MPG Halved by Boler - Page 5 - Fiberglass RV


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Old 05-17-2012, 02:43 PM   #57
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Name: Dave
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Originally Posted by Andrew Gibbens View Post
Goodyear show tire pressures down to 15 psi for their ST tires in this load/inflation table (which I believe is actually an industry-standard document and not Goodyear-specific):

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

A pair of ST175/80R13 tires are rated to carry 1340 lbs at 15 psi (though only up to 65 mph).

So this is yet another reason to know your trailer's ACTUAL weight, so you can then look it up in the inflation pressures table.

Then you can choose to follow or ignore the recommendation in the table.

I am not gonna vote pro or con on this one! I have grenaded trailer tires that were at "moderate" pressures and I have grenaded trailer tires that were at recommended max pressure. The only common factors were age (less than 2 years old) and the name on the sidewall (Goodyear)

When I put on new tires (different brand now- and ALL tires including spare are now replaced), the dealer automatically inflated them to max, but I have no idea if that is the "correct thing to do" or if it is "their habitual practice".
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Old 05-17-2012, 03:08 PM   #58
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Originally Posted by Byron Kinnaman
Well, I guess you're smarter than the Carlisle Engineers.
Not me... The guys as Goodyear.
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Old 05-17-2012, 04:17 PM   #59
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I think most small trailer owners have the same issue.

Most of them use ST trailer tires that are...

a. at or close to their max load ratings,
b. running high pressures,
c. turning at close or to their max speed rating, and
d. are of poor quality to start with.

So many negatives here it is no wonder folks have so many problems with them.
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Old 05-17-2012, 04:25 PM   #60
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Originally Posted by Andrew Gibbens View Post
Goodyear show tire pressures down to 15 psi for their ST tires in this load/inflation table (which I believe is actually an industry-standard document and not Goodyear-specific):

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

A pair of ST175/80R13 tires are rated to carry 1340 lbs at 15 psi (though only up to 65 mph).
According to the weights collected in the real world at a FGRV rally (available on this site) a 13 ft Scamp is pretty close to 2000 lbs. Using that chart 13 inch tires really should be at least 30 psi. to be rated for that load.

Legally in Michigan trailer under 26 ft can be towed at posted speed limit. Typically 70 mph on interstates. I'm not in that much of a hurry but have seen it done when the TV was big and pulling a pop up or small trailer.

On the side of my scamp is a plate reminding me to not inflate over 20 psi. Think I would go with what the tire manufacturer states.
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Old 05-17-2012, 04:36 PM   #61
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Originally Posted by mcbrew View Post
Not me... The guys as Goodyear.
Now reconcile this:
When I purchased my Scamp it "Load B" tires on it. The stickers on the sides of the Scamp say inflate to 35 psi. My Scamp weighs 1700lbs on the axle. If was evenly divided that 850lbs per tire. According t the chart that would be around 25psi. Note also that the maximum tire pressure for "Load B" is 35 psi, the same pressure as indicated by Scamp.

I would like to know what the new 13' Scamps say to inflate the "Load C" tires to.
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Old 05-17-2012, 05:12 PM   #62
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Originally Posted by Byron Kinnaman View Post
And here's what Carlisle has to say.

Always keep the tire manufacturer’s maximum recommended air pressure in all your tires, including the spare. This is an important requirement for tire safety and mileage. Tire sidewall stamping information will tell you the recommended cold air pressure.
Here is what Carlisle also has to say in the same link that you provided:

Review tire sidewall stamping information and the vehicle owner’s manual for the vehicle load limits and proper tire inflation.
Never exceed the maximum load rating stamped on tire sidewall of your tire or the maximum vehicle load rating, whichever is less. Make sure the load is spread evenly on all tires so that no single tire is overloaded. Tongue weight, tongue height and especially load leveling hitches must be set properly to avoid overloading your trailer tires.

It seems that Carlisle is contradicting themselves on the same document.
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Old 05-17-2012, 05:51 PM   #63
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Originally Posted by Andy B View Post
Here is what Carlisle also has to say in the same link that you provided:

Review tire sidewall stamping information and the vehicle owner’s manual for the vehicle load limits and proper tire inflation.
Never exceed the maximum load rating stamped on tire sidewall of your tire or the maximum vehicle load rating, whichever is less. Make sure the load is spread evenly on all tires so that no single tire is overloaded. Tongue weight, tongue height and especially load leveling hitches must be set properly to avoid overloading your trailer tires.

It seems that Carlisle is contradicting themselves on the same document.

Andy are trying to equate load rating with air pressure? It's not the same thing.
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Old 05-17-2012, 06:40 PM   #64
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Andy are trying to equate load rating with air pressure? It's not the same thing.
Yes, they are not the same thing, however they are directly proportional. Carlisle provides a chart of load limits vs tire pressure at the same link and also has the following quote:

Therefore, a load range C tire is at its peak load capacity when inflated to its maximum pressure of 50 psi. In range D, you need to be at 65 psi to handle the increased load capacity. Load range E tires must be set at 80 psi.

