235/80 or 235/85 tire size

[scottydl]

My new-to-me 2016 Keystone fifth wheel is going to need new tires before I take it anywhere this spring. The factory size is ST235/80R16, load range E. I want to step up the load range to F or G just for good measure. While shopping for tires I've seen both my 235/80 size and also 235/85 available. Would there be any issue replacing my 80's with 85's if the price and load range are right?

I'm familiar with what the numbers mean, and the 85 ratio sidewalls would be just a tad taller... 11-12mm or about 1/2" overall. That seems inconsequential and there's plenty of room in the wheelwells, but wanted to check here in case there's something else I'm missing.

 

[tlmgcamp1]

With only 1/2" of height difference, I agree that the change in height is irrelevant. A higher sidewalls would suggest more flex, which would suggest more heat. However, more sidewall would offer more surface area to disperse heat. Like you, I look forward to hear from the tire gurus on the forum.

 

[rvlifer]

According to

https://www.discounttire.com/learn/tire-size-calculator

The 85s are closer to an inch higher. If they fit the larger ones should get less wear and tear for the same miles.

The only impact i can think of is how the rv will sit in relation to the tow vehicle but an inch shouldnt impact anything.

 

[NMDriver]

Not trying to start a debate but look at Truck tires instead of ST, especially if you are going through the desert in summer.

 

[scottydl]

Not trying to start a debate but look at Truck tires instead of ST, especially if you are going through the desert in summer.

Oh that debate has happened plenty before. I’m in the Midwest so summer desert travel won’t be happening frequently for me, if ever. And I have a fairly large trailer, which I’ve read can be a downside for ST tires being replaced with LT (lower load range). Many LT tires are 10-ply and I’m already looking at 12- or 14-ply tires to handle the weight of my trailer.

 

[Lou Schneider]

Wheel well clearance may be OK but what about the spacing between the tires? If each sidewall is 1/2" taller you'll have 1" less clearance between the tires. 2" less clearance if each sidewall is 1" taller.

 

[triplethreat]

When I was looking for new tires for my Momentum 394M, which is a triple axle Toy Hauler with a GVWR of 20,000 lbs, it came from the factory with a 235/80R/16 and I went with a 235/85R/16. The replacement tires are Sailun and in addition to the slight overall height, there is also an increase in tire load capacity. The "80"s were 4080 lbs when inflated to the 110 psi cold inflation pressure and the "85"s were 4400 lbs when inflated to the 110 psi cold inflation pressure. The 85s were actually somewhat less expensive than the 80s and I went with them. I run the new ones at 100 psi, which gives them the same load carrying capacity (4080 lbs) as the 80 series when they were pumped up to the 110 psi. The 4080 lbs per tire gave me a total of 24,480 lbs total (all six tires) and with the trailer having a GVWR of 20K and three axles with a 7K rating, I was still way under the tire's total load carrying capacity, especially considering that I have a pin weight right at 4000 lbs on the truck, so the tire are only seeing about 16,000 lb if the trailer is loaded all the way to the full GVWR of 20K lb. Hope this helps.

One other thing to make sure of before you do the switch from a load range "E" to the load range "G" tire.....make sure that the wheels on the trailer are rated for that higher load capacity via the pressure rating on the wheel. That is usually stamped on the backside of the wheels and it needs to be stamped 110 psi, not 80 psi.

 

[Gary RV_Wizard]

I'm skeptical that there is any benefit from going up even one Load Range size (F), let along two (G). Check your axle ratings (GAWR) vs the OEM tire load range (E). Unless the current tire size is on the hairy edge of being overloaded, there is little or no benefit of going higher.

As for the 85 aspect vs 80, there is probably no worry but do check the the wheel well height, remembering the suspension flex lets the tire rise up a couple inches too. And do check the axle/wheel spacing because the tires will come closer together and you need to leave room for clearance and the possibility a rock or whatever gets carried by the tread far enough to jam between the two tires. Generally speaking, you should not attempt to use a size that leaves less than 1" spacing between the tires on adjacent axles. As others have already noted, the +0.5" difference in sidewall height (radius) adds 1.0" in tire diameter. That means the adjacent tires have 1" less clearance and the trailer is raised a total of 1" as well.

 

[NY_Dutch]

I'm skeptical that there is any benefit from going up even one Load Range size (F), let along two (G). Check your axle ratings (GAWR) vs the OEM tire load range (E). Unless the current tire size is on the hairy edge of being overloaded, there is little or no benefit of going higher.

As for the 85 aspect vs 80, there is probably no worry but do check the the wheel well height, remembering the suspension flex lets the tire rise up a couple inches too. And do check the axle/wheel spacing because the tires will come closer together and you need to leave room for clearance and the possibility a rock or whatever gets carried by the tread far enough to jam between the two tires. Generally speaking, you should not attempt to use a size that leaves less than 1" spacing between the tires on adjacent axles. As others have already noted, the +0.5" difference in sidewall height (radius) adds 1.0" in tire diameter. That means the adjacent tires have 1" less clearance and the trailer is raised a total of 1" as well.

Ummm, the trailer height only increases by 0.5". The 0.5" additional sidewall height at the top of the tire doesn't add to the trailer height.

 

[scottydl]

Great reminders @Lou Schneider - @xrated - @Gary RV_Wizard. My clearance between tires is 6+” so no issue there. I keep going back and forth on brand… being fairly convinced that proper inflation and care is a better predictor of non-failure than the name stamped on the side. But I don’t want to go TOO cheap.

My overall thoughts on this load range increase is that most RV tires are carrying near the top of their max capacity, which then contributes to increased heat and potential failure.

My current E load tires are rated at 3080# x4 = 12,320# total. GVWR of the trailer is 14k# (I haven’t scale weighed it yet) so assume 20% pin weight carried by the truck and that leaves 11,200# on the trailer tires.

Maybe that’s more than enough headroom. Good thoughts on verifying wheel capacities and axle ratings also.

 

[Gary RV_Wizard]

Ummm, the trailer height only increases by 0.5". The 0.5" additional sidewall height at the top of the tire doesn't add to the trailer height.

Good catch! You are correct - my fingers got ahead of my brain!

 

[Gary RV_Wizard]

My current E load tires are rated at 3080# x4 = 12,320# total. GVWR of the trailer is 14k# (I haven’t scale weighed it yet) so assume 20% pin weight carried by the truck and that leaves 11,200# on the trailer tires.

So you probably have a pair of 6000 lb (GAWR) axles that are potentially loaded to 5600 lbs each, on a pair of tires rated up to 2x 3080=6160 lbs. That's a little close to max tire load, though not the "hairy edge" I alluded to. I can see why you would be more comfortable with LR F, though.

A good tire for you would be the Goodyear Endurance ST235/80R16. It has a load index of 123 (3417 lbs) and a speed rating of N (87 mph). That would give you a healthy margin of both capacity & speed. Owners of Endurance tires praise them too.