HOW LUCKY DO YOU FEEL?
By Bill Nalle, Southwest Chapter
Some very intelligent guys have asked me if they really need trailer brakes. A few of my friends have opined that for many years they have no trailer brakes, got along fine on long trips and therefore, see no need for brakes on mid-sized boat trailers. Well, not so fast. With that question on the table, I want to get into the nitty gritty of stopping one of our rigs with and without trailer brakes.
I am a Professional Engineer specializing in accident reconstruction. In addition, I carry a USCG 100 ton, Master’s License. For more than 30 years I have practiced in the field of accident reconstruction and have seen many trailer accidents. The results are frequently deadly serious. Admittedly, my bias is towards safety and guess what? Yours should be also!
In the Great State of Texas, the Transportation Code Section 547.401 requires trailer brakes on any trailer with a gross weight of 4,500 pounds or more. With that in mind, we will deal with the mid-size units, between the little jet ski trailer and the big boat trailers that are required to have brakes. Your state may have slightly different regulations, and you should check out what your state requires.
Any boat capable of pulling much of anything (tuber, boarder, skier…) needs to be on a two-axle trailer. This is for both balance issues and emergency control during tire failures. Any boat over 2,000 pounds should be on two axles, but my conservative nature thinks 1,200 to 1,500 pounds might be a better threshold number. I also think that a two-axle trailer should have brakes on at least one of the axles, preferably the front axle. Reasonable minds may differ on these issues, but those are my thoughts.
The Reader’s Digest overview is simple. As long as you do not encounter a need for maximum braking, you may not need trailer brakes. If you drive carefully, aim high, keep a good lookout and remain lucky, you may be OK, as some of you have been for many years. The need for moderate deceleration on wet pavement or emergency braking changes everything.
If you have good brakes on your trailers or just plan on continued good luck, read no further. If you think there is a chance your luck might wear thin, read on. I will get into the numbers on braking and why we need brakes. If you are not a numbers nerd, just skip over to the conclusion.
First, we need to settle on some terminology:
Braked Weight—The number of pounds of your rig that are on braked axles
Unbraked Weight—The number of pounds of your rig that are on non-braked axles
Braking Force—The horizontal force from brak- ing measured at the tire/road interface
Coefficient of Friction—The maximum braking force available on a given surface (The ratio of horizontal braking force divided by the braked weight on the wheel)
Governing Equation— Speed (mph) = Square Root of ( 30 x Stopping Distance x Coeff. of Friction)
First, let us consider your tow truck with no trailer. As an example, say your loaded truck weighs 4,000 pounds and the ultimate coefficient of friction on a good, dry road is 0.75. The entire 4,000 pounds are braked weight and the stopping force, we shall call “F” is simply 4,000 times 0.75 or 3,000 pounds. If the road is wet the ultimate coefficient of friction will fall to around 0.50. Note, these are very general numbers and they vary with the road surface material, speed, water depth and on and on. The stopping force on wet pavement falls to around 2,000 pounds. Your 60 mph, emergency stopping distance with a coefficient of friction at 0.75 is 160-feet (neglecting perception/reaction). Your emergency wet road stopping distance is 240 feet.
Now, let us consider your trailer has no brakes and has a total weight of 4,000 pounds (maybe a 3,000 pound boat on a 1,000 pound trailer). If we neglect the tongue weight, which will have only a small effect on our final numbers, we have 4,000 pounds braked weight and 4,000 pounds unbraked weight. With an available stopping force of 3,000 pounds (dry pavement) our deceleration rate is now 3,000 divided by 8,000 or 0.375 g’s. As long as you have no need for more braking force you are OK, for now. This simple analysis is the reason so many people have made it this far without trailer brakes!
In the previous example, pulling a 4,000 pound, unbraked trailer the most braking force we can get is around 3,000 pounds. The result is a maximum deceleration rate of 0.375 g’s. Now your emergency, dry street stopping distance is 320 feet compared to 160 feet without the trailer.
