

I would recommend that you check your alignment with the coach loaded, and have your front tires balanced. If you have a radial tire pull, they should be able to identify this and swop the tires from side to side to see if this improves your handling.

If you would like more info, PM me (go to personal zone, PM, and then add me to your buddy list).
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Old 03-30-2007, 09:25 PM   #17
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Thanks, Don, for the response.

I'm sorry, I know I should've gone back to see what you had posted in the past.

I appreciate your reiterating and summing it up for me again.

I'm sure mine isn't as bad as you describe yours being initially. In fact, some might not even think I have a problem at all. Like I say, it is not a real horrendous problem. It's just a slight wander to the right ...similar to what the crown on a road might cause but I detect it even on a perfectly level pavement. I just have to keep just a slight pressure to steer it left to keep it straight in the lane. Not a real obvious defect but irritating nonetheless.

Thanks again. I may be contacting you anyway as I might persue this as I start documenting things that I need to address during the break-in period.
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Old 03-31-2007, 03:20 PM   #18
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My heaviest points on a four wheel weight have been 4600lbs left front and 8600 lbs right rear.

The heaviest side dictates the inflation to be be used from the tables.

On my 34H Journey the I run 85 front and 95 rear based on the tables for the Michelin 225/80R-22.5 tires. Is this the tire you have?

See this post for some adiditonal insight into ride/handling you can expect on the short wheelbase 34H without shock/suspension mods.
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Old 03-31-2007, 03:38 PM   #19
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I do have the 225/80R22.5 XRV's. I'm currently running 90 in the front and 96 in the rear.

Since I took the front down from 110 to 90, I haven't noticed any significant handling issues

I still want to get a 4 wheel weight distribution.
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