Measured frame flex on original Abound

[spokewrench]

For 3 years, I've wondered how to measure frame flex on my Abound. Maybe Jesus finally gave up on me and showed me the way.

The bike was on its center stand. I stepped across the BB and pressed the display button to see the state of charge. Four feet below the display, I saw the tire move. Light seesaw pressure on the bars moved the tire from side to side. My butt was against the saddle, so I knew it didn't move. Normally, the center stand lifts the back wheel and leaves the front on the ground. That's why it hadn't happened before. This time, a weight on the rack held the back wheel down and let the front hang. Each time I put pressure on the bars, the battery creaked: another sign of flexing.

Between my thumb and forefinger, I pinched the joint where the fork assembly comes from the bottom of the steering tube. I felt no movement between them when I used my other hand to push and pull the forks, side to side. I checked the joint at the top of the tube the same way. Twisting of the downtube was the only answer.

I put a brick against the tire on each side, then applied seesaw pressure to the bars. The moving tire pushed the bricks 20mm farther apart.

i guess if you sell a bike with such a glaring fault, customers like me will beat a path to your door to buy a newer model.

 

[spokewrench]

This explains a lot. Riding no-hands requires "balance" in the sense of keeping your spine aligned with the bike. That's easier coasting than pedaling uphill because each stroke down on a pedal pushes you to the far side and the bike to the near side. Alternating seesaw pressure on the bars can maintain alignment as you pedal.

A full 4-gallon gas can weighs about 30 pounds. I've used 3 e-bikes to haul one. On the first 2, the load made little difference once I was underway. The Abound is supposed to carry 440 pounds, but that little load made it dangerously wobbly. Now I see. The bike weighs 96 pounds, but the center of mass is only about 16" high, for a moment of inertia of about 130 pound feet. Sitting higher, the gas can raises it about 70% to 220 pound feet. On top of that, a gas can has head space, which allows a bit of shifting in the form of sloshing.

This bike was designed to haul kids, sitting where my gas can sits and perhaps weighing more. Their weight could shift more than gas sloshing in a can. Yikes!

If frame flex is unsettling with a small load, it's bound to be a problem without the load. I haven't noted it. I have noticed that it's dangerous if I hit bumps with only one hand on the bar. If both hands are on the bars, hitting a bump will cause me to apply the same up-and-down pressure to both bars. If only one hand is on the bar, jostling me will cause frame flex and wobble.

 

[Gionnirocket]

 

[PedalUma]

Years ago I made a 'noodle bike' like that. It rode like a wet noodle. It was a steel mixite in a deep red with a touch of burgundy and had pairs of bright blue accent stripes on the fork and seat stays. I was working for the HQ of the company at the time and got it new at less than half price because of a paint blem. I covered the blem with a sticker with two matching blue accent stripes and converted it with too much of a battery. The couple who purchased it loved the 'smooth' ride. I learn best when I screw up. A bunch of those bikes went to the Apple Campus. That one was a special color for a hotel/resort chain and had a nexus 8 IGH. I converted a Gary Fisher Trek cargo cargo bike with the same problem when kids were on it. Noodles. I also sold a bunch of Abounds; the thing is the brace that should be between the down tube and the seat tube would have blocked the battery and negated the water bottle placement on the seat tube. Because of those experiences, I now look at the heart of the bike, the frame, more critically before involving myself. Again that was many years ago. Did you hear about the Korean department store owner who removed the columns because they were blocking retail floor space? One guy wanted me the remove his top tube to make his bike a step-thru!