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Old 01-11-2019, 07:11 PM   #1
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80 to 85 series trailer tire switch?

When I switch to the Goodyear Endurance tires for my 5th wheel, I'm wondering about things to consider about changing from an ST235/80 R16 to a /85 series tire. I'm thinking the extra inch in diameter will not be a big deal.

Why even do it? It looks like you get an extra 200 pounds in load.

What I haven't done is weigh the trailer. Can you do that per axle and per side? Will do that on our next long trip in a few weeks when we're fully loaded.

Even if I'm within the limits, how could the extra capacity be a problem?

I'm not considering an LT tire so those responses will be superfluous.

TIA,
Nancy & Phil
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Old 01-11-2019, 11:44 PM   #2
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The only way to get per wheel weights is to find an outfit the does individual wheel weights like Escapee’s SmartWeigh.

You can get per axle weights at a CAT scale by pulling forward on the scale and splitting the axles on 2 of the scales. Using the “Weigh My Truck” app makes it easy to get positioned and then to capture the weight.m

As for the extra diameter- check to see the space between the tires. On my last trailer, I didn’t have room to space for anything with a larger diameter.

As for extra capacity not being bad- within reason, it’s a good thing. What you say is the increase seems fine.
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Old 01-12-2019, 10:28 AM   #3
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When changing tire size from ST235/80R16 LRE to ST235/85R16 LRE you’re actually doing what the tire industry calls “Plus Sizing”. Because the tires have different designated sizes they do not conform to the same load inflation chart. That makes the tire information placards on your trailer invalid.

What you gain is a little more height or decreased clearances in your wheelwells and between dual tire assemblies. Would your trailer’s manufacturer approve the size change?

In today’s market there is no real reason for changing designated tire sizes. Both of those tire size designations are manufactured in load ranges E, F & G. Being a brand shopper could lessen the options.
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Old 01-12-2019, 10:40 AM   #4
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Originally Posted by Airdale View Post
When changing tire size from ST235/80R16 LRE to ST235/85R16 LRE you’re actually doing what the tire industry calls “Plus Sizing”. Because the tires have different designated sizes they do not conform to the same load inflation chart. That makes the tire information placards on your trailer invalid.

What you gain is a little more height or decreased clearances in your wheelwells and between dual tire assemblies. Would your trailer’s manufacturer approve the size change?

In today’s market there is no real reason for changing designated tire sizes. Both of those tire size designations are manufactured in load ranges E, F & G. Being a brand shopper could lessen the options.
Thanks, Airdale. I saw your response on the other forum and will add my further questions here for completeness.

Just to tweak it a little more, please help me understand this. On the Goodyear site, the load range for the 235/80 tire is 3,420 pounds. The /85 is listed as 3,640. Without having weighed each tire for load, this becomes a bit of an esoteric discussion but could more load capacity be a positive enhancement just because the existing load is further away from the rating? As someone said, would it run cooler? Do manufacturers try to meet the minimum standard as opposed to trying to achieve the next level up?

On our first long trip to FL (from NY), we were on Alligator Alley on an 80+ degree day, at speed, driving a few hours, when we got two blowouts on the same side. If running cooler might be a possibility, I'm all for that. I've since installed a TPMS and intend on driving slower, especially when ambient and road temps are higher.

Thanks.
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Old 01-12-2019, 11:54 AM   #5
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Originally Posted by psikora View Post
Thanks, Airdale. I saw your response on the other forum and will add my further questions here for completeness.

Just to tweak it a little more, please help me understand this. On the Goodyear site, the load range for the 235/80 tire is 3,420 pounds. The /85 is listed as 3,640. Without having weighed each tire for load, this becomes a bit of an esoteric discussion but could more load capacity be a positive enhancement just because the existing load is further away from the rating? As someone said, would it run cooler? Do manufacturers try to meet the minimum standard as opposed to trying to achieve the next level up?

