New Tires

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Dan Walters

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Jun 15, 2006
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485
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Bellville, Texas
I am about to replace all of the tires on my 1998 Allegro Class A that I just bought because they are 10 years old according to the date code.  They only have 7,800 miles on them, but after reading this forum, I know they have to be replaced before I can go anywhere.  The tires are Michelin 7.50 R 16.  My question is, do I go back to this same size tire or can I go to a 235/85R16 which is almost identical in overall diameter but is a shade wider (9.21 section width rather than 8.35 on the 7.50R16).  The current tires are load range D with a 2470 Max. Load rating and the new ones would be the same for the same size.  However, I can get the 235/85R16 in Load Range E, with a 3042 Max. Load rating.  The Michelin's are the original equipment tires that came on the coach, which I believe has a 12,500 lb GVWR.  Is there any benefit to getting the wider tire and is there any benefit to having a larger Max. Load rating?  Thanks.

Dan
 

TNROY

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Feb 4, 2006
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Kalamazoo, Michigan
The higher load range tire might allow you to run at a slightly lower air pressure in the tire. Michelin publishes inflation charts based on the ACTUAL weight carried by the tire. Be careful of the larger size, as the duals on the rear may be too close together and cause major problems.
 

Gasser

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Feb 21, 2006
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Ada, Oklahoma
Just make sure the tire specs out for the size of rim you have.? All tire manufacturers will publish min and max rim size for a given tire.? Second as above, even though they are fine for your size of rim, make sure there is no rubbing of any kind or else you may have a catastrophic failure.

Specific points to look out for is rubbing on the front at the bumper, fender when turning and rubbing on the spring or frame.? turn the wheel lock to lock and move forward and listen for rubbing and also do a complete visual inspection to be sure you have plenty of clearance.? A large side wall tire can flex under load and in turns so you may have an inch while sitting still but rub at speed.? Just be carefull.? I have put lots of oversized tires on in my day and they look and perform great but you must be carefull.

 

Dan Walters

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Jun 15, 2006
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Bellville, Texas
Thanks to both of you for the replies.  I have since checked with a couple of tire dealers here in Beaumont and haven't found anyone yet who is knowledgable enough to tell me for sure if the wider tires will cause a problem on the dual wheels.  I probably should find a truck tire dealer who deals with duals on a regular basis.  I think I'm going to just go with the original tire size so I know that I will not have any problems with the width.  Thanks again for your input.

Dan
 

tazerman

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Jun 22, 2006
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Dan, I just went through this, this weekend.  I have a 1989 Itasca We just bought and had two blowouts on the trip home on 10 year old tires, finally got to a Les Schwab and had 235/85/16 10 plys put on. I also was concerned about the width, so the guy installed one side and set it on the ground so we could check the distance between the dually's, the distance was exactly the same as the 7.50's ??? don't know why.

Also, I do not know if you have looked for 7.50's or not, but Les Schwab did not even handle them anymore, if the distance would not have worked out he said I would have to have gone with a 225 or a 215 which as you know would have been shorter also.

Darren
 

Dan Walters

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Bellville, Texas
Darren,

Thanks for the information and for sharing your experience.  I may have the local tire shop do the same thing, if they are willing, to see if there is any difference.  If the tires weren't any wider on your duals, that same thing should hold true on mine.  How was the ride and handling after you put on the bigger 10 ply tires?  That's what I was hoping to improve by going up on the load rating and width.  Thanks again for your reply.

Dan
 

tazerman

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Jun 22, 2006
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Dan, here in lye's the problem, I have a post under motorhomes, newbie asking for experienced help, you may like to read it.? I had terrible handling on the highway once we hit the road after purchasing the home, wandered all over, had a terrible trip, tore both sides off our, new to us home with the blowouts. :-[ very sad. anyway it did help the wandering a bit to have the 10 plys I believe, but it is still so bad I can not tell you for sure if I am being honest.
 

Dan Walters

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Jun 15, 2006
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Bellville, Texas
Darren,

I did go and read your post under Motorhomes.  That's an awful experience, and it's exactly why I WILL NOT put mine on the road until I get new tires installed.  I have only driven my Allegro short distances, since I bought it from someone here in town, so I can't comment on the side-to-side sway with the current tires.  But, I did own a 1982 29' Allegro 20 years ago and I can tell you that changing to a heavier duty shock absorber made a big difference in the "rock and roll" tendencies on that model.  Sorry to hear about your disastrous trip home with your new coach.

Dan
 

Gary RV_Wizard

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Dan,
The dealer should have a tire specification chart that shows the dual tire clearanceamong other tire spec numbers (e.g. circumference, rolling diameter, tire rim width, tread width, etc.).  Unfortunately many dealers don't even know there is such a chart, let alone where they have it stashed away or how to interpret the numbers.

The actual dual spacing changes with tire inflation, so make sure you have the right inflation (+/- 10 psi) if you are going to do the "try it and measure" approach.  Check the tire inflation chart (another thing some dealers never use) for the tire make & model and use the figures for your actual axle weight.  If you don't know the actual weight, assume the rear is at the axles max load (GAWR) and divide by 2 for the tire load (divide by 4 for duals).  Because the load is rarely actually equal on both ends of the axle, allow a substantial afety margin if you use an estimated weight - I would go at least 10 psi higher than the estimate suggests.

There is little advantage in using a wider tire and there is no advantage to a higher load rating unless the current tre load rating is barely adequate.  The tire will have the actual max load carrying capacity embossed right on the side wall. If the LRE tire has a max load capacity that exceeds you needs by several hundred pounds per tire, it is sufficient and a higher load range is a waste of money.  But if an "E" tire is close to your axle limits, go for the next higher load range. Better safe than sorry.  Not all LRE tires have the same load capacity, so check the new tire rating as well as the current ones.
 

tazerman

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Jun 22, 2006
Posts
11
Hey Dan, I did not know of tire failure due to age until I got home and googled rv"s and found this site and began reading up on tires and there codes, also how they fail from age.? The tires looked 90% on the rubber side and had no weather checking at all.? The date code was the 46th week of 96 though, ten years old.

Dan and Gary, the tech at Les Schwab was very aware of his tire charts and they have them all on computer, he even showed me the difference between the two and also showed concern if they were going to be ok or not.? That's how the subject of having to go to a smaller tire came up.? The 235/85 is what they always replace the 7.50 with these days is what he told me, but that is on non dually's, that's why he wanted to check one side before moving on.

Darren
 

John From Detroit

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Apr 12, 2005
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Davison Michigan
tazerman said:
Dan, here in lye's the problem, I have a post under motorhomes, newbie asking for experienced help, you may like to read it.  I had terrible handling on the highway once we hit the road after purchasing the home, wandered all over, had a terrible trip, tore both sides off our, new to us home with the blowouts. :-[ very sad. anyway it did help the wandering a bit to have the 10 plys I believe, but it is still so bad I can not tell you for sure if I am being honest.

If your motor home is wandering all over the road you likely have further problems needing attantion.

I can think of many, some expensive, posiblities however I'll let other more expierenced folks list them for you

But I'd get them taken care of... Motor homes are not supposed to "Wag their tails" after all.  They are supposed to go straight down the road (Assuming the road is straight that is)
 
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