Think of a refrigerator door full of batteries

[Boyntonstu]

This bicycle is an extreme example of a step-through design.

A womans bicycle with low tubes could also benefit from this idea.

Either leave about 6" clearance to step through or hinge the batteries to open the step though gate.

There is plenty of room to mount batteries between the head tube and the seat tube without the top tube limit.

$399 not too bad!

http://www.thebikestand.com/sun-step-through.html

 

[dustNbone]

It looks like it's missing the piece that makes it strong.

 

[nutnspecial]

Lol, the one that provides the most rigidity between multi axis flexing between seat and bars. I have a 70's womens huffy of steel and it's horrible in side to side flex. Maybe AL properly done wouldn't be so bad. Better be beefy though, as that thing ages!!

You could really engineer something cool from that Stu. I'd maybe have the 'door' to quick release from the top part, but if it hinges down it would be a little awkward to step over depending on height on bike I think. Maybe just build the stuff in, with a low rigid bar on top like on a women's bike clamped to head and seat tubes?

 

[Boyntonstu]

Lol, the one that provides the most rigidity between multi axis flexing between seat and bars. I have a 70's womens huffy of steel and it's horrible in side to side flex. Maybe AL properly done wouldn't be so bad. Better be beefy though, as that thing ages!!

You could really engineer something cool from that Stu. I'd maybe have the 'door' to quick release from the top part, but if it hinges down it would be a little awkward to step over depending on height on bike I think. Maybe just build the stuff in, with a low rigid bar on top like on a women's bike clamped to head and seat tubes?

"Think of a refrigerator door full of batteries"

A swinging door hinged on the head tube with locking structural bar under the seat for rigidity.

 

[nutnspecial]

Hmm, yep I was thinking of a deep freezer door . Yep a laterally swinging addition would be highly valuable for an ebike with step thru action!

Are you seriously considering making a bike like that? It would be cool- personally I might choose steel because it's easier to fab on. Otherwise it's not impossible in the least but the challenge is more specific with mating a hinging latching 'door' to the seat and down tubes.

 

[John in CR]

Just do away with all the tubes like my 2nd in line project since by rolls of carbon fiber are in route. The battery box itself will replace the main tubes (top tube, down tube, head tube, bottom bracket, seat tube, and suspension pivot and shot mount) of the bike built in, similar to the NYX but customized to my battery pack and controllers. For those who aren't ready to work with composites, quality welding equipment has become so cheap that building your own steel bike is simple, easy and economical. Once you factor in the weight savings of building the bike around your battery, it can be just as light as a store bought aluminum frame with a batt box added to it.

Nothing beats the satisfaction of building your own primary transportation from the ground up. Ebike components make that a reality for the common man for the first time in history since people built their own wagons. Once 3d printers capable of handling materials useful to make lightweight main structural pieces economically, then DIY high efficiency transportation will explode, so let's start working out the designs now.

 

[Chalo]

The Sun Streamway low step-through bike is made of steel. It attempts to make up with tube size some of what's lost by using a non-optimized structure. It's intended for old and mobility-impaired riders and the way they usually ride.

For what it's worth, steel is three times as stiff for the same size tube, compared to aluminum. It's also three times as heavy. Aluminum frames only have the reputation for stiffness that they do because they usually use much larger diameter tubes than steel frames. But for frames with similar tube diameters, steel will always be much stiffer.

Also, metal frames don't get more flexible with age until they crack. That's a myth that is probably attributable to the fact that frame tubing sizes have trended larger over time, so newer frames tend to be stiffer than older ones for that reason.

 

[dogman dan]

Good bikes don't get more flexible as they age.

But IMO, bike shaped objects can, when made of thin enough, cheap alloy aluminum. Most never notice it though, because it happens in the first 500 miles or so. I've also seen steel parts of BSO frames get flexy, to the point where applying v brakes just flexes the frame, rather than grab the rim. But again, few ride a piece of shit like that more that 500 miles.

I have seen some step throughs with good stiffness from side to side. The frame on the Schwinn meridian for one. Another goodie is the ladies electra townie. best of all, though not really a true step through, is a mixte style frame.

But with batteries getting smaller and lighter, no need to carry a 20 pound ping battery anymore. Why not just carry it on a rear rack if less than 10ah, and in a pannier if it's lager? Even a huge 48v 20 ah pack is barely 15 pounds now.

I mean, with the frames you are liking, we really are not talking about a performance trail ride here. Carry the battery in back, or even in a handlebar bag. Leave that step through open so you can use it.

Step troughs are great. I'm loving my most recently bought one.

 

[cwah]

I'm looking forward to see your conversion

 

[Boyntonstu]

The Sun Streamway low step-through bike is made of steel. It attempts to make up with tube size some of what's lost by using a non-optimized structure. It's intended for old and mobility-impaired riders and the way they usually ride.

For what it's worth, steel is three times as stiff for the same size tube, compared to aluminum. It's also three times as heavy. Aluminum frames only have the reputation for stiffness that they do because they usually use much larger diameter tubes than steel frames. But for frames with similar tube diameters, steel will always be much stiffer.

Also, metal frames don't get more flexible with age until they crack. That's a myth that is probably attributable to the fact that frame tubing sizes have trended larger over time, so newer frames tend to be stiffer than older ones for that reason.

Thanks for the information.

Bikes and cars made out of a hollow steel structures can employ a simple crack detector.
Fit a Schrader valve (and am optional pressure gauge) to the frame and presssurize with nitrogen,

You will quickly know if there is a lleak indicaing a crack.

