Overweight

[RickNB]

First let me say that I do not want to put down anybodys personal preferences in tow vehicles we all feel that what we have is the best fit for what we personaly want . If somebody feels that a MDT or a dually is what best fits their needs that is fine but that is not what may best fit somebody elses needs. Someone may be fulltiming others may be weekend campers. Weekend campers may need their tow vehicle to be their daily driver as well. Running to the store to pick up milk and bread in an MTD may not be what everybody wants. For the mother of small children dropping her kids off at daycare and then off to work in downtown and finding a place to park a MTD or a dually may not be what is wanted.

I totaly agree that the tow vehicle should meet the requirements of the size of the trailer. Our tow vehicles are built with specs designed to meet or exceed the safty requirements that we expect. I do not believe that if the pin weight is exceeded by 50 pounds that the tow vehicle will disintegrate or be less safe than it was designed to be.

I would like to discuss the reply to my previous post.


"I'll bite. The dually will have increased braking as the doubled contact patch of the decreases the lockup point of the tire. To my knowledge duallies have the same brakes as a SRW. Brake shoes are slowing the wheel but ultimately the tire is stopping the unit - no friction between wheel and road = no stopping. Larger brake shoes will slow the wheel faster BUT if you reach the lock up point, the advantage is lost. Think of a drag race car, they will run slower with smaller( narrower ) tires. Same engine less friction between wheel and road."

The laws of physics and friction state that the pressure of friction is not dependent on surface area but only upon pressure (in this case weight) with materials of the same coefficient of friction.
This law of friction is discussed in many articles that can be found by doing a Google search. This law has been written by individuals much more knowledgable than myself and I am not about to argue their position.
If we follow this law then a 4inch wide tire would supply the same friction for stopping as a 8 inch tire but we also know that we have to have a sufficient size tire to carry the load that is placed on it and that will determine the size of the tire we need. Following this law then a dually would provide the same amount of friction to the road as a single wheel.

The previous poster states "To my knowledge duallies have the same brakes as a SRW. " I agree with that and will also add that as far as I know and someone may be able to prove otherwise that a 3/4 ton has the same brakes as well(at least in a GM product). With that information can we deduct that a 3/4 ton a 1 ton single or a 1 ton dually provide the same ability to bring the wheels to locking which is the maximum that must be provided any more does not matter ?
To follow the law of friction that states that the amount of friction pressure is dependent upon the amount of weight applied then we do have some small differences in the weight of a 3/4 , 1 ton single , and 1 ton dually and also in what configurations they are built extended cab,crew cab, 4 wheel drive 2 wheel drive. Given that the trailer has the same pin weight then the heavier truck should provide more friction in stopping because of the added pressure applied but not due to the amount of tire patch.

The previous poster also states "Think of a drag race car, they will run slower with smaller( narrower ) tires. Same engine less friction between wheel and road." This is like comparing apples and oranges. There is some documentation that can be found on drag racing tires and why they are built to the size they are. One reason is that they are built big so that as they accelerate the circumference of the tire expands changing the ratio of the drive train to allow greater speed with the same engine RPM without changing gearing ratio. Another reason is that to allow the burnout process to liquify the surface durning burnout to allow the tire to become sticky and change the coefficient of friction which provides more friction not due to the area but the stickyness of the surface. Drag raceing tires are also constructed of a much softer rubber producing a greater coeficient of friction.

Now to digress a little lets take a hypothetical situation and throw the laws of friction out the door as to surface area and and say that friction is dependent upon both weight and surface area in contact. Lets assume that the tow vehicle weighs 9000 lbs and compared to 4 tires on the ground we now have 6 as in the case of a dually then we have increased the patch area by 33% and given us 33% more braking friction and if 4 tires would stop the 9000 lb truck then with 6 tires we could now effectivly stop 9000 + 33% = 11970lbs or an additional 2970lbs. Now we are pulling a 13000 lb trailer and the brakes have not been maintained very well and actually they are not holding anything but we have 2970 extra pounds of breaking because we have a dual wheel tow vehicle and we have to make a panic stop. Will we be able to stop as safe as if we had well maintained trailer brakes? Will we stop in the same distance as with well maintained trailer brakes. If we assume that the laws of friction are wrong then we have about 78% of that trailer weight that we have no braking power for . The above figures are a hypothetical situation and are very open to discussion and are not a result of any actual testing on my part.

I guess what I am thinking is it fair for us to make a post that says that if you have a dually or a MDT you are going to have all kinds of braking power and nothing to be concerned about if if your trailer brakes are not working properly. You have 2 extra tires on the road so it will be OK . Why do they make dual wheels is it to provide extra breaking power ? Or is it to provide extra carrying capacity having the load distributed over more tires? Is it to provide a more stable vehicle ? Many readers of these forums do just that they read and use the information and take it as being factual and will not post to question it .

This forum is not as bad as others that I follow but on some it is getting to the point where you will need a Kenworth or a Volvo to pull a pop up. This kind of information is no better than the RV salesperson that we tend to run down saying that you can pull a 16000lb trailer with a 1/2 ton.
As I stated at the beginning if someone has the requirement for a dually or a MTD or Volvo or Kenworth or personally wants one that is great but there are units that do not need that size of tow vehicle and we see thousands of them on the road.Are they all safe and within the weight limits I am sure not all are but I do think that the most are. I do feel that it is important for all of us on this forum to supply the most factual information possible so we can make informed decisions

Regardless of the size or number of wheels it is very IMPORTANT that our trailer brake system be well maintained and checked frequently to insure proper operation at all times. False hope should not be put in the fact that we have a larger than required tow vehicle to stop the unit if the trailer brakes are not functioning properly.

