Is there a reason that the lower mounts are attached to the side of the frame rather than the center vertical axis of the frame, assuming ground clearance is not an issue? It would seem if you attached on the verticle axis you would not have to re-level the car after adjusting the lean out.
Do car manufactures mount to the side of the bike because they are trying to make the side car fit a large variety of motorcycles easily or is there another reason?
Joe,
Access to a solid mounting point is probably the determining factor here.
Most bikes do not have center tubes or other attachment places below the center of the bike. Ground clearance and accessibility would be a problem with most road bikes.
Even with a central mounting there are differences in heigth when the bike is leaned from side to side. Not as pronounced but still there.
About the only time the sidecar is mounted below the center of the bike is with a free leaner sidecar. In this case there are still geometrical issues to address to make the rig handle correctly during any deviation from a straight line. (Got Physics?)
Lonnie
Northwest Sidecars
Joe,
Your geometry is correct but it will still not be prefect. The center of the arc is at ground level so even if the lower mounts were set at the centerline of the bike there would be some movement from level of the sidecar frame up or down.Free leaners do , as Lonnie mentioned, use centered mounts many times.(Not all but some).
I had often thought of running the lower mounts on a rigid rig to a subframe on the other side (left side)of the bike. This would mean the bike side of the sidecar frame would go down instead of up as the bike was leaned out. There were quite a few other thoughts in conjunction with this but I won't bore you with them here.
One mounting method for lower mounts that does make adjustments easy is to use pinch blocks on the inside frame member of the sidecar. If the sidecar has a round tubular frame these type mounts can be loosened up and rotated around the frame rail to level the sidecar frame back up when static lean is adjusted. Yes, the sidecar will move in and out slightly due to the arc the lower moutns are moving through but it may or may not be an issue dependant upon th elength of them and ,of course, if their lengths are adjustable or not. I have done this type of lower mounting system on Ural sidecars and others that have a large enough frame tube (About 1 3/4") to allow a good clamping force of the pinch blocks. Pinch blocks made of 2" x .120 wall material will work on a 1 3/4" frame tube. They need to be massive to keep from moving or run on an angle to discourage rotational movements. If you look at Dauntless's site you may find some pics of similar mounts Jay has done on the GS type rigs.
Pivot points on lower mounts shoudl be lined up fore and aft as well as being equal distance from the centerline of the bike and at the same height above the ground. This will prevent toe in changes when static tilt is adjusted. There are combinations of the above that will produce the same effect but are a little complicated to explain with words and are also more limited in their effectiveness.
I do feel that the sidecar world can benefit through more thought out developement of the lower mount systems. It is good to see that you have been giving some though to this.
Fun ain't it?
i'm designing the mount system for my "Road Warrior" project now.i will be using a subframe under the bike that spans both sides of the frame and up to the right side upper mounts.this is an aluminum framed motorcycle and i want as little stress on the bike as possible.i will also be keeping the lower mount points as close to level as possible to make alignment easier.
Dave,
This sub-frame design works well with the Beemer K's also.
I thought I had some pix of this to post but couldn't find them. I guess it was before my digital camera days.
Lonnie
