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Old 07-12-2012, 12:34 PM   #1
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Tire Engineering help needed

Need a little input from someone knowledgeable in the engineering of selecting the proper Tires and Rims as related to the GVWR of the coach.

Not sure if anyone else has run into this problem but from the feedback I am getting from Lionshead (tire and Rim dist to FR) and FR it sounds like no one has questioned this.

In my attempt to replace the "failed" Trail Express I selected a replacement set of tires only to have the Tire Tech at the store refuse to mount them on the existing Rims. He was concerned about Liability issues if he did and provided me the PDF attached.

The RIMS I have do not have a PSI stamped on them, but do have a Max 3200LBS stamped on them, the original tires have a 3520LBS at 80PSI stamped on them. The tires I wanted to buy are 3450Lbs at 80 PSI.

Now the issue, since my unit GVWR is 14,001, my axles are 6K, I need tires to support GVWR per the highway safty doc (PDF), but since my RIMs are only 3200LBS the store Tech would not mount a tire that had to be run at 80PSI to meet the GWVR application of the coach which put it at a higher poundage level than the 3200Lbs.

Can someone tell me how this really works and if the tech is correct?

I get the delivered tire number part (how it came from FR, only using the tire number)
3520lbs x 4 = 14,080 (higher than my GVWR)
but still that is higher that the RIM 3200LBS.

Is FR delivering these units on under sized running gear, as well as cheap tires?
If this is correct then I also need to replace the RIMs.
Attached Files
File Type: pdf FMCSA.pdf (372.1 KB, 44 views)
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Old 07-12-2012, 12:52 PM   #2
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Lucy
I think you are forgeting about the pin weight. As you have 6000 lb axels, the tires should only see 3000 lbs each. 3000 X 4 = 12000 so you would need 2000 on the pin to be at your GVWR.
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Old 07-12-2012, 01:12 PM   #3
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Lucy
I think you are forgeting about the pin weight. As you have 6000 lb axels, the tires should only see 3000 lbs each. 3000 X 4 = 12000 so you would need 2000 on the pin to be at your GVWR.
Agree, that's what I thought, but not what the tire Tech thinks. as the sticker on my unit spces 80 psi, and 80 psi is over 3200LBS on the original equipment and the replacement tires. I could reduce the tire pressure to a PSI that corresponding to 3200LBS but what would the effect be on the tire long term, low PSI in what I thought caused tire blow outs?
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Old 07-12-2012, 02:09 PM   #4
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80# is hardly low pressure and they will automatically increase by 5#-10# when on the highway from what my TST monitors have shown me.

Think I would find a different tire shop that sells what you want. If nothing else, take the tires & wheels off the trailer and take them to a dealer for mounting, putting in metal stems, and balancing.
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Old 07-12-2012, 02:37 PM   #5
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I find it a little confusing that the tech is concerned that the tire has a higher rating than the rim. The fact is your axel would be over loaded by 400 lbs each if you were at the max of the rim (800 lbs total). I would be more worried about the axle than the rims. I have not heard of a wheel rim failing because of an over load, tires yes rims no. And I am shure that you are not planing on over loading your trailer.
Reducing the pressure in the tire is only going to reduce how much weight the tire can handle it is not going to change how much weight the tire will see from your trailer. If I add up the maximum weight the four tires on my TV can carry it is higher than the GVW of the TV.
In a long winded way I am saying it does not matter what the tires are rated for as long as you dont go over the 3200 lbs of the rims you will be fine.
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Old 07-12-2012, 03:50 PM   #6
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Your "tire tech" is not very well informed.

I would find a new one.
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Old 07-12-2012, 06:13 PM   #7
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Thanks for the sanity check everyone. I will find a new tire place to deal with, as this one had me thrown for a loop there

However, now that I spent a day doing research on trailer tires and rims does anyone have an opinion on changing out the OEM rims for steel ones that support 110 psi at 16x6.5
and then putting Goodyear G614 tires on the unit
Has anyone done this? Seems on paper to be a better combo then any of the ST tore options I saw
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Old 07-13-2012, 10:27 AM   #8
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What is going on, now I went to a Goodyear store and was told the same thing. The tire lbs has to be the same or lower than the rim rating. They even have this listed on their web site, under ratings. Goodyearrvtires.com. The guy told me it was because of all the tire failures on TT of late. This really limits what tires I can use and forces me to LT tires which are 3042lbs, which to me seems tight to the max 3k lbs of weight each tire should see on my unit. Going crazy.
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Old 07-13-2012, 12:06 PM   #9
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Have you tried contacting Forest River for their input on mismatched ratings of the tires and rims. As they sold the camper with under-rated rims relative to the tires I think the onus is on them to correct or assist in finding a solution.

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Old 07-13-2012, 01:55 PM   #10
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Quote:
Originally Posted by camper_Lucy View Post
What is going on, now I went to a Goodyear store and was told the same thing. The tire lbs has to be the same or lower than the rim rating. They even have this listed on their web site, under ratings. Goodyearrvtires.com. The guy told me it was because of all the tire failures on TT of late. This really limits what tires I can use and forces me to LT tires which are 3042lbs, which to me seems tight to the max 3k lbs of weight each tire should see on my unit. Going crazy.
I am concerned that the problem is apples and oranges.

When talking about PRESSURE (PSI) the rim must be rated for the maximum pressure you plan on running the tire at.

If you have a tire you plan to inflate to 65 PSI; the rim must be rated to 65 PSI OR MORE.

If you have a tire that is rated at 3200 pounds of LOAD and the rim is stamped 3000 pounds and the camper weight PER WHEEL is 2800 pounds I have NO idea what their problem is. The Load is well below the limits of the tire and rim. You can also run the tire at a reduced PSI (compared to max) as long as you are correct pressure for the actual load on the tire/rim.

PLEASE someone explain what I am getting wrong?
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