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Old 03-18-2020, 01:17 PM   #21
Geezertrekker
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Something else to consider if you put 85’s on. Most newer Montana’s are 13ft 5 or 6. Tall. Adding 2 inches height might put overall height Beyond safe for bridge clearance. Just saying
 
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Old 03-18-2020, 01:43 PM   #22
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Something else to consider if you put 85’s on. Most newer Montana’s are 13ft 5 or 6. Tall. Adding 2 inches height might put overall height Beyond safe for bridge clearance. Just saying



You are adding l a half inch to the height
80s = 30.8 dia or 15.35 radius
85s = 31.7 dia or 15,85 radius
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Old 03-18-2020, 02:02 PM   #23
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Something else to consider if you put 85’s on. Most newer Montana’s are 13ft 5 or 6. Tall. Adding 2 inches height might put overall height Beyond safe for bridge clearance. Just saying

Typically, almost all of our 5th wheel trailers are at their highest point at the front A/C if it has one and that is where the they would be measured at. By raising the height at the tires maybe 1/2" or so won't raise the front of the rig any measurable distance. So, in short, the tires will not make any difference whether series 80 or 85 or which brand. What does make a difference is which truck you are connected to as the newer trucks seem to have higher beds and rails which is forcing the front of the trailers higher. Our 2012 3402RL connected to our 2012 Chevy measured 13'4" at the top of the front A/C. If I were to need to replace the front A/C, I would probably go with one of the newer low profile A/C units which would effectively lower the height of the rig.
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Old 03-18-2020, 02:27 PM   #24
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We went with the '85 series also and the tire does rub on the plastic fender on the passenger side of the trailer. This happens when on a rough road and bouncing over bridges. Black marks on the front tire, right hand side. I also use the Swagman bike carrier which we have had for 10yrs and had no problem with after many miles. Don't know why you can't use on 5th wheels. It holds the bikes perfectly.
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Old 03-18-2020, 03:50 PM   #25
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We went with the '85 series also and the tire does rub on the plastic fender on the passenger side of the trailer. This happens when on a rough road and bouncing over bridges. Black marks on the front tire, right hand side. I also use the Swagman bike carrier which we have had for 10yrs and had no problem with after many miles. Don't know why you can't use on 5th wheels. It holds the bikes perfectly.
You would have better off sticking with the 80s. You wouldn't have invalidated your vehicle certification with them.
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Old 03-18-2020, 04:11 PM   #26
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You would have better off sticking with the 80s. You wouldn't have invalidated your vehicle certification with them.



Once again, BALONY!
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Old 03-18-2020, 04:20 PM   #27
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Staying on OP topic 80 vs. 85

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You are adding l a half inch to the height
80s = 30.8 dia or 15.35 radius
85s = 31.7 dia or 15,85 radius
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bigred715; 85 series also and the tire does rub on the plastic fender"
I Wish I had gone with 85's as I wanted a little more lift to help be closer to level but feared the rub possibility hitting bumps. Had not thought about plastic fender rubbing since tire is 85%sidewall (taller) so 5% less in tread width (narrower).
I wonder If bigred715 changed rims that effected wheel offset some.

1/2" would not be much but wish I had it. I'm at 13' 0" now at Front AC unit.
Any upgrade will change how the trailer was manufactured. This is done regularly for tires, hitch pins, brakes and axles. Axle changes from 7k to 8k is common, some do the Morryde IS upgrade or just by new axles and buy one size up for safety.
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Old 03-18-2020, 04:35 PM   #28
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Once again, BALONY!
Where is it?

His trailer has vehicle certified 6000# axles. The ST235/80R16 tires gave him three load ranges to chose from that would not have invalidated his vehicle certification label. LRE, LRF & LRG.

The ST235/85R16 is considered a "Plus Size" because it's larger than the OE tires, requiring the use of a different load inflation chart.
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Old 03-18-2020, 05:29 PM   #29
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Calandlinda, it seems you know a lot about tires. Is there some regulation you can post? I think most of us are aware about load ratings and such but if there are regs on changing sizes of tires while equaling or better the load rating, it would be helpful.
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Old 03-18-2020, 05:51 PM   #30
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I don't remember where I've read it, but the general rule that you can upgrade to a better/higher rated tire, but you don't want to go down.
If you couldn't go up all the folks that have moved to "G" rated or even those that went to 17.5 would all be in trouble with the Tire Police.
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Old 03-18-2020, 05:56 PM   #31
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Originally Posted by CalandLinda View Post
A point to remember when changing sizes from a designated ST235/80R16 to a designated ST235/85R16 is such a change is considered going to a "plus sized" tire. The tire inflation pressures and tire designated size will be invalid on trailer's certification label, in it's owner manual and on all other tire load placards.

Unless Keystone offered the "85s" as an option it's very doubtful they would approve the "85s" and tire safety wise the consumer would be out on their own limb - so to speak.
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You would have better off sticking with the 80s. You wouldn't have invalidated your vehicle certification with them.
What are you suggesting? That we are not already "out on our own"? Do you seriously think Keystone would back you in some type of tire litigation?

I could care less about "invalidating my vehicle certification"; means nothing past the date it rolled out of the factory. Besides, it would be difficult to find someone at fault because they switched to a tire with a higher load capacity.

That would be similar to saying that I "void my certification" or I am "on my own" because I upgraded from the terrible drum brakes to discs. Nonsense.
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Old 03-19-2020, 01:09 AM   #32
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Calandlinda, it seems you know a lot about tires. Is there some regulation you can post? I think most of us are aware about load ratings and such but if there are regs on changing sizes of tires while equaling or better the load rating, it would be helpful.
The answers you seek is not in any single regulation. It's within the safety standards of the industry.

