Recumbent - Sub 18 Pound SWB... in Steel?

Maybe.

One glance, and the observant 'bent homebuider will immediately recognize the potential here. It is a Haro Comp Extreme, The frame is TIG welded, Tange, double butted tubing with a bare frame weight of 2659g.

http://i54.tinypic.com/237ivo.jpg

After a litle selective surgery, I was able to trim-off 1593g. As shown below, (with chunky, 57-406 rubber, wide rims and a 950g fork), it weights 5366g (approx. 11.8 pounds)

http://i56.tinypic.com/2vmtshs.jpg

You have cut away a triangulated truss structure and left a tube that will have to work in bending, as it was never intended to work!
Potential?! Oh Yeah! Potential for disaster.....and much pain!

The next step should be the trash bin! Recycled please......

I'd also have to say that it's gonna be way too flexy. -At least, for most typical-sized adults.

And did you cut off the top half of the head tube? You need to have the head tube ends cut perfectly squared to get the head tube bearings to work well....

You have cut away a triangulated truss structure and left a tube that will have to work in bending, as it was never intended to work!
Potential?! Oh Yeah! Potential for disaster.....and much pain!

The next step should be the trash bin! Recycled please......Interesting observation. Are you
a builder?

Since you failed to ask necessary specifics to make that assumption - i.e. tubing diameter, wall thickness, span length, rider weight and static and dynamic loading location, predicted torsional moments along its span, and CoM location, I'll assume the answer is NO.

It will be great! Please continue.... and let us know how it turns out!

And did you cut off the top half of the head tube? You need to have the head tube ends cut perfectly squared to get the head tube bearings to work well....I rough-cut the HT length, then made a few finish passes on a Bridgeport Series I vertical mill. The ends are within .001" of parallel. Will that do?

I would not want to ride a monotube with such a small diameter main tube. What is it - 1 1/8"? At my weight, I would probably have the frame bent within a week, assuming I could even keep it on the road while powering it up to cruising speed. But, maybe it will work for you. I hope it turns out; your bikes always look so nice.

Interesting observation. Are you
a builder?

Since you failed to ask necessary specifics to make that assumption - i.e. tubing diameter, wall thickness, span length, rider weight and static and dynamic loading location, predicted torsional moments along its span, and CoM location, I'll assume the answer is NO.
Your assumption is correct...I am however a structural engineer . Not to confuse you further, but double butted tubes work great in tension and even compression but are next to worthless in bending! Avoid disappointment and injury......visit the dumpster....

Your assumption is correct...I am however a structural engineer . Not to confuse you further, but double butted tubes work great in tension and even compression but are next to worthless in bending! Avoid disappointment and injury......visit the dumpster....I'm really not interested in your haphazard supposition. So... either provide me with accurate FMEA data to substantiate your claims, or find another thread.

will immediately recognize the potential here. :banned:

From what I`ve read from you before, I`m surprised to see you working on a short bike. It does look like an interresting project though- sure hope you keep the build thread updated. I don`t see how you`re going to manage the steerer. Will you make a new fork, or do you have a way to extend the threads?

Are you planning on a MBB?

screw it...build it, and let us know how it gets on !

I rough-cut the HT length, then made a few finish passes on a Bridgeport Series I vertical mill. The ends are within .001" of parallel. Will that do?

Well, I'd have cut them to .00001", but that's probably good enough. ;)

It's still too thin though. The seatstays I'm not sure, but the main tube, almost certainly.
And you have cut the head tube shorter than any commercial bicycle manufacturer is willing to.

Good luck.

From what I`ve read from you before, I`m surprised to see you working on a short bike.Yes, me too. The build is for someone else, and I decided to experiment.


I don`t see how you`re going to manage the steerer. Will you make a new fork, or do you have a way to extend the threads?I'll probably use a threadless and the steerer will be telescoped and clamped - my common fix.


Are you planning on a MBB?Nope.


It's still too thin though. The seatstays I'm not sure, but the main tube, almost certainly.Seems nearly everyone is 'assuming' I'll built the frame as shown above. There'll be structural changes alright, but most won't be visible.


And you have cut the head tube shorter than any commercial bicycle manufacturer is willing to. That won't be a problem - the steer tube is 1.25" OD and if you look closely at the image, you'll see a factory gusset at the lower HT/main tube joint - much like a BMX.

Heck, I'm just interested in the final product and your pics. Sub-18 lbs in CrMo could be revolutionary if successful for the 'bent riders.

After cost, weight and perceived 'slowness' due to weight is probably the biggest detractor to the non-bent rider.