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Old 07-17-2019, 11:50 AM   #1
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Front steer tire blowout analysis

Front Steer Tire Blowout Analysis

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On the video that shows the roll over of the Thor Tuscany motorhome which is pulling a red pickup, the first thing I notice is how this video further perpetuates the MYTH (this video is almost shocking, except that the angle of departure is distorted, which IMO is what makes it almost unbelievable). I used descriptive geometry and arithmetic to discover that the angle of departure (from straight ahead) is only about 18 degrees!! But remember, “We are afraid of those things that we don’t understand”. The myth is that a sudden failure of a front steer tire (blowout) has the capability of pulling the front of a large motorhome to one side and to send it out of control. This myth is also perpetuated by other videos, and also some motorhome drivers/owners who have misinterpreted what really happens whenever a front tire blowout occurs when you’re cruising/driving a big motorhome. Therefore, I will try to explain. BTW, I happen to have knowledge and experience about this subject, but not enough to qualify me as an expert. Yet, the more you know, the better your chances of learning and executing the safe way of handling a blowout. The most important thing to learn is that if this knowledge is already in your mind, you’re not likely to instantly get a brain cramp when you hear the BANG of a blowout and while feeling the serious shaking of the steering wheel. Be aware that a brain cramp puts you out of commission for a few seconds. Beware that in the Tuscany video, it took 4 to 5 seconds for the “healthy” right side tire to reach the grass. This means that if you do NOT go into “brain fade” AND if you only keep doing what you were doing before the blowout, you can just keep on using the steering wheel to stay in your lane. YES, if the ONLY thing you need to do is seamlessly keep using just the steering wheel appropriately, and nothing with your feet, you will have a very good chance of staying in your lane. NOW, the reason this might sound unbelievable is because you have been led to believe that there is a powerful lateral force pulling the front of your motorhome to the side. Neither the blowout itself NOR the flat tire have the capability to do that. Granted, the explanation of what really happens might sound complicated, but IMO by understanding a few important key factors it will mean the difference between loss of control OR not. Therefore I will explain: The blowout allows the air pressure to escape. A flat tire has a much higher rolling RESISTANCE than the inflated tire. How does this affect the steering? Simple: take an old rear- drive beater car to the highway, park and lower the air pressure in one front tire to 10 psi, then get in, and speed up to a constant speed of 40 mph for one or two minutes, get a good feel of the steering wheel, now let go the steering wheel. You will immediately find out the effect of what and how a motorhome will “self steer” when a front tire SUDDENLY fails AND the steering wheel is UN-ATTENDED. So, why does the the driver fail to drive with the steering wheel. It’s simple, he either had a heart attack, or more likely, immediately experienced a brain cramp or a blank out, or brain freeze. In the video it looks like the driver came to his senses AFTER the motorhome went out of control. Most drivers never have the opportunity to learn how NOT to be startled or shocked by something like a front tire blowout. But, some of us are lucky to be professionally trained to handle life and death emergencies . To me, a steer tire blowout experience is similar to a V-1 cut in a high performance twin jet aircraft (in this event the pilot flying MUST instantly and correctly “steer” the aircraft, due to having a flamed out engine on one side,…just as you pass V-1 speed). There’s no time to think, you either perform correctly, or…..disaster. That’s just a small part of the training.
