over rated?

[hitchikerman]

I have a cougar 2008 with stock tires are Marathons 225/75 r15's I wanted to go to a e-rated tire but after alot of research I would be wasting my money. The wheels on my trailer are only rated for 2600 lbs so what's the sense of spending the extra money on e-rated tires when the wheels will not support them. Any idea's or help would be appreciated.

[Jim & DJ]

Just a thought. Original tires? Marathon's are bad enough but the age would concern me.

[Festus2]

Just a thought. Original tires? Marathon's are bad enough but the age would concern me.

X2 If they are the originals, I would be looking at replacing them now. They could be 8 years old - depending upon the year they were manufactured. The Marathons may look "good" but they've outlived their service life and should be replaced.

Are you certain that the wheel rating won't support an E-rated tire?

[hitchikerman]

Yup stamp right on the outside of the wheel max pressure 2600 psi the wheel has a ETO stamped on it also. Just for grins and giggles I looked at the weight stamp with a magnifing glass to make sure...could be 2800 lbs but pretty sure it's 2600lbs.

[Cyncwby]

If you ever blow a trailer tire at speed (and you will if you keep the old junk Marathons) you'll appreciate the simple fix I'm about to type. You go on www.trailertireandwheel.com and find the approriate 15" wheel that supports an E rated Maxxis or Kumho 857 tire. Yes I know it's not a cheap fix but the alternative can be life threatening.

[Ken / Claudia]

I do not think your wasting any money when buying a better or heavier duty tire. Your smart, that type tire (heavier ply etc), in my opinion will last longer, hold up better to road debris, pot holes.

[JRTJH]

The MAXXIS M8008 load chart can be found here: http://www.maxxis.com/trailer/trailer-tire-loadinflation-chart

Essentially, the ST225/75R15 tire is manufactured in three "ply ratings" C, D and E. The maximum load rating for the C (6 ply) is 2150 at 50 PSI, the D (8 ply) is 2540 at 65 PSI and the E (10 ply) is 2830 at 80 PSI.

Your wheels are rated to carry 2600 pounds (probably at 65PSI). They will carry that same 2600 pounds if you install higher rated tires (LRE). You will "gain" an added "safety loading" by installing the heavier tires, but you're correct in that your wheels will not "be rated" to the 2830 that your tires are rated. So your tire/wheel will still have a maximum 2600 pound rating.

You can think along the lines of buying a 3/4 ton truck when you only need a 1/2 ton truck. If your payload is 900 pounds, you can carry it in a 1/2 ton truck rated at 1000 pound payload, but you'll have "extra capacity" if you carry it in a 3/4 ton truck with a payload rating of 2000 pounds. You're "OK" with either choice, but have more "reserve" with the heavier duty choice.

Having the "extra capacity that's not used" isn't really "wasted" rather it's a "safety reserve"....

Last I checked pricing on Maxxis 225 75R/15 tires, the price difference between D and E rating (8 vs 10 ply) the E rated tires were about $4 more (on Amazon) and were $11 more (at Online Tire.com). They were about $8 a tire more expensive on EBay.

So, to buy tires what essentially are "stronger than your wheels" will give you some "safety reserve" over tires that are rated slightly less than your wheel load rating. That "safety reserve will cost you somewhere between $16 to $48 for a set of four. Whether you think the "safety reserve" is worth that investment or not, is pretty much a personal decision.

In either situation, buying 8 ply or 10 ply, based on the date of manufacture of your current Goodyear tires, I'd urge you, as others have, to replace them before your next trip. You're probably "living on borrowed time" with the current tires !!!

[hitchikerman]

thanks JR for great advice so if I went to the Maxxis d-rated tires I should put no more then 65 PSI in the tires

[JRTJH]

Different wheels are rated at different load capacity and different pressure capacity. On the back of your wheel should be stamped a "max load" and a "max PSI". Some wheel manufacturers only stamp the load. If you don't find the "max PSI" locate the wheel manufacturer part number, contact their customer service and ask for the maximum PSI rating for that specific wheel. They will give you the information.

To answer your question, currently, without knowing the max PSI rating, I'd only put 65PSI in the LRE tires. That will give you the load rating of 2540 per tire/wheel assembly (5080 per axle). If your wheels are rated to 80PSI, you can increase the pressure and achieve a rating of 2600 pounds per tire/axle or 5200 pounds per axle. Remember, even though the tire is rated 2830 pounds, your wheel is only rated at 2600 pounds and will be the limiting factor.

If it were me, I'd omit all the "searching/calling/deciding" and just install the LRE tires, inflate them to 65PSI and call it a day. That will give you what you've been using since 2008 with the added comfort of a "safety margin" that you didn't have previously.

