Leading Link Forks

[Diploman]

Recent photos posted on WG ( Greeves, 60's vintage BMW's, Guzzi V8, etc.) have reminded me of the former popularity and more-widespread-than-today usage of leading link/"Earles" forks.  I've never used one, but it seems like a solid design to me.  Rather than sliding like conventional or USD forks, the movement of leading link forks is axial and controlled by ball bearings or bushings, a more efficient way to decrease friction and increase fork compliance. 

With the development and ready availability of today's high-quality, adjustable dampers/shocks to use on a leading link fork, as well as modern materials such as carbon fiber and CNC machined alu, I wonder why leading links would not be a viable option for modern sportbikes.  I think this might work particularly well with a perimeter brake such as Buell fitted, so the calipers would be mounted on the swingarm very close to the pivot, resulting in much less movement of the calipers than the front axle on deflection, thus creating, in effect, less unsprung weight.

Why has the leading link fallen out of favor?  It seems to be used consistently nowadays only on sidecar rigs.  Why is this?  What factors would impede the comeback of leading links today?   

[thomas]

Excessive weight? In particular Unsprung weight?
Complexity (although modern USD forks are by no means simple).

regards
Thomas

Recent photos posted on WG ( Greeves, 60's vintage BMW's, Guzzi V8, etc.) have reminded me of the former popularity and more-widespread-than-today usage of leading link/"Earles" forks.  I've never used one, but it seems like a solid design to me.  Rather than sliding like conventional or USD forks, the movement of leading link forks is axial and controlled by ball bearings or bushings, a more efficient way to decrease friction and increase fork compliance. 

With the development and ready availability of today's high-quality, adjustable dampers/shocks to use on a leading link fork, as well as modern materials such as carbon fiber and CNC machined alu, I wonder why leading links would not be a viable option for modern sportbikes.  I think this might work particularly well with a perimeter brake such as Buell fitted, so the calipers would be mounted on the swingarm very close to the pivot, resulting in much less movement of the calipers than the front axle on deflection, thus creating, in effect, less unsprung weight.

Why has the leading link fallen out of favor?  It seems to be used consistently nowadays only on sidecar rigs.  Why is this?  What factors would impede the comeback of leading links today?

[rodekyll]

I was looking at the LL on that V8.  Odd design in that it's not braced anywhere.  It must flex horribly.

The street version of a LL is much heavier than a telefork.  Although it's a simple design (in most basic form it's simply a suspended swingarm pointed forward) it's also harder to build and more expensive.  The design lends itself to end-users tinkering with steering geometry, which is dangerous and could have a liability.  Otherwise I can't see a downside to it.  I'm liking mine!

[oldbike54]

 Technically an Earles fork is a trailing link , different from a leading link .

 Dusty

[rodekyll]

Explain. please, Dusty?

[Diploman]

I believe the Earles fork - invented and patented by an English engineer - is a variant of the leading link fork, differing in the fact that the pivot consists of an axle that crosses behind the front wheel, providing bracing and creating a torque upon braking that actually makes the fork rise, in contrast to the fork dive on teleforks.  BMW used this type of Earles LL extensively on its 60's bikes.  The more usual types of LL forks, as I understand it, have the pivot farther forward, with a curved brace extending rearward around the wheel.

[rodekyll]

I think you're right about the Earles fork.  The common thing about leading links is that they all have a swingarm pointed forward -- wheel leads the pivot link.  The length of the swingarm and exactly how and why you got there doesn't really matter -- the variants are many, including both Earles and springer designs.

The opposite -- the trailing link -- has the swing arm pointed rearwards -- wheel trails the pivot link -- like a conventional rear suspension.

Here's mine.  It's an Earles' variant.:




photo gallery online

[Huzo]

They seem to go the way of hub centre steering and other incarnations of wizardry in and around the front suspension.
Over the years, we've seen good ideas ( Tesi and others), die on the vine. Until we see them on the likes of Moto GP and Superbikes, there'll be a wall of prejudice toward such devices.
I, for one don't care if a hub centre steering front end is better than a full house Ohlins setup, I just think the Ohlins looks shit hot and for me that's it.
The leading link to me looks cumbersome and a bit pre war BMW, even if that's not factually correct.

[Chesterfield]

Basically they are not used because they are ugly looking, and in this world it`s beauty before function.

[rodekyll]

A face only an owner can love.   

How can you think this is ugly?  I think it's a classic look -- much better than the EV forks.




multiple image hosting

[rodekyll]

They seem to go the way of hub centre steering and other incarnations of wizardry in and around the front suspension.
Over the years, we've seen good ideas ( Tesi and others), die on the vine. Until we see them on the likes of Moto GP and Superbikes, there'll be a wall of prejudice toward such devices.
I, for one don't care if a hub centre steering front end is better than a full house Ohlins setup, I just think the Ohlins looks shit hot and for me that's it.
The leading link to me looks cumbersome and a bit pre war BMW, even if that's not factually correct.

