How hard a trailer is to tow is a function of the total forces tying to keep it from moving forward:
+ Rolling Resistance
+ Weight X Acceleration
+ Grade ( < 1 for downhill, > 1 for Uphill)
= Total Resistance
So what does this have to do with choosing a motorcycle trailer? Generally fiberglass and aluminum cycle haulers are much lighter than steel ones of similar size and shape. Likewise, trailers with four tires will generally have more rolling resistance than identical ones with two tires. But rolling resistance is the same whether you are sitting still or towing your bike hauler 90 miles per hour.
So what, besides towing slower, can you do to conserve fuel and money? That’s where it gets really interesting because with respect to towing ease and fuel economy, the 800 pound gorilla in the room is wind resistance. So let’s look at what that is all about..
The force required to overcome wind resistance is given by:
Trailer drag coefficient (a constant)
X The frontal area of the trailer (a variable)
X Trailer air speed squared (a variable)
X Air density factor (another constant)
= Force required to overcome wind resistance
Identical trailers have the same drag coefficient, but different trailers or other vehicles have different coefficients. If you look closely at the arithmetic above, a couple of things become clear. Holding everything else constant and then checking the first three lines in the arithmetic above one by one leads to some interesting conclusions:
- A trailer with twice as great a drag coefficient as some other trailer will require twice as much force to overcome wind resistance.
- A trailer with twice as large a frontal area as some other trailer will require twice as much force to overcome wind resistance.
- A trailer at 100 mph will require 100 times the force required to overcome wind resistance at 10 mph.
When it comes to towing ease and fuel economy, it’s hard to over-emphasize the importance of the frontal area and the drag coefficient of a particular trailer design.
The frontal area of a trailer is simply how tall it is multiplied by how wide it is. But the drag coefficient can only be approximated by some terribly complex mathematical calculations, or by wind tunnel testing.
What was that? Was that the cry of the far from extinct “yeah, but” bird? Sure it was and rightly so. Yes, but what about the fact that there’s always a tow vehicle pushing the air out of the way in front of your bike hauler? Yep, that cuts down on the wind resistance your trailer meets—some, but not as much as you might think. Just remember how much the wind buffets your bike when you tow it on an open trailer. A trailer with a smaller frontal area will still meet less wind resistance than one with a larger front area, etc.
Where can you get the drag coefficients for different trailers? Don’t hold your breath waiting on box trailer manufacturers to supply them. And unless you work for a well known racing team, you probably don’t have access to a wind tunnel. So where does that leave you? Take a look at these published drag coefficients I dug up.
. Shape Drag Coefficient
2005 Toyota Camry .28
2006 Corvette .34
2004 Dodge Durango .39
2003 H2 Hummer .57
A typical truck . .60
A person on a bicycle .90
A smooth brick 2.1
So how can use this information? Stand 100 feet back from the front of the trailer you already have or are thinking about buying. If it’s seven feet wide by seven feet tall, it may be called a low hauler low profile motorcycle trailer, but it’s frontal area is still forty nine square feet.
Yeah, but what if it’s nose is not flat? When it comes to frontal area, shape doesn’t matter, but remember that shape, primarily the shape of the nose, determines the drag coefficient of trailers. And if the trailer in question has a flat nose, it’s just like a big shiny brick. So you may as well plan on keeping your fuel card on the console next to you because you’ll need it again before you know it. What if it has a bulbous. sloped or a V nose? Well it’ll pull easier than a huge oversized brick but I expect its drag coefficient will still be a lot closer to the brick end of the scale than it will be to a Toyota Camry.