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Old 11-16-2010, 01:14 PM   #1
cgaskins
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Help me understand something.... (tires)

Ok, first know that I have done a lot of reading about replacement tires on this forum and rv.net. My intention is not to start a huge discussions or re-hash a bunch of stuff. However a tire purchase is a big decision so I want to have people smarter than me to double check what I think I have learned....

Background:
  • I have a 2007 Montana 3400RL.
  • I have 4 year old Goodyear Marathon ST235/80/R16 on it right now.
  • Specs say my trailer weighs 11,500 pounds
  • Based on replies to my other post, I think I have 6K axles

I know that I can choose between an ST235/80/R16 tire or an LT235/85/R16 tire. Here is where I need a little understanding.

How do I determine / calculate the correct weight specs needed for my tires? Do I take my 11,500 (say 12000 to round it off) and divide it by 4? That would be 3000 per tire. Is it that simple or am I missing something?

I was looking on the Maxxis web page and they show a weight rating on the tire at 80psi of 3420 for that ST tire. So obviously that tire can handle the weight of my trailer.

Now for the LT tires....

I was looking at the BFGoodrich Commercial TA All Season and it is saying 3042 at 80 psi. That is a big difference in weight load. I have seen a few members here saying they run this tire. If so at what PSI?

Finally, I know that the Firestone Transforce H/T and Bridgestone Duravis R500 Commercial LT are other recommended LT choices but I can't find the weight rating for that tire. Any pointers in the right direction to find that data?

I assume there is no highway rules/law with switching from ST to LT tires...

I am leaning towards the BFGoodrich Commercial TA All Season, by the way!

I appreciate the help and guidance in advance. I just don't want to create a problem for myself.

Regards,
Chris
 
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Old 11-16-2010, 01:31 PM   #2
awaywego
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12000 lbs minus tongue weight. 1975 lbs It is best to have the unit weighed with all your stuff in it.
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Old 11-16-2010, 01:57 PM   #3
exav8tr
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Unless you have a "Very EarlY" '07 3400, you probably have 7k axles. Fully loaded, your trailer may weigh as much as 15,600 lbs, HOWEVER, about three thousand of this will be on the pin. SO you will have 12,600 lbs over your axles. Divide this by four and you get the tire load, 3,150 lbs per tire. This is a simplistic approach to the question. You need to know the actual axle weight you have and you can take your trailer to a CAT scale and get the actual weight on EACH tire. You might also be able to get each wheel weighed at an FBO at your local airport, Check with the maintenance folks as they are required to weigh aircraft from time to time. TO BE CORRECT, YOU MUST USE ACTUAL WEIGHTS AFTER YOUR RIG IS LOADED FOR A TYPICAL TRIP.

I will let the tire folks address individual tires. Lonnie B. is our resident expert.....

Hope this helps.
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Old 11-16-2010, 03:45 PM   #4
sfish
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I want to know the answers to your questions as well. I have always been a fan of michelins.
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Old 11-17-2010, 12:32 AM   #5
Larry
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Specs do not tell you how much your trailer weights, they tell you the trailers weight rating...big difference.
Crawl under your trailer and see if the decal is still on the axle, or open your kitchen cabinet door and find the GAWR. If it says 6000lbs then you have 6000lb axles.
Buy tires that will support 6000lbs per axle. If you can, find a tire pro that you can trust and talk to him/her.
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Old 11-17-2010, 01:46 AM   #6
pineranch
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The recommendation to find a CAT scale and weigh the thing is a good first step. This will give you a good weight on your axles. I've weighed mine on a moving company scale and a CAT scale and my axle weight was the same, 11,200. This is my loaded hit the road configuration. I too am looking at the Goodrich Commercial TA since I plan on using the 4 year plan.
Mike
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Old 11-17-2010, 02:04 AM   #7
Tom S.
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Loading your trailer and weighing each wheel is the ONLY way you can know for sure how much weight each tire is carrying. Weighing the whole trailer and dividing by 4 is a bad way to go because it doesn't give you the real world weight distribution of your trailer.
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Old 11-17-2010, 02:20 AM   #8
CamillaMichael
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Agree with others, you MUST get your trailer weighed as a first step to know what you are really dealing with.
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Old 11-17-2010, 04:11 AM   #9
LonnieB
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As far as the weight of your trailer goes, exav8tr and TomS have given you the right advice. You need to weigh it while loaded for a typical trip. The ideal way would be to weigh the load on each individual tire, then use the heaviest loaded one as your guide. If this is not possible, you can weigh the front and rear axles individually, and use the heaviest axle weight divided by two as your guide. The most common way, also the least accurate, is to weigh both axles at the same time and divide by four.

The tires in question, size LT235/85R16 load range E, all have the same maximum load and inflation molded into the sidewall. 3042 pounds at 80 psi. There are however, differences in speed ratings and construction.

Michelin XPS Rib - Steel belts and sidewalls. Max speed 99 mph.
Bridgestone Duravis R250 - Steel belts and sidewalls. Max speed 99 mph.
Bridgestone Duravis R500 - Steel belts and polyester sidewalls. Max speed 106 mph.
Firestone Transforce H/T - Steel belts and polyester sidewalls. Max speed 106 mph.
BF Goodrich Commercial T/A - Steel belts and polyester sidewalls. Max speed 99 mph.

