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Old 05-19-2008, 02:01 PM   #91
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Old 05-19-2008, 03:43 PM   #92
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Quote:
Originally Posted by Bandit Bill
.188 DOM should be fine, but the machine shop i dealt with in terms of some of the fabrication couldn't handle 44.5 mm ( 1 3/4") diameter .188 DOM tubing in their bender, and we elected to go the cut and weld and gusset method. Has held up quite well for 4 years now.

If that is a 600, the triple trees are 41 mm, so i don't know if you can use 1 5/8" DOM (41.275 mm), surface machined down at the top to fit in the triple trees and it'll bend easier in a bender..

You just gave me an idea. I already have a die for 1.75 tube and my bender can handle .188 wall. Maybe I can machine some straight sections to fit the triples and slip into the 1.75 for a nice tight fit, weld together using a bunch of plug welds...hmmm...just might be the ticket.

Thanks Bill.




I need to go start my own thread so I don't muddy the waters in this one.
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Old 06-02-2008, 07:10 AM   #93
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'56 works BSA


Greeves leading links.


Trailing links Greeves.


Trailing links Triumph-Wasp.


Husqvarna leading links.


MotoBi-Greeves leading links.


'64 DOT floating front brake leading links.
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Old 06-02-2008, 04:34 PM   #94
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Sensational Vortexau

Now give us a synopsys of the advantage and disadvantages of each
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Old 06-03-2008, 05:11 AM   #95
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Quote:
Originally Posted by Pezz_gs
Sensational Vortexau

Now give us a synopsys of the advantage and disadvantages of each
Do you imagine that I'm an engineer?
I'm limited to ordinary motorcycle physics, and what I already know.

For instance, there are some advantages to the Trailing Link design, but a penalty introduced by having more mass ahead of the steering axis.

Designs with floating brake linkages produce less brake-reaction effect on the Link, but some brake-torque induced rise in the Arm may be beneficial during heavy braking.

Suspension technology (springs & shocks) has improved since these designs were in use, but the suspension geometry itself of a lot of these machines has been tested in racing.

NB. I did read that the unit pictured last was suspect in strength due to the limitations of the material used in those long, straight, steering head-to-swingarm fork stanchions.
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Old 06-03-2008, 05:30 AM   #96
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>>>Designs with floating brake linkages produce less brake-reaction effect on the Link, but some brake-torque induced rise in the Arm may be beneficial during heavy braking.<<

This can be an area of contention as a non floating caliper on a leading link can induce the suspension to partially 'lock up' on heavy braking. This, when on a less than smooth hard surface, can create an understeer situation under hard braking.
The built in 'anti dive' properties of a non floating caliper are nice if the front end is set up right and agreeive riding is not the purpose.
Maybe it comes down to simplicity and riding style versus complexity and riding style.
Just some thoughts of course :-)
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Old 06-03-2008, 05:36 AM   #97
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Question for Vortexau:
It is obvious that so many of the off road rigs have a very short swingarm. This woudl seem like it would change trail more during suspension travel than a longer swingarm would. Do they simply do this for added rigidity from the pivot to the axle and not worry with trail variations?
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Old 06-03-2008, 05:41 AM   #98
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Larryboy wrote:
>>You just gave me an idea. I already have a die for 1.75 tube and my bender can handle .188 wall. Maybe I can machine some straight sections to fit the triples and slip into the 1.75 for a nice tight fit, weld together using a bunch of plug welds...hmmm...just might be the ticket.

Thanks Bill.<<

Note the comment about 'plug welds'. This is far better than running a weld around a tube to tube junction as the chances of issues arrising at the weld area are minimized. If plug welds are utilized as THE structural connection a small weld at the tube to tube junction can be used just for sealing purposes.
Just my opinion for whatever that is worth.
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Old 06-03-2008, 05:43 AM   #99
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If anyone has difficulty finding a place that can bend 1 3/4" tubing see if there is a race car shop in the area. Many stock car racers use 1 3/4" material in the roll cage of the cars. Most use thinner wall but they could still have a bender that can handle heavier stuff.
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Old 06-03-2008, 05:50 AM   #100
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Bandit Bill wrote:
>>If that is a 600, the triple trees are 41 mm, so i don't know if you can use 1 5/8" DOM (41.275 mm), surface machined down at the top to fit in the triple trees and it'll bend easier in a bender..<<

Turning down a tube at the junction of the triple tree connection shoudl be fine BUT it is best to not leave a sharp edge where the transition takes place. The difference in size on the OD woudl be better made if a tapered transition were used to curtail the possibility of failure at that point. Another thought would be to add another tube inside the main tube at this area that runs down into and past the transition point. Plug weld and smooth the surface.
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Old 06-03-2008, 07:05 AM   #101
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Yup, we're thinking the same way Claude.

I'm a pretty experienced welder/fabricator...safety is the most important. Plug welds with a low heat dress up weld to keep water out of the joint is the plan.

I'll get a thread going here soon and I'll have the front end build in there. Fox Racing air shox limited with bump stops...
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Old 06-04-2008, 04:34 AM   #102
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Quote:
Originally Posted by claude
Question for Vortexau:
It is obvious that so many of the off road rigs have a very short swingarm. This woudl seem like it would change trail more during suspension travel than a longer swingarm would. Do they simply do this for added rigidity from the pivot to the axle and not worry with trail variations?
If you compare the unloaded axle position to the fully-loaded axle position -- you'll notice that the trail is about the same. Its just during the brief mid-travel period that the trail is somewhat shortened (discounting what the rear suspension is doing at the same interval)!

