Forum bmwbike.com

I would like to start a forum on the possibility of smashing a headlamp due to the movement of the front fender license plate bracket moving back on an Earles fork type outfit while going through at speed, over a deep pothole. I have also heard of instances where the fender will get dented by the headlamp tang while going over a pothole.

Fact: The distance between the tang on the headlamp retaining ring and the fender top on a +1955 /2 unit is 6.5 inches (front wheel off the ground). The front suspension with Earles fork has a travel of 4.3 inches with solo configuration. Given the latter how can one claim that a ding was made in the fender while passing over a deep pothole unless the bolts holding the shock units sheared off.

If the clearance between the top of the license plate bracket is less than 2.5 inches (front wheel off the ground), then it is possible to smash the headlamp....one needs to mount the bracket further to the front to prevent this.

I am trying to establish the maximum travel of the springs from preload position (wheel off ground) to full "bottom out" so that I can position a circular license plate across the top retaining bolts of the shocks and not have to worry about fender hitting the bottom of the bracket if and when I hit a deep pothole.I have sidecar springs on my R69S and figure the travel is 4 inches. Anyone with factual information please reply.

Thanks,

Pierre

"If the clearance between the top of the license plate bracket is less than 2.5 inches"

Should read: "If the quasi vertical clearance between the top of the license plate bracket and the headlamp tang is less than 4.3 inches"

Pierre,

It seems like you are missing the point. On a normal fork, the suspension causes the wheel to move vertically up and down, along the axis of the fork.

With the Earles fork, the entire wheel does actually swing in a curve (up AND back) towards the general location of the headlight... When driving over an obstacle, your shocks might contract maybe 1.5 inches, but another point, further to the front on your fender, will travel a much greater distance in an upwards/backwards curve .

Have someone pushing your bike over some obstacle, while you observe the movement of the front wheel from the side, and you will see what I mean.

Stephan,

First of all thank you for responding. Second of all I can assure you I did not miss the point!
I am really looking for specifics here. I am very well aware that " the wheel (and fender) will travel a much greater distance in an upwards/backwards curve" but what I really want to know is what is this maximum distance. Granted I could take the springs out of the shocks and go through the motion and measure but I do not have the proper spring compressor to remove the latter from the units. I have done this once and was quite happy refitting sidecar springs and new koni's that I hesitate to do it again! I am looking for minimum clearances for either fender mounted circular plates or plate installed across the two top shock holding bolts.....and or someone that has gone through this exercise and made the measurements. If I get no response to that effect, then I will just have to bite the bullet and do it myself so that I can clear my worries.

Pierre

I have done some measurements using technical drawing principles (I may do it on Autocad at the office if I get the time).

Here is what I came up with based on a factual shock suspension travel of 4.3 inches.

Earles fork in solo position: 1.5 inches clearance between fender and headlamp tang at full shock deflection
Earles fork in sidecar position: 2.0 inches between fender and headlamp tang at full shock deflection

If mounting circular plate bracket on front fender, the top rear corner of the bracket should not be more than 3 inches away from front chrome fender bow measured along the fender curvature. Otherwise the license plate bracket will hit the headlight if shocks bottom out.

If anyone has anything factual that will either agree or disagree with this data then I would be much obliged if you could let me know. I am not claiming that these measurements are in anyway accurate to a definite degree but I would really like to put my mind at ease one way or the other.

As for mounting the circular plate between the two top retaining bolts of shocks, the bottom center of the bracket needs to be at least 1/2 inches higher(front wheel up in air) than the imaginary horizontal line formed by the projection of
the centers of the two retaining bolts (solo and sidecar position).

Pierre

I have done some measurements using technical drawing principles (I may do it on Autocad at the office if I get the time).

Here is what I came up with based on a factual shock suspension travel of 4.3 inches.

Earles fork in solo position: 1.5 inches clearance between fender and headlamp tang at full shock deflection
Earles fork in sidecar position: 2.0 inches between fender and headlamp tang at full shock deflection

If mounting circular plate bracket on front fender, the top rear corner of the bracket should not be more than 3 inches away from front chrome fender bow measured along the fender curvature. Otherwise the license plate bracket will hit the headlight if shocks bottom out.

If anyone has anything factual that will either agree or disagree with this data then I would be much obliged if you could let me know. I am not claiming that these measurements are in anyway accurate to a definite degree but I would really like to put my mind at ease one way or the other.

As for mounting the circular plate between the two top retaining bolts of shocks, the bottom center of the bracket needs to be at least 1/2 inches higher(front wheel up in air) than the imaginary horizontal line formed by the projection of
the centers of the two retaining bolts (solo and sidecar position).
Pierre