New tires for 2010 Mountaineer

[philhyde]

I am looking for some advice on tires for my 2010 Montana Mountaineer. Factory tire size is listed at 235/80-16. The rig still has 3 original (I assume) Goodyear Marathon tires, with one "Radar" (chinese) replacement. The replacement tire seems to be sized up at 235/85. The difference in profile is slightly noticeable. The Goodyears appear to have a manufacture date of 2008.

We are about to embark on a 2500 mile journey to Oregon for the summer. If I were staying in TX, I probably wouldn't do anything. However, I don't want to be out in the middle of nowhere and have trouble with unknown tires.

A friend advised, at the very least, that I should consider two new Marathons for the back wheels (I assume more load ends up there?). My other options are to replace all four with something else. I know upgrading to LT tires is a popular option, but the weight limit per tire concerns me. I believe my rig has 7,000lb axles.

I would appreciate any recommendations! I've looked at Michelin XPS Ribs (don't quite hit the mark for load carrying capacity). Goodyear G614 is an option, but I don't know if my rims are up to the task. I have factory alloys.

Thanks!
Phil

[CORattler]

Phil,
What model is your Mountaineer?
Definitely DO NOT buy Marathons (MaraBOMBS). G614's are great if your rims will support the high pressures that they call for. If not, LT tires will work (I use them!... See my signature). Just look at the weight ratings. Many threads in the past regarding this. Search function is your friend here.

[philhyde]

345-DBQ

I haven't found any LT tires that will support the weight. Most seem to be rated for 3042lbs.

[seahunter]

Phil,

Here is the Tredit link to match up your wheels to check rating:

http://www.tredittire.com/Aluminum-Wheels-C10.aspx

or the weight rating is stamped on the inside side of the rims so you can see if you can do the G614s. As others will tell you, if spending the money to not replace with Marathons.

Greg

[NCFischers]

Phil,
I have BF Goodrich Commercial TA's and they work fine. 3042 X 4 = 12,168 Lbs. The trailer weighs 14400 Lbs - 2900 Lbs tongue weight = 11,500 Lbs. You need to weigh your truck and trailer on a CAT scale and get your weights. I didn't go with G614's because the stock rims are rated for 80#. Many of us run LT tires and feel safe with them. Lonnieb is our resident tire expert. PM him if you have questions.
Jim

[CamillaMichael]

While you are replacing tires, you might consider replacing your spare also...just had our spare on for a couple hundred miles and while I had it "off" the bottom of the Montana took the opportunity to check the rim's weight rating: even it is rated at 3750. Anyway, it seems like a good idea to have all five tires matched.

[1retired06]

3042 is fine. Dont forget your pinweight. 1000s and 1000s of RVers have been using LT tires for years; our first two montanas came with LT tires from the factory. Any Top Quality LT tire is far better than Marathon STs. 235/85s are a bit larger than the Marathons, and that is a good thing. I have always put the biggest tire that I can safely run, more rubber on the road and maybe just a bit cooler running.

[DQDick]

Here's what you need to know about the tire situation. We run G614's but I would be comfortable with an LT tire based on this:


I have asked many times for someone to explain how a ST tire can be rated to carry more weight than a LT tire in a similar size, without a good answer.

The answer lies in what is called reserve capacity. To quote from Trailer Parts Superstore and this same statement exist on just about every tire site:

HEAVY DUTY 'LT' TRUCK / TRAILER TIRES
'LT' signifies the tire is a "Light Truck/Trailer" series that can be used on trailers that are capable of carrying heavy cargo such as equipment trailers.

If a tire size begins with 'LT' it signifies the tire is a "Light Truck-metric" size that was designed to be used on trailers that are capable of carrying heavy cargo or tow vehicles. Tires branded with the "LT" designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.

So what is reserve capacity? It is capacity beyond the rating of the tire, capacity that is held in reserve. This reserve capacity comes from the heavy-duty sidewall of the LT type tires. LT's rank at the top of the list when we look at P, ST and LT tires.

Now I finally have an answer to how a ST tire can be rated to carry more weight than a LT tire of similar size.

The ratings of ST tires infringe into the reserve capacity of the tire. This is double bad, because the design of the ST gives us a tire with less reserve capacity to start with as it has a lighter sidewall to start with as most ST tires are much lighter than their LT counterparts.

To quote one tire site:
"Put a different way, the load carrying capacity of an ST tire is 20% greater than an LT tire. Since durability is strictly a long term issue - and the results of a tire failure on a trailer are much less life threatening than on a truck - the folks that set up these load / inflation pressure relationships allow a greater......ah......let's call it load intensity."

