grey2112
Tampa
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As some of you recall, I'm replacing my TT tires. I had 205/75 R15 C rated tires on a 31 foot TT, dual axle, GVWR 7914 lbs, GAWR each axle 3500 lbs. The trailer I have has a unit dry weight of 5163 lbs, an axle weight of 4483 lbs, and a hitch weight of 680 lbs., with of course the previously mentioned GVWR of 7914 lbs.
Given that I'm never overloaded on gear and perhaps at any one time have less than 500 pounds of additional weight in the trailer, I'm thinking that the D rated 205/75R15 tires and existing rims should be fine. I really don't want to go another size up due to limited wheel well space.
If I have to, I will get all new rims, but I can't seem to find ANY D-rated rims online. Mine are 15x5" 4.5 rims, and all I can find are 1820 pound rated ones.
Someone eralier in a thread mentioned using D rated tires on 1820 pound rated original rims with no problems - I'm just wondering if given my light-weight trailer and never overloading or going over 60 mph, I could do the same.
Or would I just be better off sticking to C-rated tires? I figure if I'm not pushing the weight limits in the first place, why not stick to C-rated tires and rims instead of D-rated tires at 65 psi on C-rated rims.
Make sense?
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BobandPatB
Navarre, Florida
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Joined: 04/25/2009
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I'm having trouble undersanding why you would want to upgrade to D load range from your present C's. I am not familiar with your previous thread, but you only have a 4483 pound load on 4 tires (have you had it on a scale?), which is 1121 pounds per tire and it seems that you are WAY under the load capacity of those. I have them on my boat trailer and they are carrying 0ver 5400 pounds 0n the tires.
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grey2112
Tampa
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I guess at first I didn't understand trialer weights. I thought GVWR of 7914 lbs. was what my trailer weighed most of the time. I didn't realize it was my RATING - i.e. the purported maximum weight when loaded. If my "unit dry weight" is what the trailer weighs empty (i.e. just stock, with no clothes, gear, food, water in the holding/grey/black tanks, etc.) then I am quite good-to-go since I never take much gear with me on our trips - even loaded with tools, food, drinks, kayaking/bike gear, books, laptop, etc. it couldn't be more than 500 pounds.
Here is a link to the earlier thread:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23303801/srt/pa/pging/1/page/1.cfm
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coolbreeze01
Redding, Ca
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On the Maxxis chart 205 75 R 15 tires in C (6ply) and D (8ply) both take a max of 50# air.
You don't need new rims. I agree on the more plys is better theory.
2008 Dodge 3500 CTD LB SRW 4X4 6-Speed Auto
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grey2112
Tampa
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That Maxxis chart is in error - I contacted them the other day and they said it should be 65psi.
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tvman44
Southwest Louisiana
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"D" is usually 65 psi.
Papa Bob
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Yahooligan
Temecula, CA
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As previously mentioned, you'll exceed other limits before you reach the tire weight limit.
You have a GAWR of 3500lb, the 1820lb-rated rims would be (1820 x 2 = 3640lb) rating, so you'd be exceeding your axle limits before the rims.
Trailer weights can be tricky. For example, your combined axle GAWR is 7000lb, the GVWR is 7914lb, so the tongue weight "can" be up to 914lb. Always a good idea to go to the scales when you're typically loaded to know what all your weights are.
In any event, you will be fine. Just remember to take the tire or rim limits and multiply by 2, as long as the resulting number meets or exceeds your GAWR then you're good to go.
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Midnightpumpkin
Concord Twp, Lake County, Ohio
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Gray 2112,
I am guessing you have a Rockwood or Flagstaff trailer?
My Rockwood 8315SS has ratings similar to the ones you quoted. The actual weight on the axles on my trailer is 6640 pounds.
The ST205/75R15 load range C tires are loaded to 92% of thier capacity. That is not taking into account that the trailer has to be several hundred pounds heavier on the curb side where the stove, microwave, fridge etc are located.
I for one, upgraded to load range D tires on the original 5" rims and run the tires at 65psi.
There was a recent thread on another forum which indicates that Maxxis is no longer producting an ST205/75R15 load range D tire. Also thier chart that indicates 50PSI for thier load range D tire has to be a typo.
At this time, I know of no non-Chinese ST205/75R15 tires that are available.
My recommendation would be to go to the 6" rims and ST225/75R15 load range D Marathon tire made in the USA.
Their will be another poster along soon who will tell you you don't need Load range D tires.
John U
Midnight pumpkin
2003 Dodge Ram 2500, HEMI, 2WD, 3.73 gears, 5speed Auto
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Reese Dual Cam HP
2007 Rockwood 8315SS Travel Trailer
Loaded Weights:
Trailer Axles 6640#, Hitch Wt 920#
Combined Gross Wt, no passengers, 13,855#
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grey2112
Tampa
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Midnight - yes, it is a Rockwood/Forest River. My problem is I don't think I have enough room in the wheel wells for ST225 tires. It is very tight.
I'm sort of wondering, especially since I've had the trailer for 3 years, it was owned for 1 year before by another person who drove it WAY too fast from what I recall, that if I got 4 years out of cheap Chinese OEM tires, I'm pretty sire I could get a good 5+ years out of the C-rated Maxxis tires I'm considering. We do, maybe, 3 trips a year, never more than 400 miles one-way at a time (and that only once a year at most) - most trips are less than 2 hours away, and I drive 60mph or under.
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skipnchar
Topeka Kansas USA
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Joined: 12/17/2003
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There is certainly NOTHING wrong with the load range C tires that came on your trailer. They will easily handle the weights you have. If you have tire PROBLEMS then you need BETTER tires not bigger ones. The C rated tires on my 8000 lb. trailer have given me over 30,000 trouble free miles so far and I'm expecting a lot more. The LAST set of C rated tires on this trailer gave me well over 40,000 before they were worn enough to need replacing. I see LOTS of folks who have problems with bad Chinese made tires so they replace them with some LARGER Chinese made tires. Much better to address the actual PROBLEM than to go off solving problems you don't have. Just my opinion 
2004 F-250 SCREW Long Bed (new)
OR 2004 F-150 HD (85,000 towing miles)
Rockwood 8314SS 34' travel trailer
We have enough YOUTH...how about a fountain of SMART
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