What is the right size tire?

[McLogger]

I recently purchased a 73 27' Overlander and I think that they had the wrong tires on this rig?? Does any one know what is the right size and where did you find this info??

Thanks in advance!

[overlander63]

OEM is 7.00X15LT, metric replacement is ST225/75R15. The 7.00x15 is direct from the Airstream service manual I have. A forum search will give you more tire info than you could take in at once.

[LI Pets]

I got mine from these guys, Mac's

[McLogger]

Well, the conversion is what I did not know and I did a search on the Airstream site but, apparently I did not search correctly because I could not find anything, so thank you! Where did you find the conversion? Also, do any of you know what your height of the side walls are from the edge of the rim to the tread?? That is what seems to be too big!

Lipets thanks for the tip from Mac's this will give me a good price reference.

[McLogger]

What does the P or S or any of the other letters mean when looking on these sites? I know a rookie in charge is dangerous!!

[bhayden]

The conversion from 7.00x15 to 225/75R15 is far from exact. The metric tire size is too small on the diameter and too wide. The width doesn't seem to cause an issue but the change will drop the trailer by about an inch. You need to look at the specs for static loaded radius (12.7" vs 13.8") not inflated diameter which is what is normally quoted when they search for an "equivalent" metric size. Not only is the 225/75R15 smaller to start with but it bulges way more than the OE tires. 700x15 is still available in both bias ply and radial (7.00X15R) but they're hard to find. Going to a 16" rim increases the number of choices and will allow you to get much closer in size to the original tires.

-Bernie

[McLogger]

Is there a problem with the 225?? And where should I look for the 7:00x15? I have them on now in a LT but, I know that they are too large of a diameter. When inflated it measures 30" and too tight for the wheel well??

[bhayden]

A lot of people have replaced the 7.00x15 with 225/7515 without problems. If you've got 7.00x15 tires on there now that's the size the trailer was designed for. As long as you don't mind giving up the ground clearance then "no problem". Other than all the problems associated with today's selection of Special Trailer tires that is; like a 55mph speed rating, no treadwear or traction info, numerous reports of poor quality, etc.

[golddigger]

Not sure if this is relevant to this discussion, but our 1964 came with original spec tires. Before taking it home we made sure to use standard rims on both sides (one had a split rim) and we then switched to Good Year Marathon 225/75R15 with a load range D.

Only caveat is getting these on and off the trailer. Not sure if the Good Year's are wider than the originals, but it is not as easy as on a new trailer to swap in and out.

Here is the trick I discovered when I rebuilt the bearings on my 64 last week. Jack up the trailer so that the tire has at least 4 inches of ground clearance. Anything less and you'll be in pain. Pulling one off just takes a bit of wiggling. Putting it back on, lean the tire at a 45 degree angle towards the trailer and tuck the top of it underneath the metal. Now comes the gotcha. Do not sit down when you push it in. That is a painful exercise. I did that on the first wheel, just like I do on my 98. Instead, stand up. Grab the wheel from the outside through the center hole with your right hand. Grab the lip of the aluminum by the well with your left hand and pull outwards. Then pull the wheel into the well. Works like a champ!! Just make sure you do not hurt your fingers on the right hand..

[bhayden]

Originally Posted by golddigger

Not sure if the Good Year's are wider than the originals, but it is not as easy as on a new trailer to swap in and out. ..

The 225/75R15 is about 3/4 of an inch wider than the 700X15. I think the difficullty in putting them on is more a styling cue. More enclosed fender skirts were popular back then I think in part because it was considered more streamlined. The smaller diameter should about offset the wider section with the metric sized tires.

You could always flare the fender wells like virtually everyone did with the original Broncos

-Bernie

[overlander63]

Okay, to answer some of your questions:
P= Passenger tire
ST= Special Trailer tire
LT= Light Truck tire
T= Temporary spare
ST tires are speed rated for 65 mph
LT tires are speed rated for 75 mph
T tires are speed rated for 50 mph
7.00x15 tires are slightly taller and narrower than the metric tires.

