opinions on frame geometry
 

here is what i want to build, don´t ask why.

wheelbase 1250mm
head angle 66
seat angle 66
effective top tube 675mm
trail 75mm
bb hight (not drop) 275 mm
front-centre 725mm
chainstay 530ish mm

upright riding position and a front rack for heavy loads.
any guesses on how it´s going to behave?

No.

< wild Guess>steering likely flop like The Stretched Chopper fork ala Easy Rider Film.


heavy front load? you would likely want less trail (see Porteur bike builds)

perhaps even adopt a 20" wheel ?

Gonna be crappy....don't ask why.

:)

Wheel/tire OD is missing. As is any semblance to normal bikes. Andy.

Of the three wheels: Are two the front, or back?

-Bandera

Might not be too far from a Raleigh DL-1, assuming comparable wheel diameter.

Wheel od is 700-725 depending on tires.
If it was like a "normal" bike, i could just buy one and save myself the trouble.

Psst! Don't tell anyone that!
Someone might ask "Why"?
And you can't tell......no,no, no, not anyway, nope your lips (keyboard) are sealed.

Wait.....Eric Snotdown is revealing THE SECRET via NSA surveillance..... mmmm, no guess not No One Cares. ;)

-Bandera

thank you for your input, almost felt like a reply on the subject. better luck next time.

You never did disclose the number & position of wheels. "Why" not?

-Bandera

similar angles and wheels but longer wheelbase.

And the op by, just buying a "normal" bike, would then have a bike that stood on the shoulders of the millions of "normal" bikes that came before it.

But by choosing to design an uncommon geometry the Op is taking on the task of ploughing that field for the first time. Not that there's anything wrong about this. This is how discoveries are made, for better or worse. But i do take issue with the OP taking issue with others expressing their questions, that they're not "allowed" to ask. Whether the Op's design has any merit or benefit is now off the table. So the Op asked for advise, but only the positive kind. Not in this forum. Andy (who should know that trying to limit replies to only the right ones doesn't fly).

Not trying to limit replies or questions, that would be a dickish ting to do. Sorry if you got that impression. All advice is of the positive kind unless it´s obvious trolling.

You really can't get any kind of an answer without a service description. How would it ride as what? Criteriums, third world work bike? Might be somewhere close to a recumbent of the easy rider kind, or it could be a bit like 1920s bike but with a really long rear end on it. Probably drive OK.

One of these:
http://buyvintage1.files.wordpress.c...pg?w=480&h=297

Crossed with one of these:


http://www.ravingbikefiend.com/bikep...ldtourist1.JPG

Or one of these:

http://www.easyracers.com/images/Cur...y/FullMain.JPG

Front rack as a part of the frame, most of the riders weight at the rear wheel
http://bikeforums.net/attachment.php...hmentid=385875
and compared to a roadster (red)
http://bikeforums.net/attachment.php...hmentid=385876

So it's a roadster with a long TT it seems. Nothing wrong with roadsters, they are still being ridden and produced in millions. The main problem is that there will be a lot of wheel flop, and this will be exacerbated with the load. Might be hard to control.

BTW you'll need about 80 mm of rake to acheive that trail figure. You'll need long blades and not all bending mandrels will work.

Wheel flop is something you get used to and a wide handlebar makes it easier to control, even with a heavy front load. This bike bike will have a long wheelbase and a larger turning radius, this makes wheel flop affect steering less, right? Or did i miss some science here?

There are bikes with same steering angle but less trail. How are those forks bent?

No trolling here but some understanding that when you go outside of the bell curve the advise will be far less based on large numbers of well received results. So don't be surprised if you go through a few iterations to find your sweet spot. Please do post your results to help those who try to stand on your shoulders. Andy.

It's hard to say really, I think everyone is speculating to some extend. I'm sure it would be ridable, but it might not be best for spirited riding and/or climbing hills, which also increases wheel flop. I just don't see the reasoning behind the deeply slack head angle. For the seat it doesn't really matter since you can use a seatpost with forward offset but for the head I don't see why since you specifically want to add a front load.

Common mandrels have a wide 12'' radius curve on a short chord and that will limit the amount of rake. You will need something tighter over a quarter circle, probably 6'' rad.

So, your answer seems to be that nobody really knows how it will behave because it's odd, and your specification is incomplete since it doesn't include the layout or the wheel sizes. Also can't tell what kind of riding it's for or what the loading might be.

One real guess is that it might be like a laid-back Raleigh-like sportster. A shot in the dark, but better than I could do.

What else would you like, holmund?

You'll find out when you sell them or do some pre-production beta testing how much people will get used to an irritant (in my opinion) like high flop with load. I tried a big front load on a high-trail bike, and after 2 hours I was glad to just let the bike fall and go for a rest. That's when I resolved to get it a new fork with more offset.

Large turning circle may be caused by a super-stable design, but it is its own limitation in use. Skilled riders (who can track-stand or nearly so) will often want to do a u-turn in a driveway or something similarly small.

Just some thoughts, echoing the comment about how more standard bikes stand on the shoulders of those who have pedaled up before.

Compare your idea to a standard Raleigh 3-speed, like a '70s Sport or Superbe. It seems like it might be intended for similar service. Are you making an improvement? Are you familiar with how one of those rides?

Another idea: Today bikes for high front platform loads (not with low-riders, like the porteurs) and their Gallic predecessors use(d) low trail and low flop, born of a lot of offset - target seems to be about 35 mm trail. That's a principle that has stood up to decades of competitive innovation. Are you making an improvement over that?

More generally, is your value proposition something that the consumer will pay for? I can't say that it is or isn't, but when in the corporate world I have suggested that we design something weird, I am held to answer such questions.

I can't go much deeper into the single-track-vehicle side of bicycle engineering, as an EE and non-framebuilder. I just ride. I also don't know what your product goals or vision are beyond what you've shared. But some principles of product design are essential.

OP, you can buy one that comes with 26 inch wheels. Damn close anyway.

http://img.bikecad.ca/1405542827406.png

http://www.pedalroom.com/p/khaki-klunker-18268_4.jpg[/QUOTE]

This was something i wanted to build for myself, it never worried me if someone else would pay for it. I wanted to make something similar to big old rough heavy roadsters with 28" wheels (before the sports and the tourists, not into that), i liked riding them and wanted to combine their ride qualities and durability with a load carrying capacity and a longer wheelbase.

This project was "maybe" until i got distracted by another thing i have been sketching that i will hopefully start building soon. More on that in another thread.

So since this thread was for a dead end pipe dream that never got beyond "I wish, I wish...but I'm not capable of fabrication due to "distraction"...will "another" get off the sketch page? And can we ask: "Why?"

Also, what are the odds "another" will also never be hardware? And Why?

-Bandera