Followup to valve stem failure
Yesterday, I finally had time to deal with the failed valve stem. I decided to take both tires in as I wanted the valve stems replaced on both. The good news is that you CAN have 100PSI rated, steel/chrome valve stems fitted to the aluminum alloy wheels used on the late model A/Ss. The bad news was that as soon as we pulled the tire off the rim where the valve stem failed, we found that in the few seconds that it took me to slow, pull over and stop (remember the flat tire was only warm to the touch immediately after I stopped), the rim had done a number on the INSIDE sidewall. The outside of the tire looked perfect and until we got inside, it appeared that replacing the valve stem would be all that was necessary. The inside of the tire contained shredded rubber and after further inspection, it was obvious that the interior of the outside sidewall had sustained damage. As the sidewall is the weakest point in the tire anyway, continued use was asking for more problems. We also pulled the other tire off the rim (to replace the valve stem) and found that the valve stem on the other tire was showing signs of wear. So as soon as Discount Tire can order in a couple of new Marathons, both tires will be replaced (a bit of overkill, but I would prefer both tires to be of similar age and wear). The way the valve stem failed as well as the way the other was wearing, it appeared that the stem was undergoing mechanical flexing where if entered the rim. The rubber stems that A/S installed seemed a bit longer than necessary and that may have provided additional leverage which over the 7-8K miles on these tires, flexed the stem sufficiently to cause failure. Anyway, switching to shorter 100PSI metal stems solves the problem for good.
As there had been some discussion regarding running the Marathons at 65PSI, I looked up the inflation vs load capacity on the Goodyear website. the ST225/75R-15, D range tires have a per tire capacity of 2540# at 65PSI. At 50PSI, the capacity is diminshed to 2150#s. As the loaded '02 Bambi is rated at 4500#s, 50 PSI in the Marathons would NOT carry the load. 55PSI gives a capacity of 2270, which WOULD just barely carry the load. To provide a bit of capacity cushion, 60PSI gives 2380 (total of 4760#) and might provide a slightly softer ride on the A/S. Goodyear also states that their tires are designed to run at the FULL rated pressure and loads, and they state, "If you run tires with reduced air pressure, nothing but problems will occur. Irregular wear increases, mileage goes down, and fuel economy also gets worse.". So I will probably stay with the 65PSI inflation on the new tires.
I would HIGHLY recommend that everyone out there with load range D Marathons AND rubber valve stems to have them replaced (ESPECIALLY Bambi owners). Valve stems are cheap and ruining a otherwise perfectly good tire (not to mention the inconvenience) is NOT worth the risk.
david & bret
'02 Bambi LS
'99 34' Limited
Air Forums # 2159
Past President Heart of Texas Camping Unit
WBCCI # 7548