Manky Monkey Motors

these 8" over girders are destined for a customers vw trike, made from 32mm od dom mechanical tubing for the legs. the harley wheel; will be used but until the type of caliper to be used is decided theres no lugs fitted as yet. the bronze welding is only used on the less stressed low carbon steel parts
http://s104.photobucket.com/albums/m185/dracken1/girders/

Nice workmanship Wynne. ;)

yup nice looking :) i seem to be surrounded by girders atm :)

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

me too..... ;)

Lovely work, looking really good Wynne.
Can someone please explain to me how these actually work :-[ Girders look really nice but I can't figure it out from the pics. :-[  :-[
REgards
K

It's pretty basic K, which is their attraction.
They just pivot off the yokes, against the spring, like so.

Thanks Andy, I felt a bit DOH! with that question but I've only ever seen pics of girder forks, never seen any for real. It is a simple set up but easy to muck up if you don't get it right I think. I found some plans for girders, springers and leafers as well as frames on the chopper builders site http://www.chopperhandbook.com/neatstuff/index.html (http://www.chopperhandbook.com/neatstuff/index.html) here. Look in the downloads section.They say it is ok to put things on other sites as long as you give them a reference. Sounds fair enough to me.
Thanks for the explanation, maybe one day I'll get around to building some for myself ;D ;D
Regards
K

We didn't make ours. flc did them so I haven't got a clue on how to build them.

He made a lovely job of them too.
I love leaf sprung forks on old 50s bobbers.

Thanks andy :-[ im just designing a new version, i will pop some stuff on about them if you want.
you can keep the shock if it works :) i have just put claires bike through mot and the other shock had to be cut off the frame (rusted solid) :o

Oops! Been meaning to sort out a replacement so we could send yours back to you!
We're always looking for articles for the site. If you fancy writing us a bit on putting a set of girders together -the basic principles, geometry, pitfalls, recommended materials etc that'd be fantastic. Not necessarily a step by step guide to building them -though that would be great too, just giving readers an idea of what's involved so they can decide whether girders are for them would be fine.   

A couple of basic questions....probably :-[, I've seen a reference somewhere to do with girder forks, the girders were made from D O M (Drawn Over Mandrill) tube. The first question is, is this the same as Cold Drawn Seamless?  The second is.. could ERW be used, please don't shout at me coz I know that ERW is not as strong as CDS, I just want to know if it could be used and how much bigger would the tube have to be than CDS to withstand the forces applied.
Thanks for not telling me off :-[ :-[
Regards
K

One for you FLC?

Hmm, I know that DOM starts off life as ERW and then is reworked to get rid of the internal weld seam and give a much more constant and accurate inside diameter, so i can understand the use of DOM in the pivot and axle mounts, to give a better finish for brass bushes to fit into ect, but for the main tubes i would think ERW is fine.

Electric Resistance Welded (ERW)
Cold formed, electric resistance welded tubing can be produced in round, square or rectangle shapes. ERW tube is produced by processing a flat rolled steel into strips which are cold-formed, welded and seam annealed or normalized (depending on the manufacturer). You can usually identify ERW tube by the blue strip down one side of the tube (which is the welded area). The ERW process can guarantee the weld to be as strong or stronger than the rest of the tube body. The origin from a flat strip results in a more concentric product than Cold Drawn Seamless (CDS). ERW can also be known as CREW (Cold Rolled Electric Welded).

Drawn Over Mandrel (DOM)
DOM is formed from strip and Electric Resistance Welded (ERW) then cold drawn through a die and over a mandrel resulting in improved inner surfaces and dimensional quality. This process, called cold drawing, may be repeated more than once to reach the planned OD, ID, or wall dimension. Multiple draws can also be used to increase the strength or improve the surface finish of the tubes. During the drawing operation, the tubes may be process annealed to increase the ductility of the material. Lower cost alternative to CDS with equal or superior physical properties.

Cold Drawn Seamless (CDS)
General purpose seamless tubing, which is a solid bar of carbon steel drawn over a mandrel to form the tube section. CDS allows selection of chemistry and rough tube size. Cold drawing produces higher physical properties without heat treating. Offers widest range of sizes and chemistries in mechanical tubing. Better tolerances and reduced machining allowances over Hot Finished Seamless (HFS).

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

  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!

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.

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?

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.
 

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

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.

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

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

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

Excellent workmanship and beutiful to look at. 8) 8)

Very informative thread, thankyou. :)  Most enlightening.

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 (http://www.chopperhandbook.com/neatstuff/girder-1.htm)

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

I'd love a set of them as well

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

I bought a set of chromed girders off e-bay for my trike. They had been fitted to a chopped '45' back in the seventies and since that bike had been put back to stock, had been used as an ornament in a guys front room. He even gave me the plush velvet covered pad that had sat under the legs to protect the carpet. I sold on the low apes, but kept the risers and maltese cross mirror.
Despite what I had read about girders, these were very heavy but that turned out to be, once the chrome was stripped off, because they were made from solid bar, not tube or pipe. Further forensic examination showed that the back legs of the girder had been hitting the lower yoke under full extension. The bolts holding the links in had been tightened onto small pellets of lead to set the free play, but the bushes were all worn and much sloppyness was apparent. The spring was of barrel type but the way it was held in was a bit dodgy to say the least, subjecting it to twisting as well as compressive loads. I take on board what Durfee say about barrel springs and the way they work but that shape is about getting more travel without bind in a short space than any clever progression.
Old girders were not as good as early teles because of the damping or lack of it and the unprogressive nature of a short spring working a large unsprung weight over a long distance rather than any natural superiority. Teles, when worn are just as 'bad' if not worse.

