Tire Choices: I'm confused!

Fire Instructor · 07-14-2011, 10:15 AM

Good morning, All!

Currently running 3507 (week 35, 2007) Carlisle "AQ" (Chinese) ST205-75R14's on my signature TT. The tires were "new" on the TT, delivered new in March 2008, and are starting to show signs of wear. I use a TPMS, and I'm religious about making sure that all 10 tires, TT and TV, are at the correct pressure, especially when towing! I've probably put about 5000 miles on these tires, and it was likely towed from the factory, another 1500 miles, maybe?

I've been reading the many and various threads related to these tires, and the possible replacements. I've looked at both the Marathon's and the Maxxi's, in the comparable ST size, and both are still only load range C. I've also read some of the arguements pro and con to switching to an LT tire to get a higher load range, and hence, a higher allowable max speed. (I typically run between 65 snd 70 mph on open road. Not comfortable towing at faster than 70 mph.)

So what's the conclusion? I'M CONFUSED!!! That's the conclusion!

It's not one of the "heavyweight" toy haulers or 5ers that typically get the larger wheels and heavier rated tires. Is there an ST in that size anywhere with a higher rating? What do the tire guru's on this site recommend for a replacement?

DAISY BOYKIN · 07-14-2011, 11:48 AM

Your RV came with a "C" rated tire, go up one grade to a "D" rated tire, you will not be sorry. Try the Good Year Marathons, I do not think you can go wrong.

My Rockwood 8285WS 5 ver came with the "C" rated tires, I just switched to "D" rated tires for a 6,000 mile trip.

I could tell the difference just pulling my RV home from the place where I purchased the tires, the "C"'s that came off carried a tire pressure of 50 PSI, the new "D" rated tires carry a tire pressure of 65 PSI.

Fire Instructor · 07-14-2011, 12:41 PM

As best I can tell, the Marathons only come in a "C" rating in my size. I'd have to up-size rims to go to a bigger tire, and I'm not sure that the clearance is there to do that.

**Herk7769** · 07-14-2011, 01:01 PM

Quote:

Originally Posted by Fire Instructor

As best I can tell, the Marathons only come in a "C" rating in my size. I'd have to up-size rims to go to a bigger tire, and I'm not sure that the clearance is there to do that.

I have US made (Gadsden Alabama) Goodyear Marathon STs in D size on my fiver right now. Don't know about 14 inch tires though.

Fire Instructor · 07-14-2011, 01:23 PM

Looking at this Goodyear link: Goodyear RV Tires, it apears that the 14" Marathon tires only come in "C" range.

MtnGuy · 07-14-2011, 04:56 PM

Fire Instructor, I can understand your concern with not maxing out a C rated Marathon. But even if you load your trailer to the listed maximum of 6580, 6000 lbs. of that weight is split up between 2 axles (580 lbs on the tongue), so each axle is carrying 3000 lbs. That is probably the axle rating. The combined weight rating of your 2 tires is 3520 lbs, so you have some leeway of 250 lbs. per tire. Yes, that doesn't seem like a lot, but I betcha you won't even have that kinda weight in your trailer.

My trailer is rated to carry 3500 lbs. on each axle, so the C rated tires are getting a little closer to the maximum weight rating. But in reality, I only have 4800 lbs. split between the axles ready to camp, so I am way under the maximum rating.

On a different note, when I had my Trailmanor I did go to 15" tires, but still stayed with the C rated. That was a single axle trailer, and I was right around 3400 lbs. on the axle, giving only about 50 lbs. leeway on each tire. The earlier Trailmanors were famous for tire failure, and now Trailmanor puts 15" tires on their trailers.

flyrotor · 07-14-2011, 09:04 PM

My tires are on 15" rims, when I went to the tire dealer a few weeks ago to buy new tires I asked for LT's instead of ST's and he was telling me that in a 15" tire the options for LT's would actually be a down grade in ply rating and in load rating, he highly recommended staying with the ST's, even though he would make more money if he sold the LT's to me.

Fire Instructor · 07-14-2011, 10:23 PM

Quote:

Originally Posted by mtnguy

I can understand your concern with not maxing out a C rated Marathon. But even if you load your trailer to the listed maximum of 6580, 6000 lbs. of that weight is split up between 2 axles (580 lbs on the tongue), so each axle is carrying 3000 lbs.

My concern for the C Rating is more the 65 MPH max, vs the extra strength that the D's provide. I often run a about 70mph, just to stay in the flow of traffiic, and with tires that max at 65mph, I'd be more comfortable doing it with a "stronger" tire.

