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Old 12-31-2014, 07:27 PM   #1
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Vexing tire question - apologies for the length

I need at least 4 new tires for my 2000 Holiday Rambler Endeavor 40PDB. This is the Freightliner XC chassis with CAT 3126B engine. The OE tires are Michelin XRV 255/80R22.5, load range G. The maximum load capacity of this tire is at 110 PSI. Originally, Monaco Coach specified operating tire pressures of 100 front, 90 rear. After many blowouts and lesser tire failures, the NHTSA directed a safety recall which required Monaco to change the basic tire pressure settings on the placard to 105/95. The GAWR for the front axle is exactly twice the maximum load capacity of the OE tire. I suspect, but cannot yet confirm, that the GAWR is being limited by the tires, not the chassis.

Based on similar experience with other vehicles, I am wary of running tires on a vehicle this large at the ragged edge of their load-bearing capacity. I see plenty of commentary in these forums about poor performance and reliability from both Michelin and Goodyear tires in this application. These companies, in my opinion, are two of the most reputable tire manufacturers in the world. It makes me think that the OE tire specification, which was a disaster from the start, is insufficient to meet the demands being placed upon it in this installation, even with the updated pressure settings.

From my research, I see that I can buy 275/70R22.5 tires in load range H from Goodyear, Firestone/Bridgestone, and others. They are slightly smaller in diameter. Revs per mile are about 548, compared to 541 for the OE size. Most speedometers are not accurate enough for this to be noticeable. They are significantly heavier than the OE tire, in the 95-100 pound range vs. 89 for the Michelins. Undoubtedly, the ride will be firmer. From my rough measurements of my current tires, I'm nearly certain that my current rear wheels have sufficient spacing for these tires in a dual configuration. The lowest pressure setting in the load inflation table is 400 pounds (per tire) greater than the rear GAWR, so there is no way of precisely matching the tire pressure to the load. It will be slightly overinflated. FWIW, the OE tires are the same way - the pressure spec is higher than required by the load inflation table. It looks like these heavier tires will work with a margin of safety that the OE tires do not provide.

The cost of 6 new tires being what it is, I have to ask if anyone else has been down this path. I know people feel more compelled to post about negative experiences, so I'm not surprised at the lack of glowing reviews for the OE-size tires.

Am I over-thinking this and worried about nothing? Will load range H tires be uncomfortably harsh?

Has anyone done this? Please share your experience.

Mike
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Old 12-31-2014, 07:47 PM   #2
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I replaced the OE Michelin XRV 255/80R22.5 LRG tires on my Vectra with Goodyear 275/70R22.5 LRH ones and I've been very happy with them. The original tires were in fact the limiting factor in the GAWR and I didn't like being at the upper limit of the tire's capacity. I can run the 275/70 tires at 95psi front and back and end up with a much better ride as well. Although the difference is indeed small I did have the ECM tweaked to adjust for changed rev/mi.
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Old 12-31-2014, 08:21 PM   #3
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Thanks for that, cbeierl. Just what I was hoping for.

Mike
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Old 12-31-2014, 08:34 PM   #4
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Mike
We have the dreaded Monaco RR4R chassis with undersized trailing arms. We got the Source Engineering trailing arms as well as their Ride Enhancement Kit installed and still had a rough ride. It was due to a 2700 lb heavier passenger rear (discovered at Josams in Orlando via 4 corner weighing during an alignment after trailing arms installation. This heavy side required max air on rear tires, and made our 255/70R Goodyears ride like solid rubber tires. My buddy owns a tractor trailer repair facility and is very knowledgable about all things trucking. Under his direction we went up two tire sizes to Bridgestone Ecopia 295/75R trying to get tires that would hold more weight at less psi. We used Dynabeads for balancing and used his laptop to change the speedometer since the tires are 3.9" taller. He contacted Allison and was told there was no need to change anything with the transmission. No problems whatsoever and now our coach rides about as well as it can be made to. It is enjoyable now, and is much better than I had even hoped. MCC Monaco should never have made this coach/chassis, but OTOH if they hadn't then we could not have afforded a new Monaco at the time (or now) I can easily say I would not hesitate to go this route, but that's really not very scary for me having such a good buddy to lean on. Good luck!
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Old 12-31-2014, 08:50 PM   #5
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In August 2009,I replaced my xrv 255x80x22.5 with Sumitomo 727 tires in the 275/70R22.5 size. The load range H vs the G's I removed gives more load carrying ability and/or the ability to run less tire pressure for better ride. I checked the dual spacing, and it is still good with the 275/70 size.