 

[Warren]

"Bikes and cars made out of a hollow steel structures can employ a simple crack detector."

Not if it has vent or drain holes, as many do.

http://noviceframebuilder.co.uk/personal-articles/vents-and-drain-holes

 

[Boyntonstu]

"Bikes and cars made out of a hollow steel structures can employ a simple crack detector."

Not if it has vent or drain holes, as many do.

http://noviceframebuilder.co.uk/personal-articles/vents-and-drain-holes

Vent holes or drain holes may weaken the structure and may not be necessary.

Safety first.

"February 2, 2009
Years ago, Porsche built the spaceframes of at least some of their 917s of tubular aluminum. The state of the aluminum fabrication art was not so advanced - so cracking was a very real worry.

In order to allow for easy crack detection they would pressurize the inside of the tubular structure via a simple tire valve fitting - as long as pressure "held" all was well. Any loss of pressure indicated a crack - and finding the crack required only soap bubbles! Clever, yes?

Of course, upon initial construction of the frame, one would provide for the interconnection of all the tubes using a drilled connection at welded tube intersections as well as a high level of welding precision. Any structure that reliably holds pressure can be viewed in good confidence.

Internal corrosion of such a structure would be easily prevented by eliminating oxygen & moisture inside the tubes by simply evacuating the structure using a vacuum pump, (to 500 microns or so, holding for 30 minutes), and providing a mild positive pressure,(5 - 10 psi - no more), using DRY nitrogen.

No oxygen & no moisture equals no corrosion, EVER!

If one added a pressure gauge permanently piped into the tubular structure, you would have an clever & reliable corrosion prevention & crack detection system. One which weighs nearly nothing - costs almost nothing - with maximal reliability.

 

[Chalo]

If you don't put vent holes in the frame tubes, you get holes in the welds instead. Inspect any welded frame; you'll find them.

 

[nutnspecial]

For what it's worth, steel is three times as stiff for the same size tube, compared to aluminum. It's also three times as heavy. Aluminum frames only have the reputation for stiffness that they do because they usually use much larger diameter tubes than steel frames. But for frames with similar tube diameters, steel will always be much stiffer.

Tube size is not proportional to weight in steel VS aluminum. That's why aluminum's characteristic in bike building is known typically as 'lighter' and 'more rigid'.

Also, though a material (strictly speaking) may not flex more with age cromoly is the only common ferrite metal used on bikes that doesn't have the flex of 'steel'. I'm not sure if AL or Cro is considered more flexy when considering typical uses on bikes, or in lab tests.

Steel is well know for it's ability to 'deflect' before failure (permanent bending, twisting, crumpling). At least generally speaking AL deflects much less and also has a well known but very different loading failure mode.
I don't see why steel wouldn't deflect more after enough cycles, before failure. Maybe not though, and on bikes the usual mode of steel construction failure is welds/joints anyway. Still doesn't mean it's fun to have a flexy ride, unless it's purposed suspension.

 

[Voltron]

When I read refrigerator door and batteries I thought it was going to be about something that looked like this...

 

[Chalo]

Also, though a material (strictly speaking) may not flex more with age cromoly is the only common ferrite metal used on bikes that doesn't have the flex of 'steel'.

All alloys of steel have fundamentally the same stiffness, whether they're weak and soft or super hard and strong. The measured value is called "elastic modulus" or "Young's modulus" and you can look it up for any given alloy. If you compare 4130 chromoly to, say, the 1010 steel that Schwinn used for their Electro-Forged frames built in Chicago (the mildest steel I ever saw used in bike frames), you'll see the Young's modulus is just about exactly the same.

Both alloys have almost exactly three times the modulus of aluminum. Meaning a tube with the same dimensions will be three times stiffer.

 

[Boyntonstu]

When I read refrigerator door and batteries I thought it was going to be about something that looked like this...

Is the little door the icemaker?

 

[nutnspecial]

Yes, technically correct. But potentially technical to a fault lol?

It would seem 'specific strength' is more applicable here than 'specific modulus'. In case there's confusion on your end (which I doubt :wink, when I say/said 'more stiff' 'less stiff' in VS materials here, I'm referring to strength-to-weight ratio . . . . because comparing materials @ 'same weight' or 'same tube size/cross section' is too restrictive/narrow. Bikes (among other things) often see great benefit in the superior stiffness and weight reduction that an aluminum or cromo structure allows.

You don't you think 'specific strength' is a little more applicable here? https://en.wikipedia.org/wiki/Specific_strength

 

[Chalo]

Sure, a frame must be strong enough to do its job, so the material has to offer adequate strength. The frame also must be stiff enough for the job.

In the '70s and early '80s, steel tubes for bicycle frames were of customary small diameters, and steels had gotten good enough that some frames could be made strong enough for a strong heavy rider, but not stiff enough. Large, tall, or strong riders got extra thick walled tube sets to meet their needs, but these added weight even more than they added strength. Eventually "oversized" and "double oversized" frame tubes became more common than the traditional sizes, because they allowed new higher strength steels to be used to their potential. So that's one example of frame weight being driven by stiffness issues rather than material strength.

When you get away from the fully braced diamond frame made out of straight round tubes, then materials stiffness becomes much more critical to making usable bikes. The Sun Streamway is a good example of a bike whose stiffness is impaired by its frame layout, which thus needs special treatment in terms of material and structural element size.