new set of girders almost completed

[klogan45]

Thanks for the info Tbone you reply has really cleared up a very grey area for me. It can get a little confusing with the different types of tube and pipe.
Thanks again
Regards
K

[brock]

  yeah, interesting reading, would it be rude to ask the source ?

[tbone]

  yeah, interesting reading, would it be rude to ask the source ?

Not at all lol, descriptions are taken from Zookpower, an offroaders forum.
Thread link http://www.zookpower.ca/forums/showthread.php?t=4593

The observations on erw for the girder forks are my own!

[flc]

As tbone says i can only give you my own opinion, on other forums arguements have raged for weeks on the pro's and con's of different materials.
I use 25mm x 3mm wall, cds nbk (natralised) tube for the legs, for two reasons 1, its what my frame was made from and i had loads spare and 2, all the arguing i have witnessed no one has said that cds was a bad choice strength/safety wise only that its much more exspensive compared to erw. and as it was my first go at a frame i wanted all the safest tackle to do the job.
as manky has put on his web page "if in doubt seek advise from profesionals, were not called mankys for nothing"
As for erw not being as strong, well cut up a std bike frame , i have an old factory gpz 1100 frame that is made from thin wall erw.
 it looks like the seams have been placed were they would not be exposed to much stress, but kawasaki can spend thousands on testing to get the best results, something most of us cant, so i try to over engineer the stuff i build, and test stuff were i can, to me saving a few quid on materials or risking it doesn't seam worth it, i always remind my self that we are building prototype stuff here and should be treated as such when first riding, until you have convinced yourself that the parts you make are up to the job,
 I hope this hasn't put you off, i have seen some radical frames made from erw that have stood the test of time built by experienced builders, so pay your money and take your choice... and test ride your stuff and lookout for signs of failure.

[BikerGran]

For those of us less knowledgeable, could someone also explain the good and bad sides of using girders (rather than the making of them).

Is it just a choice for the way they look, or are there actual advantages to using them?

[tbone]

When selecting a custom front end for your next project, there are three main styles to choose from,  Hydraulic, the Springer, and the Girder. These three are the most commonly used by custom bike builders, because they are proven designs offering good looks and performance for road handling. Generally, the Hydraulic is currently the most popular, to the point of being boring and is sometimes thought to be the best performer of the three. This may or may not be true because if designed properly, a girder offers some benefits that a Hydraulic or Springer can't -- yet gives outstanding performance and great looks, which is what most bike builders seek in the first place.


The Girder gets a lot of its strength from its triangular design. It has been proven that the triangle is one of the strongest structures for support as can be evidenced by looking at almost any bridge, railway trestle or trike frame. The triangle in the Girder is incorporated into the design by using two legs, with the rear one bent. A long triangle is then formed from the axle hole to the yokes. The triangle is then divided into two smaller triangles with the addition of the cross member at the bend of the rear leg.

Beyond being a superior design, the girder is light weight. A complete, ready to bolt to your next custom  Girder can weigh less than 29 pounds in standard length. A "billet" Hydraulic can easily weigh twice that amount.

But don't let the girder's light weight mislead you, because it possesses extreme strength for the weight that no Hydraulic or springer can duplicate. The diameter and wall thickness used on the some Girders means they will withstand 58,000 pounds of force before they start to bend.

An additional benefit of the girder design is that the length of the forks and the rake in the forks or frame does not determine how well a girder works -- the pivot points still pivot, and the spring compresses and rebounds as it should. In the Hydraulic design and to a lesser extent in the springer, your frame rake angle and front end length dictates how well the "suspension" part of the design works. Changes in rake and length from stock dimensions and geometry can diminish suspension action commensurate with the amount of change. The telescoping feature of the Hydraulic and the rocker arm in springers was designed to work in an up and down motion. As you increase the angle (as in additional rake) you have less and less "suspension" and more bending of the legs. In long front ends with extreme rakes, your Hydraulic or springer morphs from telescope or springer actions into a suspension action that only exists from the flexing of the legs. The girder, if produced properly makes it all but impossible to bend or flex the legs.
This is the mechanical end of the girder, but the real trick part lies in how it absorbs the shock for the front end of the motorcycle. The girder uses a single coiled spring at the top of the fork legs. The spring oscillates with the pivot motion of the two legs, which share two common cross members. The secret to the good handling of the front end is the barrel spring. By barrel, i mean that it is shaped like a barrel: large diameter in the middle and narrow at both top and bottom. This gives it a two-way, multi-stage, progressive wind, helping to prevent any pogoing of the spring under shock absorbing conditions. This effect is a result of non-linear dynamics, which is physics beyond the scope of my knowladge, but it all boils down to the fact that the different diameters of the coils in the spring acts as a team. When one section is constricting, the rest is preparing to do the same when asked to. If compression is released, then the spring will go back to its original state, with no effect to the rest of the spring. In the end, the entire spring will be working in harmony with, instead of against, itself.

But its really all about choice, money, availability and what you think looks good for your project.
 

[BikerGran]

Cheers Tbone, I didn't know a lot of that -  I do like to know how things physically work!

[Manky Monkey]

I've always thought of girders as just more rigid than teles or springers -probably cos they look more substantial. So less flex. Never thought about the fact that the suspension travel remains constant, no matter what angle they're mounted at though. Makes sense when you think about it & makes them an attractive option for chops & trikes.

[ByzMax]

Girders are the best all round and they look great too!   

[Manky Monkey]

Just as well we have a set for our next trike then!

[morrag]

Well, the workmanship on the girders is excellent,however, as one who is so old that I started out on girder forked bikes, and other than Webb's, as fitted to my early Velo's, they were decidedly average in the solo handling stakes, and generally the best of them poorer than the worst of the early Telescopic forks, such as Triumph's! really. throw into the equation the fact that most of my early girder forked bikes were worn out when I had them,i.e.bushes and pins in need of renewal, and they were pretty awful, but there you go, nostalgia, and a need to be different can make for strange bedfellows, but then, thats only my take on it! Morrag

[Dicky]

Excellent workmanship and beutiful to look at.

Very informative thread, thankyou.   Most enlightening.

[dracken1]

here is an excellent site for reading up on pro's and con's of most things bike/trike.
this link is to girders
http://www.chopperhandbook.com/neatstuff/girder-1.htm

and this one to the home page
http://www.chopperhandbook.com/neatstuff/index.html

[willy]

They're beautiful!  I'd love to have a front end like that on my trike!

I'd love a set of them as well

[morrag]

Why do you think the girder fork almost universaly "died" after WW2? well the telescopic fork, in all its variations, was and is generally a better piece of kit, unless asthetics is your bag, but engineering wise, its got to be teles. sorry, Morrag