[Festus2]

I have the Maxxis 225/75R15 LRE (10 ply) and keep them inflated at 70psi - slightly more than the 65 but less than their 80 lb rating.

[hitchikerman]

thanks again for all the help going with the maxxis E-rated tire @ 65psi.

[CWtheMan]

The ST225/75R15D inflated to 65 psi is the same tire as the ST225/75R15E inflated to 65 psi. The controlling factor for getting a specific amount of strength from a tire is the amount of inflation pressure used. It is engineered that way and that's why the inflation charts are a proven strength measurement tool standardized across the board for each tire design.

When plus sizing with replacement tires its an industry standard to insure the tires and rims are appropriate for the increased task. Should you do less? The only way you can use the reserve load capacity in the LRE tires is to increase their inflation above 65 psi. Otherwise its dormant.

Note: Because your axles are set at 5080# you can still use the 2600# rims and inflate the tires to 80 psi if the rims qualify for that pressure. The 2600# is immaterial because you would have to severely overload your axles to have that much weight on the rims/tires.

[EVMIII]

I'm certainly no expert, but I have always been told that is especially important to run ST tires a max PSI. A large portion of tire failures are attributed to under inflated tires, it doesn't seem reasonable to start that way. Don't take my word, go find a tire expert. Good luck, safe travels.

[notanlines]

"Don't take my word, go find a tire expert" In all my 67 years I don't believe I have ever come across more knowledgeable people concerning RV tires then on this site. Start with CWtheman and go from there. We have many members who are exceedingly informed where tires/rims are involved. Drive into your first Tire Kingdom, Goodyear, or Firestone and ask any of the people in there to tell you what your rims are rated at.......seldom will you get a satisfactory answer.

[shiggs68]

I hate to step into tire threads since there always seems to be too many experts.

However, most steel wheels do not have ratings or max psi but are rated at 65 psi max. Only Aluminum wheels are required to have the rating stamped into the back side.

The correct tire inflation is dependent on the chart published by the tire manufacture and the weight they will be carrying. Not some magic always the same number or the max psi printed on the tire. If it was on the tire, it would say recommended not maximum. For instance, review this document published by Goodyear http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf.


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[CWtheMan]

The DOT does not require the rims on our trailers to have load capacitie or psi limiting figures displayed on each individual rim.

However that information is often provided by OEM suppliers on request from vehicle manufacturers for ease of identification for various fitments with like sized tires with different load capacities. (Example; ST235/80R16D has a load capacity of 3000# and the next load capacity, LRE, is 3420#).

On vehicle certification the DOT says rims must be appropriate for the tires fitted to them at the time of first sale. You can search 571.120 for verification.

Rim specifications are a product of SAE testing and quality assurance.

Rim manufacturers must provide serial numbers and part numbers on each rim tag along with a means to communicate with them. They have the answers and will provide them when asked.

I would not expect a vehicle manufacturer to have rim specifications unless they are the installers of the tires to the rim. The OEM provider that married the tire to the rim must surely have the information. It would be a serious safety violation if they did not.

BUT, bottom line, vehicle manufacturers are the final certifiers. Somewhere in that process whoever married the tires to the rims had to sign off on it as a safe and appropriate fitment. If called to the task, IMO, the vehicle manufacturer must answer for their actions. So, somewhere in the maze of paperwork needed for final vehicle certification there is an answer for Original Equipment tire/rim specifications.

[carlc51]

In regards to wheel ratings and tire max PSI will a tire that is rated for max cold setting of 110 psi say Goodyear 614 mounted on a wheel that has a rating of 110 psi be appropriate when tire is run and heats up and psi exceeds the 110 PSI rating of wheel? Have been wondering about this and have kept my tire pressure at 100 and haven't climbed over the 110 mark yet butwould like to know opinions and thoughts of this.

[Ken / Claudia]

I asked the same question years ago to the manager at a tire shop. After I had 2 blow outs on my truck. That problem was due to not having full metal valve stems. But, I found that the tires would be checked in the morning at 80 psi (max for a Max load). Hours later while driving they could be 92psi and highest I checked was 96psi. He said all that max psi is based off cold test psi and the wheels/tires have the factor built in to allow them to exceed that psi when hot. If CW has a different reason of better explanation. Take his words over mine.

[shiggs68]

In regards to wheel ratings and tire max PSI will a tire that is rated for max cold setting of 110 psi say Goodyear 614 mounted on a wheel that has a rating of 110 psi be appropriate when tire is run and heats up and psi exceeds the 110 PSI rating of wheel? Have been wondering about this and have kept my tire pressure at 100 and haven't climbed over the 110 mark yet butwould like to know opinions and thoughts of this.


If you refer to the Goodyear document I attached above, you will find that the proper tire pressure depends on the weigh it is carrying.

