Shortening front forks.
in [Tech]
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From: Greg.Procter on 25 Oct 2009 23:35 On Mon, 26 Oct 2009 16:13:52 +1300, little man upon the stair <macmiled(a)gmail.com> wrote: > On Oct 25, 7:20�pm, "Greg.Procter" <proc...(a)ihug.co.nz> wrote: > >> The leading link design >> appears to have been used by the designers so they could use "parts- >> bin" rear suspension units rather than making new telescopic forks. > > Well, an Earles fork with rear suspension units is not all that bad an > idea, if you're interested in suspension compliance. > > The shock absorber shafts are small diameter, so there's little > stiction compared to a strut type fork. > > 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! > > I rode a friend's 250cc Greeves MX-5 in the Mojave desert a few times. > It had too much weight on the front tire and the front end waggled and > hunted in the dry sandwashes. > > I couldn't go fast enough to get the front tire up on top of the sand, > so the Greeves wallowed along like a pig. > Sounds like there was insufficient trail. > Another Earles fork-equipped machine in those days was the popular > Sachs 125. > > Problem was that the front brake drum was anchored to the Earles fork > swing arm, and if the brake was applied it affected suspension > compliance. > > Not good, having the brake make the front tire skid early. Too true - the front of the bike rises under hard braking as the links roll around the pivots. Conventional forks sink under hard braking transfering weight from rear to front - back wheel locks :-) > > The next motorcycle my friend bought bought was a pretty Ossa Stiletto > with conventional forks and much less weight on the front tire. It > handled more like a Yamaha Enduro model like I was riding. > > But, by that time, the Japanese had caught onto lightweight > motocrossers with long travel suspensions and those machines could > skitter across the whoop-de-doos like they weren't even there... > Hmmm, Euro off-roaders were ahead of the Japanese, although they tended to be higher priced specialist bikes. (1960s-70s) Japs eventually made them cheaper and within a decade just as good. I wonder if the US experience came from demanding the smaller front wheels?
From: The Older Gentleman on 26 Oct 2009 04:21 Greg.Procter <procter(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! That's USKrusty for you: thinks he knows, but doesn't. :-) -- BMW K1100LT Ducati 750SS Honda CB400F Triumph Street Triple Suzuki TS250ER (currently Beaving) Damn, back to five bikes! Try Googling before asking a damn silly question. chateau dot murray at idnet dot com
From: Greg.Procter on 26 Oct 2009 17:26 On Mon, 26 Oct 2009 21:21:40 +1300, The Older Gentleman <totallydeadmailbox(a)yahoo.co.uk> wrote: > Greg.Procter <procter(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! > > That's USKrusty for you: thinks he knows, but doesn't. :-) > The point of the Earles fork, which was invented _after_ the telescopic fork is a) it's lighter, b) it gets over the telescopic fork problem of binding under braking. 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. (I'm not getting into discussions about who knows what - we all know different things and there's always something to be learned) Regards, Greg.P.
From: The Older Gentleman on 26 Oct 2009 18:05 Greg.Procter <procter(a)ihug.co.nz> wrote: > The point of the Earles fork, which was invented _after_ the telescopic > fork is a) it's lighter, b) it gets over the telescopic fork problem of > binding under braking. > 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. So true. And then they nicked the Hossack design (or maybe bought it?) and everything was nice again. -- BMW K1100LT Ducati 750SS Honda CB400F Triumph Street Triple Suzuki TS250ER (currently Beaving) Damn, back to five bikes! Try Googling before asking a damn silly question. chateau dot murray at idnet dot com
From: little man upon the stair on 27 Oct 2009 13:19
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. 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*. Once grip is compromised and the fork starts oscillating, the inertia of the masses will work against a return to stability. > 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. 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. > 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. 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. |