MtnGuy · 07-15-2011, 10:58 AM

Quote:

Originally Posted by Fire Instructor

My concern for the C Rating is more the 65 MPH max, vs the extra strength that the D's provide. I often run a about 70mph, just to stay in the flow of traffiic, and with tires that max at 65mph, I'd be more comfortable doing it with a "stronger" tire.

I understand where you are coming from. Occasionally I will have to do 70 to get back into traffic. And our dear governor decided to raise the speed limit in Virginia to 70.....bad idea. I still do 65.....the traffic behind me will just have to go around.

acadianbob · 07-15-2011, 01:38 PM

Try this tire.

Kumho Radial 857

It is D rated and also rated for 99 mph.

You would need to do the 195 size to get the same rolling circumference (it is aspect ratio 82 instead of 75). But your overall load rating will still be up and you won't have to worry about the occasional 70 mph; at least from the tires . . .

Fire Instructor · 07-16-2011, 11:50 AM

Quote:

Originally Posted by acadianbob

Try this tire.

Kumho Radial 857

It is D rated and also rated for 99 mph.

You would need to do the 195 size to get the same rolling circumference (it is aspect ratio 82 instead of 75). But your overall load rating will still be up and you won't have to worry about the occasional 70 mph; at least from the tires . . .

I couldn't find a speed rating on the Kumho, just the "D" load rating, so if the 99MPH that you state is accurate, that's GREAT for me, as I don't exceed 70 MPH when towing.

Not sure what you mean regarding the different "aspect ratio", but if staying with the 205 raises me slightly, then that would be a good thing. My Reese drop hitch is on the bottom setting, and is still about an inch too high.

acadianbob · 07-17-2011, 10:04 AM

KUMHO Radial 857 tires feature blackwall styling and are available in Q-speed rated 82-series

This is from the Tire Rack site. Q speed rating is 99 mph.

acadianbob · 07-17-2011, 10:10 AM

Aspect ratio is the ratio of the sidewall height to tread width. Your 205/75 means the sidewall is 75% as high as the tread is wide. So, the Kumho is a slightly taller tire for the same 205 size (It is 82%; e.g. 205/82R14). That means a larger diameter for the same tread width. I have only 2" between my tires on my Surveyor. So, I would need to do the 195 size Kumho to get the same diameter tire. The larger 205 would not fit on my trailer. You need to see how much clearance you have between your tires to see if the 205s would fit. The good news is, the D rated 195 Kumho still has quite a bit more load capacity than your C rated 205s. Look at the specs for the 205/75 (your current tire) and the Kumho. Look at diameter and revs/mile.

acadianbob · 07-17-2011, 10:23 AM

I'm switching from 205/75R14 Marathons to the Kumho next spring. The Marathons have been flawless in performance but the advantage in speed rating and load capacity with the Kumho is too much to pass up. My Marathons will be 5 years old and have about 25,000 miles on them; time to retire them.

Fire Instructor · 07-17-2011, 10:01 PM

Now I'm hearing from others (I posted my original question on the other forum, as well) that my factory rims may not be capable of receiving 65psi.... They are rated for 1870# mximum, but I can't find anything on them that gives a tire rating or a max psi.

**Herk7769** · 07-17-2011, 10:20 PM

Quote:

Originally Posted by Fire Instructor

Now I'm hearing from others (I posted my original question on the other forum, as well) that my factory rims may not be capable of receiving 65psi.... They are rated for 1870# maximum, but I can't find anything on them that gives a tire rating or a max psi.

On my steel rims they were stamped on the inside of the rim. Look at your spare (if you have one) since the brake drum won't be in the way.

My steel rims were stamped 50 PSI max, but my tire dealer said that if I upgraded the stems to a metal 100 psi stem I could go to 65 PSI and a D rated tire without worry. I run my D rated Marathons at 55 PSI as that gives me the allowable load carrying capability I wanted (assuring full tread contact) and the extra plies for strength; without an overly hard tire (IMO it was bouncing too much at 60 PSI).

**wmtire** · 07-17-2011, 10:23 PM

Quote:

Originally Posted by acadianbob

Aspect ratio is the ratio of the sidewall height to tread width. Your 205/75 means the sidewall is 75% as high as the tread is wide. So, the Kumho is a slightly taller tire for the same 205 size (It is 82%; e.g. 205/82R14). That means a larger diameter for the same tread width. I have only 2" between my tires on my Surveyor. So, I would need to do the 195 size Kumho to get the same diameter tire. The larger 205 would not fit on my trailer. You need to see how much clearance you have between your tires to see if the 205s would fit. The good news is, the D rated 195 Kumho still has quite a bit more load capacity than your C rated 205s. Look at the specs for the 205/75 (your current tire) and the Kumho. Look at diameter and revs/mile.

