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Old 04-30-2013, 10:07 AM   #1
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C/D tire

If you run C tire at 80% around 1600 lbs....is there any reason to increase to a D tire?
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Old 05-01-2013, 07:01 AM   #2
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Then there is no reason to chanche, is my first impression. You have enaugh reserve to cover , unequall loading R/L and a little overloading.
But to be shure I would have to fill in the data in my caravan/trailer- or CamperR V- tyre-pressure-calculator.
Then I need the maximum load or loadindex of your tires and the reference-pressure ( the yyy in fi maximum load xxxx lbs AT yyy psi( cold)) wich is not the maximum pressure of the tire.
From the caravan or RV I need the GVWR or GAWR's and the number of tires the load is resting on.
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Old 05-01-2013, 07:34 AM   #3
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In my opinion, if you have enough reserve capacity to increase the required pressure to support the actual weight plus 10 PSI for the speed rating increase, then there is no need to change to a higher pressure tire.

For example, if you have Maxxis ST225/75R/15 C load rated tires and the ACTUAL load on them is 1880 pounds (requires 40 COLD PSI to support that load); then inflating to 50 COLD PSI at that load will increase your speed rating from 65 MPH to 75 MPH.

If your actual load is 2020 pounds per tire (requires 45 COLD PSI to support that load); you would only be able to push the pressure to 50 COLD PSI for a speed rating increase of 5 MPH (70 MPH).

If you are closer than that to your max load, a Load range bump to D would benefit you by a speed rating increase potential as well as a greater strength and excess capacity for road hazard protection.
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Old 05-01-2013, 08:12 AM   #4
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2150 lbs @ 50 psi....GVWR 8786.....GAWR 4000 per axle (2)
Trailer axles 6600 pin 1400 TV 6900 Varible water 0-300 lbs just rear of rear trailer axle moving to balance over axle and slight to front axle in tanks....

Rear trailer tire start somewhere around 1725 going to 1650 as water changes position.....Maybe a litte less depending on black/gray tanks.....usually start trip with 100 lbs h2o fresh rear tank 50 lbs middle gray 50 lbs front black....with water weight moving forward as trip progresses....the intial water weight is included in the 6600......Max addition water weight increase could be 700 lbs with all tanks full...but quickly looking for dump station under that condition...LOL.....so pretty much stay near the 6600.....top speed range is 56 mph to 58 mph.....
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Old 05-01-2013, 08:19 AM   #5
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Quote:
Originally Posted by sail2liv View Post
2150 lbs @ 50 psi....GVWR 8786.....GAWR 4000 per axle (2)
Trailer axles 6600 pin 1400 TV 6900 Varible water 0-300 lbs just rear of rear trailer axle moving to balance over axle and slight to front axle in tanks....

Rear trailer tire start somewhere around 1725 going to 1650 as water changes position.....Maybe a litte less depending on black/gray tanks.....usually start trip with 100 lbs h2o fresh rear tank 50 lbs middle gray 50 lbs front black....with water weight moving forward as trip progresses....the intial water weight is included in the 6600......Max addition water weight increase could be 700 lbs with all tanks full...but quickly looking for dump station under that condition...LOL.....so pretty much stay near the 6600.....top speed range is 56 mph to 58 mph.....
So that would be a "No, switching to D rated tires would not reap you the benefits that others closer to their max would see."
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Old 05-01-2013, 08:30 AM   #6
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Thanks herk, I now won t be a concerned about tire and trailer fodder when they pass me going 65-70.....And is nice to know I have a cushion to increase my speed some, if want to get in the race for the last campsite.....but probably will just keep going 56-58 mph and stay at wally world or the VFW if the speedballs get there first.....
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Old 05-01-2013, 08:50 AM   #7
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Stamped on the aluminum rim is 2150J.....since J is a speed rating.....does that mean the rim is limited to 65 mph? And load max for the rim is 2150? Not sure where to get this info? More help Herk pls.....thanks
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Old 05-01-2013, 09:14 AM   #8
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Then I made 2 pictures, one with the 6600/1400lbs as you gave, wich gives 42 psi as advice, and one for 8786GVWRand 10% pinload.
Shows a poor reserve for the full loaded, but yust slightly .
Other thing is, if they are Specialtrailer-tires(ST) those are calculated in their maximum load for a lower speed,and often give problems.
Better then would be to chanche to the same sises in LT tires, wich have lower maximum load but can carry that up to higher speed.
The reason for ST to give problems, is that they mostly have off-road like profile wich cover a part of the sidewal, so that may deflect lesser then the deflection the tire-maker used to calculate the maximum load, probalby you have to substract even 20% of that maximum load, printed on the sidewall.
And then things change and you better do swich to D-load/8ply to have enaugh reserve.
But asuming your tires are calculated right, and the loads are right, use 42 minimum psi. If it apears that your loads are at the level of maximum for the 5thwheeler, use even 51 psi minimum ( see 2nd picture), and this is within the 10psi the tire maker allows ( so under 60 psi ).
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Old 05-01-2013, 09:31 AM   #9
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Quote:
Originally Posted by sail2liv View Post
stamped on the aluminum rim is 2150j.....since j is a speed rating.....does that mean the rim is limited to 65 mp
h?
Usually J is a common bead profile/rim contour designation.......but it's usually stamped where the rim diameter/width is like 15 X 7 J .....but I guess it could be placed anywhere.

Let me go see if we have any trailer wheels still in stock to look.
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Old 05-01-2013, 09:35 AM   #10
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Quote:
Originally Posted by sail2liv View Post
Stamped on the aluminum rim is 2150J.....since J is a speed rating.....does that mean the rim is limited to 65 mph? And load max for the rim is 2150? Not sure where to get this info? More help Herk pls.....thanks
You read right so yes that is what it means.
But it does not write maximum psi so 65 psi might be ok.
In Europe we also have 3,75 bar/ 55psi tires so inbetween C- and D-load.
They are also called C-tires for Comercial, and is the European term for LT.
C-load/6ply and Dload/8ply are also called C-tires in europe and LT in America.

They could have that 2150 lbs max load with on road profile so max load written is what it is. That the tires have higher speedrating then J would be now problem then, but you still are restricted to the 65m/h maximum speed, because of the rimms.
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