Hi I wonder if anyone can shed light on this one.
I don't normally have any problem setting up my outfits but this one is making me think too much!!
This is the first outfit I've had with car wheels and tyres, its also got bmw earles forks. The bike is a BM R/80 and is attached to a watsonian palma sidecar. The wheels are 15" with a 125 tyre on the rear and 135 on the front.
The problem I'm facing is the rig wants to put me into the oncomming traffic, I'm used to them pulling into the kerb and I deal with this by towing in untill it becomes neutral. I've now got about 3mm tow OUT and it still has a slight bias away from the kerb. I'm only using the rear wheel and sidecar wheel to align the rig as you should, the phisics is all wrong on this bike or am I missing something. The sidecar lead is 11.5"
Cheers
George
First:
Is your rear wheel/swing-arm assembly in true alignment with the bike?
Since you're in the UK I'm assuming this is a left mount sidecar that is pulling to the right.
Is there a possibility of too much leanout of the bike from the car with normal loadings. Weak shock absorbers could come into play here.
You're toe-in settings are figured at what distances apart? At the bike axles? Two metres?
The width of the rig's track is also a factor. Usually the wider the track the more pronounced the toe-in.
Are you using the wheel flanges or tyres as your measuring base? Either could be off or have run out. Even tire lettering will give a false reading and wheel flanges vary in rotating trueness. The tyre bead seat is true but the rim flanges seldom are.
Automobile flat tread tyres, especially radials also have a propensity for going in a straight line and resistance against turning that is not noticable with the rounded motorcycle tyres.
Just some possibilities,
Lonnie
Lonnie thanks for the reply.
Correct it's pulling to the right and yes s/c is on the left so everything is the reverse for you - well spotted!!! as I did not mention it!
I've set it up with zero lean in or out with no load BUT I have backed off the preload on the front and rear springs, so that is one easy thing I can try at once but it's raining cats and dogs at the moment and I'm taking the opportunity to mark schoolwork, I'm on half term and I've been putting off marking as I've been spending tooo much time playing with my new toy every time the weather is fine. I've no garage and do all my work in the road outside my house.
Tow in is measured in front of front tyre and rear of rear tyre.
VERY good point about not using the tyre and lettering etc. this is what I'm doing. I'm using two 1" thick wall square tubes resting against tires not rims so I'll weld some stand offs on my two bars and measure again.
I'm only using the rear wheel and s/c wheel to true up as I've had sidecar tugs that have bent their frames over time and it's only really the interaction of the s/c wheel and rear tire you trying to balance as the front wheel is moveable.
Thanks for the reassurance that car wheels want to go in a straight line!!! The steering is light due the the earles forks set in the sidecar position and the wheels being a smaller - I'm not going to work out the trail just yet.
Thanks again for you reply
George In wet windy Dartford Kent (UK)
George,
If you have cast wheels (or the same width wheels front and rear), another method of measuring that works for me is using the 1"x1" square tube, on blocks for better separation, tight against the sidecar wheel.
Visually align the front wheel so that the same amount of rear tyre shows on either side.
Take your measurements from below the axle(s)from the rim center flange to the 1"x1". About 1.5 cm +- positive toe-in should do, it I would think.
Some of the Palma setups I've seen have gotten by with somewhat less sidecar wheel lead than yours, but that's more about handling than directional pull.
Keep tweaking, It'll come around,
Lonnie
Lonnie
Again thanks for your input.
Yesterday did not go to plan - after about an hour of marking school projects the rain stopped and sun came out sun came out - I have no will power so I put on my gear and went for a ride with my 10 year old daughter in the chair. Much more fun than work. Tried preloding the suspension to different levels front and back. I runs better on softest setting (I've newish Hagon shocks all round including the sidecar). It seems to pull more towards oncomming traffic the harder the ride. I don't know what make wheels I've got but they are steel rims with tubing spokes welded up to a steel hub, so the method you suggest will work fine. As you know all watsonion fittings are clamp and slide, I could do with a bottle screw type (sailing boat rigging screw) of fitting for my lower front to help setting up tow in more easily. I put on white paint let it dry then undo fittings and put my weight on the sidecar with my knees and rear end on my forks and watch the paint line crack then measure what I've got. I use stands to support the bike and chair. I'm almost at the point of forgetting the measuring and just moving and trying, it is because of the crude adjustment method that I still measure before riding.
Many thanks
George
