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Old 04-30-2013, 07:12 AM   #1
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MotorHome Fish Tails

I have a Allegro 2003 35' class A motorhome. I recently replaced the 4 rear tires with Mitchelin. When traveling at speeds around 60 mph, the motorhome fishtails. I know Mitchelin tires have a softer side wall to give a comfortable ride. Is there something I can do to eliminate the swaying/fish tailing? Thanks

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Old 04-30-2013, 07:21 AM   #2
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Check the tire pressure first. It is possible they over-inflated them to the max on the sidewall, rather than what a load sheet will show for your actual weight.

2016 EC Aspire 42RBQ / 2014 CR-V
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Old 04-30-2013, 07:25 AM   #3
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You should check the air pressure in your Michelins. Your MH should NOT be fishtailing if the air pressure is high enough. Make sure the air pressure is at least what the coach manufacturer recommends and if necessary go a little higher. The tires will also last longer if the air pressure is correct for your rig.
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Old 04-30-2013, 01:48 PM   #4
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I assume that the motorhome did not do this prior to installing the new tires?

I'm wondering of one of the tires is not running true and at that speed it starts a side-to-side wobble. If your pressures are OK then it might be worth taking it back to the tire shop and have them check for any kind of runout or wobble.
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Old 04-30-2013, 02:11 PM   #5
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Yeah, if this started when you put the new shoes on it... weigh the rig and get the pressures correct. Tire shops will frequently just inflate to the max sidewall pressures.

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Old 04-30-2013, 02:49 PM   #6
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Originally Posted by edgray View Post
Check the tire pressure first. It is possible they over-inflated them to the max on the sidewall, rather than what a load sheet will show for your actual weight.
On Michelin and others the pressure on the sidewall is NOT the maximum the should ever have. It's the MINIMUM cold pressure to support the MAXIMUM rating of the tire. The same with the tire charts, the pressure given is the MINIMUM cold pressure to support that weight.
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Old 04-30-2013, 02:58 PM   #7
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I would add
if the new tires are just a bit different in tread width, they are not possibly encountering the same road ridges the front tires do and this will cause a rear swag

the fronts ride in a groove or try to climb out of a groove and your rears are not or they are crawling the sides of the groove. compound this by the human element behind the steering wheel ( not saying your at fault, just a helper by the nature of being human) so if the fronts try to groove ride or wiggle from our wonderful highways grooves or ridges, you will instinctively counter this action by inputting a force on the steering wheel and it can cause rear sway depending on the groovyness (new word) of the road way

i sometimes get bored driving and will do some small driving experiments and drills
grooves and paved ridges even the real small ones will provide a means for the human to induce some sway

and tire pressures adjusted base don the weight at each one will go miles in helping you control sway and fishy wiggle
overinflated fronts tend to wiggle real easy and the same for rears, less contact patch at higher pressures.
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Old 04-30-2013, 03:17 PM   #8
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Motorhome Fishtails

Had 6 new Sumitomo's installed on me 2005 Providence last week when I left the shop I noticed a severe shake in the front at speeds of 55MPH or higher then at 70 it smoothed out. I called the shop and they agreed something was wrong and agreed to fix so today I went back and they said they noticed a bent steel rim in the rear and that they had mentioned it to me last week. However I sure didn't hear it..... Alzhiemer's is one condition I don't have yet. So this AM the owner of the shop and I traveled to pick up a steel rim swapped it out and the shake up front was no different after a test drive. Owner of shop next decides to re-balance front end steer tires. The owner balanced the front end tires himself and used a different setting then the one used last week to do the front tires. Then the front tires were swapped sides. After installation took a test drive and it ran smooth as silk. Clearly the men balancing the tires last week did not use the correct code in balancing the tires. The supposed bent rim was probably not bent but I was assured it was even though there was no physical indications of it being bent. The fishtailing you are experiencing could be a number of things extremely high air pressure is the most common; however if you take it back to the shop and they start scratching their heads find a shop that can do it right and if you are allowed on the shop floor watch what is being done.
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Old 04-30-2013, 03:37 PM   #9
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I had a similar problem with the Michelins on my dp aired to 120 psi as recommended on the sticker.
Weighed the coach and inflated the tires according to Michelin's charts (110 front and 90 rear) and the wandering stopped.
As recommended above, weigh your coach and go by their inflation chart.
I'll bet your rears are at the max on the sidewall.
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Old 04-30-2013, 04:38 PM   #10
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Check and set pressures, yes.
But, sometimes they gotta break-in a bit.
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Old 04-30-2013, 04:48 PM   #11
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Michelin has a tire pressure guide on their web site. Once I lowered my tire pressure to their recommendations mine drove & rode much better.
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Old 04-30-2013, 08:59 PM   #12
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Originally Posted by Mr_D View Post
On Michelin and others the pressure on the sidewall is NOT the maximum the should ever have. It's the MINIMUM cold pressure to support the MAXIMUM rating of the tire. The same with the tire charts, the pressure given is the MINIMUM cold pressure to support that weight.
Mr_D: You and I have had this little discussion / disagreement before. It can be found here: Tire and pressure

I try very hard not to give bad advice. In this case, all I posted is that "the installer may have over-inflated to the max on the sidewall" which may be more than the OPs actual weight calls for.

