At last we are ready to leave for the 2007 Targa Newfoundland. With Michael Oritt as my co-driver we have been lucky enough to join a “marque” team called “Brick and Brute Racing” The other team members are cars #301, a 1963 Mini Cooper “S” crewed by Dyrk Bolger and Terry Milnes and #307 the highly modified 1959 Mini run by my buddy Dick Paterson with Tony Mattson from New Zealand as co-driver.
After consulting with various people I decided to use Avon CR6ZZ tires for this year. These have a wear rating of only 80 and are so soft that your finger almost sinks up to the first knuckle when you press into the tread. Apparently these are what the “hot shoes” in Europe and Australia are running, and although they are somewhat narrower than the tires we have run in previous years they are much stickier. These tires don’t have the radical tread pattern that you see on the tires most of the other cars are running but, by most reports, they still work well in the wet….we shall see. You will be able to track our progress throughout the event here.
After having the rear bodywork on AHX12 damaged during transportation in 2004 we decided to haul both cars down to Newfoundland with my transporter (see below) and I have built a special trailer for Dick’s mini which will tag along behind.
In desigining the mini’s trailer I chose to ignore the advice that I received on draw bar weight and my first attempt resulted in some “issues” with trailer sway on test drives. Good trailer design calls for 12 – 15% ot the total weight of the trailer to be the tongue weight. I enquired of a couple of trailer makers but no one could explain why a zero tongue weight trailer would not be satisfactory so that is what I built. Well….it turns out that there is a very good reason for that tongue weight rule and it was only after thinking about it for a while that I have concluded what it is. I will try to explain and I’m sure that Steve Byers will correct my terminology after he reads this through ;-).This is the way I understand it.
If you have a single axle trailer hooked onto the back of a car and you push sideways on the back of the trailer you will find that the trailer tends to rotate horizontally about where its wheels contact the ground and a horizontal force is applied to the tow ball on the car which makes the back of the car jiggle sideways on its tires. This is essentially what trailer sway is all about. In other words if you apply an oscillating force sideways on the car’s tow ball the car will start to rotate about a vertical axis, and if this oscillating force happens to have a similar frequency to the rate of “jiggle” the “jiggle” will get bigger…fast.
When the car is traveling down the road the “jiggle” also results in the car changing direction slightly and this can further accentuate the “jiggle” which, by this time, has become “sway”. It turns out that the way to prevent this is to minimize any side loads which are applied to the tow ball as a result of the trailer moving from side to side on the road.
Now you would think that if half the trailer’s weight was ahead of the trailers wheels and half was behind (i.e. no toungue weight) a side force on the trailer would have no reaction at the tow ball, but that is not how things work.
When the trailer is moving from side to side, say as it would if one wheel dropped into a bit of a hole, the trailer is actually rotating about the tow ball on the car like a pendulum. This means that the mass behind the trailer’s wheels has a greater momentum than that ahead of the wheels so that there is a net force sideways on the tow ball. I guess you could best visualize it like this.
Lay a ruler flat on a table and restrain one end so that it can spin around the restrained end. Now, place a heavy object on the table such that the ruler strikes the object as it rotates. If the ruler strikes the object at the mid point of the ruler there will be a tendency for the restrained end to kick sideways when the object is struck. If however the object is moved away from the restraining point a position will be reached where there is no resulting side force at the point of rotation when the object is struck and, if the object is moved still further away, the ruler will tend to kick in the opposite direction at the restraining point.
Now that may all be as clear as mud to many but the end result is that you require 12 – 15% of the total weight of the trailer to be on the tongue to reach the balance point where there is a minimal side reaction on the cars tow ball; so if you are building, or even just loading a trailer keep that in mind.
Anyway here is the rig all loaded and ready to go…The whole contraption is 37′ 10″ long and sure does attract a lot of attention on the highway. I suspect that we will see a lot of camera phones on the way to Newfoundland!!
WISH US LUCK!!