There it is in print to be read. They make a calculated decision to give the ST tire a higher load rating because a failure is less life threatening.

I have on a number of occasions pointed out the weight difference between the different tires and have been told that does not matter. Well it does matter. The rubber in the average tire only makes up around 40 some percent of its weight, the rest is in the steel belts, gum strips, steel beads, and the carcass plies. The remaining 60 or so percent of the stuff in a tire is what builds in the reserve capacity.

So to review again, here are some weights:
1. Michelin XPS RIB LT235/85R16 LRE (rated to 3042lbs) Weight 55.41
2. Goodyear G614 LT235/85R16 LRG (rated to 3750lbs) Weight 57.5
3. Bridgestone Duravis R250 LT235/85R16 LRE(rated to 3042lbs) Weight 60
4. BFG Commercial TA LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
5. Uniroyal Laredo HD/H LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
6. GY Marathon ST235/80R16 LRE(rated to 3420lbs) Weight 35.4

So which tires on the list have the most reserve capacity? Well that is not a completely simple answer, as one of the tires is a G rate 110 lb tire and the rest are LRE at 80lb inflation. So if we disregard the G614, then the Michelin XPS RIB and the Bridgestone Duravis R250 due to their all-steel ply construction will have the most reserve capacity inherent in their construction. The twin Commercial TA and Laredo will be next and the Marathon would have little or no reserve capacity available because it was used up in its higher load rating, AND because of it's much lighter construction it had much less inherent reserve capacity to start with.

So what have we learn from this?

I think that the first thing that we learned was that a LT tire can be used at or near it max rated loading without having issues, as they built with "substantial reserve capacity to accept the additional stresses of carrying heavy cargo".

The second thing we may have learned is why ST tires are failing on mid to larger 5th wheels, in that they do not have inherent reserve capacity beyond that rated max loading. Again this is because they have less reserve capacity to start with and their greater "load intensity" used up any reserve capacity that might have been available.

Now, here is an interesting bit of information. I just called Maxxis Tech Line and asked the weights for two tires.

ST235/80R16 LRD 3000 lb rating at 65 lbs of air weights 38.58
ST235/80R16 LRE 3420 lb rating at 80 lbs of air weights 43.43

What??? The Maxxis load range E tire weights almost the same as the Commercial TA?? This is a ST tire that has heavier construction than the GY Marathon at 35.4 lbs. So it has more inherent reserve capacity due to its heavier construction.

Those that claimed its virtues maybe did not know why it was a better ST tire than some of the others, but there it is! It is a heavier built tire with more reserve capacity.

So as one chooses a replacement tire or is asking for an upgrade on a new trailer please get educated on where the reserve capacity exist. Is it inherent in the tire you choose or do you have to factor it into the weight rating of the tire you choose.

Those with heavy trailers that are switching to 17.5 rims and tires rated to 4805 lbs and getting a double injection of reserve capacity, in that they are using a tire with lots of inherent reserve capacity and the tire has much more capacity than the application. It is all starting to make sense.

[DonandJudy_12]

DQDICK's explanation of the difference between ST and LT ratings is right on- Another thing to consider is availability of a replacement ST out in the real world if such a need arises- As a retired tire man [ 30 plus years experience in retreading and retail ], I understand some of the nuances of tire capacity, etc. Lonnie is currently in the retail side of the industry and is well versed in how and why tires do what tires do- JMHO- Good luck with your decision- Don

[PatnRich]

Nicely said Dick.

[camper4]

I may have missed it in the excellent writup above, but, the rating of ST tires is at 65 miles per hour. The LT tire rating is at 99 miles per hour. That has to make a difference in favor of the LT's.

[mhs4771]

Just as long as you don't plan on doing 99 MPH just because the tires are rated for it!!! LOL

[camper4]

Lost your sense of adventure?

[CORattler]

Can we get Dicks post made into a sticky for this subject?? It's a frequent question and I believe it covers the subject.

[mlh]

quote:Originally posted by mhs4771

Just as long as you don't plan on doing 99 MPH just because the tires are rated for it!!! LOL

Most new trucks defuel at about a hunderd anyway, just takes all the fun out of pulling your camper. Darn.
Lynwood

[philhyde]

The higher speeed certainly is a vote in favor of LT's!

[philhyde]

Thank you for all of the replies. I have decided to go with the BFG Commercial T/A's.

[philhyde]

I had the Commercial T/A's installed today. They look awfully close to the fender skirt. Anyone had issues?

[seahunter]

When I checked, the difference between the 80 and 85 profile tires is an inch taller which is quite a bit... hopefully someone can add if that will be a problem??

[philhyde]

Couple of pictures.