Before we get to the front end stuff, a comment on Labor Day Weekend. We spent the week before the weekend parked on the shores of Lake Winnipesaukee in New Hampshire. Friday we headed for Wiscasset Maine to attend a wedding and meet up with daughter Becca, her husband Tobin, and an eight week old grand daughter Elise. Elise is a keeper. But the other eye opener was the lack of folks, traffic, and campers in Maine on Labor day weekend. There was not a No vacancy sign to be seen and the camp ground that we stayed in, a Passport America affiliate, West Side Campground in Wisscasset was only a third full. The economy is taking it’s toll.
Like I said last week, reading a tire is not rocket science as Sean and Kristie Michel, authors of the Long Long Honeymoon blog, recently found out. They wacked a curb with the Airstream and then began a wear tire problem resulting in blown tires. Sean published a photo of the ruined tire and it plainly showed a camber condition. Excessive wear on one side of the tire.
Camber wear will very seldom extend down onto the side wall. When wear does that it is usually low pressure. Camber when excessive will create a pull to one side or a drift. It is simple. When a tire is rolling down the road and the center line of the tire is parallel with the ground the tire will roll straight ahead. If we tip the wheel in, one side of the center line will point up into the air while the other side will extend down and the intersect with the pavement. This makes the tire think that it is an ice cream cone rolling and will roll around the point of the cone. Meaning the open end of the cone (tire) will not roll straight but rather around in a circle, pulling to one side.
In the old days with bias ply tires we used to off set the camber when aligning front ends to over come the tendancy of the car to drift down the crown in the road. Radial tires tend to track truer making the vehicle handle these problems better. So camber is first a tire wearing angle with positive camber being the wheel tipping out at the top while negative camber the wheel tips in at the top. When camber changes the contact point between the tread and the road surface does not change, the tire tilts around this point. There are several angles that also use this patch of contact as the meeting point. These angles are called the Included Angle and is a major part of steering geometry.
Caster can best be illustrated by looking at a shopping cart the next time that you are in a grocery store. If you drew a line through the pivot point for the front wheels of the cart it would intersect the ground in front of the wheels. This leaves the wheels to trail the pivot point and follow. If we try to make thw wheels stay out in front of the pivot, they will swivel right around and follow. In a vehicle caster is changed by tilting that line forwards or backwards so that we can control the angle and the tendency to provide more or less of a tendency to track straight ahead. In other words more positive caster, more straight ahead stability. And as a result uneven caster will create a pull in the direction of the wheel with the most negative caster.
The problem with tilting the pivot line front to back will cause the wheel to lay over when going around a corner. This means that tire edge wear will occur but it will be on both the inner and outer edge, like camber wear but on both sides, so there is a limit to the amount of caster that you can dial into the front end.
Well enough for this week, we will wrap all this up next week and then move on to more stuff. have a great week and keep camping.
Brad