Pleased so far with the tires, ride, and handling. I do think they are a little stiffer than the xrv's, but I feel safer.

My coach is much heavier on the driver side front, so the original 255x80x22.5 tires were overloaded in that position.

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Old 12-31-2014, 08:59 PM   #6
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Quote:
Originally Posted by cbeierl View Post
I replaced the OE Michelin XRV 255/80R22.5 LRG tires on my Vectra with Goodyear 275/70R22.5 LRH ones and I've been very happy with them. The original tires were in fact the limiting factor in the GAWR and I didn't like being at the upper limit of the tire's capacity. I can run the 275/70 tires at 95psi front and back and end up with a much better ride as well. Although the difference is indeed small I did have the ECM tweaked to adjust for changed rev/mi.
Same here but I went to 305/70's in front on our DSDP, but that was to get the full rated axle capacity of the 14,600# axle that Newmar had Spartan install in 2004. The 275/70's were just not up to the weight, in fact neither was the 12,000# OEM front axle!
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Old 12-31-2014, 11:55 PM   #7
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Here's a tool that I've found to be very helpful.

255/80-R22.5 vs 275/70-R22.5 Tire Comparison - Tire Size Calculator

My other comment regarding moving from G to H.

I replaced my Dunlop G steer tires with Bridestone H tires. While doing so, I was concerned that the ride would be harsher.

I was surprised to find out that the H tires provide a much smoother ride than the Gs!

The problem with all this is, I don't know if it's the tire brand or the change in load rating that made the difference.

I guess we'll never know.
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Old 01-01-2015, 07:51 AM   #8
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I replaced the 9R22.5 Goodyear that were on the Sahara when I bought it with Yokohama 255R75, load range H. Also a smaller diameter tire. I haven't gone far on them yet, but the ride seemed better than the GY on the trip home from the tire place.
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Old 01-01-2015, 02:07 PM   #9
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Hi slowmachine,
If you are looking for more carrying capacity, consider the Michelin 275X70X22.5 load range J. That is what I have been running since I got this coach. With a 20K rear axle, the recommended PSI is 90. My front axle is 12.5K. The recommended PSI is 100. The ride is smooth/quiet and there is plenty of reserve in the tires.
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Old 01-01-2015, 03:13 PM   #10
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Quote:
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Hi slowmachine,
If you are looking for more carrying capacity, consider the Michelin 275X70X22.5 load range J. That is what I have been running since I got this coach. With a 20K rear axle, the recommended PSI is 90. My front axle is 12.5K. The recommended PSI is 100. The ride is smooth/quiet and there is plenty of reserve in the tires.

I have looked at this size from several tire manufacturers. My rear GAWR is 17,000. I don't want to make the rear end ride like concrete tires, and I don't want to compromise the braking capability. I am going to the nearest Freightliner repair center on Monday to discuss fitment, capability and suitability of the various options. I'm assuming that they will have access to the engineering data from FCCC that will tell me what I can get away with. I have a local independent shop that I am hoping to rely on for much of the heavy lifting once I decide on a course of action. When I get the input that I want from all of the subject matter experts, I will figure out who to trust with implementation. I'm itching to get on the road, but I need to know that what I am doing is safe and manageable.

Mike
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Old 01-01-2015, 04:04 PM   #11
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Quote:
Originally Posted by slowmachine View Post
I need at least 4 new tires for my 2000 Holiday Rambler Endeavor 40PDB. This is the Freightliner XC chassis with CAT 3126B engine. The OE tires are Michelin XRV 255/80R22.5, load range G. The maximum load capacity of this tire is at 110 PSI. Originally, Monaco Coach specified operating tire pressures of 100 front, 90 rear. After many blowouts and lesser tire failures, the NHTSA directed a safety recall which required Monaco to change the basic tire pressure settings on the placard to 105/95. The GAWR for the front axle is exactly twice the maximum load capacity of the OE tire. I suspect, but cannot yet confirm, that the GAWR is being limited by the tires, not the chassis.

