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Old 07-19-2006, 03:41 PM   #1
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Tire Questions

The 69 Overlander needs new tires. It has 7.00X15 on it now and that is what the manual says. But I read comments about the 225/75 15.

Is there a difference?
What should I put on my trailer?

Thanks,
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Old 07-19-2006, 04:58 PM   #2
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Tires, Tires, Tires,,,,,,,, this is such a tough question around here, I asked the same question about a month or so ago , I personally went back to the 700X15s D load range , one resson is my Airstream pulls great with no sway and I didnt want to change the way it pulled, it had the 700X15s before, There is a lot to be learned by doing a search , I did learn that trailer tires are not made to go over 65 MPH !!!! I will remember that !!!
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Old 07-19-2006, 05:04 PM   #3
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Quote:
Originally Posted by Hind-Sight
The 69 Overlander needs new tires. It has 7.00X15 on it now and that is what the manual says. But I read comments about the 225/75 15. Is there a difference?
Short answer, yes. Indisputably there is a difference in size. 7.00X15 is approximately 30 inches in diameter with a loaded radius of ~13.8". A 225/75-15 is about 28.3" in diameter with a loaded radius of 12.5-13". The 7.00x15 has an overall width of ~8" and the 225/75-15 has an overall width of ~8.8. So the switch to the 225/75-15 will decrease your ground clearance (and hitch height) by over an inch. It will also be almost an inch wider but that's unlikely to be an issue.

Just as important as size is load range. 7.00X15 or 225/75-15 both come in different load range ratings. You need to match that with the requirement of your trailer. More is not necessarily better. Higher load range is accompanied by a higher inflation pressure which may exceed that of your rims. Running a tire at much less than it's max inflation rating can cause other problems

Another factor is if the tire is radial or bias ply construction. Both are available for the 7.00-15 (7.00R15 for the radial) but selection and availability is very limited. 225/75-15 is very common as a radial (225/75R15) or "Bias Metric".

Saving the best for last the letter(s) in front of the tire size designate "purpose". No letter or P means Passenger car tire. Highly unlikely any of these have the load carrying ability to be used as a trailer tire. The controversy surrounds LT (Light Truck) and ST (Special Trialer) designations. On the surface you'd think Special Trailer would be exactly what the doctor ordered but when you dig deeper you find these tires are only rate for a maximum speed of 65mph and even this is derated for temperatures commonly found when towing. Also, to my knowledge there are no 7.00R15 tires with the ST rating and also no ST rated tires that have even an "All Season" let alone winter (M&S) traction rating.
Quote:
What should I put on my trailer?
For a given load range an ST tire is almost always going to be the cheapest option. Undoubtedly that is a major factor in the decision of most if not all trailer manufacturers to use ST tires. Not so much Airstream but SOB trailers often are equiped with load range tires that are barely adaquate for the dry weight of the trailer. People report success and failures with just about every option. Options with no history of failure are always a small sample size and conversely the more popular options have the most horror stories associated with them. Your call

http://www.discounttire.com/dtcs/inf...rTireFacts.dos

http://www.championtrailers.com/tire_art.html

http://www.advanceautoparts.com/engl...0040501tt.html
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Old 07-19-2006, 05:16 PM   #4
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I replaced the old 7.00x15 on our Overlander with 225/75 15. Seems to ride better. I have not noticed any sway problems, or any problems for that matter, in the 700 or so miles I've put on it since. It did seems as though the 7.00x15 was not as readily available around here as the 225/75 15, so I figured if I ever have tire problems on the road, the 225 would be easier to find. --dave
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Old 07-20-2006, 08:57 PM   #5
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Hi Hind-Sight--I have stayed with the originial 7:00 15LT C and have experienced no tire problems in 18-years (3 sets of tires and ready for the 4th). Tires track well, have strong side walls, and never get very warm, on the hottest days, running 65mph. My next tires will be Goodyear Workmaster, 7:00 15LT D, from WalMart (don't make C load range any more).--Frank S
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Old 07-21-2006, 04:55 PM   #6
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Quote:
Originally Posted by Hind-Sight
The 69 Overlander needs new tires. It has 7.00X15 on it now and that is what the manual says. But I read comments about the 225/75 15.

Is there a difference?
Thanks,
The difference is the sizing of the tires.

The 7.00X15 is the old system

And the 225/75 15 is the newer system for passenger tires. It this size started with a "P" it's for a passenger car or vehicle. "LT" in front of the munber would designate Light Truck. And a "ST" would be for Special or Trailer application. NOT recommended for passenger car usage.

The sizes from one system to the other are close just not exact. Actually the physical tire size of one brand to another may not be exact even in the same sized tire.

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Old 07-21-2006, 06:47 PM   #7
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Frank S,

What are the Goodyear Workmasters rated for? The last belted 700X15 tires I looked at would have maxxed out at a weight 2,040 lbs (Load Range "D") The Goodyear Marathons can carry up to 2,540 lbs. (225X75X15 Load range "D") Big difference, esspecially if you have a single alxe.
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Old 07-21-2006, 06:57 PM   #8
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Workmaster or Workhorse? The 7.00-15LT Workhorse is rate Load range D, 2040 pounds at 65psi. There's a difference in the way they rate LT vs ST tires. It's not an apples to apples comparison because the ST tires are only rated at 65mph. I don't remember what the minimum speed rating is for vehicle tires. It used to be 75mph but it may be higher than that now. Other sizes of load range D Workhorse tires are Q rated (100mph).

I think LT tires are also derated by ~10%. There's a note in the Goodyear specs that says when replacing LT tires with Passenger tires you need to add 10% to their load rating.
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Old 07-22-2006, 12:27 PM   #9
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Quote:
Originally Posted by bhayden
I think LT tires are also derated by ~10%. There's a note in the Goodyear specs that says When replacing LT tires with Passenger tires you need to add 10% to their load rating.

That's interesting. I would pick a load rating of a tire(s) based on actual total load + 10% divided by the number of tire. Then select a tire based on the stsed capacity of the tire.

Example. My Overlander dry weight is 4250. Fully loaded I am at 5140. Add 10% and I am at 5665. Divided by 4 tires and I am looking for a tire with a load capacity of 1420 or better.

An LT tire will be stiffer side wall than a ST. And don't think I would use a P tire for my trailer. And especially a P radial tire because it would be too squishy.

P = Passenger tire
LT = Light Truck
ST = Special tire designed for trailers

Going the route of load ranges (B, C, D, E) just simplifies the process.

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