Leading links are a really old design, and have a deep history in competition.  They might not be on superbikes, but they're well represented both on and off the road.  They're more popular with the 3-wheel crowd than the bikes though.  Easier to do suspension maintenance on, too.

[Old Jock]

ISR's Hub center steering

https://www.youtube.com/watch?time_continue=80&v=YMy5TXhcVcg

[Chesterfield]

A face only an owner can love.   

How can you think this is ugly?  I think it's a classic look -- much better than the EV forks.




multiple image hosting

They look OK in your application

[ohiorider]

BMW's Telelever seemed to offer many of the benefits of leading link with less unsprung weight.  For years, it was standard on most of their bikes ....... better hidden on some of the K1200 'flying bricks' than on the Twins so as not to disturb the 'standard fork' look.  Seems like it has fallen out of favor on some of their newer offerings, such as the R9T Series.

I owned two Beemers with Telelever, a 1995 R1100RS and a 2004 Rockster, and I was ok with it, although on the Rockster, it seemed to contribute to the rear end unloading under heavy braking.  The fact that BMW had to engineer in a slight amount of front end dive was a concession to those of us who expected a bike to, well, dive under heavier front wheel braking.

I don't think is would have been a replacement for leading link on sidecar applications, but perhaps.  I've read where the never-popular R1200C cruisers are being purchased on the used market as tugs on several large sidecar rigs.  Anyone else confirm this?

Bob

[Huzo]

 

They look OK in your application

Yes, for beasties such as Rodekyll's, they are probably a necessary evil. On two wheeled devices such as motorbicycles, there are no significant assymetric loadings, the resultant of centripetal and gravitational forces resolve to place the forces directly from the contact patch up through the steering stem. On trikes and sidecars, assymetric loads are trying to tear the living guts out of the front end, so such a construction becomes necessary.

[Diploman]

Nicely done trike, Rodekyll!   Like it!  I haven't seen those Lester wheels for years....  I now understand why leading link forks are routinely fitted to trikes and sidecar rigs:  to withstand the lateral loads generated by steering rather than leaning.  Your adaptation looks great!  Can you carry luggage in the rear section of the trike?  How are your rear wheels driven?  Differential or just a bevel box?  It seems to me there is enough distance between the rear wheels that you would want to accommodate a speed differential between the two when turning.  Is this an issue?

[n3303j]

My R27 and R60/2 were Earls forks. Bought the R27 just about the time BMW went to telescoping forks. Dealer said BMW dropped the Earls fork because it was heavy and BMW didn't want to pay the royalties for use of the Earls fork.

The brake static anchor on the BMW was on the swing arm. Hard braking tried to rotate the swing arm downward. It counteracted the diving tendency on hard front wheel braking and made for a very level panic stop.

[rodekyll]

Nicely done trike, Rodekyll!   Like it!  I haven't seen those Lester wheels for years....  I now understand why leading link forks are routinely fitted to trikes and sidecar rigs:  to withstand the lateral loads generated by steering rather than leaning.  Your adaptation looks great!  Can you carry luggage in the rear section of the trike?  How are your rear wheels driven?  Differential or just a bevel box?  It seems to me there is enough distance between the rear wheels that you would want to accommodate a speed differential between the two when turning.  Is this an issue?

Thanks.  It's a work in progress.     That leading link in the picture was meant for some other bike, but I made it fit.  I think it's an early "UNIT" incarnation.  I had a topic recently about the sub-project.

http://wildguzzi.com/forum/index.php?topic=92950.0

The rear suspension is IRS.  The wheels are driven directly from a torque converter through a 7.5" Mustang differential (5.11 gears) with CV jointed open axles.  So there are no issues with wheel speed difference -- only with wheel speed at all.    It will run 75 all day, depending on when in the day you started accelerating.  It's a true, non-posi differential rather than a live axle setup, so it doesn't try to push straight when I want to turn.

Yes, if it looks like storage, it probably is.  There's an open "pickup" bed in the back with an overhang from the top part and a working tailgate for larger things.  It's good for about 150 liters, or two big dive bags and a bunch of other stuff.  There are three watertight hatches on top, with a large center area and two smaller bins above the fuel tanks.  I think there's about 70 more liters under cover.  My fire shovel and Pulaski fit in an area behind my left leg, which can also accommodate camera tripods, fishing gear, long guns, or anything else tall.  A duffel bag rests sideways behind the saddle and doubles as a back rest.  So I can look like Jed and the Clampetts motoring down the road.   

Straying back to the topic -- the LL also allows for trail adjustments to tune the steering/stability tradeoff, and because of the geometry, allows the front wheel to "lean" into a turn more than a more vertical for arrangement (outside fork leg rises while inside drops, offering the edge of the wheel to the road).  The leaning reduces steering effort and shortens the turning radius compared to telescopic forks.  I dropped about 3' off my turning circle by changing from telescopic forks.