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olds-cool

Leading link front suspension

26 posts in this topic

I met a local guy one day selling the start of a home built chopper. What I liked most about his bike was the forks that he was working on. He was building a canilever, or leading link, front end using the rear shocks off of an old Kawasaki and some straight tubing. The only thing I was worried about with his design was that the fork tubes appeared to be bowing a bit. My guess is that he used a thin walled tubing. Eversince I saw what he was doing, I've been looking for more pictures or information on this type of fork but most of my searches result in cantilever front brakes on bicycles. I only found 1 builder that made them and he didn't really provide much info on them. They look bad ass and so few bikes have them that it would really make my upcoming chopper build stand out from the rest at bike night. I know BMW made a version of this before (I'll throw a pic in below). Can someone tell me where to find more information on designing these or even better where to get plans?

BMW

bmw_r60-2_1967.jpeg

Some from the other builder (can't remember where exactly I found them now)

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Ok, after realizing that they are called leading link instead of cantilever, I found some more info on them. They are often used on bikes with sidecars to reduce trail. I still have not found plans though.

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you can get one of those exact frontends off of an old greeves.

heres a pic of one and yes they sometimes do wind up for sale on ebay.

Edited by blackchop1

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those I believe were called earls leading link forks. ill do a little searchin. goin by memory there were bout 6? types. I had a pic chart showing dif's but its on a crashed putor.

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How about some trike sites that have build plans for front ends? These seem to be a common thing for trike builders to use.

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heres a few pics, blackjack oughta know ths how to on this on account Im purty sure he's an old sidehack guy.

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heres a few pics, blackjack oughta know ths how to on this on account Im purty sure he's an old sidehack guy.

Dude!

Sidehack guy? That's low.....

But I did work for the guy that's generally accepted as building the best leading link forks you can buy.

On the other hand I've got a ton of stuff to write, so I'm a little busy.

Stuff that's not immediately obvious...

Swing arm should point slightly uphill with the bike stationary to avoid nasty trail changes.

Brakes need to float (like a springer) if you don't want the front end rising evertime you brake. Locked wheels all sorts of nasty shit can happens there. See fixed brakes on sidecars, but you don't tend to fall off those if the front locks up...

Top shock mount ought to be the same distance from the swing arm pivot (or greater than) the lower one. Shocks hitting the leg as the suspension moves, is unpleasant. This what that bend in the legs is often about...

If you fix a tube at one end, and apply a load to the other (like say a fork leg...) the amount of deflection for a given load rises as the CUBE of the increase in length. Or, double the fork length, thing flexes EIGHT times as far. Long forks, thick wall tube.

Edited by Blackjack

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heres a few pics, blackjack oughta know ths how to on this on account Im purty sure he's an old sidehack guy.

Dude!

Sidehack guy? That's low.....

But I did work for the guy that's generally accepted as building the best leading link forks you can buy.

On the other hand I've got a ton of stuff to write, so I'm a little busy.

Stuff that's not immediately obvious...

Swing arm should point slightly uphill with the bike stationary to avoid nasty trail changes.

Brakes need to float (like a springer) if you don't want the front end rising evertime you brake. Locked wheels all sorts of nasty shit can happens there. See fixed brakes on sidecars, but you don't tend to fall off those if the front locks up...

Top shock mount ought to be the same distance from the swing arm pivot (or greater than) the lower one. Shocks hitting the leg as the suspension moves, is unpleasant. This what that bend in the legs is often about...

If you fix a tube at one end, and apply a load to the other (like say a fork leg...) the amount of deflection for a given load rises as the CUBE of the increase in length. Or, double the fork length, thing flexes EIGHT times as far. Long forks, thick wall tube.

so why are some leading link and some trailing link? wazup with that.?

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so why are some leading link and some trailing link? wazup with that.?

There's some theoretical advantages in trailing link.

No one ever seems to get them to work right though.

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Hey- I joined this group SPECIFICALLY because I found this thread and have built an Earles fork for my trike. 

All started out pretty good- and then slowly a low speed wobble began to show up (not running a steering stabilizer). At first it was just annoying, crack the throttle and it would go away. Then it became more pronounced and found myself fighting it for the first few mile after which it just plain wasn't there for the rest of the day, repeat the next day though.

