Flexible steering mast...

[trapdoor2]

Just an 'off the wall' question regarding the steering 'mast' design.

I notice on the Conversion and the Softrider that the mast is simply an extension of the fork steerer...with a set of handlebars stuck on top. One adjusts the height of the bars to clear ones knees (assuming you've adjusted the BB distance appropriately) and off you go.

Is there any reason a flex connection could not be employed to move the handlebars both aft a bit and lower (presumably aft of the knees). I use a Terracycle "glideflex" on my Baron so that I can move the tiller up and out of the way for entry/exit but also so I can position it exactly where it needs to be.

This folding stem would allow one to change the angle of the handlebar stem to suit. Of course, the further aft of the fork centerline, the more "tiller" you encounter (the handle bar swings from side to side rather than twists). The Silvio appears to position its bar a bit aft of the fork CL, so I'm assuming it wouldn't be a big problem (certainly not for me, the Baron has about 18" of "tiller", I've gotten quite used to swinging it about).

I guess my initial concern is the riding position, that is, with my hands at shoulder height. It looks uncomfortable to me (not having been on one, of course, and further understanding that I won't really know till I try it out). Go here: http://www.springcity.org/news/sccc0610.pdf and look at page 2, bottom right picture. That's me and the Baron. My hands are actually above shoulder height but I'm riding considerably more laid back (and yes, there is a bike under there somewhere). On a Cruzbike (again, Conversion and Softrider) ones arms are outstretched and the hands appear to hang from the bar at quite a height. I would think that having the handle bars aft of the knees would allow the bars to be set lower and perhaps with more comfort.

I'm just thinking out loud, of course. The glideflex unit I have ought to swap across, provided the steerer tube dias are the same between the donor bike and the Baron.

 

[Mark B]

Marc,

In most CB setups, the Telescoping Front Tube (TFT) attaches to the steerer above the headtube. So, this would preclude the useage of a flex glide type system. Also, due to the input needed from the upper body, I don't think you would want that stem moving around much. :shock:

Mark

 

[trapdoor2]

Mark B wrote: In most CB setups, the Telescoping Front Tube (TFT) attaches to the steerer above the headtube. So, this would preclude the useage of a flex glide type system. Also, due to the input needed from the upper body, I don't think you would want that stem moving around much. :shock:

Hmmm...I guess I should have titled it "Folding steering mast" as it does not "move around" at all unless you want it to (say, for steering). The folding portion is an adjustable friction joint with a "down" limit, so you can set the bottom angle to where you need it and then set the friction to keep it in place until you need to fold it up. Although the Baron does not need upperbody input under power, you tend to do it anyway...and you also use the tiller a bit to help haul yourself up out of the seat (sort of like doing a sit-up) just prior to hitting a bump.

Yes, the TFT attaches to the steerer but then an adapter (or just the mast, I presume) is poked down the steerer to create a steering mast...which effectively just extends the steerer (Man, I gotta come up with another topic. "Steerer" is hard for me to type for some reason). The glideflex would clamp to that...and then a tiller clamps to the glideflex post.

Yeah, it seems a bit complicated. The difference in the Baron setup is that there is no TFT clamp to add height to the stack on the steerer. Like I said, I'm just talking out of my hat. I was wondering if anyone had attempted such a thing.

 

[Mark B]

trapdoor2 wrote:

Mark B wrote: In most CB setups, the Telescoping Front Tube (TFT) attaches to the steerer above the headtube. So, this would preclude the useage of a flex glide type system. Also, due to the input needed from the upper body, I don't think you would want that stem moving around much. :shock:

Hmmm...I guess I should have titled it "Folding steering mast" as it does not "move around" at all unless you want it to (say, for steering). The folding portion is an adjustable friction joint with a "down" limit, so you can set the bottom angle to where you need it and then set the friction to keep it in place until you need to fold it up. Although the Baron does not need upperbody input under power, you tend to do it anyway...and you also use the tiller a bit to help haul yourself up out of the seat (sort of like doing a sit-up) just prior to hitting a bump.

Yeah, I know what they are, I had the same setup on my Strada. I hardly ever moved it, to tell the truth.

trapdoor2 wrote: Yes, the TFT attaches to the steerer but then an adapter (or just the mast, I presume) is poked down the steerer to create a steering mast...which effectively just extends the steerer (Man, I gotta come up with another topic. "Steerer" is hard for me to type for some reason). The glideflex would clamp to that...and then a tiller clamps to the glideflex post.

Yeah, it seems a bit complicated. The difference in the Baron setup is that there is no TFT clamp to add height to the stack on the steerer. Like I said, I'm just talking out of my hat. I was wondering if anyone had attempted such a thing.

Lessee, it's been awhile since I built my conversion, but if I recall correctly, the riser fits down over the steerer tube and the TFT clamp squishes down on it to clamp it to the steerer tube. In theory, I guess, if you had a fork with a long enough steerer tube, you could shim the TFT clamp with something, then put the Glide-Flex above it. Problem is, your donor bike probably isn't going to have such a steerer. In fact, you'll be lucky if you don't have to buy a 1" to 1-1/8" quill stem adapter and that is certain to not be long enough.

I still contend that you are not going to want that stem moving, or even having the potential to be moving, especially when you're first learning.

Mark

 

[defjack]

One nice things about the kits is how easy it is to change things.Try it with a stock setup first then take it from there.My Giant conversion has a lot of recline even with a hard tail the ride isnt too bad.I rode an Optima Lynxx before going Cruzbike it had a movable tiller also and since you are always pulling back or sideways that should work. ps sold the lynxx to get a Silvio it was the right choice for me. Dougs right you can really put a lot of torque on the bars. Jack

 

[Doug Burton]

A great deal of Cruzbike development has focused on transfer of power through the steering assembly. This power transfer is what sets MBB apart from other designs.

