Shortening front forks.
in [Tech]
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From: Greg.Procter on 27 Oct 2009 21:35 On Wed, 28 Oct 2009 06:19:10 +1300, little man upon the stair <macmiled(a)gmail.com> wrote: > On Oct 26, 2:26�pm, "Greg.Procter" <proc...(a)ihug.co.nz> wrote: > >> >> > Problem with an Earles fork is that there is a lot of mass in >> front of >> >> > the steering pivot, so the front end will waggle and hunt on rough >> >> > pavement. >> >> >> Err, most of the mass is _behind_ the pivot! > > Depends on where the spring/shock units are located, which depends on > whether it's a trailing link or a leading link set up. Earles is "leading link". Trailing link only exists on the odd motorscooter like Vespas. They dive like hell on braking! > > The inertia of masses disposed in front of, or behind the pivot is > helpful in maintaining stability *while the front tire is firmly > planted on the pavement*. Sure, I like to keep mine right there!;-) (Apparently I don't always do that but ...) > > Once grip is compromised and the fork starts oscillating, the inertia > of the masses will work against a return to stability. Huhh, why would the wheel start to oscillate when it's clear of the ground??? > >> The point of the Earles fork, which was invented _after_ the telescopic >> fork is a) it's lighter, > > That's debatable. I have no doubt that the strut portion of an link > type front suspension can be made lighter than round tubes if it's a > pressed metal welded structure or if it's made from carbon fiber like > Britten used. No, my bad ... The _sprung weight_ is lighter on an Earles fork than with telescopic forks. Sprung vs unsprung weight is the vital factor. > > b) it gets over the telescopic fork problem of binding under braking. > > Yes, the link type fork does away with stiction, but having the link > motion restricted by application of the front brake is as bad or worse > than stiction. > Err, the telescopic fork has the forces horizontally rearward during braking. The rake angle divides that force two forces, a) along the forks. b) rearward. depending on the fort angle. The rearward force binds the forks, the upward force compresses the forks and causes dive. That dive would be much worse if the rearward binding force did not exist. The Earles fork takes all the force rearward. An additional force is rotational around the axle - transfered vertically by the link arms to the rigid part of the forks and to the frame. The lifting force is approximately countered by weight transfer of the bike itself. (no binding) >> Older enthusiasts will remember BMW staying with Earles style forks for >> years after the market demanded telescopics - they knew what they were � >> about. Eventually they were forced by fashion to go to teles. > > Don't get me wrong. I love the idea of a link-type front suspension, > especially what BMW has done with the latest multi-link front end. > > But if *you* want to graft a modern motorcycle front suspension onto > your scooter, you're most probably going to use telescopic struts from > a mass-produced motorcycle after acquirng the parts from a breaker. > Yes, exactly - provided I can find some that can be reconfigured/shortened. > I know what it's like to have a machine shop full of lathes and mills > and grinders, but whatever you produce in your shop is going to be one- > off and, if you break it, your motorscooter will be out of commission > until you make a new part. Certainly. However, the scooter is intended as a testbed for the motor and as such won't travel very far. My intention is to make it so that it won't break! |