Tire Tutoring 101 - Page 2 - Montana Owners Club

sreigle · 07-11-2009, 12:12 PM

The first picture was a tire on a Jayco Eagle. All of the others were tires on our Montanas. These and some others I don't have pictures of are why I'll never put another Goodyear Marathon tire on our rig.

sreigle · 07-11-2009, 02:45 PM

All three of our Montanas, 2001, 2003, 2007, came from the factory with ST tires. For awhile, somewhere between our 2003 and 2007, Montanas were delivered with LT tires from the factory. Further, our 2003 came with D load-rated tires rather than E. When I questioned this our dealer gave me a copy of the following letter. Note this letter is from 2002. Also note the discussion on LT vs. ST tires. I don't presume to say any of this is accurate but thought it might be interesting for some to see what Keystone had to say back in 2002. I had to reduce the size of this picture to conform with forum guidelines. If anyone has trouble reading it, you can email me (envelope icon above) and I'll send you a more readable copy. Our 2003 Montana had the tire size mentioned and we found it very difficult to find replacement tires in that size.

Art-n-Marge · 07-11-2009, 03:52 PM

I know my Monty had Mission ST tires (not LT) when I bought it but I don't recall if they were D rated or E rated.

I did replace the Missions after the first separation of a tire on a road trip. While it did take a week for the new Goodyear Marathons I ordered (sorry Steve, I was not a member of the MOC yet, to make a different decision), I was fortunate that the dealer was able to make arrangements with me to replace all the tires on my rig, including the spare, AT THE CG so as not to inconvenience me (that was nice of them and lucky of me).

I don't have a bad story about Goodyears so I am happy with them so far, but I do have bad stories with Missions. I definitely have no experience with using LTs on a rig and while the letter corresponds to some information I read from the turn of the century and the letter is dated in 2002, it seems that LTs have made some progress since then. It has been almost 7 years.

Personally, I will probably stick to STs. But I will no longer argue with anyone wanting LTs if they are aware of what their decision yields. There are still many factors that will be factors for your tire experience, such as driving speed, good and bad tire care, climate, storage, availability, experience, tire usage, tire abuse, weight ratings, axle ratings, weight distribution, overloading, age, and luck (okay fate).

Thanks for the information Steve!

KathyandDave · 07-12-2009, 02:33 PM

On the letter, note the pressure for the ST is 65lbs., although the max shown on the tire is 80lbs. The charts for this tire state the same thing. Running them at the max 80lbs. all the time contributes to a rough ride, IMHO. I have set the pressure on our Marathons to 65 and I've noticed an improvement.

dsprik · 07-12-2009, 02:50 PM

Dave, not sure, but don't you lose your weight rating at less than 80#? And I'm not sure but I think heat buildup may more at 65 than 80? I could be wrong on both points though...

KathyandDave · 07-12-2009, 02:58 PM

Dave - if you go to http://www.goodyear.com/rv/tirecare/...iontables.html
and click on the link to the pdf file, you'll see the ST's in the first table. The listing for the heavy trailers is at the bottom right. The next table is LT's, which may inform this thread.
Edit: I noticed that the trailer brakes were "grabbier" at the recommended inflation, which may indicate that more tread is on the road. At this point, I'm trusting that the increased flex of the sidewalls at the lower inflation pressure is within the design parameters of the tires. I have felt the tires and have noticed no heat buildup.

Glenn and Lorraine · 07-13-2009, 02:33 AM

Quote:

quote:Originally posted by KathyandDave

On the letter, note the pressure for the ST is 65lbs., although the max shown on the tire is 80lbs. The charts for this tire state the same thing. Running them at the max 80lbs. all the time contributes to a rough ride, IMHO. I have set the pressure on our Marathons to 65 and I've noticed an improvement.

YES Dave you will notice a ride improvement due to the lower inflation pressure BUT this has nothing to do with PROPER inflation pressure.
The chart you referenced in your following post is correct BUT only for the "D" range tires. The STs on our rigs are "E" range and the E range STs are not listed on your link.

Follow this LINK and scroll down to page 9 and SPECIAL ST METRIC TIRES FOR TRAILERS IN HIGHWAY SERVICE. You will see the ST235/80*16 does have a listing for "E" range tires and at 80PSI the load is 3420.

