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Old 05-05-2010, 02:03 PM   #1
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Question Load range D instead of C?

Hate to start up yet another tire thread but bear with me. The latest thread on this I could find was 3 years old.
Has anyone had any experience running load range D tires instead of Cs on a vintage tandem axle trailer?
Iíll be mounting Goodyear Marathons despite all the warnings of a looming catastrophe.
The local dealer warehouse only stocks Ds. I can get them same day. I can get Cs from Tire Rack sometime next week, but, with shipping and handling that adds another $80.
The tire dimensions spec out the same, but Iím wondering about the sidewall flex due to the lower inflation pressures. The Goodyear inflation chart lumps both Cs and Ds on the same line indicating comparable pressure for both tires up to the max load of the Cs. Ball-parking my weight Iíd be running about 35psi. Seems low to me.

Thatís all Iíve got. Thanks for any input in advance,
Tom.
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Old 05-05-2010, 02:10 PM   #2
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I have "D" rated. I would stick with those. I know vintage weighs less than late model, but I think the two extra plies (sp?) is not a bad thing. I don't believe the extra 2 plies will be too stiff for your coach IMHO.

You can read a bit about the difference here:

Tire code - Wikipedia, the free encyclopedia
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Old 05-05-2010, 02:17 PM   #3
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I'm running P235's with the XL (extra load rating). The 23 tows great with these tires and I like them because they run at 36 lbs. They are also rated for 2,165lbs each so lots of head room for the 4,500lb road ready trailer.
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Old 05-05-2010, 02:26 PM   #4
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I have run both D and even E on my 5000 lbb tandem tradewind.. Due to the generally questionable quality of some trailer tires I won't even use C. Be aware of the inflation rating of your wheels also. I usually run 60 lbs or so even though the E will take more.
It does seem like the tires are starting to get a bit better than in past years
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Old 05-05-2010, 02:32 PM   #5
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It boils down to whether you have the stock stamped steel wheels of have upgraded to aluminum wheels.

Stock steel wheels have a nasty habit of brittle fracture when stepping up load ranges - not a pretty sight, Andy has posted on it many times. Even if you have Aluminum wheels it might not be the best choice...

I went with 'C' range from Tire Rack; if you bump up the load range with the stiffer sidewalls on lighter 1970's trailers there might be a trade off of lower air pressure (tire runs hotter) to keep the slightly "low on air" (bulging) look that radial tire sidewalls NEED to maximize handling and performance.

Explanation of radial tire characteristic advantages
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Old 05-05-2010, 03:10 PM   #6
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tom

the D rated tires don't appear 2 have any more PLYs than the Cs...

they DO have 4-5 lbs MORE RUBBER per tire and perhaps larger threads in the poly/steel belts...

and the reports of "stiffer sidewalls" don't hold water...

just a couple of weeks ago i personally FIDDLED with c, d and e ST tires...

the sidewalls ALL felt the same and flexed the same by touch.

the caps/tread sections ARE thicker and that can be felt,

but the sidewalls had no PERCEPTIBLE differences.
____________

the questions really are

1. do you WANT 5 lbs more rubber at each contact point...
2. what does that 5 lbs ROLLING do to the current suspension...
3. what does that 5 lbs ROLLING and FLEXING do to heat retention...
4. what does that 5 lbs ROLLING FORWARD do the the braking distance/time and magnet/shoe wear...

in addition the only 15 C rated gyms are 205 width (per the TR chart) while the D rated are 225s...

so IF that's correct info, nearly 1 inch wider tires IF u go to the Ds...

given how light the trailer and the load per tire, functional GRIP may actually go down with the LARGER contact patch...

5. will the 225s FIT in the wheel well space correctly...
6. what impact will the 225s have on the RIMS (wider tires)...

shipping cost aside TR generally has very FRESHly made tires and ships to MOST usa location in 2-3 days.

get the C rated tires and properly inflate them.