Good info from Acadianbob. I am going to copy some info I posted in another trailer forum that Chap and I both frequent from 2007, that explained the differences between metric sized tires and Euro metric sized tires and expounds a little more on it.

I don't know if I ever explained the differences between sizing systems of the metric sized tires and the Euro-metric tires before. If I did, then please ignore all this boring stuff below:

OK, the Goodyear Marathons that come on our trailers are sized in what's called simply enough "metric" tire sizing. Tires can be "P" metric , "LT" metric, or "ST" metric (which the marathons are). The P, LT, or ST designate the type of tire use, but the numbers behind that designation mean the same.

Just using the 14 inch tires for example, our trailer tires are ST215/75R14.

This means this tire is a "Special Trailer" (ST) use tire. It is 215 millimeters wide when loaded at it's normal carrying capacity (this is the space between the bulging parts of the sidewall, and not the actual tread width), the sidewall is 75 percent as tall as the tire is wide when at it's normal carrying capacity. It's a Radial (R) constructed tire and it fits a 14 inch rim.

These ST tires can come in 4, 6, or more plies, which will be designated by a Load Range letter of B, C, or higher. This Load range letter won't be in the sizing, but somewhere else on the tire.

-------------------------------------------------------------------

Ok, now the tires that many of us are trying on our trailers are sized in what's called Euro-metric sizing or Euro tires as I call them. This sizing system is a little different.

Most everyone is trying an Euro-sized tire that is 195/R14C

The 195 means the tire is 195 millimeters wide.

Now note, that there isn't an aspect ratio number, which was 75 in our tire above. Euro-sized tires of this type don't put the number in their sizing. If they did, it would be an 82. This means our Euro tire is actually a 195/82R14C if we tried to make it come out to the same metric numbering system as our 215/75R14 tire above. Because this tire is 82 percent as tall as it is wide, it gives it more sidewall to stand up to the heavier loads.

It's a Radial (R) constructed tire and goes on a 14 inch rim.

Now to the C after the rim size. It's easy to confuse this for a Load Range letter, which it is not. In our Euro-sized tire, this C means it is a commercial rated tire used in heavy hauling applications. It would be similar to our "LT" or "ST" designation used above. It's just at the back of the size instead of the front

These Euro Tires will also have a Load Range designation letter located somewhere else on the tire. These tires will likely have a C, D, or higher. Most everyone is using a D (8 ply) rated tire.

--------------------------------------------------------------

Now that we know the difference in the tire sizing used for the tires, we can also understand why our metric ST215/75R14 is practically the same height as the Euro-metric 195/{82}R14C tire..........and works easily as a replacement. 75 percent of 215... is close to 82 percent of 195.

One more thing is these Euro tires are kind of a cross. They are designed not only for LT applications, but ST too. It says so even on Kumho's webpage.

http://www.kumhotireusa.com/Tire.asp...5de416c&cat=39

Fire Instructor · 07-17-2011, 11:03 PM

Between AcadianBob, Lou, and now wmtire, I'm now begining to understand this!!!!

Thank you, Gentlemen!!!!

MtnGuy · 07-18-2011, 07:19 AM

I had asked Bobby to take a look at the thread to see what he thought, and as usual he came through.

Thanks, Bobby.

Blkvoodoo · 07-18-2011, 09:36 PM

I have a pair of the 857 Kumho's 185r14 on my camper,just installed them Saturday, took the trailer for a drag Sunday afternoon, 88° out side, nice and sunny.

the ride was more to see how the tires acted to various vehicle inputs, swerving, and to check clearances of suspension movement. these tires are 1.6" taller than the 175/85R13's they replaced ( 25.6" vs 24" )

they did well, there seems to be adequate room for movement in all but the worst road bed situations.

when I got home, total trip mileage was probably 11 miles. I felt the TV tires, just to see and compare the heat build up in the trailer tires. the trailer tires were quite a bit warmer, almost uncomfortable to the touch. should I have any concerns with this ?

tire pressure was 64psi before I started ( electronic digital tire gauge )

I suppose I should dig out the IR temp gun and do this a little more scientific like.

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