Just know, this is really bad. As long as you, as the driver, never let the need arise for maximum braking then you might be OK. BUT, you do not have control over everything that occurs around you on the highway. Using these simplified numbers, if you keep the demand for deceleration below 0.375 g’s, which most of us do most of the time, we are fine…. Most of the time!
But wait, there is more. Let us consider the same example, but in the rain. The maximum brake force we have available is only 2,000 pounds (4,000 pounds at 0.5 g’s). We still have the rig’s total weight at 8,000 pounds. The resulting maximum stopping rate is now 0.250 g’s (2,000 divided by 8,000). Now your 60 mph, wet street, emergency stopping distance is 480 feet. Recall we started at 240 feet for just the truck on wet pavement. Unless you have exceptional following distance, almost every stop you make will be approaching the maximum limits. Once the maximum limits are exceeded, you run a serious risk of collision.
In the following chart I have presented some minimum stopping data for your consideration. Note, these are general numbers and every rig will be a bit different. I have neglected tongue weight which should be around 10-15% of the trailer weight, but most of our units have much less, usually around 5% tongue weight. Thus, shifting a bit of the unbraked trailer weight onto the braked truck will have a small effect on the final calculations.
A quick comment on trailer brake maintenance. Disc brakes are easy to examine. It is very easy to determine uniform wheel performance of disc brakes by checking for equivalent disc temperature with your finger (lick your finger first to avoid burns!). Drum brakes are very suspectable to rust, electric or hydraulic issues. In my opinion, drum brakes are a poor choice for boat trailers. If you have drum brakes, with an annual tear down, they can be kept in serviceable condition, but it takes a lot of diligence.
The takeaway from this chart is reasonably clear. On a wet street the truck stopping distance goes from 240-feet with no trailer to 273-feet with two braked axles. That is good. With no trailer brakes the stopping distance goes from 240 feet to 480-feet. That is just dangerous.
The numbers on a dry street are almost as dramatic. On a dry street the truck stopping distance goes from 160-feet with no trailer to 182 feet with two braked axles. Again, this is good. With no trailer brakes, the stopping distance goes from 160-feet to 320-feet and that is dangerous.
You guessed it, having good brakes will improve your emergency handling. In the meantime, luck does not hold out forever. Even if the law does not require it; put brakes on your trailers. It might just save your life or your boat!!
Thanks Bill, this is written well with your Engineering Knowledge and expressed with your get down to business attitude. I have towed may boats to shows from less than 50 miles and as long as 450 miles with no trailer brakes. I use my Oilfield training and leave myself triple the following distance and less than maximum allowable speed. That being said it has taken a number of you to help me get out of my vehicle at the show because of the seat cover wedged in a tight place. With the drivers that are on the road today “the Luck has Gone”
It is quite nerve racking pulling our precious babies down the road.
Thanks again, plan to see you in the spring.
Burban & Water
Awesome safety information. Easy-to-follow mathematical equations dramatically illustrate what we need to consider when trailering. Thank you for your excellent article, Bill !
Great article and certainly information to consider for our towing of boat trailers. I would also like to point out the value of good tire tread and tow vehicle brake systems. Tread depth has a dramatic effect on stopping distance on wet pavement. Additionally tow vehicle brake systems can be compromised by worn pads, rotors, and old brake fluid. Add those factors to this articles information and your stopping distance could extend significantly.
I totally agree with the need for trailer brakes. My one concern is all cars and trucks today are equipped with ABS and I have not come across trailers that have them. In an emergency stop the tow vehicle will be using its ABS whereas the trailer brakes will most likely be locked up.
Great article! What do you recommend for a brake conversion or addition to your existing vintage trailer?
Good argument. But it leaves out another important reason to have brakes on a trailer. During deceleration a trailer – any trailer – is inherently unstable. In fact the better the braking of the towing vehicle, the more unstable the trailer during braking. Any sideward movement moves the trailer’s center of gravity out of alignment to the hitch, which will cause the trailer to swing wildly on that side and try to overtake the towing vehicle – i.e. to “jack-knife”. Trailer brakes create a drag force stabilizing the trailer and preventing the “jack-knife”.