THEN I decided I needed some softer springs to keep the wheel in better contact with the road surface and it was FULL ON wobble- not just low speed any more. Switched back to the stiffer shocks, that helped but it was still there... fitted a stabilizer from a big Suzuki crotch rocket- didn't change anything.

The pivot point on the swing arm is above the axle center point. Info here that Blackjack gave says the swing arm needs to run uphill to the axle-is the angle more critical or the swingarm pivot point more critical? I want to fix this cause I love the trike but would rather do it once than many times over!

Any and all help appreciated!

I have a 5 X 16" wheel on the front so I COULD put a flat tread car tire on it as well...

Pat

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Have you checked the rake and trail?

Dusty

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Rake is kinda a moot point as long as the trail is correct to the rake. Trail is 1 7/8". It steers great-

Thanks!

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Oh yeah- and despite being a "grease spot" I'm a monetary supporter here> :)

 

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Lots of people got into trouble with those because the trail changes with the ride height.Did you check it with the arm parallel to the ground and an inch or two up and down? Of course looseness anywhere even the rear suspension can cause a wobble! When Harley changed from 18" tires to 16" the tire height and steering geometry was the same but they shook because the rolling resistance was radically increased one more degree of rake cured it. So you might play with air pressure to see if it's related to rolling resistance.

Dusty

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Greater the air pressure, less wobble- I'm at 38 pounds now. 170/70-16 Shenko in the front. It's a round tread tire so not much rolling resistance.

Everything in this is brand new and tight.

Really think this relates to either the front tire or the angle of the front swingarm (on the fork).

 

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Think I would make a longer leading link, more rake and trail is usually the cure when they respond to less rolling resistance. I know that it's not very accurate but laying straight edges on the photo looks like negative trail or real close to it. It also looks like lots of positive camber on the back which will contribute to instability. The rear should be real close to o camber generally straight up and down with a level is close enough. Also the rear should be toed out between a sixteenth and a eight inch equally from a center line.

Dusty

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Dusty is right, all my short forked, minimum rake trykes had low speed shake until I raked out a little more......that's a nice tryke,btw

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Thanks guys for the suggestions. The rear camber is zero (checked with a level on the wheels- optical illusion). Zero on the toe as well.

I'll look into some accurate figures on the trail next week but as it stands in construction, I had 1 7/8" trail with the ability to increase that to about 3 1/4"- I have tried adjustments there to no benefit.

I used the top part of a Gold Wing frame, steering head- I added 5 degrees rake to that so I'm not sure that really comes into play.

Yesterday with the stiffer shocks on it I did an experiment. Drove it thru my neighborhood at 15 MPH for about 2 miles (wobble would start to happen @ 20), kept it to 15 and no wobble then took it out on the higher speed road and no wobble occurred - go figure...

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My vw tryke would wobble with a passenger until I reset my rear torsion bars stiffer...

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Shoot a center line and set the toe to,1/8" out in front.  Wheels that are pushed set 0 to 3/8 in driving wheels about 1/8 out. since the fork self centers to the steering head the rear must also center to the steering head. Probably be a good ider to check that the measurement from a plumb off the center of the neck to each lower ball joint measures the same. I think that more rake and trail is going to be the solution but this is so easy to check and a definite possibility.  

Dusty

 

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Thanks guys for the suggestions. The rear camber is zero (checked with a level on the wheels- optical illusion). Zero on the toe as well.

I'll look into some accurate figures on the trail next week but as it stands in construction, I had 1 7/8" trail with the ability to increase that to about 3 1/4"- I have tried adjustments there to no benefit.

I used the top part of a Gold Wing frame, steering head- I added 5 degrees rake to that so I'm not sure that really comes into play.

Yesterday with the stiffer shocks on it I did an experiment. Drove it thru my neighborhood at 15 MPH for about 2 miles (wobble would start to happen @ 20), kept it to 15 and no wobble then took it out on the higher speed road and no wobble occurred - go figure...

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And THEN... checking everything after having those say something MIGHT be loose... It got considerably colder here (as all this came on) and although all is tight mechanically, I wondered about the rear tires (which I only run 15# in). Checked and they were down to 8.5#!!! There's a "loose" spot! Took them up to 15# and there's no HINT of a wobble now!

Amazing how things all have to be in tune in order to work right!

 

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Since they are driving wheels o is wrong toe 1/8" out would be a better starting place. Glad ya fingered it outs. It's always amazing when the back makes the front shake.

Dusty

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