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Old 05-15-2012, 08:09 PM   #18
BMWzenrider OP
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Quote:
Originally Posted by Roundworld View Post
Quote:
Originally Posted by BMWzenrider
There is also a 155/60R15 which is slightly smaller at 22.3" diameter if you really want to get maximum drop and lower gearing in your bike.
That tire would put the rear axle about 1.65" (42mm) lower than stock. But remember by dropping the rear axle that far without altering the front ride height it will also result in the head angle changing by around 1.6-degrees (reduced steering angle, and increased trail).
If I put the car tire and used the 155/60R15 and increased the trail would that also then make the steering better as if I put an easey steer? Just a thouhgt or am I off base
For easier steering with a sidecar rig you want to REDUCE the trail of the front wheel.
That is what the various "easy steer" modifications do.
(also known as trail reducers...)


Trail is what makes the front wheel want to stay going in a straight line because the contact patch literally "trails" behind the point where the steering axis intersects the ground.
In the following diagram the red dashed line is the steering axis, and you can see how dropping a line from the front axle shows that the wheel is "trailing" behind the point where the steering axis intersects the ground.



For a two-wheeled vehicle more trail means that the bike is more stable because the front wheel doesn't want to flop over as readily when the bike is tilted off of vertical at speed. For a sidecar more trail simply means that the friction of the tire has a longer lever arm to resist steering inputs at the handlebar. Reducing the trail shortens the lever arm of the centering force on the front wheel, making it easier to turn.
The diagram shows how the trail is usually reduced for a TeleLever front suspension by the addition of an adapter to push the wheel farther forward in the suspension.

Some high-performance sidecars have center-hub steering with extremely small (or no) trail for a lighter feel at the bars with the wide car tires that they use up front.

So in the case of a sidecar rig, increasing trail by going to a much smaller wheel on the back without also reducing the ride height at the front will make it HARDER to steer.

Does that explain it adequately?
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