The start of summer is around the bend which means for some builders another winter project is getting close to completion. Jason Rodman sent us an update on his very cool girder project. The impressive aluminum, arc’d design is carried out with excellent machining.
During the intial mockup, RMD and Jason found proper trail numbers could not be achieved using the original straight legs with the stock 24 degree rake of the Yamaha R1. RMD Billet and Jason eventually came up with the arc in the legs to obtain the desired trail instead of cutting the neck of the frame (for new rake) or fabricating offset races.
After 60 hours of machine work, the resulting milled lattice structure retains rigidity while reducing weight (and also looking trick). The weight of the front-end is about 30 lbs. with 12 pounds attributed to the Penske shock.
Look for his bike at the following events this summer to get a close-up view:
• LA Calendar Show in Long Beach
• Laguna Seca at the MotoGP in July
• BUB Moto Speed Trials at Bonneville in September
Imagine a mass-produced and affordable modern sportbike with little dive in the front-end….
John Britten’s racebike worked very well with a modern interpretation of the girder front-end. The Kneeslider looks forward to hearing about the performance of Jason’s hard work being adapted to the R1. Great job Jason and RMD!
More photos and links below:
Link: R1 Engineering
Link: RMD Billet
Link: Machining video
Related: Yamaha R1 Girder-Front Suspension
Check out a new R1 girder project out of Australia from SuspensionSmith
Matt in NC says
That right there is what the new V Max needs.
hoyt says
Looking great!
I will look for this in print and in person as I’m interested in the performance. The look is getting better and better. Straightforward engineering with good materials and components.
Prestons says
Very nice to see something other than telescopic forks. I would like to rid my bike its pro dive in braking characteristics.
Tapering the legs above and below the lower linkage could save weight without a loss of stiffness. This is what the Vincent and other girder forks have done. The moment of inertia about the steering axis looks a little high. This can aggravate some steering instabilities. It’s always a compromise to get all the parts to fit and optimize the design.
todd says
This looks nice (in a fabricated sort of way). It will be great to see what a production version would be – die cast legs, extrusions, or forgings(?). At that point an entire front end could cost a manufacturer a fraction of what it does now. Plus with such a loss of weight -both unsprung and inertial- it will perform better to boot.
Now we’ll have to lengthen the wheelbase to counteract such a large loss of weight on the front end or acceleration will suffer.
-todd
WRXr says
“A modern sport bike with little dive in the front-end”
It seems to me that BMW has already done that with the Telelever and their Duo-lever designs. Of course “Sport bike” is a relative definition. “Sport” does not necessarily mean race replica.
I applaud the efforts in creating these forks. They look great with the twin spar frame. But is there an engineering reason to not use a welded/tubular structure?
Most girders back in the bad old days were either lugged/welded tubes or pressed steel. I can’t recall ever seeing any forged or cast forks. I have to assume there is a reason why beyond just cost. There have always been bikes were cost is no object: Brough, Crocker, Vincent,etc.
Doug says
WRXr – thanks for stopping by and commenting.
I thought of BMW as I wrote the above comment but failed to clarify “sportbike” as a mass produced “race replica”
The K bike did have its own cup series with the impressive duo lever front-end, but that model isn’t produced in the numbers that the GSXRs, Ninjas, CBRs, & R1s are produced. So, as I wrote the above text, I had in mind the kind of production numbers that would foster more alternative front-ends. I am still puzzled that, after all of Britten’s success, no other major OEM besides BMW (and Yamaha once) have tried anything but teles.
Jason might stop by to answer your other questions.
hoyt says
Jason – here’s a thought…leave the spring open in all of its glory and see what kind of thin, vertical lighting you could get along the sides of the radiator.
Cycleguy says
This is nicely done, very cool, however, there was a good reason why the Tele fork ended up replacing the old Girder forks. The major issue with the Girder fork setup is it’s high steering inertia.
When you add the weight’s of the girder, upper and lower control arms and the shock assy and hang them out there so far from the steering axis, it dramatically increases this steering inertia well beyond that of a Tele fork. This is the main reason it ultimately lost out to the Tele fork.
Girders do have some advantages though, mainly suspension compiance and some degree of anti-dive depending on design angles. I don’t think this is enough to offset it’s major shortcomings though.
I much prefer the Fior/Hossack design which BMW now calls their Duolever. Essentially a Girder fork with the control arms and shock unit attached to the frame and not steered. This reduces steered mass even lower than a Tele without loosing the benefits of the Girder, it also shortens the load path into the frame allowing some frame weight reduction as well.
Doug says
Good points.
Although the duolever addresses the girder disadvantages, doesn’t the duolever introduce more connection points and bearings which would take less abuse than a girder while leaned over at racetrack speeds?
Maybe not, the K-bike Cup series may not have had any issues (anyone know?)
I find the challenges and solutions applied to alternate front-ends as interesting as trying to decide the optimum engine configuration for a given application.
Nonetheless, this girder probably will offer a thrilling, capable ride while looking stellar and being truly unique. The more I look at it, the more I like it.