IMO while cruising on the open highway, if you experience a front tire blowout, if the ONLY ONLY thing you do is to instantly use the steering wheel with authority for the purpose of staying in your lane, you will get a feeling of being in control… (one reason is that you’ll realize you can do it ). I urge you to use all your concentration on steering correctly/appropriately FIRST. The fact is, you have been using the steering wheel for steering since the first time you drove. So, why quit just because of a blowout? Yes, impact torque will be generated on the steering wheel whenever a significant difference in rolling resistance occurs between the two steer tires. It’s nothing new! Just like when one steer tire hits the big puddle of water at high speed. The driver feels it at the steering wheel. It’s just a STEERING ACTION coming back through the steering system. AND, it’s a good thing because this is what tells the driver what to do with the steering wheel. YES, a motorhome CAN SELF STEER right off the road! All it needs is a significant DIFFERENCE in the rolling resistance between the steer tires, PLUS an UN-ATTENDED steering wheel. WHERE is the PROOF that a blowout by itself can “PULL” the front of the MH to the side??? Heck, there’s at least 2 examples, on this forum, of tires blowing out while the MH is standing still. And, the motorhome did NOT move sideways one inch. This is proof enough that too much credit is given to the actual blowout. Analytically, one must look for OTHER cause-and- effect areas of chassis dynamics. For example, MANY drivers will get in their vehicles, and as soon as the engine starts up they start turning the steering wheel, BEFORE the car begins to move. And, when it starts moving it moves in the direction that the steer tires are pointing. So, the vehicle has to generate some momentum for the vehicle to go in the direction the driver chooses. And, the reason the vehicle does not move straight ahead is because a path to the side, of LESS resistance, is offered. AND, if the subject MH is moving forward, it will PUSH, yes PUSH, the front of the motorhome in the direction the front tires are pointing. And, if one steer tire is flat, no matter….the steering system will still work, as long as the rear tires and the inflated steer tire remain on dry pavement (where there is sufficient traction). And, I repeat, if the steering wheel is unattended, it will self steer to the side of the failed tire, by itself. If you do NOT believe it, simply ask the chief steering engineer at a place that has been doing research on the subject of ELIMINATING the onboard human factor. They know exactly what the robot driver has to do immediately upon the first sense of a steer tire blowout… AND, it does NOT include depressing the accelerator. They know that their driver does NOT need more than a few nano-seconds to keep steering and start slowing down. The robot already knows the real-time obstacle map around him. Yes, I know they now have blowout-proof tires, for these driverless delivery vehicles.
It takes a steering action to duplicate what the subject Tuscany does. The driver would need to quickly turn the steer tires about 15 degrees to the left. Of course, no driver in his right mind would do that at 65 mph. IMO he was NOT in his right mind. For me, it’s the only explanation. Please don’t tell me that a driver would say different. I already know what he’ll say. He’s a smart man. “The force was horribly strong, it took the steering wheel out of my hands.” It’s a good defense. Except that the science of it does NOT agree.
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Old 07-17-2019, 12:00 PM   #2
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Oh no.......here we go again..........
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Old 07-17-2019, 12:17 PM   #3
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Some experts here may challenge your analysis. I have had a left front explode on me.
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Old 07-17-2019, 12:20 PM   #4
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Interesting analysis - but hard to read.
Suggestion - break up your writing up into short paragraphs so its easier to read.
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Old 07-17-2019, 01:03 PM   #5
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Interesting analysis - but hard to read.
Suggestion - break up your writing up into short paragraphs so its easier to read.
I will second that
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Old 07-17-2019, 01:41 PM   #6
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Michelin has an excellent video on catistrophic tire failure and how to recover from it. When I took a driver confidence course, they used it and explained it well. It works for both the steering tires and the drive tires.

