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Thread: New to RV
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05-22-2020, 06:03 AM #51
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The tires on my 450 (rears) are rated for 3975/ea (19.5 in, G rated). My rear axle, towing the 351, is about 7K lbs, so a single tire on each side is still within ratings. No derate necessary (well, not to tow any normal RV), my truck can tow with 2 tires out and not overload anything (but probably not make whoever is behind me really happy as the tires shred into pieces!). And yes, for those towing crazy heavy, or those with less capable tires, a single failure COULD cause another failure immediately, but that's a COULD, not a will. In a SRW, if you lose a rear tire, you WILL have no more rear tires on that side of the vehicle, 100% of the time. What percent does the cascading failure happen on a DRW? IDK, but I'll bet my life it's <100%. I'd be surprised if it was over 1%, but I think we can agree, that's a far less likely situation than losing a single rear tire, especially if your rear tires are rated, individually, to carry the payload you have.
As for all the stability arguments, both vehicles have to pass the same stability tests at their weight limits. The only difference is that the DRW trucks have a LOWER requirement for all of the performance rating tests, but their stability at their respective load limits is exactly the same.
You are speculating that a DRW is safer than a SRW. When there is a study to prove that I will believe it. There are far too many other single point failures in both designs to support a conclusion that adding a dual rear tire makes any significant difference. I hear quite often that a DRW is better in a tire failure.
I can't see any amount of rationalization that says it is ok to knowingly drive with an illegal condition on your vehicle. When we get behind the wheel of a vehicle there is some risk involved but we are expected to follow the law.
I guess, in conclusion, this is a "you do you" issue. Do what feels safe, if you're close, weigh it, look at your ratings, honestly assess your skill level, your level of fitness (how quickly can you respond) and your exposure (do you tow 100 miles a year or 500 miles a day) and make a decision. I don't fault people towing big rigs with SRW heavy duty pickups, that would make me a hypocrite, I did it, I lived, nobody got hurt, and I didn't feel unsafe doing it. No scary moments at all, although I did find that engine braking could make the rear end squirm a bit, it never felt like it was going to come around on me. Max tow on my SRW was about 20K lbs, I was way under that, under on axles, under on tires, and over on GVWR. Was I legal? Probably not, but I honestly don't know for sure. On the 450, I'm under on everything, so I suppose now I could be considered "legal". Except for one thing, I pull with a Goosebox and because of that, need safety chains. The 450 has these strange bars in the bed to connect safety chains to that the chains from my GB will not attach to, so I had to get U shackles to be able to connect. I couldn't find any that were rated for the weight of my trailer's possibly dynamic load, I'm not sure they exist, so, honestly, I'm probably breaking a law there because the part I need doesn't exist. But only in some states, some don't require chains for the Goosebox. <sigh>.
One thing I will tell you, this whole experience for me, and this is coming from someone who's been towing for 25 years, gave me a tremendous amount of respect and understanding for what commercial truckers go through. It's a blizzard of regulations, one contradicting the next, varying by state (and even by highway in some cases). I read many trucker boards where guys are complaining that the "law" around trucking has basically turned into a "tax" because if they look, they're going to find something wrong and you're going to get a ticket. There are so many laws/regulations, you're almost always doing something "wrong" or "illegal". And that's a crying shame, it really is, because it makes determining if you're "safe" into an investigative reporting segment rather than a "look here and here, if OK, you're good to go". It's a real shame, and threads like this are just a symptom of the problem, there's so much room for discussion and interpretation it ceases to have a clear answer anymore.Last edited by Overtaxed; 05-22-2020 at 06:06 AM.
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05-22-2020, 06:47 AM #52
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For the risk reduction of the DRW, the one area that the risk does increase is there are 50% more tires to fail. That is of course mitigated by the increased chances of a failure are where you have the dual tires. However, given all the other single point failures (like the front tires, the entire front end assembly, both axles,...) I really am not sure there is a significant difference in the overall reliability. I specifically use the word significant because as an engineer I am used to looking at the impact on the entire system. I agree that one failure mode is improved. I am just not sure it makes an overall difference in the likelihood of a catastrophic failure.
DRW trucks do have some obvious advantages. Payload and towing are the most obvious. I would probably own one except for the ride difference between my F-350 SRW and the DRW. We test drove both, and the spouse said she wouldn't accept the ride in the DRW. I had to agree with her on the ride difference, and since I had done the analysis on the towing limits, that made the decision for us. If we drove another truck or newer F-350 we might come to a different conclusion just for the payload differences.
I agree completely on the respect for professional truckers! I have a whole new appreciation for what they go through, not only for the regulations but putting up with everything on the road. I do my best to give them room and respect on the road, regardless of what I am driving or towing.
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05-22-2020, 10:55 AM #53
Exactly!
It’s obvious and common sense that a dually is safer to tow with. Anyone that uses the “two additional points of failure” excuse doesn’t understand odds. If I had 10 tires sure there’s more points of failure but the odds of me have multiple blowouts is astronomical.
I have a better chance of running over a unicorn.
A dually is a lot safer to tow with period.
Sent from my iPhone using TapatalkResistance is Not Futile, It's Voltage Divided by Current.
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05-22-2020, 11:57 AM #54
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I am sorry, I do understand odds. And statistics and reliability analysis and safety analysis. Having three technical degrees and 38 years of engineering experience leading the design, development, and fielding of multi-billion dollar systems has provided me that background. It also has trained me to look at the entire system and see when one small fix does not make a significant impact in the big picture. That is exactly why I said that adding a second rear tire doesn't address all the other single point failures and doesn't make a significant difference in the overall safety.
