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how much trail on leading link?

1.How much trail does a leading link front suspension need?2. Also, what is the rake angle of a '77 BMW R100 steering head?(if it matters to leading link set-up)3. I have an R69 Earl's unit, but I think it might be easier and better in the long run to fabricate my own. The mods for the Earl's will kinda mummock it for its original purpose.. R69. I've studied and read all that I can find and my questions are not addressed to particulars. I sent it to Ask Oak and Vech; stumped them. 3. Once the trail is established, how far back past 1/2 way of the wheel diameter should the shocks be mounted? The Earls has the pivot at the very rear of the wheel yoke (one of the reasons the Earls needs mods..bend the down the down yoke to miss the timing cover) , but others I have seen pivot futher forward. 4.What is the ideal relatonship of the pivot point to the shock mount and down tube, and the location of the axle? ooooh that was a big sentence..my questons are clear as mud, I guess.
Help?

Pete at Steerite is a very knowledgeable guy and has been doing sidecar mods for a very long time, he did my triple tree. get in touch with him by email or better yet by phone, he can be a little hard to corner but once you do be prepared to learn a lot, the man likes to talk but more importantly,,,he has answers, his business is in Kamloops BC should you need a time zone reference.

http://www.sidecars.ca/steerite.htm

Steering head angle is about 27deg. On bmw twins I use under 1" of trail and as little as 1/4". ---robtg

Thanks, robtg. I got a good reply from 'sidecars' at Steerite saying a reduction of 66% with a tad of positive camber. I also got a thick packet of articles and brochures from Sidestriders in Van Nuys, CA. Thanks guys.
With the two different numeric indications , and the rake , I believe I can do some measuring and drawing.

I have found that I prefer a not so rigid suspension on my rig, 77 R100RT w/ Velorex 700, so that I can'physically' adjust to severe road crown conditions without as much handle bar pressure as when the suspension is quite rigid. One article pointed out that the electric control type suspension is great for continuous crown conditions, but on roads where the crown changes alot, it is hard to keep up using the control button.

I welcome more comments on the amount of trail. Now, I am especially interested in the idea of camber modification incorporated into the leading link. jon

Some prefer more trail than others. Personally I prefer some feel of the road so run a tad more trail than some may like. There is no macho deal either way and if able to do so you will settle on a trail setting that feels 'right' for you. My rig has about 1 1/2" of trail. Racers may run down to zero static trail.
Lots of things to consider in addition to just trail.
1)Floating vs fixed calipers is a big consideration of course.
2)What to use for pivot bearings?
3) What materials to make th eforks tubes and the swingarm out of.
4) Pivot point location on swingarm related to amount of bend in fork tubes.
5) Shock spring rate
6) Fender mount design
7)swingarm angle after initial sag is set

If the trail on the front end you have now is known you can just measure from the front axle back to a reference point on the bike. This will allow some easy calculations to reduce the trail by 'x' amount when you do your leading link regardless of rake angle etc. You must make sure the ride height remains the same to be abel to compare apples to apples.
You could make the trail adjustable of course. Various holes will work placed maybe an inch apart for mounting the fork tubes to the swingarm.
As far as the pivot point location goes I am just about convinced it is a Chevy vs Ford argument. There are leading link designs out there with the pivot point placed all over the place. In theory the trail will change more on bump and rebound with a short effective swingarm but heck the sidecarcross racers run a very short coupled design as a rule and do well. Of course short means less chance of flexing etc...yadda yadda.

If you click on the link below you will see quite a few different leading link designs.
http://www.advrider.com/forums/showthread.php?t=308801&highlight=leading+links

or if that did not work click here:
http://tinyurl.com/4hrxkl

Attached is a picture of one of our CSM leading links. This one is on my own rig and has adjustable trail.

Attached files