[bhayden]

Originally Posted by overlander63

ST tires are speed rated for 65 mph

If the speed limit is 55 the means you can drive 65 right

LT tires I think have a minimum 75mph speed rating. Many exceed this, S rated LT tires are common. It's important to remember that the speed rating is determined by heat disipation. While we may not want to race our Airstreams at Daytona we do have to drive in summer temperatures that exceed the test conditions by a good margin. That 112mph speed rating of an S rated tire may only be marginal when the asphate's hot enough to fry an egg. OK, you do get some slack if the tire pressure is correct and the load is less than the maximum but still...

Here's a couple nice links with tire terminology explained:

http://www.offroaders.com/tech/AT-MT.../tire-tech.htm
http://www.discounttire.com/dtcs/infoTireTerm.dos
http://www.tritontrailers.com/tiresafetyinfo.htm

[Silverhobby]

Originally Posted by McLogger

Is there a problem with the 225?? And where should I look for the 7:00x15? I have them on now in a LT but, I know that they are too large of a diameter. When inflated it measures 30" and too tight for the wheel well??

I am wondering if you may not have a problem with the axles? I am sure Andy will get in on this thread when he see it. The angle of the spindles may be at a neutral or negative angle and this may explain the why the tire diameter doesn't seem quite right. JMTCW(just my two cents worth)

[golddigger]

I have always wondered: what is a trailer tire? What makes it different from, say, a truck tire? Why would I not want to put an LT on a trailer? Could I swap the Good Year Marathon load range D 225/75R15 for 225/75R15 LTs with load range D?

[AlbertF]

I have seen 7.00 x 15 Toyos on a '76 Tradewind. I think they're actually LTs, like the original Airstream tires were.

Yokohama or Bridgestone may also supply 7.00 x 15s, if you are interested in having the correct size for the trailer. You would have to ask a knowledgeable dealer to find them.

[LI Pets]

I don;t think the speed rating is determined by the "ST" label

• Speed rating: VR (V-rated radial)

• In this case, V identifies a speed rating above 149 mph.

• Table 1 lists speed ratings.

• The R means the tire is a radial. Virtually every new tire is a radial, unless you have a special tire for a classic car or a racing car.

Table 1: Speed Rating Designations
Speed Designation
Maximum Speed Rating
N
87 mph
P
93 mph
Q
99 mph
R
106 mph
S
112 mph
T
118 mph

Why Use An "ST" Tire

• "ST" tires feature materials and construction to meet the higher load requirements and demands of trailering.
• The polyester cords are bigger than they would be for a comparable "P" or "LT" tire.
• The steel cords have a larger diameter and greater tensile strength to meet the additional load requirements.
• "ST" tire rubber compounds contain more chemicals to resist weather and ozone cracking.

[Silverhobby]

Originally Posted by golddigger

I have always wondered: what is a trailer tire? What makes it different from, say, a truck tire? Why would I not want to put an LT on a trailer? Could I swap the Good Year Marathon load range D 225/75R15 for 225/75R15 LTs with load range D?

Trailer tires and wheels are subjected to side loading. This explained to me was when we turn tightly towing the trailer, more force is exerted on the tire and wheel in a direction that it is not necessarily rolling in. ie (scrubbing)Sideways forces are not applied to the tow vehicle in the same manner. When our tow vehicles are turning, there is no wheel or tire "scrubbing" therefore our tires are "rolling." ST or special tires are designed for these sideloads. LT light truck tires are not. Also, If you look at the weight ratings for the LT tires, they usually carry a lot less weight than the trailer special tires.

[Action]

Originally Posted by Lipets

I don;t think the speed rating is determined by the "ST" label

• Speed rating: VR (V-rated radial)

[LIST]

Bob,

I believe the speed ratings that you listed (and there are more) apply only to "P" or passenger tires. I have not seen any of those speed ratings on an LT or ST tire.

>>>>>>>>>>>>>>>>Action

[overlander63]

Originally Posted by Lipets

I don;t think the speed rating is determined by the "ST" label

Having been in the tire and automotive industry for more decades than I care to think about, believe me when I say an ST tire is speed rated for 65 miles per hour, NOT 112.

[LI Pets]

Isn't the ST tires on all new A/S's, hard to believe they are limited to 65mph?

Not that I doubt what your saying, but where is this stated by tire manufactures?