My rig has a 1987 BMW K75C as the tug, a Dauntless subframe and suspension, and a Chinese mutt car. It is set up with about 2-degrees of lean-out and 5/8" toe-in.
I've noticed that the rear tire wore unevenly -- more heavily worn towards the sidecar. I have just recently replaced it. The original tire was an Avon with a flat, car-like tread. The replacement is a Metzeler with a similar tread.
While the rig goes down the highway very nicely, in a right-hand turn I perceive it wanting to 'push', especially when the sidecar is occupied. I feel I am cornering much slower than I would, simply because I feel the front tire wants to slide out.
I have never fully understood why a sidecar rig needs toe-in, and I have read that rigs with heavy sidecars, like mine, don't need it. And I have never come up with a good reason why my rear tire would wear more heavily on the right when the bike is set up to lean to the left.
I am thinking about trying a set-up with no toe-in. I believe that toe-in tends to fight the front tire when turning right, resulting in the 'push' I am experiencing. I think the uneven rear tire wear is telling me something is out of kilter, and perhaps that the rig is crabbing down the road, even though the steering feels neutral when going straight.
Other than the cornering issue I have been very satisfied with my Dunlop 404 front tire. It provides great stopping traction. In a recent panic stop it kept the rig straight, even though I was carrying a passenger. I keep the tire pressure low -- about 28psi -- for maximum grip. Front tire wear is not an issue. I was willing to trade short tire life for better traction, but it seems the tire life will be very acceptable.
Can anyone give me a clear explanation of what toe-in is for, and what the impact of a neutral setup, or even toe-out might be? And why my rear tire was wearing unevenly?
Ed Bianchi
