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Open Roads Forum  >  Class C Motorhomes

 > Tire lbs Per this chart. Help

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donscomp

Camarillo,CA

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Posted: 06/08/02 12:20pm Link  |  Print  |  Notify Moderator

We are trying to figure this out.
We weighed our RV. NOT per wheel but.
Total was 12,780 With a max per rv paperwork of 14,050. GVWR

GAWR was 3,980 Front with a Max of 4,600

8,800 Rear with a Max of 9,450

We went to THIS chart.
http://www.dickmantires.com/loadlimits.html

The tire is the LT225/75R16. Yes, the dreaded SteelTex.

Would you take the rear axle weight and divide by 4 to get the lbs per tire?
ie 2200 for a dual would be 70 lbs?

And the fronts? Would you divide by TWO? If so, that would only be 50 to 55 lbs and that doesnt sound right. Pretty much running 75 all the way around.
Any help would be grateful and or if this isnt a good chart to use?
Thanks a lot.

Don & Debbie





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rawdi

Seattle, WA

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Posted: 06/08/02 02:58pm Link  |  Print  |  Notify Moderator

Assuming your tires are load range E (10 ply), inflate them to 80 psi. I am waiting for Firestone to tell me what the maximum safe inflation is.

Dual LT225/75-16 LR E tires are supposed to be able to carry 2470 lbs at 80 psi. That is, your rear axle tire rating is 9880 lbs (2470 X 4) assuming they are loaded equally left and right. Ford rates the axle (9450 lbs) at a meer 96% of the tire rating.

Numbers for the front axle are similar except 2X the individual tire rating. Single tires are rated for more load than duals. Not sure why.

Running your tires at less than the pressure for maximum load rating increases the chance you will have an overloaded tire failure (blowout).

Regards,
Bob

gswanson

Yucca Valley, CA

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Posted: 06/08/02 03:53pm Link  |  Print  |  Notify Moderator

Looks to me like you have done the arithmetic right. You obviously have the standard Ford E450 chassis of 14050# and the standard Ford supplied Firestone tires. They are Load Range E rated, but are not 10 ply. I still have one old Steeltex carcus and 6 new Steeltex II tires and they all say 2 polyester + 2 steel on the tread and 2 polyester sidewall. The numbers you quote for weight rating look good to me, too.

You should, on a new 2002, have a white sticker on the side of the drivers seat, closest to the
door, with the recommended tire pressures listed as well as GVWR and GVAR's. I'm going to bet they say 65 psi for the front tires and 80 psi for the rear. That's what mine says and I have been running that since new in December 1998. Yes, I did experience a blowout of both right rear duals at 22,500 miles. The tires were at 80# and looked as good as new in every respect and had 3/4 of the tread still on.

My Tire Guru says that is the correct pressure to run for my rig. I would tend to follow that rather than someone elses chart, wouldn't you?



gswanson

Yucca Valley, CA

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Posted: 06/08/02 04:25pm Link  |  Print  |  Notify Moderator

I went out to get my figures and found I was already "posted" here. My figures compare very closely with yours - - weighed full of fresh water, gasoline, propane, and normal stored items. It did not include passengers, clothing, food, or black & gray. I'm a model 26 but measure just under 27 feet. Front axle was 3660, rear 8540, total 12220 [yes I know there is a 20# error]. Your chart tells me to run at 50# front and 65# rear. No thanks, I'd be scared to at this point...but I do not run at 80# all around, either.

Note: Due to invalid formatting, all formatting has been ignored.

MELM

GA

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Posted: 06/08/02 04:50pm Link  |  Print  |  Notify Moderator

It looks like you've done the math correctly. I've seen many recommendations to add 5 lbs to the calculated value to accomodate weight variations, etc.

You can do a search on tire pressures, and have lots of reading. I just went to the Michelin site, and found their brochure on RV tires: http://truckus.webmichelin.com/tires/RVTIREGUIDE1.pdf.

While aimed at their tires, most of the information applies to any RV tires. And you used to be able to order a video tape from them, but I must have missed that link today.


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gswanson

Yucca Valley, CA

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Posted: 06/08/02 06:40pm Link  |  Print  |  Notify Moderator

Well, well, well - - whatcha know, I've learned something here today........

I have been following the threads on this tire issue on this forum for about a year. Most that has been said is pretty good, but I can see that few have not looked beyond their noses at this. Now it seems to be pretty clear, at least to me.

I have printed out both the Michelin pages refered to above and the Les Schwab pages above. It takes both to make a complete story. Michelin gives a lot of good info, but not numbers we can use. Les Schwab gives the numbers. As far as I know, Firestone does not.

Putting the two together, I can see that the Federal Certification Tag, that I refered to on the side of your drivers seat, gives the GAWR ratings for both front and rear axles. The recommended pressures listed on that tag are the nearest higher numbers to those ratings, according to the charts from Les Schwab. Simple as that......end of story.

So, maybe you really can run at lower pressures, but before I would do that, I would make darn sure I followed every step in the Michelin guide for weighing each wheel AND THEN using the highest weight on a particular axle for the pressures on the tires of that axle. It seems to me that our weights are so close to the actual GAWR's that, I for one, will continue to do exactly what the sticker on the drivers seat says to do. It also proves to me that to run 80# all around is truly OVERINFLATION in our cases and should not be done.

Whew, now my old head hurts........needs a beer.

donscomp

Camarillo,CA

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Posted: 06/08/02 06:53pm Link  |  Print  |  Notify Moderator

Thanks for the info. Man. You would think it would be a simple thing. Hey gswanson? I didnt mean to make you do all that work. But I thank you much. Tell the truth. I just found the Mich. tire chart and was comparing when I checked back here.
Thanks again all.

Don & Debbie



MELM

GA

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Posted: 06/08/02 08:02pm Link  |  Print  |  Notify Moderator

I put in the link for Michelin for the information in the brochure, but don't use the Michelon inflation table for other tires - Michelon tires often require less pressure than other brands. (Don't know why, it's my observation from data in tables.) Other brands tend to be more comparable to one another in pressure.

You can call Firestone, or stop by a dealer, and they should give you a chart for your tires - same for other brands.

Also, note that some wheels on MH's are not rated for the same maximum pressure as the tires - there are a lot of wheel rated at 95 psi max with tires rated at 110 psi max on them. The wheels have the maximum stamped on them. (Learned from other threads on tires on the forum.) I don't want to be around when a wheel blows out - a tire is bad enough!

donscomp

Camarillo,CA

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Posted: 06/08/02 08:58pm Link  |  Print  |  Notify Moderator

Yes Mel,
This is why I am working so hard to get it right. LOL

We had a valve stem come out on the I-15 on the way to Vegas. Because the factory steel extender for the inside dual came off. It wasnt a shreader but was scary enough.
Thanks

Don & Debbie



HiTech

Texas

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Posted: 06/12/02 08:13pm Link  |  Print  |  Notify Moderator

Does the +10 psi rule apply to all tires if you want to drive over 65mph? Obviously it does not apply if it puts you over the max pressure.

The point about weighing left to right is a good one - it is very unlikely that the weight is perfectly balanced across the axel, and I believe the pressure for all tires on an axle is supposed to be that of the one(s) with maximum weight on them.

Still learning this tire pressure stuff. I am running the OEM sticker recommended pressure on my tires until I get an accurate weight.

-Jim




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