Michelin LTX 235/75R15 XL Upgrade?

[switz]

I understand the concept that the Michelin LT 225/75R16E tire could work on nearly every Airstream model and is available from the factory as an option. The added cost over five of the 15" tires installed for about $880 includes five EB style 16" wheels (exceeds $530) plus about a $370 adder for five of the 16" tires installed at the local Costco.

Depending on which Michelin website is visited, the 15" tire rating is either 1,983 or 2,183 pounds at 50 psi. At the local Costco, I looked at the actual tire sidewall and the tire rating is 2,183 pounds. The 16" tire has a 2,680 pound rating at 80 psi. The 15" tire radius is about 0.3" taller than the ST tire radius and the 16" tire radius is about 0.5' taller than the ST tire radius.

I am looking for what size (length) tandem axle (and it's axle weight rating) Airstreams have shifted away from the GYM ST 225/75R15D or some other 15" brand to this specific Michelin 15" tire.

Thanks

[MaxTow]

The lower of the weight ratings for the LTX 235/75R15 is for taller vehicles (i.e SUV) with a high center of gravity. For the AS with a low center of gravity, the higher weight rating is appropriate. (2183 lbs)

I have installed these tires on our 30' Safari Bunkhouse (6250 lbs Dry / 8400 lbs GVWR) following the lead of others with this same AS model.

[bwoodtx]

I have a 1997 30' Excella wide body that I have installed the XL tires on. My GVWR is 8300. Bear in mind GVWR, unless I am mistaken, and surely will be corrected here, Is with all tanks full and essentials on board. I never travel with ANY tank full, so I would presume I am not close to GVWR>

[daveswenson]

Originally Posted by bwoodtx

I have a 1997 30' Excella wide body that I have installed the XL tires on. My GVWR is 8300. Bear in mind GVWR, unless I am mistaken, and surely will be corrected here, Is with all tanks full and essentials on board. I never travel with ANY tank full, so I would presume I am not close to GVWR>

GVWR is the max weight you should bring your trailer to. It doesn't matter whether you bring the weight up with water or canned goods or dead hookers. Pounds are pounds, doesn't matter how you get there.

Only way to know for sure is to weigh it.

[dkottum]

We considered the same thing with our new trailer and decided to buy 4 new 16" wheels and the Michelin tires for our unit. The present spare will suffice in the unlikely event it is now needed.

Then you have (with faint argument) the best possible tire to protect your new trailer from blowout damage, and you from changing tires on the interstate.

A puny cost difference considering the cost and lifetime of your new trailer. Sell the old wheels/tires as a combo to improve the deal.

doug k

[MaxTow]

Originally Posted by dkottum

We considered the same thing with our new trailer and decided to buy 4 new 16" wheels and the Michelin tires for our unit. The present spare will suffice in the unlikely event it is now needed.

Then you have (with faint argument) the best possible tire to protect your new trailer from blowout damage, and you from changing tires on the interstate.

A puny cost difference considering the cost and lifetime of your new trailer. Sell the old wheels/tires as a combo to improve the deal.

doug k

You would consider the 16" if you feel you need more load capacity. One of the downsides however is that running the tires at maximum pressure (as recommended) results in a very stiff tire. This translates into a rougher ride for your AS.

Also, check the clearance to make sure 16" tires will fit your unit. I was seriously considering the 16" tires - and very glad that I did not. One of my axles looks to be slightly askew. The 16" tires would have rubbed. Now this axle issues needs to be sorted out - but I had to get the tires on to get the trailer home from where it was purchased. I would have been stuck with 16" tires.

[BlackAces]

There are two things that must be considered here and cannot be overlooked, because, in doing so, you will be in direct violation of DOT regulations any time less than the regulations minimum requirements are used.

ALL “P”, passenger tires, must have their load capacity reduced by about 10% when fitted to RV trailer axles. Divide the actual load capacity by 1.1 to get the acceptable load capacity for trailer service.

The minimum tire load capacity required for trailer service MUST equal or exceed the trailer’s certified GAWR.

BlackAces

[switz]

The 2013 25FB International has two axles with a GAWR of 3,800 pounds each. Two of the 15" Michelin tires have a combined weight of 3,970 pounds using the derated specification of 1,985 pounds for each tire. Thus the letter of the law is met per the post above.

However, this particular tire seems to be in limbo between the P or LT rating. The sidewall of the tire shows the 2,183 pound rating @ 50psi. That is the number that is seen when viewing the side of the tire by an inspector.

[BlackAces]

Originally Posted by switz

However, this particular tire seems to be in limbo between the P or LT rating. The sidewall of the tire shows the 2,183 pound rating @ 50psi. That is the number that is seen when viewing the side of the tire by an inspector.

You're right, there is something remiss with the description for the Michelin tire. The load capacity for an XL "P" tire would have a load index rating of 108 = 2205#. A little research is needed here.

BlackAces

[Pepthedog]

All I know is I put a set of Michelin LTX 235/75R15s on and really enjoy the ride now. I had a Marathon fail but got stopped before it came apart totally and dodged the bullet. Now I don't even consider the gun loaded. Peace of mind goes a long way.