Without going into thousands of words that would have to be written to combine the safety regulations involved with validating my statements I'll just provide a short answer.

Even though it's not practiced in the application of RV trailer tires it is still provided in the vehicle owner manuals. "When seeking replacement tires look on the vehicle certification label for the correct size or get approval from the vehicle manufacturer for another size". By not doing that you violate a safety standard.

The proper nomenclature for a tire size is designated size. That includes the prefix, such as ST235/85R16.

When a consumer uses a replacement tire that is not on the vehicle manufacturer's approval list, such as using a ST235/85R16 to replace a ST235/80R16 you invalidate the vehicle certification label because the designated size differs. Which in the tire industry is called a misapplication.

Everything changes when the vehicle manufacturer agrees to the larger tire size. NHTSA allows the use of an axillary tire placard describing the new designated size and recommended cold inflation pressure. The axillary placard is placed adjacent to the original placard.

Load ranges and tire speed letters are not part of a designated size. Designated sizes are identical, except in internal construction, which allows the higher load range to be inflated to an increased inflation pressure to obtain more load capacity. For instance; The ST225/75R15 LRC and LRE provide identical load capacities at 50 PSI.

The USTMA writes tire industry standards in support of the standards vehicle manufacturers must follow when building your trailer. This is a verbatim quote about replacement tires. "Replacement tires should be the same as the OE size designation, or approved options, as recommended by the vehicle or tire manufacturer".

Bottom line: The vehicle manufacturer set a minimum Original Equipment tire standard when they did final certification. Within the standards, the vehicle manufacturer must comply with a statement that directs them to provide tires that are appropriate for that vehicle and set a recommended cold inflation pressure for them to provide load capacities sufficient for the certified GAWRs.

It's been my observation that RV trailer manufacturers will not approve any replacement tires that do not meet the appropriate sized they provided at vehicle certification, unless they had offered, prior to delivery optional designated sizes.

References for this post have come from FMVSS (standards), 49 CFR vehicle certification, Keystone generic owner manual and the USTMA.
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Old 03-19-2020, 01:15 AM   #33
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What are you suggesting? That we are not already "out on our own"? Do you seriously think Keystone would back you in some type of tire litigation?

I could care less about "invalidating my vehicle certification"; means nothing past the date it rolled out of the factory. Besides, it would be difficult to find someone at fault because they switched to a tire with a higher load capacity.

That would be similar to saying that I "void my certification" or I am "on my own" because I upgraded from the terrible drum brakes to discs. Nonsense.
Vehicle certification rules can be found in 49 CFR part 567.

https://www.law.cornell.edu/cfr/text/49/part-567
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Old 03-19-2020, 05:33 AM   #34
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I am getting tired from reading this thread.
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Old 03-19-2020, 07:14 AM   #35
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go for the throat

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I am getting tired from reading this thread.
Yeh me to....Lets argue about the Andersen hitch some more.

As far as this thread goes, Are your tires black? are your tires round? will they hold up the same weight or more than your original tires? Then your good to go. I`ve washed my camper so much I can even read my place card any more.
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Old 03-19-2020, 08:18 AM   #36
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The only way that I could see bigger/higher capacity tires affecting the safety of a trailer is if they were considerably taller, thus raising the center of gravity. Half an inch won’t do that!
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Old 03-19-2020, 09:48 AM   #37
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Yeh me to....Lets argue about the Andersen hitch some more.

As far as this thread goes, Are your tires black? are your tires round? will they hold up the same weight or more than your original tires? Then your good to go. I`ve washed my camper so much I can even read my place card any more.
Yeah, I'm not sitting my 17000 pound trailer on those flimsy aluminum pipes, lol.

My new Hercules tires are round.

My old rainiers, well some of them weren't really round.
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Old 03-19-2020, 09:56 AM   #38
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Our 2020 Montana came with Saliun Radial tire ST235/80R16G and pressurized to 110 psig. They are rated for 4080 lb load. No need for taller tires since our hitch has height adjustment.
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Old 03-19-2020, 12:45 PM   #39
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Our 2020 Montana came with Saliun Radial tire ST235/80R16G and pressurized to 110 psig. They are rated for 4080 lb load. No need for taller tires since our hitch has height adjustment.
And they barely provide 15% in load capacity reserves at 110 PSI. However, that's what most recommend, so keep them at 110 PSI and drive happy.

Maybe Keystone is becoming more prudent with their OE tire selections and fitments. The polyester ST235/85R16 LRF at 95 PSI would have exceeded the RVIA load capacity recommendation.
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Old 03-19-2020, 01:02 PM   #40
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The only way that I could see bigger/higher capacity tires affecting the safety of a trailer is if they were considerably taller, thus raising the center of gravity. Half an inch won’t do that!
It's an industry thing. When a consumer provides their vehicle for replacement tires the tire installers are going to compare the consumer's replacement request with the vehicle certification information. To follow industry standards they can't use tires with a different size designation without vehicle manufacturer approval, it constitutes a misapplication of the replacement tires. Normally they will consult their computer files to see if their are recommendations from the vehicle manufacturer. If not they may contact them for verification.

When a consumer walks in with their wheels in hand it frees the tire installer from performing a misapplication. All they have to do is verify the wheels and valve stems can withstand the load and pressure ratings of the replacement tires and that the tires are appropriate for the wheels. The bill of sale is not going to show any vehicle identification or VIN numbers.
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