Old Schwinn Road Bike Chop Chop Build

I thought some of you may be interested in what's going on with my Latest build - I am doing some radical engineering to rig up a swing arm dual suspension bike.

First, I started with a gigantic road bike that was given to me, set up for very tall riders. I chopped the head tube and the seat tube, removing almost 4 inches of tubing.

I'm going to affix a 1/2" axle perpendicular to the seattube with heavy welded steel. The swingarm axle hold a welded double sprocket offset about an inch that will feed the left side 36 tooth sprocket, anchored via clamshell on a 24" wheel. The swingarm width will be 7 inches, with my custom hub being 6 1/2" wide. The hub will ride on a 1/2" axle! It will take something to break that.

I am shooting for a 47" wheelbase.

I did some test fittings on the frame to get an idea of how it would look.

I'll need to dish out some money for sprockets, tube and tire, stepup drillbit (to put 5/8" bushing into swingarm), and two shocks to support the swingarm.

I will be running a 1' piece of heavy Duty unistrut along but slightly below the top tube/ down tube interface. That will hold a spring saddle and grab the top of the shocks.

 

[Timbone]

The swingarm axle will also serve as the sprocket axle, after a short kick to the left. No tensioner necessary. I'll rig up some kind of tensioner for the pedal side.

I also made a kind of upraised flange for my disk brake rotor - a bit over 1/4", but it clears the motor chain very easily. I'm wondering if a 160mm caliper will fit? Maybe I'll just order a 203mm caliper and save myself some headaches.

My shocks are on order. When I see what I am working with I'll fab some custom clevisses to weld to the swingarms. All this is complicated and tedious. The shocks will be angled out and backwards, so I need to account for the angles at the top and the bottom.

 

[Timbone]

This is a rough idea of what I am doing. A little more welding, a little more grinding. New paint. Still need sprockets and a rear disk.

 

[FurryOnTheInside]

Reminds me in some ways of the BMW Master Plan.. the level top line, use of square tubing, seeing it without paint too I guess..

 

[gary55]

View attachment 79385
This is a rough idea of what I am doing. A little more welding, a little more grinding. New paint. Still need sprockets and a rear disk.

So who get's your other bike after you've passed?

 

[Timbone]

The OCC Chopper Bike?

The rear triangle is bent and fried. But it may live on in a new dimension. I'll cut the rear off and maybe rig up an entirely new bike.

 

[Frankenstein]

Is there any way to shove a steel tube down in the spot where those 2 muffler clamps are about mid seat tube, I would be worried about it crimping and with a prying type of force bend it rear and collapse the front triangle.. Seems like a weak point to me a bit.

 

[Timbone]

I did that! When I split the frame, I was sure to put steel in the seat tube. I used a seatpost - maybe the one from this frame? - and it runs down well past the point where the swingarm axle grips. It also goes up through and past the welded seam that is reinforced on the outside, too! The original bike was huge, one of the biggest frames I've ever dealt with. I think I cut close to 4" out of the seat tube. I could not have ridden the original bike and I am 5'11".

This is long and low with wheelbase 49"!

 

[gary55]

I did that! When I split the frame, I was sure to put steel in the seat tube. I used a seatpost - maybe the one from this frame? - and it runs down well past the point where the swingarm axle grips. It also goes up through and past the welded seam that is reinforced on the outside, too! The original bike was huge, one of the biggest frames I've ever dealt with. I think I cut close to 4" out of the seat tube. I could not have ridden the original bike and I am 5'11".

This is long and low with wheelbase 49"!

Love the idea. The materials are going to fail you. The swing arm/ chain stay is going to collapse. To many holes, to square. I think you should reconsider at least that. their is a opportunity for failure at every inch.. With a single member and a single mid way stress point the stay should be solid and taller on the sides than the width at the top. Hold on tight.

 

[Timbone]

Love the idea. The materials are going to fail you. The swing arm/ chain stay is going to collapse. To many holes, to square. I think you should reconsider at least that. their is a opportunity for failure at every inch.. With a single member and a single mid way stress point the stay should be solid and taller on the sides than the width at the top. Hold on tight.

I truly appreciate your concern but pictures can be deceiving. These channels are crazy strong, much stronger than any tube on a standard bicycle. I can't imagine the force it would take to bend one!

The weak points will be my welds, in particular the clevisses that I've welded to grasp the bottom of the shocks. I'll need to watch the Grade 8 studs that grasp the top of the shocks as well.

Everything is overdone. That's the whole point of this: max dependability, max trust.

 

[Frankenstein]

Love the idea. The materials are going to fail you. The swing arm/ chain stay is going to collapse. To many holes, to square. I think you should reconsider at least that. their is a opportunity for failure at every inch.. With a single member and a single mid way stress point the stay should be solid and taller on the sides than the width at the top. Hold on tight.

Too many holes? I think you are being too judgemental of them, they are just holes, holes may not even make it weaker depending on how they were punched, can actually add strength.

Too square? OK well you got me on that I never thought something could actually be too square unless you had a round hole to deal with. You don't even know the thickness of the wall to be saying it will fail with so much certainty, I've seen plenty of darn ass strong square tubing, I also find it harder to crimp and bend the square stuff compared to round tubes that don't seem to have as much support against being bent, realize that bending a square tube requires the stretching of 2 vertical walls and really stretching a top layer and bending a lower, usually easier to actually crush the walls inwards towards the center of the square tube on 3 sides to create a bend.

I think it will be fine, other than the seat tube the only possible weak point could be the part of the arm holding the wheel right before the spring, between that attachment and the axle. It could possibly slowly bend and eventually fail right there though a piece of 3/4 - 1 inch angle steel bolted onto it from underneath with a few inches past and before that point could prevent the square from wanting to bend upwards. It would also help it resist the twisting type force of the spring pushing not just downwards but partially outwards away from the centerline if the bike, since it will increase the outward pressure the less steep of the angle of the suspension spring.