The first reaction most untrained people have is to hit the brakes which is the worst thing you can do.

The short version is that when you have a tire failure, step hard on the accelerator and keep a firm grip on the steering wheel. Most of us have power steering so the forces should never get out of your ability to handle it. Once you have control, allow the coach to slow and move to a place where you can safely pull off the road.
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Old 07-17-2019, 01:44 PM   #7
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My composition, which i have in my Microsoft Word, is double spaced between paragraphs, and in a more readable Font. By the time I got back to checking this, the window for editing had closed,...sorry.
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Old 07-17-2019, 02:33 PM   #8
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Do not be mislead, the blowout is not the source of energy and neither is a flat tire. But, we know the energy has to come from somewhere. In fact, the only force that a flat tire can play a part in is a resultant force. The only lateral force that will occur is if the motorhome actually begins to turn, BUT that force is in the opposite direction.
Another thing is, when the word "recover" is used, exactly what are they recovering from?
Do they mean that a driver lost control and they are talking about recovering from loss of control?
IMO there's only ONE MOST IMPORTANT action you must NOT fail to do. It's shown on the Michelin video, BUT it's not mentioned as the most important item in the instruction.
Instead, they make a big thing out of depressing the accelerator. Yet, they do not give the analytical explanation of how and why whatever force it produces will help. I'm really curious because I have not found a single scientist who can explain it. They all agree that there's already PLENTY of forward momentum to do what you need.
Meanwhile, I will keep trying to find someone at Michelin who can answer some questions. I'll report what I find, thanks.
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Old 07-17-2019, 03:20 PM   #9
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It might help if you could state your qualifications for this analysis and the findings of the scientist you have contacted. Any hard evidence or studies would be appreciated otherwise it is just an opinion. I have an open mind and willing to learn. As I understand the purpose for accelerating immediately is to put more weight on the remaining tires immediately after the explosion. In other words it seems to keep the MH stable and level while friction slows down the MH. It did work for me so to change my thinking I need something solid. My old XC chassis seems to well balanced and at no time did I feel danger.
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Old 07-17-2019, 03:28 PM   #10
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Interesting... I would like to hear from a member who had a blowout at highway speed and what they did or what they felt the MH doing as they tried to pull over. Thanks for the post.
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Old 07-17-2019, 04:59 PM   #11
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Interesting... I would like to hear from a member who had a blowout at highway speed and what they did or what they felt the MH doing as they tried to pull over. Thanks for the post.
I've had several, on account I started many years ago. I'm on my 6th Class A. The most recent steer tire blowout was LF while driving at 70 mph in my Vectra. I was not startled, I ignored the vibration (the tire was coming apart and doing damage), I never hesitated to work the steering wheel, while turning off the cruise control and turning on the emergency lights. I coasted to a stop, never even considered putting my foot on the accelerator. What for? It doesn't transfer more weight. The transfer of weight happens when the blowout tire loses all airpressure and can no longer support all the weight it was supporting (gets a lot shorter). The weight transfers diagonally to the rear tire(s) and also to the other steer tire. Therefore, this healthy steer tire NOW has MORE traction, plenty of traction to be able to easily steer the motorhome with.
The other steer tire blowouts were on racecars, at pretty high speeds. I've never experienced a loss of control due to a blowout.
I don't blame you for wanting to know my qualifications. I'd like to know the qualifications of the narrators on the blowout instructional videos.
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Old 07-17-2019, 05:27 PM   #12
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That in the first several seconds makes me wonder about the more technical aspects.

I have exploded a left steer tire on a big truck at high speed and didn't have a problem, but the more I read / see I believe a blowout on a coach steer is a different animal due to the higher weights and CG on the steer axle, plus maybe a little on the experience factor. None of the other three big trucks that lost left steer tires that night turned over or even went on field trips. The State of Tennessee paid for a new tire, wheel and hood on the truck I was driving, plus the other trucks and cars that lost tires that night after a steel plate in a bridge expansion joint came up.
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Old 07-17-2019, 06:13 PM   #13
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The "hitting the accelerator " really only makes a difference in a powerful car that has the power and torque to transfer weight from the front wheels to the rear even momentarily this would make the front wheels lighter and easier t steer but only momentarily so in reality not a good thing to do. If you have a blowout on any vehicle and the tire is shredded you are now on a metal rim it will veer either left or right. If you take your hands off the wheel and the left front rim digs in I bet you will veer left.
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Old 07-17-2019, 08:32 PM   #14
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I understand this thread to be about controlling a motorhome during a front tire blowout, and about a motorhome wanting to turn towards the blown out tire.
I have read on this forum people reporting their motorhome being a real bear to control during a blowout and others that basically said it was a non-event, just slow down and pull over.
So the question is, why the two significant differences?
Many comments are made here that I consider just to be repeats of what the poster either herd or read what someone else said and they think it sounds good, so they take that same position, repeat it and hope that others will give some credibility to what they post.
Anything posted here on the forum that can't be demonstrated or proven, I always highly question, as I advise you to do.
I've never had a front tire blowout, and hope I never do, but if I ever do, I'll be one of those drivers that is probably half asleep, have one hand loosely on the wheel, and day dreaming about what our trip will bring next. I'm sure setting on top of the tire when it blows will bring me to my senses. I've been beside a semi when a tire blew, and at the back end of the trailer when another blew, both on an interstate, and they are loud. Can only imagine what setting on top of one would sound like.
No one ever brings the subject of alignment into these discussions, most likely because very few really understand alignment.
My opinion of difficulty of control and turning toward the blown out tire primarily comes from the alignment settings on the chassis. I have only read people giving advice to increase the caster or increase it to the max here on the forum. Doing that will increase the turning force of the good tire toward the blown out tire as the increased weight is applied to the remaining good tire. That is fact and can be easily demonstrated so you can form your own opinion from what you see. I decrease my caster to get the trail figure I want to run , have done this with the last three coaches and will be getting it done with this one. Freightliner caster specs are 4 1/2* to 6* caster, my last coach was set to about 2 1/4*. Better control and less turning force during a blowout is only one of the advantages of a lower caster setting on a motorhome.
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