Maintenance & Restoration

Legacy Posts · 03-08-2003, 09:10 PM

I noticed on my 84 , 17ft Bigfoot (which I purchased last year) that after a season of use the "driver side" tire had wear on both the inside and outside of the tire. The other tire is fine. The trailer came with a single Reese anti sway bar on one side of the hitch. I found this a little odd being a first time RVer, thinking that there should be a pair of sway bars. Would this explain the tire wear? Is it a bad tire? Any other ideas? Any advice would be greatly appreciated.

Legacy Posts · 03-08-2003, 09:20 PM

This is caused from under inflation. The sway bar is correct with just one.

Legacy Posts · 03-08-2003, 09:55 PM

Hi Ron and Bernice. Thanks for the reply. How could I overlook under inflation?! I'll make sure I check tire pressure before each trip. Just a little thing but an important one!

Legacy Posts · 03-09-2003, 06:38 AM

The Goodyear web site has inflation pressure tables to use as a guide but you must know the weight on each tire in order to use them properly. The loaded weight of my Casita 16' SD, ready to go camping, is between 2600 and 2800 pounds. Logic tells me to deduct the hitch weight and divide by two. Using the chart for the ST205/75R14 tire size, I would only need 25 PSI for proper inflation. That does not take into consideration that the load will be unequal left to right. If for example, it turns out that I actually have 1100 pounds on one tire and 1300 on the other, the proper pressure would be 30 PSI. Goodyear suggests balancing the load left to right, but with three water tanks, I wonder if that's possible. My thought is to fill all tanks and get each wheel on a scale separately. Than if there is not much difference left to right, I would set the pressure for the tire with the heaviest load. With the weight of a small car on two wheels instead of four, 25 or 30 PSI sounds low to me. Am I overlooking something? Any thoughts on this subject would be welcome.

http://www.goodyear.com/rv/tirecare/loading.html

http://www.goodyear.com/rv/tirecare/loadin...tiontables.html

http://www.goodyear.com/rv/general/RVTable1.pdf

Legacy Posts · 03-09-2003, 09:40 AM

Dan, as other's have said, equal wear on both the outside and inside edges is almost always from underinflation ... and since the tire has been run for quite a while underinflated (to cause the wear), I'd think about replacing it, if I were you!

Craig ... I run 45 - 50 psi on the Carlisles on my 17 footer ... even slightly lower psi on my first two 16 footers ... and never had a problem.

But, as I'm sure you've heard, a lot of folks have had trouble with properly-inflated Carlisles ... so I guess I'm just lucky.

I looked at Goodyear's tire chart ... and it does appear that running at 35 psi would be acceptible for a 16 footer.

I think Casita recommends running a 50 psi. But, Goodyear is whom you'll be dealing with on warrenty issues ... so I'd follow their guidelines.

Legacy Posts · 03-09-2003, 09:44 AM

Casita suggest that you maintain 50 lb. of pressure on the standard 14 in. tires on their trailer. I wouldn't lower them any unless I noticed some center wear. Under pressure causes more flex resulting in heat and blow outs. Standing weight on a tire is a lot different than what the tire goes through on the highway. It would be hard to determine how much weight is on a tire when it has a bouncing trailer on it. And if you hit a high spot or pot hole there is no telling how much weight is transferred to one of the tires.
Keep the pressure up and speed down to 65mph.

Legacy Posts · 03-09-2003, 10:09 AM

Craig,
You're correct in your interpretation. The reference URLs you provided are excellent. by the way.

Some confusion arises when people put "P-Metric" (P204/75R14) car tires on their trailer rather than special purpose "ST-Metric" (ST205/75R14C) tires. The P-metric load tables should be divided by 1.1 to get proper loads and inflations for trailer applications. To be safer still, the fine print of the Tire and Rim Association tables state that "vehicle normal" loads should only be 80% of the Tire and Rim recommended loads when using P-Metric tires

The Tire and Rim Association also states that non service rated "ST" tires are limited to 65 mph unless additional inflation is added, and/or loads are reduced. A service rating would be indicated by a number such as "109S" where "S" would be the speed rating. Goodyear Marathons aren't speed rated. At least the ST205/75R14s aren't.

By way of providing my bonafides, I'm a tire engineer for an auto company. although I must state that I can't/don't represent them in any official way.

In one of the addresses you provided they reference the RVSEF (RV Safety Education Foundation) as one way to get vehicle weights. I've arranged for the RVSEF to come to the National Fiberglass RV Rally this June in Lexington and put on a couple seminars and to weigh our rigs, for a fee.

With steel belted radials, it's very difficult (but not impossible) to get center row wear with tire over inflation. However, it IS very easy to get shoulder wear by under inflation.

Legacy Posts · 03-09-2003, 10:13 AM

>>determine how much weight is on a tire when it has a bouncing trailer

Good point Ron! But I wonder if Goodyear factors that in? I was a little surprized when I looked at Goodyear's inflation chart and saw 35 psi (as Craig pointed out) for what appears to be the proper weight.