There is no law prohibiting you from switching to LT rated tires. Nor is there a law prohibiting us ( tire dealers ) from recommending, selling, and installing them as long as they meet the load requirements. A reputable tire dealer will go by the scale ticket you take him when making recommendations.

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Old 11-17-2010, 07:13 AM   #10
DarMar
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Quote:
quote:Originally posted by LonnieB

The most common way, also the least accurate, is to weigh both axles at the same time and divide by four.
The least accurate way for sure, with our previous 3400 we were like 300 lbs. heavier on the street side than the curb side. Now with our 3455 the difference is even more. Fully loaded with pantry full and 30 gal of water our street side axles weigh 5972lbs and our curb side weight only 5192 lbs. we do have the new four door refer that must add to the imbalanced situation. So as one can see running with our BFG tires we are running right at maximum on the one side with room to breath on the other curb side. We will never push the speed limit on the BFG tires to the 99 mph and I still have more faith with these tires running at maximum than I did with either the Missions or the new Marathons that came with the new rig and are rated for a lot more weight. JMHO!
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Old 11-17-2010, 09:42 AM   #11
pineranch
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I've been in the "get rid of the Marathons" mode for 6 months. But the more you guys talk the more I like them since no one seems to agree with trailer weight, speed rating, psi limit, or load limit. I beleive in the KISS principle. Not everyone has the ability to find individual scales so I took the CAT recommendation and now a few think this method is wrong headed. The previous thread has a 780lb differential, that's alot. Real boderline for an E rated tire but that appears to be the norm for most MOC'ers. Think I'll park it until Feb. and buy whatever is on sale.
Mike
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Old 11-17-2010, 09:53 AM   #12
CamillaMichael
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Quote:
quote:Originally posted by pineranch

I've been in the "get rid of the Marathons" mode for 6 months. But the more you guys talk the more I like them since no one seems to agree with trailer weight, speed rating, psi limit, or load limit. I beleive in the KISS principle. Not everyone has the ability to find individual scales so I took the CAT recommendation and now a few think this method is wrong headed. The previous thread has a 780lb differential, that's alot. Real boderline for an E rated tire but that appears to be the norm for most MOC'ers. Think I'll park it until Feb. and buy whatever is on sale.
Mike
You have to wonder about the long winded explanations...at times they are priceless and at times they just confuse me. As far as tires go, thought trailers needed trailer tires and trucks needed truck tires, since they both are supposed to have individual characteristics. But some will tell you different. I listen to everyone's input and hope to eventually reach a decision on what tires to replace my Marathons...still listening.
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Old 11-18-2010, 04:48 AM   #13
DonandJudy_12
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We use LT235/85R16E tires on both TV and Monty- We buy 4 new tires every 3 years- The new tires are put on the Monty and the Monty tires are put on the TV drive axle- We have not had a tire failure since instituting this procedure- We get 6 years service from each tire and feel we save big bucks while getting the most SAFE use of each tire- Our unit came equipped with LT235/85R16E tires which helped make our decision easier- Incidentally, I am retired from Firestone Tire and Rubber Co Retread Division and think I have some knowledge of tire constuction and capabilities- JHMO- Don
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Old 11-21-2010, 07:22 AM   #14
sreigle
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I have not read all the way through this thread so I hope I'm not duplicating.

The 7k axles were put into the 2007 models beginning with December builds. If you don't want to crawl under to find the axle tag, just look at the GVWR rating. It's on a cabinet door and may also be on that tag near the front corner, outside. If the GVWR is just a little under 14,000 lbs, you have the 6k axles. If it's around 15,000 lbs, you have the 7k axles. Per a Keystone engineer (I asked), the GVWR increase was because of the heavier axles. No other changes were done to increase weight capacity in the 2007 models.

As for how much tire you need, keep in mind your actual weight is divided between the axles and the pin. You're not likely over 12,000 on the axles, total, unless you run very heavy.

Also, if you can find a way to weigh the weight on each tire, that's the best scenario. Then you can use a tire inflation chart to find out how much psi you need to handle the heaviest corner. Put that same psi in all the tires (don't forget the spare!).

On our prior Montana, a 2003 3295RK, heavily loaded, we put the BFG Commercial T/A tires on the rig and they did very well. We only put 9,000 miles on them before trading the rig, though. From what I've heard, this tire is very popular among rv'ers. I'm sure there are a number of good quality tires but I don't know about many of them. We currently run the Load Range G Goodyear G614RST tires but they might be overkill if you don't run heavy.

Good luck.
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Old 11-21-2010, 07:34 AM   #15
sreigle
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By the way, here's a couple of reasons I dumped my Marathons (made in China, by the way) on the 2003 3295RK. One of these is from a prior trailer. There were several failures beyond these.





This one is not a Marathon, it's a Freestar tire, also made in China, that blew in San Diego last April, on our 3400RL. I included this to show what CAN happen when you blow a tire.


and a better view of that Freestar


and yet another blown Freestar
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