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Old 04-17-2010, 12:59 AM   #1
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Fitting LT235/75R15 LR C on our '71 Tradewind...

Our '71 Tradewind needs new tires before we can hit the road (our new axles will arrive soon.... ). I'm partial to Michelin tires as that's what we use on our TV w/ excellent results. With a load rating of 2183 lbs @50psi, we should have plenty of reserve load capacity with LT235/75R15 tires as our AS will have 3000 lb axles.

Has anyone had problems fitting these size tires? There are ancient 7.00x15 XCA radials on there now that trailered very nicely on the way home, but they look like they date from perhaps the early 80s.....

- Bart
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Old 04-17-2010, 06:57 AM   #2
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Bart... We have been using P235/75R15XL tires on our 73 for many years. Rated for 2135lbs. Although 225's would be the ideal size we had no problems with the 235's. These extra load rated tires also run 35lbs which have a great ride for vintage Airstreams. They will have a softer sidewall than the LT version but for us with a very stable TV the trailer tows great.

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Old 04-17-2010, 07:06 AM   #3
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I have to 1972, 31 foot, Sovereign which is heavier than your Trade Wind. It was suggested to us that the load rating on the tires is more important than the size. Our trailer had class C rated tires on it when we got it and the previous owner had experienced a far share of blow outs. The plastic wheel wells are really torn up. The rating was just at the maximum and on a hot summer day, they would heat up and let go. We decided to go with class E rated tires. I think they were rated for 10,000 pounds. They were only $10 more a piece than the class D tires. We have had no problems to date.

I would not buy bigger tires until you try to fit the old ones onto the new axles to see how much clearance you have.

The new tires and axles sure did smooth out the tow and made it look much better too. Good luck, Bill
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Old 04-17-2010, 11:13 AM   #4
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Quote:
Originally Posted by Airdog View Post
I have to 1972, 31 foot, Sovereign which is heavier than your Trade Wind. It was suggested to us that the load rating on the tires is more important than the size. Our trailer had class C rated tires on it when we got it and the previous owner had experienced a far share of blow outs. The plastic wheel wells are really torn up. The rating was just at the maximum and on a hot summer day, they would heat up and let go. We decided to go with class E rated tires. I think they were rated for 10,000 pounds. They were only $10 more a piece than the class D tires. We have had no problems to date.

I would not buy bigger tires until you try to fit the old ones onto the new axles to see how much clearance you have.

The new tires and axles sure did smooth out the tow and made it look much better too. Good luck, Bill
Interesting... ok, waiting until I get the news axles installed makes sense. I have load range E tires on the TV (3000 lbs capacity each), but we really don't need that sort of thing (nor would they fit) on the Tradewind. The new axles have a heavier load rating than the stock ones, so the new setup should ride quite a bit higher...

Our wheel wells appear in fine shape, so I'm guessing the previous owner didn't have too much trouble w/ tires - not surprising, given the relatively light weight of this trailer.
I've towed our steam launch on 5.80 x 12 tires perhaps 25K miles w/o issues; staying within the load rating and not running too fast seems to help matters a lot.

Quote:
Originally Posted by Road Ruler
We have been using P235/75R15XL tires on our 73 for many years. Rated for 2135lbs. Although 225's would be the ideal size we had no problems with the 235's. These extra load rated tires also run 35lbs which have a great ride for vintage Airstreams. They will have a softer sidewall than the LT version but for us with a very stable TV the trailer tows great.
That's good info... we also have a large TV (F250 4x4 crewcab) which really doesn't notice the AS very much.
It's good to know you've not had any problems.

- Bart
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Old 04-18-2010, 01:20 PM   #5
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I should have included the size we running is ST225/75R15. This size was available in classes C, D, and E. They fit the 72 sovereign fine.
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Old 04-18-2010, 02:53 PM   #6
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Originally Posted by barts View Post
Our '71 Tradewind needs new tires before we can hit the road (our new axles will arrive soon.... ). I'm partial to Michelin tires as that's what we use on our TV w/ excellent results. With a load rating of 2183 lbs @50psi, we should have plenty of reserve load capacity with LT235/75R15 tires as our AS will have 3000 lb axles.

Has anyone had problems fitting these size tires? There are ancient 7.00x15 XCA radials on there now that trailered very nicely on the way home, but they look like they date from perhaps the early 80s.....

- Bart
Bart.

Question?

When making tight turns with the trailer in tow, stop and notice the twist to the side walls of the tire.

Auto tires were not designed to take that, but the ST series will, without harm.

That being the case, now which one do you feel is better for the trailer?

Andy
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Old 04-18-2010, 05:26 PM   #7
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Bart.

Question?

When making tight turns with the trailer in tow, stop and notice the twist to the side walls of the tire.

Auto tires were not designed to take that, but the ST series will, without harm.

That being the case, now which one do you feel is better for the trailer?

Andy
The sideways motion of the tire in a double axle configuration is the same thing that happens in a car when cornering rapidly; the tire is slipping sideways.

This is of course much easier to see in a trailer, since rather than happening only when cornering vigorously it happens at slow speeds, and if you stop in the middle of a turn can even be seen statically.

The worst case condition would occur when the tongue is moved sideways; each tire would scrub sideways but not roll at all.

The minimum turning circle on my truck is about 52 feet; if we assume that there's an even weight distribution on both trailer axles, with the axles about 33 inches apart, each tire will undergo about 1.5 degrees of slip. This is well within the linear region of slip, which extends to four degrees or so for regular car tires.

Stiffer sidewalls produce more side force per degree of slip; this is why (besides style) wheels are getting bigger; as long as the suspension can cope w/ the reduced cushion provided by a low profile tire, low profile tires give more responsive handling in sport oriented driving.

The tire is not damaged by this slip other than normal wear; however, sidewall damage is an issue for trailer tires - it's very easy to catch a curb w/ the trailer tires. Here the heavier sidewalls of an ST tire make sense - just as the heavier side walls of a LT tire compared to car tires make sense in 4wd situations.

Clearly, when backing and/or using the front hitch on my truck, these slip numbers will be exceeded. But tires have to be able to handle side slip - that's the only way to corner at all, and the trailer will spend a lot more time at highway speed than tight backing conditions on pavement.

My trailer came with Michelin LT radials originally, and that's what was on there when we bought it. I'm inclined to continue, esp. given the problems others have had w/ ST tires.

- Bart
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Old 04-18-2010, 07:17 PM   #8
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Trade offs!

There is no perfect tire for a trailer and each persons combination or situation is specific and may have different requirements.

ST tires. Generally speaking they are the poorest quality of all tires and the chances of having a negative issue of one kind or another is high.

LT tires are tough like ST tires and are more durable and dependable.

P rated tires are very reliable but have limitations. Because of the lower pressure they are great for towing vintage Airstreams. If used on a trailer you must deduct 10% of its rating and as Andy mentioned the sidewalls may not be as durable. This may be an issue if towing on gravel roads or if curb rubbing is being practiced.
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