I also have G614s and only inflate to 85psi as once I weighted, that is what the chart calls for. They do go up about 10 lbs after heat buildup.


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[CWtheMan]

If you refer to the Goodyear document I attached above, you will find that the proper tire pressure depends on the weigh it is carrying.

I also have G614s and only inflate to 85psi as once I weighted, that is what the chart calls for. They do go up about 10 lbs after heat buildup.


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When one starts researching tires each aspect must be reviewed to come to a correct conclusion.

In this case its tire inflation pressures.

So lets start off with the correct tire inflation pressure for your RV trailer. Like all other vehicles its determined and set by the vehicle manufacturer. That’s undisputed for Original Equipment (OE) tires. Refer to 571.120.

Inflation pressures are very important. As air pressure is added to the tire its load capacity is increased. Tire manufacturers develop tire inflation charts, normally in 5 psi increments for load ranged tires. Those charts are approved for all different sized tires and their different designs and load ranges. Vehicle manufacturers use those charts when setting OE tire pressures as directed by FMVSS. Tire retailers and other properly trained people use those charts when changing tire sizes and designs.

The major misunderstanding about tire pressures is the starting point. To the trained installer its going to be found on the vehicle’s certification label/ tire placard. If the OE rims have a rating that includes load capacities and inflation pressures up to and including the pressure listed on the tire side wall the tires can be inflated - cold - to that value.

Because medium to heavy duty truck tires are sometimes used on RV trailer axles does not mean they can be inflated as a heavy truck tire. When on the RV trailer they are RV trailer tires and are regulated by the FMVSS.

Because more than 90-95% of all RV trailer tires are LT or ST ties their normal recommended inflation pressures are going to be 100% of the pressure listed on their sidewall. There is no adjustment to be made.

Replacement tires are almost always going to be larger than the OE tires with more load capacity. When properly installed with appropriate rims they can often be adjusted to suit the owner. The minimum adjustment is to use inflation pressures that will provide the load capacity the OE tires provided.

When anyone inflates a tire to a value equal to what it is going to carry there is zero wiggle room for error. Is the air gauge calibrated right to the psi? Do you check before every trip? Do you know that 1 psi below recommended pressure equals a 1.6% loss of tire load capacity?

Here is an example of why everyone needs to read everything about tire inflation. When tire manufacturers are writing something about a subject they will take the stance that you know about that subject and will present it accordingly. (The starting point for tire inflation manipulation is the recommended cold pressures depicted on the tire placard).

http://www.goodyearautoservice.com/content/content.jsp?pageName=TirePressure

In this one your going to find an industry standard that says, in part, NEVER use less inflation pressure than recommended on the tire inflation label.

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

[hitchikerman]

o-k after further review I talked with the wheel manufacture and he suggested that since the wheel is only rated for 2600# that I would be overloading the wheel so I guess I'll be replacing with the D range tire. So after looking at the specs of my fifthwheel the load carrying capacity of trailer 3100#...and if I have four tires at 2540# each totaling 10160# total capacity. The dry weight of the trailer is 8630# leaving me 1530# carrying capacity. Is this where the pin weight makes up the difference?

[cw3jason]

yes, except you do not use the tire weights, you use the axle weight ratings. the tire weights are usually and should be slightly more when added then the axle weight.

the carrying capacity of the frame and suspension is what makes up your trailer GVWR

[Desert185]

Discount Tire sells me Carlisle LRE's for the same price as LRD's for my car hauler and two-axle enclosed utility trailer. With metal stems and a balance job, I feel better prepared for what lies ahead. Carlisle or Maxxis are the only LRE trailer tires I use anymore.

[CWtheMan]

You know, ST tire manufacturer's are very adamant about tire inflation pressures for their tires and always recommend 100% of tire sidewall pressures to be used for Original Equipment tires.

Some time ago in a phone conversation with a Maxxis tire rep the subject for replacement tires was discussed. His "canned" answer was to use whatever was recommended by the vehicle manufacturer. That would include using LRD tire pressures for LRE replacements. Advantage of the LRE tires? Not measurable. My recommendation; New rims and LRE tires at 80 psi. For the OP that's going to provide about 13% excess load capacity in reserve.

[GaryWT]

I understand that rims and tires might not always match but I have been told and have experienced that runnung at less than the sidewall psi of a tire will damage the tire. Might not have a blowout right away but the tire could heat up to the point the tread comes off the rest of the tire.

[dcg9381]

Almost every car tire I own gets run at less than sidewall pressure. My understanding is that sidewall pressure is maximum and also the setting that warrants rated load.

[CWtheMan]

Almost every car tire I own gets run at less than sidewall pressure. My understanding is that sidewall pressure is maximum and also the setting that warrants rated load.

