Shortening front forks.
in [Tech]
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From: little man upon the stair on 25 Oct 2009 17:28 On Oct 25, 1:23 pm, "Greg.Procter" <proc...(a)ihug.co.nz> wrote: > I'm not really sure what you mean by "out-tracking"? > (perhaps the infamous separation of two cultures by language :-) You Kiwis still keep left on the roads, don't you? Imagine you're riding on a curvy road in the hills and you're trying to see around a hill that blocks your view of oncoming traffic, so you're riding near the center dividing line to see whatever is coming at you sooner. So you see the lorry coming around the bend and he's taking up more than his share of the road and you countersteer by pushing the left hand bar forward. If the scooter initially out-tracks, the chassis follows the direction of the front wheel, which is pointed towards the lorry for a terrifying split second, before the scooter begins to turn left. Initial out-tracking is the scary part, and initial weight transfer makes the out-tracking worse. There can also be a persistant tendancy to out-track if the front and rear tires are of different widths and profiles or if the front ride heigth is too high or the rear ride height is too low. In the case of persistent out-tracking you'll need to maintain pressure on the handle bar to keep the scooter from widening it's line in a curve. An equally annoying condition is when the motorcycle doesn't out-track in the least, but tends to fall into the inside of the curve. Sport riders have to learn to time their countersteering input exactly so they don't have to countersteer oppositely to keep the motorcycle from falling into the corner, with a resulting widening of the arc, followed by yet another input to have another attempt at establishing the correct line. Riders may not realize that their problem is front/rear ride height or a problem with tire profiles and they may insist that they have their front/rear sag set up correctly and won't want to change it. That type of rider may also be unwilling to slide the fork stanchion tubes up and down in the yokes. So he continues to have to make mid-corner changes in his lines. That's a safety problem on the street, and is annoying to racers who are trying to pass him on the track. There was an engineer at Michelin who came up with a set of formulae for tire profiles and diameters and coning angles and how everything related to rack and trail and wheelbase. I found his name on the interweb once but have never run across his formulae. > I'm stuck with the original wheel diameter of 12" plus 3.50 - 19" > overall diameter. That factor is fixed for authenticity. That's still a fair bit larger than the tire diameter I had envisioned when you first mentioned that you wanted motorcycle forks on a scooter. I suggest that you go to some of the tire manufacturer's web pages and see what they have available in that size. A quick way to get a list of the tire manufacturer's pages is to go to www.mawonline.com and click on "tires". This will take you to a list of tire manufacturers and there is an URL leading to each manufacturer. > As I say, my wheel diameter is fixed - I need the suspension to do the > work. With a smaller diameter tire, the suspension is going to have to work harder. A soft rubber compound on the front tire will help the suspension to deal with the surface roughness by absorbing the smallest bumps.
From: The Older Gentleman on 25 Oct 2009 17:32 little man upon the stair <macmiled(a)gmail.com> wrote: > So you see the lorry coming around the bend and he's taking up more > than his share of the road and you countersteer by pushing the left > hand bar forward. > > If the scooter initially out-tracks, the chassis follows the direction > of the front wheel, which is pointed towards the lorry for a > terrifying split second, before the > scooter begins to turn left. <snip> As you've never actually ridden a scooter, let alone on (for you) the 'wrong' side of the road, where does this advice come from? -- 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 25 Oct 2009 17:38 On Oct 25, 1:36 pm, "Greg.Procter" <proc...(a)ihug.co.nz> wrote: > Of course. But what you perceive may be different to my perception > thereof. Also, I'm aiming at a much lighter bike that that which you > might consider a "normal" sports bike. Are you aware that all the manufacturers have been building very light sportbikes since the mid-1990's? A 1993 Honda CBR900RR weighs about 350 pounds without fluids and a battery. The Yamaha YZF-1000R1 that came out around 2000 also weighs about 350~375 dry weight. What annoys me about the lightweight sportbikes is that they typically have a 33-inch seat height. I'm riding around on a 550-pound FZR1000 with a plywood seat so my feet will reach the ground and keep me from falling over if I get experience vertigo while stopped for a traffic light. > (With only one leg, I can't pick up a dropped 700lb bike. 300-400lb > would be my absolute maximum) Go to alt.motorcycle.sportbike and start a thread titled "Ping Bob Nixon". He has no right leg and still rides a Suzuki SV650. Ask him how he copes, and he will tell you. Some of the riders on alt.motorcycle.sportbike would like to hear about your association with John Britten, too.