[Jim Flower]

I did the same as Doug. I also use a TPMS that indicates 0 air loss since May. I really like the benefit of having the Airstream up a bit in order to try and eliminate the tail drag at some fuel stops. ( only once so far)

[Bob4x4]

Originally Posted by BlackAces

There are two things that must be considered here and cannot be overlooked, because, in doing so, you will be in direct violation of DOT regulations any time less than the regulations minimum requirements are used.

ALL “P”, passenger tires, must have their load capacity reduced by about 10% when fitted to RV trailer axles. Divide the actual load capacity by 1.1 to get the acceptable load capacity for trailer service.

The minimum tire load capacity required for trailer service MUST equal or exceed the trailer’s certified GAWR.

BlackAces

Interesting.........I have never heard that or read it in any trailer tire discussion.

I went with the 15" version they have more than enough wt capacity for my trailer.On the last trip out I measured all the tire temps,the front tires on the tv were at 88,the rears at 92 and the trailer tires were between 81 and 84 degrees.This was towing slightly above the speed limit across the high desert

[slowmover]

De-rating of P tires shows up often . . but there are, now, too many threads/posts to easily find the information. TIRE RACK has a decent tech section to go through, and BARRY'S TIRE TECH website is the other (specifically, on ST tires).

Wheels ought to be rated more highly than the tires placed upon them, and the tires should have a load reserve of 15% above stated maximum load (GVWR).

TT GVWR would include the weight imposed by the distribution of TW when the hitch is properly leveraged.

.

[switz]

GVWR can be an interesting number to think about.

I take a 25FB Airstream trailer and set it on the scales perfectly level, unhitch and drive away. The trailer will have axle weight (AW) and the jack post will have weight (JP) [including 140 pounds of the Hensley hitch head]. That total number should be at or below the GVWR rating by the door of the trailer.

I back the TV onto the scales and hook up the Hensley hitch and put it at the proper tension. The JP weight is off the scales and suspended along a line between the trailer tires and the TV tires. The number shown on the weight ticket for the trailer will now be lower since the JP is not touching the trailer section of the scales. In my case, I have about 1,150 pounds on the jack stand of the GVW rating of 7,300 pounds. That tells me that in theory there is 6,150 pounds spread between the two axles on the trailer. Each trailer tire is supporting about 1,540 pounds, not 1,825 pounds of the GVW. Suddenly the safety factor looks much better. If the Hensley is doing a correct theoretical job of spreading the JP weight 1/3 to the trailer and 2/3 to the TV, then about 380 pounds will be assigned to the trailer. That raises the per tire load to 1,635 pounds per tire. 1,635 is about 82% of 1,985, so that is a 18% safety factor for the tire. But the reality is that the sidewall says 2,183 pounds. That calculates out to a 25% safety factor in real numbers.

Thus even with two 3,800 pound rated axles and 7,300 GVW, the 15" Michelin in reality provides the payload capacity and meets the intent of the regulations by exceeding the minimum values even using the derated capacity of the tire. It even has reserve capacity exceeding the mentioned suggested (not legally required) 10 to 15% reserve in prior posts. All this with a maximum 50 psi inflation which will provide a softer ride for the trailer.

YMMV

[dkottum]

switz, what happens when one tire blows out, say, on a curved downhill 10% grade?

That's why I don't like static measurements, and prefer the maximum load the ties can provide.

Softer ride is desirable as well, but Airstream does recommends 80 psi in my 16" Michelins, same as on Eddie Bauer.

doug k

[Andrew T]

Airstream always recomends the maximum pressure for any tire they install. That is because lawyers study so much about tires in law school.

If you run 80 PSI in those 16" tires you are going to really shake the Airstream badly and if you have to make a panic stop in the wet they will have almost no bite.

Your foot print on the road in square inches is roughly the tire load divided by its PSI. So you if you have 1600 pounds on a tire with 80 PSI in it you only get about a 20 square inch contact patch.

The best way to determine tire pressure is to get your actual axle weights. Many truck stops have scales that are divided into sections. Park on the scale so your tow vehicle front axle is on one section, the back axle on another section and the trailer axle on a third section. Once you know your weight per tire you can check load inflation tables for the correct pressure to carry. A tire will be more reliable, ride smoother and have more traction at the correct loaded pressure. Goodyear's RV section has most of the tires used on tow vehicles and trailers listed. Toyo has one with almost all the other sizes.


Andrew T

[Steve & Mary]

I run them on my 31ft Classic Limited since we blew out a GYM and did $7k worth of damage. We love them. I will probably go to a 16 inch when we start to pull the trailer more often. For now.....what I have makes me feel better than having a set of GYM back on her :-)

[Bob4x4]

Well put switz,that was my way of thinking when I decided to go with the 15's.
My temp readings have confirmed it was a good choice for my Safari

[Bill M.]

I have a 25' Excella. Gross weight rating is 6800 lbs. When I weighed it hooked up and loaded on 2 different trips we had 5800 lbs on the axles. Half full of fresh water and fairly empty on the holding tanks.

[Bob4x4]

Originally Posted by dkottum

switz, what happens when one tire blows out, say, on a curved downhill 10% grade?

That's why I don't like static measurements, and prefer the maximum load the ties can provide.

Softer ride is desirable as well, but Airstream does recommends 80 psi in my 16" Michelins, same as on Eddie Bauer.

doug k

What happens in your tv under that same scenario?