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02-18-2012, 11:35 AM
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#1
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Senior Member
Join Date: May 2011
Location: Full-timing
Posts: 447
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Is a tire upgrade worthwhile?
Like everyone else I just don't want any problems with tires (none yet on this unit, but...) so doing the numbers on my 325SRX: 12,200 lb. gross weight rating, assuming 15% pin weight that's 10,370 on the axles (which is also the limit of the two 5200-lb. axles.) Unit is currently equipped with four 235-80/16E tires rated at 3,420 each at 80 psi, or a total of 13,680. It would appear that there is a pretty decent 30% safety margin on the tires even at full gross weight so it would seem that there would not likely be much if any advantage in going to G-range tires (in fact the combined tire weight rating already exceeds the axle ratings by a significant amount.). I have not weighed each tire individually but still, with that much margin I'm pretty unlikely to run into trouble. Am I figuring this right?
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02-18-2012, 01:27 PM
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#2
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Senior Member
Join Date: Feb 2010
Location: Taylors, SC
Posts: 3,031
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Yes!
cw
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02-18-2012, 08:27 PM
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#3
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Site Team
Join Date: Jun 2009
Location: Venice
Posts: 5,346
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I would look at pin weight closer to 25% on a loaded 5er making your safety margin on the trailer even better. Unless all your weight is in the garage.
__________________
 Hank & Lynn
2007 Cougar 290RKS, E-Z Flex, 16" XPS RIBs ( SOLD  .. Gonna miss her ... looking for new 5r)
2004.5 Dodge 2500 QC, LB, 5.9HO, WestTach gauges, Ride-Rite
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02-19-2012, 08:55 AM
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#4
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Senior Member
Join Date: May 2011
Location: Full-timing
Posts: 447
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Yes, wouldn't disagree that the pin weight is likely going to be greater than 15%, just being conservative (i.e. as with a heavy load in cargo area, etc.)
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02-19-2012, 09:37 AM
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#5
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Senior Member
Join Date: Feb 2010
Location: Oswego Il
Posts: 820
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Have you run the truck and trailer across the scale yet? If not I would do this before you up date the trailer tires. I would also look into weighing each individual tire on the camper. Only in this way will you know the correct mass on the tire and wheel combination that is required for safe towing.
I would than choose a tire/wheel combination that will give you a safety margin for use on the trailer.
I have a 318SAB Cougar with ST235/80R/16 that I am changing to Michelin Ribs LT245/75R16 LRE XPS tires this year.
Jim W.
__________________
Jim & Jill
2010 318SAB Cougar
2008 Dodge 6.7LCummins the original 6.7L engine, w/68RFE Auto
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02-19-2012, 10:30 AM
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#6
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Senior Member
Join Date: May 2011
Location: Full-timing
Posts: 447
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As I said in the OP, I have not weighed each tire individually but given the large margin with the OEM tire it would be nearly impossible to overload a single tire even at full gross weight. And of course if I am above gross weight the correct option would be to reduce weight, not increase tire capacity.
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02-19-2012, 01:25 PM
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#7
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Senior Member
Join Date: Mar 2011
Location: Colorado Mountains
Posts: 422
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IMHO a tire "upgrade" would only be called for if the current tires were made in China, or are over 7 years old. DOT code tells where and when made. If you can't "decode the code", post it here.
Your size seems fine.
__________________
Chuck
Wonderful Wife
Australian Shepherd
2010 Ford Expedition TV
2010 Outback 230RS Toybox, 5390# UVW, 6800# Loaded
Not yet camped in Hawaii, 2 Canada Provinces, & 2 Territories
I can't be lost because I don't care where this lovely road is going
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02-19-2012, 03:45 PM
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#8
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Site Team
Join Date: Jun 2009
Location: Venice
Posts: 5,346
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Quote:
Originally Posted by Jim W
Have you run the truck and trailer across the scale yet? If not I would do this before you up date the trailer tires. I would also look into weighing each individual tire on the camper. Only in this way will you know the correct mass on the tire and wheel combination that is required for safe towing.
I would than choose a tire/wheel combination that will give you a safety margin for use on the trailer.
I have a 318SAB Cougar with ST235/80R/16 that I am changing to Michelin Ribs LT245/75R16 LRE XPS tires this year.
Jim W.
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Jim, Check the section width on those 245s, I had to go with 215/85R16s on my Cougar in order to clear the slide mechanism. It was only the drivers side that had the clearance problem on mine so check all four sidewalls. Your 318SAB may be different but I don't want you to get a surprise.  , Hank
THIS tire calculator may help with the height difference.
__________________
Hank & Lynn
2007 Cougar 290RKS, E-Z Flex, 16" XPS RIBs ( SOLD .. Gonna miss her ... looking for new 5r)
2004.5 Dodge 2500 QC, LB, 5.9HO, WestTach gauges, Ride-Rite
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02-20-2012, 07:16 AM
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#9
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Senior Member
Join Date: Feb 2010
Location: Oswego Il
Posts: 820
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Quote:
Originally Posted by hankpage
Jim, Check the section width on those 245s, I had to go with 215/85R16s on my Cougar in order to clear the slide mechanism. It was only the drivers side that had the clearance problem on mine so check all four sidewalls. Your 318SAB may be different but I don't want you to get a surprise. , Hank
THIS tire calculator may help with the height difference. |
Hank, thanks for your input. I have checked the tire cross sectional area and OD of tire before I made my choice. The ST235/85R/16G tire has a section with of 9.5 inches with an OD of 30.7 inches. The LT245/75R16 LRE XPS ribs have a section with of 9.8 inches and an OD of 30.7 inches. So I feel comfortable with the .3 of an inch difference between tires.
For my camper the LT215/85R16 would not be compatible due to the load carrying capability of the LT215 tire which is 2680 Lbs at 80 psi.
Thanks again
Jim W.
__________________
Jim & Jill
2010 318SAB Cougar
2008 Dodge 6.7LCummins the original 6.7L engine, w/68RFE Auto
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