((the ONE upside to D rated, IF they will fit the rims and wells is....

the extra 800 lbs of rating would come in handy, IF you don't have a spare and need to roll on ONE))

cheers
2air'
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Old 05-05-2010, 09:24 PM   #7
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Thanks all.
I did read 2Airs thread a while back. A lot of meat to chew on.
I did see the thread concerning wheel failures. I’m not too concerned about that aspect of the equation. I’m not intending to increase the weight of the rig. The wheels are getting cleaned and painted before I mount the tires so if anything looks odd I'll deal with it then.
In fact the dinette conversion currently underway will weigh 20 to 30 pounds less than the stock front couch, cabinetry and pullout table. The better half packs heavy so I think we’ll even out.
Dimensionally the 225/75 R15 Marathons are speced out nearly the same in diameter and only a Ĺ inch wider that the 13 year old LT 7.00 15s on there now. Plenty of clearance.
I’ll have the parts guys order up the Ds tomorrow. I am still concerned about the sidewall flex/heat aspect, but I’ll bring my IR thermometer and keep an eye on it the next trip.

See you on the road,
Tom.
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Old 05-05-2010, 11:32 PM   #8
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good choice

post pics after mounting and installing.

the 35 psi is a bit unsettling with a max pressure of 65 as the norm?

there are folks here who report running that low,

but on a 75 series tire that might be an issue...

just how much lateral stiffness will a 75 series tire provide at 35 psi?

and what will the contact patch look like?

IF the trailer is parked long term, what cracking/sidewall changes might occur...

at such a LOW pressure?

lookin' forward to the f/u reports.

cheers
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Old 05-06-2010, 04:42 AM   #9
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I'm experiencing that pain right now

Quote:
Originally Posted by Tom Nugler View Post
... Iíll be mounting Goodyear Marathons ...The local dealer warehouse only stocks Ds. I can get them same day. I can get Cs from Tire Rack sometime next week...
I decided to go with load range C Marathons and found my Goodyear dealer only stocks Ds. But his computer indicated two other stores had two LR Cs each, and he could round those up in the space of a couple of days. So, on the 22nd of last month, I pulled my Overlander's wheels off, and started a new thread on something else I noticed.

My Overlander is still on stands.

At least one of the tires the other store had was more than a year old, and no one else had any newer LR Cs. It appears I am waiting for rubber to be molded. If that does not occur soon, I will probably have to go with LR D and take my chances.

I am surprised acquiring trailer tires is this much trouble.

Tom
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Old 05-06-2010, 06:16 AM   #10
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Adding load is said NOT part of the steel wheel failures - it's just stepping up the load range and differences in the tire husk.

I bead blasted my rims and saw multiple crevices of corrosion inside the bead seat area extending 60į or 90į around the rim from years of weathering & wicking in morning dew and such I'm pretty sure its a valid engineering issue...
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Old 05-06-2010, 07:06 AM   #11
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I run my tires at 60 psi even though load charts based on weight would suggest a lower pressure. I get excellent tire life and don't think I am beating the trailer to death based on the "gas lite lantern mantle test" One mantle is usually good for the season.
I also run my truck tires near maximum inflation, regardless of load and typically see 100 k plus per set of michelins.
The only time I purposely lowered my tire pressure was on the haul road in Alaska to keep from beating both the trailer and us to death. Of course our speeds were limited to about 30 miles an hour also on that dirt road.
I am using aftermarket rims rated at 65 PSI since I had to replace the old split rims.
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Old 05-06-2010, 07:16 AM   #12
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We went to Carlisle "D" rated last year and so far, so good. Time will tell.
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Old 05-06-2010, 09:55 AM   #13
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My goodyear dealer wanted to put me on Es for my 63 Overlander that currently weighs 4,000 lbs. I told him it needed Cs. But he only stocks Ds and Es. He doesn't want to sell me Cs at all.

So, I'm looking for another dealer.
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Old 05-06-2010, 10:27 AM   #14
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there is no E rated gym in 15s.

unless it's an unpublished size.

E rated gyms are limited to 16s.

on the PLUS side and 2 add to confusion gy does make C rated 15s...

in two different widths and with 2 different load ratings

Click image for larger version

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(TR only shows the 205s on their site)

cheers
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