Running a loaded, under inflated tire will cause heat build up and irregular wear to the tires. Yes, there is more rubber on the ground possibly giving you a false sense that the brakes are more "grabbier". The "increased flex of the sidewalls at the lower inflation pressure is NOT within the design parameters of the tires". The increased flex is exactly what causes heat build up. That same increased flex and heat is putting undue stress on the entire tire and a blow out or catastrophic failure is just waiting to happen.

LonnieB · 07-13-2009, 02:55 AM

Quote:

quote:By Glenn and Lorraine

Running a loaded, under inflated tire will cause heat build up and irregular wear to the tires. Yes, there is more rubber on the ground possibly giving you a false sense that the brakes are more "grabbier". The "increased flex of the sidewalls at the lower inflation pressure is NOT within the design parameters of the tires". The increased flex is exactly what causes heat build up. That same increased flex and heat is putting undue stress on the entire tire and a blow out or catastrophic failure is just waiting to happen.

I'll second what Glenn said.

KathyandDave · 07-13-2009, 03:15 AM

In our situation, the actual weight for the two Monty axles is 11,990lbs, so roughly (but not more than) 3,000lbs per tire. From the chart that Glenn referenced (thanks for the correction), our proper inflation pressure is 65lbs. Coincidentally, this is the maximum for load range "D" and less than the maximum for load range "E". It gives me some comfort that we are not running these tires at their rated maximum.

Glenn and Lorraine · 07-13-2009, 03:40 AM

Well you got me on that one. Just keep in mind any rearranging of your load can change everything. Just traveling with a full tank of freshwater can make a difference. Not dumping the 3 waste tanks can also make a difference.

To be perfectly honest the only true way to know you are running the proper air pressure is to do exactly what Dave did. Weigh the rig! Use the inflation charts! Set the proper PSI and check it regularly! It is just that simple.

We have a tendency to generalize and that is what can get us in trouble. I have never weighed my rig and therefore I don't know what the exact air pressure should be. BUT, I do check my tires frequently for tread wear patterns. If I see any signs of over or under inflation I take corrective action.

alandaudrey · 07-13-2009, 07:56 PM

Art, I'm glad that you started this thread on tires. It's always a question of great interest to RV'ers. I for one will be watching the comments of others to your questions.

I have a comment to add. We have a 2009 Monty with Chineese Goodyears (ST's of course). We are 6500 miles into a 18000 mile trip. At present we are sitting in an RV park in Fairbanks, AK. We have been on "Top of the World Highway" and other gravel and rough areas on the Alaskan and Klondike Highways. All I can say is, "So far so good". I keep a close eye on my tire pressure monitor.

I'll give a report on the condition of the tires

when I get back to Houston around Thanksgiving. All I can say is these tires are being put through the test.

sreigle · 07-14-2009, 04:56 AM

Quote:

quote:Originally posted by KathyandDave

On the letter, note the pressure for the ST is 65lbs., although the max shown on the tire is 80lbs. The charts for this tire state the same thing. Running them at the max 80lbs. all the time contributes to a rough ride, IMHO. I have set the pressure on our Marathons to 65 and I've noticed an improvement.

Dave, the tires in question were D load rated. The usual max psi for D load rated tires is 65 psi. For E, it's 80.

I neglected to mention that I did not question the D rated tires because they were D rated, since the sidewall weight rating was sufficient. I questioned it because the sticker on the side of that Montana said it had E rated tires but it came with D's.

After reading through the prior posts, since I last read this thread, I noticed the comment about a better rid with lower pressure. I am NOT suggesting running tires underinflated. But this brings a question to mind:

Question:

We never had the breakage problems with our rear kitchen 2003 3295RK that some folks reported here. Could that be because it was equipped with a D-rated tire and thus was run at the maximum pressure of 65 psi rather than the 80 psi for those with E-rated tires? In other words, might the lower pressure of the D-rated tires contributed to our having no problems in the rear kitchen? It sounds obvious that it would be the difference but since the tires have different load ratings I'm not sure the construction is the same. The weight ratings were just about the same as an E-rated tire, though. Thanks.

KathyandDave · 07-14-2009, 06:52 AM

Steve, thanks for the correction about the "D' rating of the tires mentioned in the letter.