If you want to discuss odds, I would look at how many times you actually have a blow out (defective tires like Westlake Es aside) versus a gradual flat tire. After 45 years of driving I have never had a blowout on any vehicle. Many flats, never a blowout. Modern properly maintained tires are specifically designed to NOT do that. A tire typically goes flat with more than enough warning to safely stop, especially when used with TPMS. I would also look at the odds of having a failure of a truck tire versus a trailer tire. Losing one tire on a dual axle trailer immediately puts most trailers in a drastic overweight condition. In the big picture, I don't think adding another set of rear tires to the truck does anything to really significantly improve the safety.
For the dual tire failure, that is what we would refer to in engineering as a cascading failure. The failure of a single tire would overload the second tire, increasing the odds of it having a catastrophic failure. This is very different than having two flats or running over a unicorn. It happens all the time when the system isn't designed to be fail safe.Last edited by BobKilmer; 05-22-2020 at 12:22 PM.
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05-22-2020, 12:18 PM #55
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What other "single points of failure" do you see commonly leading to accidents that's not addressed by DRW? Blowout of a front tire, agreed, no question about it. Blowout of a trailer tire (probably the most likely), no, a dually doesn't "fix" it, but I think anyone here would rather be in a dually with a trailer that's lost a tire than a SRW, that commonly causes a huge sway as the weight transfers, something where more contact patch with the ground on a TV is better. And, of course, you have the other things, not "failures" but more common situations, needing to stop quickly, more tires on the road, more stopping force. Wind kicking the trailer around, more tires, more lateral stability.
I've also never had a blowout, but they do happen, there are plenty of stories (and sadly, sometimes pictures) of the outcomes that can happen from that. Does it happen "often"? No, I don't think it does. But that one I kind of see like wearing my seatbelt, no, don't need it 99.9% of the time, but, when you do need it, wow, it's important to have it.
I agree, DRW is only addressing a few of many failure modes for a tow rig. But it's addressing some of the ones that have the most catastrophic outcomes, which, of course, is important. Not going to keep me from backing into my barn while parking the RV, probably a much more common failure mode, but also much less damaging to people/property.
I don't think anyone here is telling you or implying that you should get a dually. I know I'm not. But at the same time, if someone here came on (and I know this has happened on other boards) to this thread and said "You shouldn't get a dually, you should get a semi, it's safer and better at towing". Guess what? He's right, it is safer and better at towing than any dually pickup truck. And there are failure modes that a semi will handle that my 450 will not, no question about it in my mind, if I had a semi, there are certainly some accidents that I could avoid or better survive than in a dually. Now, I don't have a semi, and the reason is cost and utility, a semi is expensive and it's very single purpose, no dropping into the local town diner when your driving a big rig (in most cases). But I'm under no illusions, a semi is better and safer at towing a big trailer than my dually. We all have to examine those odds for ourselves, some land on a 250 class truck towing a 16K trailer (where I started) and others don't feel comfortable until they are in a semi. But each step "up" in size/wheels/brakes/etc does, without question, increase your safety on the road.
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05-22-2020, 01:09 PM #56
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I think you commented on the two biggest single point failures, the front tires and the trailer tires. Additional single point failures exist along the suspension, axles, and drivetrain. It is hard for me to say it is ok to have single front tires and single trailer tires and then rationalize that a dually really helps increase the overall safety. I haven't seen any blowouts, especially on one of the two tires on the back of a dually. You are more likely to have a failure of one of the other tires just due to the fact there are more of them.
For me, I think the dually discussion is very different than seatbelts. Regulations require a seat belt and there is data to show they save lives (although some people still manage to argue that point).
I agree completely with your last paragraph. It is a trade and everyone needs to do what they are comfortable doing. As I mentioned previously, I might have owned a dually if the one we drove had a better ride.
If I can digress for a second, in engineering there are typically two types different design philosophies. One is called Fail Safe and the other is called Safe Life. Fail Safe is just like it sounds, when something fails it is still safe. A Safe Life philosophy is all of the parts should be designed to be safe (not fail) for the life of the product, assuming regular repair and maintenance is done. This is how every vehicle in production today is designed. A good example is the front wheels. In a Fail Safe car if one of the the front wheels fell off the vehicle could continue to run and steer without it. In a Safe Life car, the front wheels would be designed to not fall off as long as they were properly maintained. Fail Safe is almost always safer than Safe Life, but only if the entire system is Fail Safe. It is also almost always much heavier and much more expensive. That is why cars don't have redundant front wheels and trailers have single tires. My point of discussing this is adding the second tires to the rear axle may make them Fail Safe (assuming no catastrophic failure) but the rest of the car is still only Safe Life. The result is the rest of the system (front tires, trailer, hitch, axles,..) are all still the driving factor in safety. Hopefully that didn't make anyone's head hurt. Geek mode off now.
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05-22-2020, 05:36 PM #57
There it is. You just agreed that adding second tires makes the whole setup safer.
No one said perfect, no one said it resolves all other points of failure.
I don’t have 3 degrees and 38 years of designing multi-billion dollar widgets but that seems pretty clear to me.
Sent from my iPhone using TapatalkResistance is Not Futile, It's Voltage Divided by Current.
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05-22-2020, 06:23 PM #58
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Actually no that is not what I said. Making a single part fail safe doesn’t make the system safer. That is the whole point of my comment. You should read the words I wrote. I said it makes no significant difference. If it did the engineers who built the truck would be equally worried about the front tires failing.
My widgets are what make it safe for you and everyone else to enjoy their freedom You’re welcome.
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05-22-2020, 06:30 PM #59
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05-22-2020, 06:34 PM #60
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Thank you!
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