You are correct about the rigidity of a short swingarm which, requiring less material gives less moment-arm for flexing, and on the whole means less weight and less pendulum effect side-to-side on the steering.

http://www.matus1976.com/akira_bike/...ntprogress.htm
(Akira replica with raked leading link)


60 million Honda Supercubs . . . . leading links over 43 years!

. . . . . . . . . . . . .

Compare the /2 Earls Fork to the current Ural leading-link! The Ural design is better for rough terrain, while the /2 Earls is mainly a tarmac design. The Earls will have more pendulum effect side-to-side on its steering but that's not a big problem on smooth roadway.

(Still, if you do have some significant mass its better behind the axle than in front. My '74 Moto Guzzi 850-T came with a single leading position brembo caliper. After the upgrade to twin-disc front end, I swapped the telefork lower legs to position the TWO brembo calipers to a trailing position. . . . that meant the mass of the calipers had a smaller side-to-side arc when the forks were turned lock-to-lock. I ended up with crossed brake hoses but there was no stress on them.)
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vortexau screwed with this post 06-04-2008 at 04:47 AM
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Old 06-05-2008, 03:56 PM   #103
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Quote:
Originally Posted by vortexau
Compare the /2 Earls Fork to the current Ural leading-link! The Ural design is better for rough terrain, while the /2 Earls is mainly a tarmac design. The Earls will have more pendulum effect side-to-side on its steering but that's not a big problem on smooth roadway.
The Earles fork is a specialised case of the leading link design where the pivot point is aft of the wheel. It is an important point because it is that variation that allowed Ernie Earles to patent them. It should also be noted that a great many off-road bikes were built with Earles forks. The design is well triangulated and very rigid and can be quite light though production considerations often caused them to be quite heavy.

The Ural leading link was designed to mimic the Earles fork within the design constraints imposed on the engineers. It had to be cheap and use the same shock absorber as used at the rear and sidecar. The engineers simply took their usual motocross sidecar fork and modified it have the same rake and trail as the telescopic forks. It should be noted that Ural triple clamps are raked 5 degrees at the steering stem.

I've seen several versions that the engineers would have made if released from those design constraints and I can say that the peeny-pinchers have a lot to answer for.

Almost any type of front end can be designed to handle well and all can be poorly designed and incapable of handling well at certain or even all speeds. A good place to talk about designs is http://micapeak.com/mailman/listinfo/mc-chassis-design It is frequented by such greats as Tony Foale and Ian Drysdale so the quality to noise ratio of discussions tends to high.

Over the years I've ridden bikes and scooters with girders, leading links, Earles forks, Diafazio HCS, trailing links, single sided trailing link, single sided leading link, Hossack steered upright and telescopic forks. All have advantages and disadvantages and most are in truth only theoretical. All can be set-up to work well and all can be badly designed. A lot of compromise goes into design and a lot comes down to what considerations are given the greatest importance.
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Old 06-05-2008, 05:13 PM   #104
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G'day Ural Australia

Can you post some pics of what you have seen and ridden please
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Old 06-06-2008, 08:42 AM   #105
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There are two designs that impress me the most-
The design from Norman Hossack, and my variation on Hub Centre systems that I label Trailing Hub Centre.

I grasped the mechanics and advantages of the Hossack design when I first saw it in a motorcycle magazine back in the late seventies or early eighties.
Norman testified that he was surprised to encounter people labelling his system as a Girder Fork:
Quote:
"Can it be these people have not bothered to look or do they lack technical savvy?"
The simple fact is that the swinging links on a girder fork are outboard of the steering head and swing side-to-side with the turning of the handlebar.

Hossack's suspension A-frame arms (wish-bone) support the steering bearings (ball joints) at their forward extremity, and do not turn but simply accomodate the up-and-down suspension movement.

I encountered the same sort of misunderstanding during correspondence with Craig Vetter! Initially he considered Hossacks to be Girders!

Norman had difficulty getting any motorcycle builders to try his system, and only BMW seemed to appreciate its advantages. Then, BMW's main version was only half-Hossack until the K1200S with its (full Hossack) Duolever front end.

. . . . . . .

Often Hub Centre systems present problems! Multiple (sometimes vague) steering links to the handlebars, a lack of self-centering effect, and the problem of retaining enough steering lock.

I feel that the placement of the steering axis, running through the centre of the hub is the major mistake. The forces that make the average spinning motorcycle front wheel act the way it does, precession, have a lot of that effect because more than 53% of the spinning mass of the wheel is ahead of the steering axis.

If the Hub Centre 'type' system is built with the steering axis behind the actual axle, by as much as 20-40mm, then that Hub Centre 'type' will exhibit the same strong precessional (self-centering) effects as the usual fork-mounted front end.

As to that steering lock problem, if only 47%-42% of the wheel is swinging in the arc behind the steering axis then this version will have greater steering lock when the side clearance displacement is equal to a more 'standard' true Hub Centre. In addition, a full 'U' shape doublesided leading arm design (where the suspension pivot passes BEHIND the wheel) as the Difasio version has, will have a shorter (and lighter) pair of arms in a Trailing-Centre Hub build.


Usual Difasio Hub Centre diagram where 50% of wheel is ahead AND behind the steering axis. When the steering axis lateral support (like an 'axle') is positioned 35mm more to the rear than the true wheel centre, the leading arms can be shorter and more steering lock is available for an equal side displacement ('elbow') in the shape of both arms.
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