From: paul c on 25 Oct 2009 18:12 Greg.Procter wrote: >> ... > I think changing the rake would be more than I'm prepared to attempt, > given that it's set by and within the body structure. It shouldn't be > hard to increase the trail a fraction. (it's 75mm/3") Either making new > and extended leading links or triple plates if I go with alternative > front forks. > ... Okay, you're closer to it than I am. I just assumed that using non-leading forks would move the wheel rearward so the rake would have to change. Photos seemed to suggest same, but my eyes aren't too hot, so maybe I was wrong to think about rake.
From: Greg.Procter on 25 Oct 2009 22:03
On Mon, 26 Oct 2009 10:28:15 +1300, little man upon the stair <macmiled(a)gmail.com> wrote: > On Oct 25, 1:23�pm, "Greg.Procter" <proc...(a)ihug.co.nz> wrote: > >> I'm not really sure what you mean by "out-tracking"? >> (perhaps the infamous separation of two cultures by language :-) > > You Kiwis still keep left on the roads, don't you? Still??? You yanks still drive on the wrong side, don't you? > > Imagine you're riding on a curvy road in the hills and you're trying > to see around a > hill that blocks your view of oncoming traffic, so you're riding near > the center dividing line to see whatever is coming at you sooner. > > So you see the lorry coming around the bend and he's taking up more > than his share of the road and you countersteer by pushing the left > hand bar forward. > > If the scooter initially out-tracks, the chassis follows the direction > of the front wheel, which is pointed towards the lorry for a > terrifying split second, before the > scooter begins to turn left. > > Initial out-tracking is the scary part, and initial weight transfer > makes the out-tracking worse. Hmmm, seems I always rode the wrong sorts of bikes - toss your weight the way you want to go and the bike goes that way. The technique probably requires that the rider has his feet under his/her centre of gravity. It always worked for me! > > There can also be a persistant tendancy to out-track if the front and > rear tires are of different widths and profiles or if the front ride > heigth is too high or the rear ride height is too low. > Silly design for motorbikes! > In the case of persistent out-tracking you'll need to maintain > pressure on the handle bar to keep the scooter from widening it's line > in a curve. > > An equally annoying condition is when the motorcycle doesn't out-track > in the least, but tends to fall into the inside of the curve. > > Sport riders have to learn to time their countersteering input exactly > so they don't have to countersteer oppositely to keep the motorcycle > from falling into the corner, with a resulting widening of the arc, > followed by yet another input to have another attempt at establishing > the correct line. > > Riders may not realize that their problem is front/rear ride height or > a problem with tire profiles and they may insist that they have their > front/rear sag set up correctly and won't want to change it. > > That type of rider may also be unwilling to slide the fork stanchion > tubes up and down in the yokes. > > So he continues to have to make mid-corner changes in his lines. > That's a safety problem on the street, and is annoying to racers who > are trying to pass him on the track. > > There was an engineer at Michelin who came up with a set of formulae > for tire profiles and diameters and coning angles and how everything > related to rack and trail and wheelbase. > > I found his name on the interweb once but have never run across his > formulae. > >> I'm stuck with the original wheel diameter of 12" plus 3.50 - 19" >> overall diameter. That factor is fixed for authenticity. > > That's still a fair bit larger than the tire diameter I had envisioned > when you first mentioned that you wanted motorcycle forks on a > scooter. That's why I'm interested in the particular model - plus there's only a partial dip between steering head and seat rather than the usual "U" spring frame design that comes from a flat floor. It's a very rigid scooter. (one might say overengineered) > > I suggest that you go to some of the tire manufacturer's web pages and > see what they have available in that size. > > A quick way to get a list of the tire manufacturer's pages is to go to > www.mawonline.com and click on "tires". > > This will take you to a list of tire manufacturers and there is an URL > leading to each manufacturer. > >> As I say, my wheel diameter is fixed - I need the suspension to do the >> work. > > With a smaller diameter tire, the suspension is going to have to work > harder. > > A soft rubber compound on the front tire will help the suspension to > deal with the > surface roughness by absorbing the smallest bumps. > -- Using Opera's revolutionary e-mail client: http://www.opera.com/mail/ |