Both these indicate a direct relationship, but they say the maximum pressure must be used and also say to use the lower load rating.
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Old 05-17-2012, 07:06 PM   #65
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There is at least one tire manufacturer ( and I can't find the link right now, sorry ) that states their ST tires should always be run at the max pressure on the sidewall. They state that it has to do with the design of the tire needing the high pressure to maintain sidewall stiffness to help in not only keeping the tire cool, but to minimize sway.

Here is a general observation on my trailer tires. And first here is my disclaimer: this is just one data point of one user on one specific trailer and brand of tires.....so as always, YMMV !

But, my thoughts are this, some folks claim that running a tire at max pressure, when there is not enough load on it to warrant that inflation, will result in "wearing in the center of the tread" that is typical of over inflation. I understand their theory but at least in my case that is not happening. I have 7040 pounds of carrying capacity ( 4 x 1760 pounds at 50 psi ). My camper weighs 3780 pounds. About 3300 of that is on the tires. So.....according to the pundits, I have no need to be at 50 psi. And yet the tires are showing just a very slight amount of wear, and more important, it's exactly even across the tread. About 5000 miles on them now. So I am not seeing what would be called an over inflated wear pattern, even though the tires are only running at 47% of their rated capacity.

I'm going to keep running them at 50psi. It's working, and they run at typically about 10 to 15 degrees above ambient air temp, according to my non-contact IR thermometer.

....all of which has really kind of gone off topic that the OP started this with. But regarding inflation, I think that even those who recommend running low inflation pressures, would admit that it will result in using more fuel. It is pretty well established as fact that higher inflation pressures reduce rolling resistance.

So to the OP, regarding getting best fuel economy as relates to the trailer tires, my recco would be radial trailer tires inflated to the "proper" inflation. You yourself can choose how to decide "proper" inflation.
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Old 05-17-2012, 09:09 PM   #66
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I have a tandem axle (7000 lb. capacity) cargo trailer that I start the day at about 3500 lbs and gradually unload to empty (about 1500 lbs). My tire store recommended running the (50 psi max trailer) tires at about 35 psi for best wear. They said that based on the trailer's weight, if I kept them at 50 the center of the tread would wear before the sides of the tread. Based on how they actually wore, I've found that 40 psi seems to be about right (they were close).
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Old 05-17-2012, 09:42 PM   #67
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For the record, I did not talk about tire wear. My biggest concern with over-inflated tires is bounciness. A lot of you folks with big trucks probably don't notice it, but you will in a car. I can tell that with MY trailer, there is a lot of bounce when inflated above 30 PSI. There is no doubt in my mind that this is wearing on the frame, coupler, and hitch more than it needs to. It also tosses my belongings around the Scamp. Lowering it to the recommended 15-20 PSI has solved this problem. As for mileage, I got 24 MPG on my last long trip with the Scamp. I doubt it would have been any higher with overinflated tires.

I'm not recommending low tire pressure. I'm recommending PROPER tire pressure. However, I'm not trying to change anyone's mind. Everyone here has decided what thy want to do... What data points they trust.... Which experts they want to believe. I think this is the last time I will talk about it publicly.
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Old 05-17-2012, 10:01 PM   #68
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Originally Posted by mcbrew View Post
For the record, I did not talk about tire wear. My biggest concern with over-inflated tires is bounciness. A lot of you folks with big trucks probably don't notice it, but you will in a car. I can tell that with MY trailer, there is a lot of bounce when inflated above 30 PSI. There is no doubt in my mind that this is wearing on the frame, coupler, and hitch more than it needs to. It also tosses my belongings around the Scamp. Lowering it to the recommended 15-20 PSI has solved this problem. As for mileage, I got 24 MPG on my last long trip with the Scamp. I doubt it would have been any higher with overinflated tires.

I'm not recommending low tire pressure. I'm recommending PROPER tire pressure. However, I'm not trying to change anyone's mind. Everyone here has decided what thy want to do... What data points they trust.... Which experts they want to believe. I think this is the last time I will talk about it publicly.
I think it was Ford Explorer that tried to use lowered tire pressure to improve ride.
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Old 05-17-2012, 10:36 PM   #69
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I think it was Ford Explorer that tried to use lowered tire pressure to improve ride.
Crappy drivers who did not maintain the posted tire pressure and expected a truck to handle like a sports car.
Rangers had the same suspension and drive train while running on similar tires.

Tires are a very active part of the vehicle's suspension. The sidewalls are supposed to flex and absorb most of the small road variations.
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Old 05-18-2012, 07:39 AM   #70
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Yes.... AGAINST the recommendation of the tire manufacturer.
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