Please feel free to post disagrements or agreements good discussion usually provides in the end good information.

Have Fun
Rick

 

[Ken Washington]

WOW Rick,
I almost got dizzy reading that post! All that I can say is that I feel safer with 2500 lb.'s pin weight plus all my stuff with four wheels in back instead of two. I think that what ever we are pulling with, we need to slow down and know that a lot can happen in the blink of an eye! I have been reading this thread as well as all the others and this is one of the most confusing one there is. We can go back and forth with it and turn things upside down but safety is of most importance.

Ken

 

[jpmorgan37]

If we follow this law then a 4inch wide tire would supply the same friction for stopping as a 8 inch tire but we also know that we have to have a sufficient size tire to carry the load that is placed on it and that will determine the size of the tire we need. Following this law then a dually would provide the same amount of friction to the road as a single wheel.

Same friction but 2 times the stopping force because you have two times the area of contact patch, assuming the only difference in the tire is the width. Go to any race track in the country and look at their tires. It's for traction and traction is caused by friction. It also applies to stopping power.

 

[dieselengineer]

The Physics equation does not contain a value for area. The fiction force is only proportion to the weight on the wheel. More wheels can carry more weight, therefore more fiction force. Case in point, when driving in snow, adding weight will improve traction. Just adding wide tires without adding weight will not improve traction.

 

[RickNB]

dieselengineer great example wish I could have said it that simple. Makes me remember many years ago when they would take the outside dual off the snow plow trucks to give them better traction in that case they had the same weight but less area.

Have fun
Rick

 

[nhunter]

"Makes me remember many years ago when they would take the outside dual off the snow plow trucks to give them better traction in that case they had the same weight but less area."

Wouldn't they have the same traction then as they have the same weight? Surface area apparently doesn't apply to friction.

 

[phranc]

Just as the dually has less traction in the snow , Does it follow that it has less traction in wet grass and on asphalt ??
I would heartily agree that the dually has more stability and more carrying capacity because of more tires ..

 

[RickNB]

nhunter I believe that the advantage in snow and ice is because the smaller footprint allows more bite into the snow compacted under the tire the total friction would be the same but concentrated into a smaller porus area. Try dragging a small spoon across packed snow and then a large shovel using the same amount of down pressure.

phranc
As for does a dually have less traction on wet grass that would depend on how hard the ground was under the grasss you might have a better situation with duals if the ground is soft because the weight per square area would be less and the tires would not sink in as bad if it was extremly hard under the grass then the single might be the better. Wet asphalt depending again on how wet is it a downpour with a layer of water on top of the asphalt then the duals would tend to hydroplan more than a single in this case there would be more contact with water than asphalt thus the coefficient of friction would be reduced in turn reducing friction.
The amount of friction does not change unless the weight changes it just gets distributed over a bigger area the same as the down pressure is distributed.

Great questions makes us all think about it .

Have fun
Rick

 

[nhunter]

I just don't get how surface area has no impact on friction. I know some smart guy said it but I don't get it.

 

[Forrest Fetherolf]

The moral to these stories is to drive within the capability of your
vehicle(s) and more so the capability of the driver. If you exceed either, then you might get hurt regardless of the tire size, number of tires, weight, or coefficient of friction. One tire will stop you if driven properly, a dozen won't if driven improperly.

 

[phranc]

Ricknb, thanks for taking the time to explain. I was trying to add a little
'tongue-in-cheek' type of wording .. Not always successful in a written word.. But what sucessful was the many explanations of a important subject..
Ya'all be careful out there !!

 

[RickNB]

phranc

Thanks I enjoyed it
Whatch out for the big snow coming this week

Have Fun
Rick

 

[BluegrassMan]

Hey Guys:

I might as well throw my hat into this volley of theory and ideas. If you go WAY back in these posts, you will find the saga of my experience with heavy trailer, down hill, braking, not stopping, passing 2 cars on the left while sliding to a stop in the median in the grass.

First off this is a must....HAVE YOUR TRAILER BRAKES ADJUSTED UP FULLY before leaving home. That was my first mistake. Long story short, my rotors warped and were purple, pads were cracked BAD, wheel bearings burned up. But the good Lord kept his hand on us, and we made it through this unscathed.
For my liking, A dually has better braking because the Rotors are much thicker, the wheel bearings are heavier duty (on the Front) where most of your stopping power derives. I don't really see how the SRW 1 tons are any different than a 3/4 in the brake dept. All this discussion of Physics is all well and good, IN the real world of towing there are SO many variables you don't have any constant values to work with. Hot asphalt is slippier than cool, rain vs dry, down hill inertia vs level, PLANNED stop vs PANIC (which is ALWAYS TOO little TIME) to stop.

All I know is I went through what Ya'll are speculating, and was VERY close to losing everything on I 79 S in WVA. I hope to have a F 450 this spring, the brake rotors are 15 inches and rear DISCS (which I don't have). AND I won't be over loaded ANYWHERE. Just my thoughts.....