I'm wondering if the loose use of the term "under-inflated" leads to problems. The tires under any vehicle are part of the suspension system. To perform effectively, they need to offer a certain amount of compliance (is this the right word?) to absorb the shocks of the road surface. I regard the maximum pressure shown on the side of the tire as exactly that - it means that you can load the tire according to its design (as shown in the charts) until you hit this number. If you add more load and need more pressure to keep the tire from squashing, then you need more tire. To habitually over-inflate the tire might mean that the benefits of the tire's compliance are discarded, perhaps resulting in axle and spring problems, reduced stopping power or broken dishes and bicycles (my personal starting point for this train of thought). Maybe an over-inflated tire doesn't last? Would it overheat more easily than a properly inflated one? How is the maximum pressure rating determined, anyway? By statistical analysis of testing? If the tire is always at the maximum, then maybe it is now in a failure rate deemed acceptable by the manufacturer.

Art-n-Marge · 07-14-2009, 08:04 AM

As mentioned in other topics previously, a tire is typically engineered and tested thoroughly within its documented recommendations. When a tire is stamped with its rating, it means that it was tested for bouncing, cold, heat, weight, stress, turning, load rating, storage, handling, and a bunch of other stuff and the tire meets the rating under those conditions. THEN it must be paired with a vehicle or trailer that has a specific weight and utility rating. This is why certain vehicles get certain tires, for example - race cars get wide tires, trucks get LT tires, trailers get ST tires and passenger tires get P-series tires.

Exceeding any requirement is risky, for example, overinflating, over-sized, different type or underinflating a tire different from what a vehicle needs, or what is a tire's rated recommendation. This can cause handling problems and product problems during any one of the criteria under what it was tested. On the surface that's why we should stick to what the specs are AND how you actually use it.

What this topic has revealed is that there a very limited cross consideration. For example, an LT tire CAN satisfy an ST need as long as the consumer knows how to substantiate that the LT tire meets or exceeds its ST tire counterpart. I don't think this applies anywhere else, like putting a P-series or ST tire on a truck does not help a truck, putting anything other than a P-series on a car is not applicable and wide, low profile tire belongs on a trailer. Doing this will absolutely require changes in suspension, wheels, brakes, etc. An example of this is a truck with large tires also requires a much different suspension.

We must be very careful how some of our justifications are determined - for example, nothing falling out of the kitchen may not be caused by softening tires. The kitchen items falling out in comparison to others could be because you know how to pack the heavier items at the bottom of the cabinet or away from the doors or you use sticky pads on the shelving to prevent movement or your cabinet latches are stronger, etc. This should not be fixed by changing the pressure in the tires, because underflating the tires COULD create a bigger problem.

I like that this topic is allowing others to admit their usage, so it can be promoted or demoted in favor of what's right and what's safe. Collectively we all gain by becoming more aware and helpful.

KathyandDave · 07-15-2009, 05:37 AM

I prioritize safety first, then performance. Inflating the Goodyear tire to the value recommended in the Goodyear charts is not under-inflation - it's proper inflation according to the manufacturer's recommendation. So, it's safe - there is no more risk of blowing a tire at the recommended pressure than at the maximum rated pressure. However, if the brakes work better at the recommended pressure, because there's more tread on the road, then safety is improved. So, by running the pressure at the recommended level, I have increased our safety. The performance benefits are improved ride and longevity of suspension components, which I get for free just by being safe.
All opinions I express are mine alone and are not intended to give direction to others. As Art points out, I am grateful to all for the ideas that come out in these discussions.

Art-n-Marge · 07-15-2009, 08:01 AM

I am referring to underflation as BELOW what is allowed. Most heavy duty tires have a range of acceptable tire pressures. The maximum is pretty obvious and what's less than that, might need some investigation. I agree KathyandDave are within spec and NOT underinflated.

I have a 2006 Ford F-250 4x4 and the tires have a maximum PSI of 80. The truck documents specify 75 PSI all around which also satisfies my GVWR and is what I use even when towing. My previous Ford 4x2 specified 55PSI in front and 70 in rear. The point is these are not underinflations.

My point is for each of us to KNOW what is safe, which will then provide performance. What is safe for one may not be the same for another. I like to learn how to determine what is right for my configuration for the best in safety and performance.

Good stuff, indeed.

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