They are regulated differently. Read FMVSS 571.110 paragraph S4.2.2.2

[outwest]

The DOT does not require the rims on our trailers to have load capacitie or psi limiting figures displayed on each individual rim.


That corresponds with what I'm dealing with right now. I was debating about whether to upgrade to load range E's or not (trailer came with D's) and I couldn't find any stamp referring to max PSI on the back side of the wheel spokes.

I did find the Max load rating, which made me think it was rated as compatible with the E's (it says 5/2150&6/2830lbs) and since it's a 6 lug. . .

This was further verified on wheel mfg website http://www.sendelwheel.com. Website says mine are rated for 80PSI as long as it's the 6 lug version.

But anyway, yeah, it won't necessarily have the PSI on the back of the wheel. If it says SenDel on it, though, that's the mfg and the specs should be able to be found on the website I linked.

[CWtheMan]

In an earlier post in this thread I said the tire pressures for your Tow Vehicles (TV) are different. It’s a confusion factor that needs more explanation.

All automotive tires such as those on cars, SUVs, multi passenger vehicles and even motorcycles must provide a percentage of load capacity reserves via inflation pressures. (Do a test, look a tire placard for your TV and do some math with a tire chart).

RV trailer manufacturer's are not required to any percentage of reserve load capacity. In fact, a trailer manufacturer can install two 3000# tires on 6000# (GAWR) axles and meet the minimum DOT fitment requirement. Most ST tire manufacturers quit making the 3000# tires because of that.

Vehicle manufacturer have the authority to set GAWR loads by making a 5200# axle a 5080# GAWR axle. Some still do it. Some will find tires rated at 2540# on those 5080# axles. I call any of those tire fitments trailer manufacturer bombs. I’m hoping that the next round of the NHTSA tire rules committee meetings will enact a 12%/15% minimum load capacity reserve rule for all trailer tire fitments. The RMA lobbied for that in the last go-around and was out voted. Availability and costs were contributing factors.

[slow]

CW,

First, thanks for all the great info. I always find your posts informative.

I hope you can clarify something for me:

You indicate that there is no load carrying benefit in using a ST E rated tire at 65 psi, since the load capacity only increases above 65 psi to a max at 80 psi. That makes sense to me.

What is not clear to me is if there are any negative consequences in terms of tire durability and tire life if running a ST E rated tire at only 65 psi.

The reason I ask is that I have nearly 50% reserve capacity running ST D rated tires on my relatively small and light trailer (GVWR 6800, GAWR 4400 tandem axles, 2540 ST D tires and 2830/80 psi max wheels). On the surface it would seem that I really have no reason, when the time comes, to upgrade to a ST E rated tire since I already have nearly 50% reserve capacity with the ST D rated tires. But if I was to upgrade to ST E rated tires for the few extra dollars, my thought was to still run at 65 psi since I would not want to roughen the ride. But is there a durability or reliability benefit, or consequence, in running ST E rated tire at 65 psi over a ST D rated tire at 65 psi?

Or should I not be concerned with the assumed rougher ride running a ST E tire at 80 psi and benefit from the 60+% load carrying reserve?

I look forward to reading your insights.

[CWtheMan]

You indicate that there is no load carrying benefit in using a ST E rated tire at 65 psi, since the load capacity only increases above 65 psi to a max at 80 psi. That makes sense to me.

What is not clear to me is if there are any negative consequences in terms of tire durability and tire life if running a ST E rated tire at only 65 psi.


Every engineer I’ve talked with about going up a load range says the same thing. It’s in the charts. They say a LRE tire inflated to the PSI of a LRD tire makes it a LRD tire. You might find a tire that is more durable but if that’s so, it’s probably more durable in all load ranges.

Inflating a LRE tire to LRD inflation pressures is a subject for the tire manufacturer. Carlisle has always touted full sidewall pressures for their ST tires. Maxxis will stick to whatever the vehicle manufacturer recommends. Most others are like Carlisle. You’re always going to be safer with a higher inflation pressure because you’re less likely to heat the tires.

The bottom line probably has the best answer. Use replacement tires that provide equal or greater load capacity than the OE tires. That would mean a tire of the same size and design would use the same tire inflation pressure as the OE tires. The Keystone owner’s manuals are going to tell you to seek their advice. IMO they are going to tell you to use the same size as the OE tires unless they have previously authorized an optional fitment for your model trailer. Personally I went up a load range and inflated to max sidewall. Works very good for me. My trailer came with ST235/80R16D tires on 6000# GAWR axles. I went up to the ST235/80R16E, problems solved.

Note: I would not recommend fooling around with rims not having the PSI rating of the installed tires.

[slow]

Thanks for the insights CW, much appreciated.


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