I'm trying not to parse words here, but IMO, the maximum pressure shown on the sidewall IS the maximum "cold" inflation that should pumped into the tire. Perhaps your statement about the sidewall number being the "minimum" is confusing me, but I hope you will agree it could also be the maximum INFLATION pressure COLD. My experience is that the pressure will increase as a tire heats up, and 120PSI or more is "typical" for a tire driven at highway speeds, but that does not mean an owner should start out at more than the maximum sidewall pressure, which in my case is 110 PSI. My actual weight does not need the maximum capacity of the tire, and therefore I don't run at maximum inflation because too much pressure will have me running on only the "center" portion of tread and that leads to control issues. Ed
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Old 04-30-2013, 09:55 PM   #13
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The inside drivers rear dual tire blew on my rig last July. I replace all 6 Goodyear tires, that were 7.5 years old, with new, 3 month old, Goodrich tires. I also went from load range “F” to “G”.

With my new tires my RV became very unstable. My wife wanted to know what was going on. I didn’t have an answer. I went to camping world and had them add a trac bar to the rear of my RV and a steering stabilizer. The RV already had a front trac bar. That helped but the RV would still track on roads more than it ever did with my old Goodyear tires.

We made our winter trip from Washington State to Arizona. The last time the rig tracked badly was as we were passing through Tucson, AZ. We hit a grooved section of freeway and the RV was jumping left and right.

Our RV handled OK on the way back home. We had a day of driving in 25 MPH winds and I had to be alert all of the time. Our windy day ended with our arrival at Redding, CA. The next day we departed Redding and our RV has never driven better. My Goodrich tires are driving better than my old Goodyear’s ever did. This was probably because of the added trac bar and steering stabilizer.

I posted on- line and there were a few ideas. One was that the tires need to age (cure) and another was the miles helped break in the tires. I don’t know what changed I’m just happy the RV has calmed down.

I did weigh my rig after I bought my new tires and with my new load range “G” tires I could use the minimum pressure, 80 PSI, from the Goodrich tables. I decided to run the tires at the RV Manufactures suggested tire pressure, 85 PSI. I have a TPMS and my cold inflation pressure remained within a few PSI during the entire trip.

I’m not sure if you are experiencing something similar but others have said that they have with new tires.

Safe Travels.

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Old 05-01-2013, 10:19 AM   #14
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Originally Posted by 1lukeduke View Post
Thank you guys so much. MR_D, thank you for the extra info. Well I am going to put new tires on the rig. I have a W22 chassis. This brings up more questions. Does anybody use or know about Roadmaster tires? They are Mastercraft or Cooper I think. Also most tires my size are G rated not F rated. I would rather go with a higher rating but is this a bad thing? Thank you guys for the time that you give. New people like me learn a lot from your knowledge.
Luke, I had the same issues with the load ratings. Something that is really important to me, I had a great debate when I replaced my rear 4 tires last November, that was after 10 months of him hawing and scrutinizing and listening and gleaning information.

My coach manufacturer built the coach in 2003 and the load rating on the factory supplied tires which were Goodyear GV670 RV 245-70-R19.5 was Load Range F. I verified this fact with the manufacturer (Fleetwood).

When my coach was delivered to me, the dealer (Holiday World of Dallas/Houston/Katy Texas) had installed new front axle steering tires, they were a truck tire called Gladiator $181.73 - Gladiator 245/70R19.5 1933294196 tires at SimpleTire.com Load Range H I talked to the manufacturer of the Gladiators, and they do have a 5 year warranty here in the United States, with dealers around the country, so I am comfortable enough to run them another couple of years before replacing them.

When I bought the new tires for the rear axle, I bought Michelin 245-70-R19.5 XRV Load Range F, as the manufacturer recommended.

The front of the coach with the Load Range H tires is much noisier and bumpier than the rear of the coach. I have 95# of pressure in the front tires, and 82# in the rear tires, which is some of that difference. But I believe another part of that difference is the difference in the Load Ranges F and H. The H load range is a stiffer tire, as its rated to carry more, but since the coach is only rated at so much weight, to do so is very dangerous.

The higher load range tires are a lot cheaper, but, you get what you pay for, usually. They are not rv tires, they do not resist UV damage, and they sure weren't built for the ride, which rv tires are built to provide a better ride than truck tires. This is all my opinion, and my belief, and by so stating will shield me against any attacks from others You will hear a plethora of opinions on the tire issues, so hope some of this helps!

I might also add to the OP that my new rear Michelins I did not have any fish tailing or anything like that, I installed dynabeads and had them inflated to 82# when they were installed, which is the correct pressure for my coach weight (from certified CAT scales and the Michelin load range/pressure chart and the Manufacturer's specifications chart on the driver window wall).

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