On our first long trip to FL (from NY), we were on Alligator Alley on an 80+ degree day, at speed, driving a few hours, when we got two blowouts on the same side. If running cooler might be a possibility, I'm all for that. I've since installed a TPMS and intend on driving slower, especially when ambient and road temps are higher.

Thanks.

We don't know what your certified axle ratings are (GAWR). Reserve load capacity above the axles ratings is a good thing. The new minimum recommendation from RVIA is 10%. I've always used 15%+ with my replacements but not to the point of over kill. Normally, going up a load range- if available - will do the trick.


This is the acceptable standard the tire industry uses and publishes. Never use a replacement tires with less load capacity than the original tires provide.


It's a slippery slope and often misunderstood. The government regulations and tire industry standards folks are fixated on the description; designated tire size. It's more precise with an emphasis on tire design. Here are examples, ST235/85R16 is a complete designated size. So is LT235/85R16. See the difference? You pull your trailer into a Discount Tire retailer and tell them you want some good LT tire put on it. The tire installer is trained to look at the tire placard on the trailer. When they see the ST on that placard they are not going to put LT tires on that trailer. It would be considered a misapplication. A word often used in tire warranty packages.
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Old 01-12-2019, 12:05 PM   #6
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Thanks!!! All great info for me and any others contemplating a similar move or just wanting to increase their understanding.
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Old 01-12-2019, 02:03 PM   #7
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Just do what you want. Im sure you know more than the people that designed your trailer.
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Old 01-12-2019, 02:19 PM   #8
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Just do what you want. Im sure you know more than the people that designed your trailer.
So I'm guessing you just blindly do what you are told without doing any thinking for yourself?

For the OP Psikora: Most everyone in my group goes to a taller tire and upgrades their load range by one, if they can. With today's taller trucks, any gain in trailer height helps with pulling level. As previously advised, just ensure your new tire is not rated lower than your original.

As far as the PSI indicated on the yellow placard, I honestly don't know anyone with a towable who pays much attention to it. In our RV group we air up our tires to the max cold PSI on the tire, or at least close to it.

What you want to do seems perfectly plausible, given you have the room for a taller tire.
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Old 01-12-2019, 04:34 PM   #9
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Originally Posted by NMWildcat View Post
So I'm guessing you just blindly do what you are told without doing any thinking for yourself?

For the OP Psikora: Most everyone in my group goes to a taller tire and upgrades their load range by one, if they can. With today's taller trucks, any gain in trailer height helps with pulling level. As previously advised, just ensure your new tire is not rated lower than your original.

As far as the PSI indicated on the yellow placard, I honestly don't know anyone with a towable who pays much attention to it. In our RV group we air up our tires to the max cold PSI on the tire, or at least close to it.

What you want to do seems perfectly plausible, given you have the room for a taller tire.
Isn’t your group a sort of do-it-yourselfer group? Do-it-yourselfers have to pay for their own mistakes.

There are safety standards that are mandated to be in every vehicle owner’s manual. Here is one of those safety standards from a RV trailer manufacturer’s owners manual. “To maintain tire safety, purchase new tires that are the same size as the vehicle’s original tires or another size recommended by the manufacturer.” When an owner bypasses that safety standard they take all the responsibility for their decision to do otherwise.
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Old 01-12-2019, 04:50 PM   #10
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Isn’t your group a sort of do-it-yourselfer group? Do-it-yourselfers have to pay for their own mistakes.

There are safety standards that are mandated to be in every vehicle owner’s manual. Here is one of those safety standards from a RV trailer manufacturer’s owners manual. “To maintain tire safety, purchase new tires that are the same size as the vehicle’s original tires or another size recommended by the manufacturer.” When an owner bypasses that safety standard they take all the responsibility for their decision to do otherwise.
I don't disagree with any of your comments. I also don't always agree with every CYA manufacturer's statement. And all of us are always responsible for our own actions.

I don't see anything wrong with going with a bigger tire, with better load ratings, as long as you have room to do it.
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