I know I'm always in a quandary when it comes to airing up the tires on my tow vehicle.

The max PSI stamped on the tire by the tire company is always way higher than the manufacturers suggested PSI sticker on the door. (And the same "bouncing" tow vehicle stress applies!)

As a result, I usually run somewhere between the two figures.

Legacy Posts · 03-09-2003, 10:15 AM

Aha! Hey Steve! Given your job .... Great!

Can you explain why/how/who figures out what PSI to put on the vehicle door sticker?

And which one should we follow? The vehicle manufacturer's suggested PSI or the tire manfacturers max PSI?

Legacy Posts · 03-09-2003, 10:25 AM

Quote:

Orginally posted by Charles Watts

Aha! Hey Steve! Given your job .... Great!

Can you explain why/how/who figures out what PSI to put on the vehicle door sticker?

And which one should we follow? The vehicle manufacturer's suggested PSI or the tire manfacturers max PSI?

That's easy Charles, Use the door lable up to the max pressure on the tire.

Legacy Posts · 03-09-2003, 10:38 AM

In my company, someone like me takes the estimated maximum vehicle weights and determines the minimum inflation pressure the planned for tire size requires. The minimum tire inflation is a function of load carrying capability and other corporate requirements. We pass it along to a group who models vehicle stability and then on to the ride and handling group. The ride and handling group generally tries to get the tire manufacturers to provide a tire that, well, rides and handles acceptably at the tire pressures I recommend. However, they are free to bump up the pressures at one end of the vehicle or another to fine tune things.

If we do our job properly, the inflation pressures are the best compromise of ride, handling, traction (wet, dry, snow), fuel economy, noise, wear, durability, yada yada. (I'm definitely not paid enough considering everything they want to blame me for. Fortunately I'm always right so not much sticks. ;) ) Specific qualities can be emphasized but others will always suffer. Since people are different, so they tell me, we shoot for the best overall performance in the assumption that it will satisfy the most people. With respect to cars/trucks, my wish is that people would inflate to what is on their cert. label. Never less, certainly.

Legacy Posts · 03-09-2003, 11:47 AM

Charles, I have been reading about the problems that Casita owners have had with Carlisle tires but from what I read, the problem was mostly with the 13" variety. If the Goodyear chart is correct, the problem is obvious. The 13" load range C tires inflated to the max of 50 PSI have a capacity of only 160 pounds or so more that the fully loaded Casita 16'. That's not much margin. Add a few souvenir rocks and you get tire failure. It's no wonder that Casita recommended inflation to 50 PSI.

My 1999 Casita came with 13" and I will be making the change to 14" before I head out on my first trip of the season. If they won't fit under the fenders on my boat trailer, I will have 2 new (never used) 13" Carlisle tires and wheels for sale cheep.

Steve, I can't make it to National Fiberglass RV Rally in Lexington but I hope you will remember this discussion and give us a report.

Legacy Posts · 03-09-2003, 02:20 PM

Thanks for the help everyone. All the advice leads me to other questions! The tires that are on my trailer are Sears P195 75R14. I'm wondering if these are suitable as the Bigfoot specs for new 17's like mine specify ST2205/75R14C. Are there tires made specifically for RV's? Am I correct to assume that the tires currently on my unit are regular tires car tires? Should I replace them with what Bigfoot now specifys? If there are specific RV tires, what's the main difference?

Legacy Posts · 03-09-2003, 07:50 PM

Steve is the expert around here. Read his first reply again. The difference between tires made for a car and special use tires is the amount of flex in the side walls. For a trailer it is best not to have a lot of flex. You get more sway, heat build up, and tire failure. I wouldn't worry about it as much on a tandem wheel trailer, but on a two wheel one it's affects are more important.

Good Luck

Legacy Posts · 03-09-2003, 08:48 PM

Got it now! I'm definitely going to upgrade this spring. Thanks for the excellent help everyone.

Legacy Posts · 03-10-2003, 06:31 AM

Dan ... yes, there are tires made specifically for trailers.

They carry an "ST" on the sidewall.

From your tire markings, it sounds like you are running your trailer on passenger car tires ...

You should upgrade to the proper size in a ST tire!

Legacy Posts · 03-20-2003, 09:54 AM

Wow, I just got the new 14" tires for my Casita 16 SD and can't believe the size difference. This should be a big improvement but now I have another problem. The spare tire mount bolt on the back of the Casita is below the center of the hole in the wheel. I could just use it as is but it seems to me that the stress on the fiberglass will be considerable. The 14" tire and wheel is much heaver and the majority of the weight will be above the attachment point. I can't help thinking about levers and that mechanical advantage stuff that I learned in school. Anyone have a better idea? I would hate to have the rear end fall out in the road.

Legacy Posts · 03-20-2003, 10:50 AM

Craig:

After the conversion, the bolt is an inch or so off center. But with the tire resting on the bumper, the fiberglass 'washer' still covers the center hole of the wheel and holds it snug against the trailer.

Seems to work OK?! :)

P.S.: If you have a tire cover, you know the routine for fitting it?!