The front triangle of the Silvio, Sofrider and Freerider are exceptionally-rigid assemblies. This is carried-over as much as possible into the conversion kit as well; this is why two kit components, the stem extension tube and the fork triangle brackets, are made of steel instead of aluminum.

I think that once you have mastered MBB riding, the adjustable stem will at best be a source of constant re-adjustment and aggravation due to slippage, and at worst a hazard.

Think of how much force you can put on a 1-foot breaker bar if you hold something down on the floor with your foot, and then pull up on the bar. Do you think you could break the adjustable stem with this force if that were your objective?

The Sofrider V1 used a long aluminum steerer tube, instead of the extension tube. It was replaced with a Cromoly tube on the V2, partially to improve power transfer potential and rigidity.

Also, I think you'll find that once you're proficient on MBB, you'll want the grips very closely aligned to the steering axis. I find that if the grips are more than about 50mm behind the steering axis, the steering/power relationship degrades. If you look in the Yahoo group's photo album, you'll find that the most ridden bikes have gravitated to this configuration.

On the other hand, I built all my bikes contrary to John's advice, and researched my way back to what he told me to begin with. I feel like I know a lot about the bikes, but I did have to pay my own self-imposed tuition! :roll:

In any case, enjoy the build!

Best,

 

[trapdoor2]

Hardtailcruzer wrote: A great deal of Cruzbike development has focused on transfer of power through the steering assembly. This power transfer is what sets MBB apart from other designs.

The front triangle of the Silvio, Sofrider and Freerider are exceptionally-rigid assemblies. This is carried-over as much as possible into the conversion kit as well; this is why two kit components, the stem extension tube and the fork triangle brackets, are made of steel instead of aluminum.

First, thanks to everyone for their comments. Indeed, I fully intend to build it "to spec" initally, learn to ride it and then change (or not) things to suit me. I've been hot-rodding virtually everything I've ever been interested in as long as I can remember...some good, some not, all learning experiences though!

I'm not surprised to hear the extension and triangle are steel components. The legs are home to the largest muscles we own and can exert a huge amount of force under the right circumstances.

Quote: I think that once you have mastered MBB riding, the adjustable stem will at best be a source of constant re-adjustment and aggravation due to slippage, and at worst a hazard.

Think of how much force you can put on a 1-foot breaker bar if you hold something down on the floor with your foot, and then pull up on the bar. Do you think you could break the adjustable stem with this force if that were your objective?

Believe me, I fully understand the concept of torque. I have broken any number of surprizingly large items in my day...because I gave that wrench 'one grunt' too much.

I have had the glideflex under considerable tension...but there is no appreciable twisting moment in the system (on the Baron). With the Cruzbike (as I have read) you can actually get out of the seat and pull on the handlebar much like one would do on a road bike. That generates a lot of lateral force on the stem...and a dynamic bending component as well (which is reacted by the handlebars...to your upper body). The bending forces generated at the pedals are transferred to the handlebars via the solid 'tetrahedral' design of the system. The "glideflex" connection would introduce a slip-joint (however strongly clamped), so it is entirely possible that the connection would slip under hard pedalling. And...the glideflex system is certainly not designed to react large torque loads...if it didn't slip, it might well break (although it is quite stout). Of course, this 'slip joint' can be made 'solid' quite easily.

I would like to see analysis of the forces in this system. The forces are large but the lever arms are not. Actually, the loads are not much different that those encountered in a DF bicycle...except that those loads in the Cruzbike are solely reacted by the handlebars (due to the MBB. A DF reacts those loads thru the frame and thus to the rider's butt, should he be seated, or thru the handlebars/arms if standing). If these forces were overly large, one would not be able to ride this system 'hands off' at all and if you think your arms can overpower your legs just by pulling on a handlebar...

Quote: Also, I think you'll find that once you're proficient on MBB, you'll want the grips very closely aligned to the steering axis. I find that if the grips are more than about 50mm behind the steering axis, the steering/power relationship degrades. If you look in the Yahoo group's photo album, you'll find that the most ridden bikes have gravitated to this configuration.

On the other hand, I built all my bikes contrary to John's advice, and researched my way back to what he told me to begin with. I feel like I know a lot about the bikes, but I did have to pay my own self-imposed tuition! :roll:

That's what I'm wanting, the voice of experience! Thanks for that!

So, the "steering/power relationship degrades". In what way? Large quantites of tiller often makes people nervous if they've never encountered it; the handlebars cease to 'turn' and become, well, 'tillers' rather than 'steering wheels'. In my mind, this is just a learning curve issue (one which taught me to buy protective padding for the first few weeks of falling down). You learn to 'swing' the bars rather than 'rotate' them. A side benefit would be adding a lever arm to the system on the aft side of the headset. This would also change how the loads are reacted by the handlebars, introducing a side-to-side load and reducing the torque load (depending on the amount of tiller).

Just to reiterate, I'm still talking out of my hat! Hopefully I shall have some experience soon.

 

[trapdoor2]

Ok, having gained a bit of "sitting" experience, I'll add a bit to this thread.

#1. The steering mast is far closer to my, um, "belly" than expected. Probably not going to need to have the mast tilted aft. I did move the seat back a few inches but will reserve judgement until I can get some ride time.

#2. A folding mast still may prove to be a benefit for entry/exit. I don't have the TFT connected to the headset at the moment, so I can fold it forward to mount/dismount. Without a fixed stem/handlebar, the bike is difficult to mount/dismount (things are a bit floppy), so this benefit may be just a figment of my imagination.

I'm keeping my options open!