crollman
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Re: Truck tires on tt?
My point is that whether you pick an LT tire or an ST tire may be the lesser issue. There needs to be a significant margin between static load and tire load rating to stay safe when towing. Manufacturer's recommendations don't achieve this on the trailers that I've examined. Whether LT or ST, you need to go up a couple of notches in load rating from the factory installed tires to make sure they're not overloaded when underway. Other parts of the suspension are also at risk, but this can be discussed some other day.607Views0likes0CommentsRe: Truck tires on tt?
This poster is still here. I'm really ticked off at the RV industry. This problem is real, pervasive, commonly ignored, but explains a lot about the prevalence of unexplained tire failures on trailers. We're all put at risk of having a tire failure as a result. Mine occurred at a really bad location (Monarch Pass) where I could easily have driven over the cliff at the side of the road. Grumble.608Views0likes0CommentsRe: Truck tires on tt?
"The tire engineers here on the forum tell us that "the dynamic forces involved when the tires in motion" are accounted for in the specifications of the tires. To put it simply, the figures the tire manufacturer states include the forces exerted on the tire while in motion, such as "increases of weight loading when traversing bumps in the road at speed". Which make sense, as it would be difficult indeed for us to foresee actual loads in motion." Those 'tire engineers' are wrong. The test spec for ST tires (FMVSS 109) only requires that they be stressed to 100% of rated load, and be tested for puncture resistance. There is no overload test embedded in that spec. When you tow on a curve there is a constant and huge increase in force on the outside tires that is not allowed for in the testing. When you tow in a cross wind there is a similar increase in force on the leeward tires that can also be in the many hundreds of lbs. Neither of these effects is taken into account unless the resulting force on the tires is less than their load rating.607Views0likes0CommentsRe: Truck tires on tt?
"The tire engineers here on the forum tell us that "the dynamic forces involved when the tires in motion" are accounted for in the specifications of the tires. To put it simply, the figures the tire manufacturer states include the forces exerted on the tire while in motion, such as "increases of weight loading when traversing bumps in the road at speed". Which make sense, as it would be difficult indeed for us to foresee actual loads in motion." Those 'tire engineers' are wrong. The test spec for ST tires (FMVSS 109) only requires that they be stressed to 100% of rated load, and be tested for puncture resistance. There is no overload test embedded in that spec. When you tow on a curve there is a constant and huge increase in force on the outside tires that is not allowed for in the testing. When you tow in a cross wind there is a similar increase in force on the leeward tires that can also be in the many hundreds of lbs. Neither of these effects is taken into account unless the resulting force on the tires is less than their load rating.607Views0likes0CommentsRe: Truck tires on tt?
rbpru wrote: If you want to buy a tire designed and built specifically for trailer use by the tire makers, then you are looking at STs. What worries me is that I suspect ST tires are specified with the best interests of the RV manufacturers in mind, not necessarily the best performance and safety that would benefit you and me. My Kumho 857s are a good example of how it's possible to make a significantly more capable trailer tire than ST's, but the RV industry isn't going down this path.328Views0likes0CommentsRe: Truck tires on tt?
rbpru wrote: Why would anyone expect a tire that was specifically designed to be use for trailer service; straight running, a non-steering axle, straight running tread design, stiff sidewall and service below 65 mph expect it to be suitable for two vehicle service? It's actually not that black and white. The FMVSS 109 spec that defines how ST tires are to be tested also applies to pneumatic bias ply tires for passenger vehicles, and to passenger vehicles with very small tires. The FMVSS 109 spec is 40yrs old, is outdated, and was due to be replaced, but this was apparently aborted for political reasons.327Views0likes0CommentsRe: Truck tires on tt?
Boon Docker wrote: " Not for Passenger use " Thats on the side of every ST tire That would because they are not rated for the high speeds that some morons like to drive. Actually they don't all say that. The Constancy Ly188 ST205/75R14s gathering dust in my garage say "for trailer use only". The meaning is a little different.327Views0likes0CommentsRe: Truck tires on tt?
Huntindog wrote: Your quote is accurate but,,, It is not the complete set of regulations. The point I was making is that the FMVSS 109 standard doesn't include wheelbarrow tires and the like. :-) Having said that, the comparison between ST and LT testing specs is very illuminating. This is nicely done and well worth the read. Thanks for resurrecting it. The other point I've been trying to make is that the RV manufacturers put us all at risk because the factory installed tires aren't rated for the loads they'll see when underway. Even the RVSEF messes up on this issue by not considering dynamic forces when checking load at each wheel. Either ST or LT tires with a higher load rating can help with this. But ultimately the NHTSA is remiss in not requiring a margin between tire load rating and tire load at GVWR.268Views0likes0CommentsRe: Truck tires on tt?
westend wrote: Also, upon further research, ST tires are subject to the same testing as gold cart tires and wheelbarrow tires.. That's not accurate. A trailer ST tire has a regimen of tests done at speed and with load. There is a specific test protocol just like an LT tire has a specific test protocol. Those test parameters have been posted/linked to, previously, on this Forum. The test is FMVSS 109. Words from this document are: "This standard applies to new pneumatic radial tires for use on passenger cars manufactured before 1975, new pneumatic bias ply tires, T-type spare tires, ST, FI, and 8-12 rim diameter and below tires for use on passenger cars manufactured after 1948." FMVSS 109 requires that tires be tested up to 100% of rated load, and no more. So there is nothing in the test that allows for lumps, bumps, and other dynamic forces that might exceed the tire rating during use.268Views0likes0Comments
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