Nathan says
Im supprised they didnt do anything fancy with the girders.
Id kinda like to see the headlamp doubling up as the mudguard, like a one piece cast with a rectangle slot in the front that sweeps back over the wheel into a point.
B*A*M*F says
A Hossack/Fior/Duolever fork is a lot like a double wishbone set up in some cars. I imagine that some forces are different, or act in different ways on a car vs. A bike, but both perform the task of allowing vertical wheel travel while steering.
Loomis says
Even though it is cast aluminum, I see they are shaped as to give the impression that it is a truss(or frame) built up from welded tubing. I think a weight savings could be realized if it really was constructed of welded tubing. Also, I might suggest that it be made a little too weak, then add a short “kingpost” projecting forward from the lower linkage pivot point and then add a tensioned cable that runs from the wheel axle, over the “kingpost” then up to the top of the girder. You could do something similar to augment lateral stiffness as well.
Tom J says
Where does one mount the clip-ons/handlebars?
Sean says
I think a lot of you guys, and a lot of bikers in general, think that Britten did everything in the pursuit of performance, and it all worked so extremely well because he developed each and every component with the same degree of care and attention. In actuality, according to his own biography, it wasn’t much like that at all.
He chose the girder front end to be different, that’s all. They continually suffered from problems with it, mainly a vibration in the front end that couldn’t be fixed. At one point, near his death, everything came together and the vibration stopped. The guy riding said that he knew he was now riding the fastest motorcycle in the world. A few laps later, and the vibration returned. They never figured out what caused it, or what fixed it.
Other little things like the bike being able to wheelstand at 160 just by opening the throttle wasn’t down to a hugely powerful engine. It was because the fairings generated a small amount of upforce, and this is what caused the front end to lift. The question of making front ends lighter, causing adverse effects on acceleration? I can think of a few things I’d put up around my forks, if their weight was mirrored by the weight loss.
Cycleguy says
The Britten didn’t use a Girder Fork, it was a Fior/Hossack/Duolever as described previously.
I believe what the Britten was experiencing was front tire chatter which is a common problem among current MotoGp bikes, caused by too much Fork/Frame rigidity. This causes the front tire contact patch to loose and regain grip in high frequency succession due to the frame or forks inability to dampen out these forces.
Someone experienced in riding/racing many different types of alternative front ends once told me that the benefits of these designs will never be realized until special tires are created tailor made for these designs.
machinerage says
Looks like a Japanese knock-off of the Confederate Wraith motorcycle. Seems to be just another mod for showcasing precision machining. Yawn.
Doug says
“…just another mod…”
Completely replacing the front-end of a Yamaha R1 with a front-end of your own design (based on a girder) is not just another mod by any stretch.
Showcasing precision machining is part of the whole project; it is anything but boring.
machinerage says
To those who don’t deal everyday with CNC machining, yea maybe it looks cool. But to me… boring. Like I said… another showcase for CNC machining. Can you say “Orange County Choppers”?
Jason from R1E says
The original design of this front end does have legs that were extruded and not machined. Different materials and different methods of shaping them could indeed be experimented with. If future demand would ever call for a lower cost replacement of the machined billet arc’d legs, we would would exhaust those possibilities. But for our money and resources, due to machining and design for machining being RMD’s core compentency, building the arc’d legs out of billet was our first choice.
A rendition of drag bars/clip-ons will be mounted from risers in the top wishbone.
Orange County Choppers? I live in Orange County…why haven’t I heard of them.
B.Case says
Jason, it seems like no matter what you do, when your work provokes a reaction in people, you’re going to get a few people who only want to put your idea down to make themselves feel better. Those few are the minority, so they usually have to say something shocking to get attention. And I’ve found, it usually comes from the people who do work similar to what your displaying, or want to.
I say, putting any project out there before it’s finished, whether it’s perfect or not, takes guts and you are to be commended for sharing your work. Keep it up.
Doug says
People (who know what they are looking at) look at this project with interest.
Who is Orange County Choppers, anyway?
Jason from R1E says
Yes, thinking differently no doubt provokes reactions – good, bad or indifferent. Making change demands that you change the way you think. We just have to hope you’re not mad we’ve knocked off your baby with a cheap Japanese version. Ha.
BigSteve says
It looks like someone likes the Girdaulic forks on the 1949-1955 Vincents…..
ovidiu says
that swingaarm looks pretty solid
is it custom? or what…
fred harmon says
O.C.C., for the uninformed is a wildly popular t.v. drama show loosly based around a family of guys that build theme bikes. They send out for frames and engines and fabricate parts fit to the bikes, for example a carb designed to look like a fire hydrant for the 911 bike. They fill a need for a great many armchair builders who sit around saying”I could do that.” Artistic? Yes, to some degree. Performance minded? not a bit. But you must keep in mind that this was a reality show, designed to get ratings, and the fact that it imploded with various lawsuits between family members and the whole thing collapsing because of the top heavy egos and distractions just goes to show it was a great success. I watched it and enjoyed it,….. as a distraction, not to be inspired.( Poor Mickie…. I hope rehab got him better.)