Anyway, I decided to fit a Harley single-disc 21" wheel so we split the girder down the middle and widened it to fit - it looked s**t! We then split the wheel down the middle and narrowed that by an inch and then rebuilt it - much better.

At this point we set the girder up in place with the frame at ride height so we could set the rake and trail with the links sitting about level, or at 1/3 travel. Following advice on the web-site, we set trail at 1 inch although I appreciate that that might mean we need a damper at some point.

The problem with most girders is having room in the top for a large enough spring/damper, so we relocated that to below the bottom yoke and we are now making new yokes, links and bushes to put the whole thing back together.

A girder has lots of potential for adjustability and all the other good technical things but my main point for choosing one was because they look fantastic!

Fantastical beats practical every time as far as I'm concerned!
Photos of the fork re-build please.  ;)

according to people in the know a well set up set of girders is far better than either springers or tele's, damned if I can find the tech article I got that from though  :-[ :-[

Shaun your right. It comes from the chopper builders handbook see drakens links below and gives all the reasons why girders are best.

Morrag. The real reason teles were succesful was cost/ease of manufacture. Many bikes manufacturerr are going back to using girders. Check new BMW bikes.

 

This is one of the e-bay pictures from my original purchase. You can see the piece of plush-covered carpet protector!

and the top with slabby links and three-tonne risers

Them's jolly shiney.  8)

Which is why I must have been blinded when I bought them!
The latest part of their rebuild is to make a spindle and spacers that cater for the fact that the locating 'tubes' at the bottom of each leg have been worn to different sizes than the 3/4 inc original axle size. Couple that with a forkspindle made from gas pipe and incorrect geometry from new and I'll bet that old '45' handled like a plate of jelly. If I look carefully I'll bet there are teeth marks on the risers.

 ;D

If their so good, I wonder why GP race bikes don't use Girders? or off road comp. bikes!the fact is that generally, and for most applications, the traditional Telescopic fork is still the most effective "compromise" when it comes to front suspension on a motorcycle,and it's always a compromise between practicality, suspension travel, and cost effectiveness, and from my Trialling days,on Montesa, Bultaco, Matchless, etc.... believe me I'd go with a set of Ceriani's over any girder design, including Vincent or present day BMW,when negotiating some of the "hairy" drops and climbs that you were required to attempt! something of a case"rose colloured specs" I think, gents, when it comes to girders as practical alternatives, but if you just want to be different, or asthetics are you're bag...........Morrag

I just think they look cool, which is good enough for me.  :)

Like I said Mr M, if it's looks what grabs yer!go with it, but better, please...... and to use "chopper" suspension technology to suppory a suspension/handling arguement! well i rest my case. Chopper style is just that, all style, but technically, I dont think so! Morrag

Have a look at these :) not starting an arguement ,but another slant on fork technology, i agree on the style arguement but like all things, advancements in technology and material research have improved a lot of old ideas,
http://www.motorcyclespecs.co.za/bikes/Britten.htm

Girders don't have to look like peanuts ones. As far as I understand many of the racing teams are looking at girders of different designs to improve the bikes handling.

For driving over a parked car or rocks/ steep muddy hills i'm sure teles are better and you can see why but It's not just about style/appearance they do in many cases work alot better especially at high speeds and under heavy braking.

But it really don't matter because most of us will never drive fast enough to notice the difference.  ;D

'But it really don't matter because most of us will never drive fast enough to notice the difference.'
and never was a truer word spoken.
fastest bloke I ever saw on track was at a Mallory track day on an ER5, complete with racks. The guy had only been riding for 6 months, almost all as a despatcher and was put up a group in every session until the travelling marshalls just took him out on his own. He had no idea what he was doing, what tyres he had on or how many clicks of what he had on which, but he just blew around everyone.
 I reckon that he had never crashed and so didn't know how to!

That's really the point I'm making, that overall, and on most case scenarios, the ubiquitous "Tele" will come out on top. If you want to use a different criteria, IE.visual appearance/style, well, possibly a different result will occur, I agree. As far as Peanut's comment, well I can't really understand where it fits into this discussion, and as for the Britten fork, have you checked the detail and complexity of its manufacture? and at what cost, perhaps that's why nobody else uses them.The 'Hub Centre' steering concept on bikes like the Elf Endurance racers of a few years ago, was, in many ways, an improvement over existing telescopic forks, but again were never universally adopted due to them not being a sufficiently useful an improvement over the telescopic fork to warrant their expense and complexity!So it depends what you require,really, appearance or effect, which is,of course, up to the individual, but at least be honest with the reasoning when making the choice! Morrag

Sorry Morrag, got a bit excited and unintentionally forgot the correct etiquette about not hi-jacking posts with irrelevant nonsense.

Just to add my two pennith. Forks are perfect, cant beat them, if your on two wheels. After all, motorbikes dont steer in a conventional way. Have you tried leaning a trike into a bend at speed? or tried steering a bike into a bend without leaning? both are dam hard to do, not impossible but hard.
Forks are undoubtably the best thing for two wheels, but are a cheaper and easily available option for three wheels.

Tbone, I think that a reasonable "summing up" of the discusion! but some interesting views expounded,never the less,Morrag