I have been reading and think I have a grasp on this, but want to bounce this off you pros to be sure.
My CB750 with Spirit Eagle sidecar has been a bear to steer since I bought it a few months back. After reading the Spirit install instructions I found here, I discovered that the 16" lead was too much. So I realigned the sidecar to have around 10" lead and it made a big improvement. But it still takes a good bit of arm strength to turn, especially right. I know these sidecar rigs by nature turn harder, but it still seems a bit much.
I discovered today while looking the bike over closer and doing some checking on the CB750 forum that a previous owner welded an alternate rear shock mount hole on the swingarm. Obviously to lower the rear. Also, this bike came stock with 18" rear wheel and it has a 16" wheel currently installed. I am guessing a previous owner may have been vertically challenged and maybe did these two mods to help out?? Or maybe did it just for looks. Dunno.
Anyway, I am thinking that by lowering the rear of the bike as much as they had, they have increased the steering trail and could be making it harder to steer than it should. And, I am thinking if I move the rear shocks to the stock mount location and put a 18" wheel back on it, that would decrease the steering trail and should help with the hard steering.
Am I understanding how trail works correctly??
In all likelihood the combination of the repositioned rear shocks and the smaller front tire have brought the bike bake to it's original trail if it was lowered evenly.
Raising the rear of the bike and dropping the front by slipping the fork tubes farther up through the triple trees will give a small reduction in trail as will the use of a smaller front wheel. The CB's have a lot of trail so these fixes won't give a lot of steering effort relief. For a fingertip steering front end (like power steering) only raked trees or LL's will do the job for you without drastic frame modifications.
Lonnie
Northwest Sidecars
Negative. It is not a smaller front wheel. The front wheel is stock size. He lowered the rear shocks plus added a smaller REAR wheel hence lowering the rear even further. Now that I realize what someone did, it is obvious the rear squats pretty low when I look at it.
Really not looking for or expecting 'power steering' ease, but trying to make any improvements I can. I want to avoid any mods like raked trees or trailing link forks that detract from the original look if possible. I am wondering if raising the shocks and putting correct size rear wheel might make any improvement, even if just a little.
Just a very little, if you go with Lonnie's proposal you will get a huge difference.
Same I hope to achieve by getting a hole new bike prepared by the factory for my rig. (change stock Jawa 350 to Jawa 650 with Earles fork) The 350 will stay solo for down town messenger trips.
Sven
Sliding the fork tubes up through the trees will reduce trail some. Be sure there is clearance for suspenion movement. Raising the rear supension will also reduce trail some. Note that both of these methods are ding this due to the steering head angle being changed in relation to the ground.
One can also run wider bars for more levearge, possibly reduce sidecar wheel lead, track width, reduce front tire diameter and even possibly run a more narrow tire on the sidecar etc to help get steering easier.
Some bikes, th eearly BMW K bikes, fgor instance can have trail reduced by reversing the forks and swapping the side to side.
Some bikes , the XS1100 Yamamha being one, have been made with different forks on different model. Theses forks can be swapped around to reduce trail.
Note that if your forks tubes have the axle in the center of the tube maybe you can find some that havbe the axle in front of the tube and swap them out.
The efects of these type of mods with the forks will reduce trail. How much will vary. A steering damper may be required or may not. Riding the bike as a solo once trail is reduced is not good in most cases and in some cases is a ticket to the crash house.
TheDoug Bingham has posted some good pictures at the sidecar indutry council site on how trail is measuered.Google sidecar industry council or sidestrider.com.
ALSO See pic below.It shows negative trail in th eright side picture but shoudl relay the idea anyhow. No, you do not want to rteduce trail too much. Negative trail is not controlable..if you want to feel what negative trail is like run your rig up and incline , put it in neutral and coast back down backwards. No self centering effect at all...not good. The more trail is reduced the less self centering you will get.
If you want to measure what you trail has been reduced to after mods it can be done pretty easily if you know the stock specs first. Before doing any mods measure from your front axle centerline to some reference point on the bike.After any mods are done take this same measurement and the difference between it and th efirst on will tell you how much you have reduced the trail. FEEL is the best tell tale thing though but the numbers give some good reference and make for good conversation.
Claude