Based on similar experience with other vehicles, I am wary of running tires on a vehicle this large at the ragged edge of their load-bearing capacity. I see plenty of commentary in these forums about poor performance and reliability from both Michelin and Goodyear tires in this application. These companies, in my opinion, are two of the most reputable tire manufacturers in the world. It makes me think that the OE tire specification, which was a disaster from the start, is insufficient to meet the demands being placed upon it in this installation, even with the updated pressure settings.

From my research, I see that I can buy 275/70R22.5 tires in load range H from Goodyear, Firestone/Bridgestone, and others. They are slightly smaller in diameter. Revs per mile are about 548, compared to 541 for the OE size. Most speedometers are not accurate enough for this to be noticeable. They are significantly heavier than the OE tire, in the 95-100 pound range vs. 89 for the Michelins. Undoubtedly, the ride will be firmer. From my rough measurements of my current tires, I'm nearly certain that my current rear wheels have sufficient spacing for these tires in a dual configuration. The lowest pressure setting in the load inflation table is 400 pounds (per tire) greater than the rear GAWR, so there is no way of precisely matching the tire pressure to the load. It will be slightly overinflated. FWIW, the OE tires are the same way - the pressure spec is higher than required by the load inflation table. It looks like these heavier tires will work with a margin of safety that the OE tires do not provide.

The cost of 6 new tires being what it is, I have to ask if anyone else has been down this path. I know people feel more compelled to post about negative experiences, so I'm not surprised at the lack of glowing reviews for the OE-size tires.

Am I over-thinking this and worried about nothing? Will load range H tires be uncomfortably harsh?

Has anyone done this? Please share your experience.

Mike

Congratulations on having the good sense to research what your options are. I would think that your ride would improve along with your margin of safety. You can lower your inflation pressure and still have more weight carrying capacity than your current setup. Don't worry about not being able to match your inflation exactly with your GVWR. The inflation tables list the minimum pressure to carry the weight an extra 5-10 psi will just give you a margin of safety.


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Old 01-01-2015, 05:31 PM   #12
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Hi slowmachine,
With a 17K rear axle, one can go to the minimum of 85 PSI on the load range L tires. for the L tires, 85 PSI is the minimum Michelin accepts regardless of how light the axle load is. Don't know if this makes the tires too hard for your coach. You're going about this the right way. Good luck.
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Old 01-02-2015, 06:54 AM   #13
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You have been advised about what psi you can use based upon axle ratings as well as the manufacturer's suggestions. But that does not take into account what your tires are actually carrying. Blowouts don't care what the axle rating is. Get a four corner weighing when you are loaded as for a long trip with full tanks so your coach will be as heavy as its ever likely to be. This is the only method that really tells you what you need to know. If you just weigh the rear axle, for example ours--which I admit is extreme, you would not know the passenger rear is 2700 lbs heavier than the driver rear. Just taking the total axle weight and dividing by the four tires and using the tire manufacturer's chart to find the psi would therefore leave the heavier passenger rear tires seriously under inflated--which is the number one cause for blowouts. Four corner weighings are hard to get and typically cannot be done at a public scale due to the coach leaning and skewing the weight. We got ours at Josams in Orlando. Many Monaco rallies have featured four corner weighings and with a bit of research you can find one. RVSEF RV Weighing
Otherwise you are just guessing. We certainly were shocked at our weight difference and the tech at Josams said lots of coaches are not the same weight side to side. Good luck.
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Old 01-02-2015, 07:53 AM   #14
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I am curious about the side-to-side weight distribution. Both slides and the kitchen are on the left side. The MH is winterized and empty. I'm tempted to have it weighed as-is and use the numbers to help me distribute weight as I load it. When I'm finished with the basic load, I can take it back and fine-tune the results. There is a Pilot Travel Center about 28 miles from here that can do it. I can probably delay buying tires until I have actual numbers.

At the moment, my top priority is to reseal the roof seams. The roof is aluminum, and has a long, taped seam (Eternabond?) running lengthwise up the middle, and a side-to-side seam at each end of the center seam. I have a cover on it now, so water infiltration is not an immediate concern. I have an appointment next week to get the MH into a heated service bay and (much to my dislike) pay someone a ridiculous fee to do this. It's too cold here to do the roof in my yard, and I won't wait until April.

Mike
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