Alta layback seat post with Radrunner

[handlebar]

I bought my Radrunner largely on the basis of the video by Electric Bike Review, paid for by Radpower. On his demo ride, one of the reviewer's first claims was that it was stable. I think he said he was riding with no hands. When my bike arrived, I found it so unstable that even after two months of daily riding, it was hard to make a u-turn on pavement 18 feet wide. I didn't dare take a hand off the bars to return a wave. I quickly developed tennis elbow from fighting for control with my right hand when I lifted my left hand to signal a turn. I'd been riding daily for six weeks when an insect landed on my eye. I let it stay. Taking a hand off the bar to brush it off would have courted disaster.

Was I too tall? My leg length is only an inch longer than the published average for male bicyclists. I looked at the video again. The reviewer had his saddle about the same height as mine. When he turned the camera down at his front wheel, I saw that he, too, had wobbly steering. At one point, I saw Cory, from Radrunner, wobble. If they had less trouble than I, they must have been on smoother pavement.

I'd grown up on classic English touring bikes: 26 x 1-3/8" tires, three speeds, and an upright position. Steering was stable because my perch was stable, with my torso and arms forming a sort of tripod. It was 26" from the seat post to the steering head.

The Radrunner's seat post  was only 19" from the steering head. That felt too short for a stable tripod. I bought an Alta layback seat post. it set my seat clamp back to 26". With a more stable perch, I can make a u-turn on a 10-foot driveway. I need throttle because there's a lot of rolling resistance in turning a fat-tire bike so sharply. My stable seating allows precise throttle control.

The layback cured a worse problem. Riding with one hand, you no longer have a tripod. You sit up so your weight is divided between the seat and the crankshaft. With the straight seat post only 6" aft of the crankshaft, it's like hanging a coat on a rack with a 6" base. Bumpy pavement could cause me to lurch a bit, so I would have to apply a lot of torsion with my wrist to keep the bar steady. The layback puts my seat clamp 13" aft of the crank. My legs can provide much more stability. The day I installed a layback, my tennis elbow began a rapid improvement.

Side streets around here have lots of washboard bumps. The layback rides more comfortably than the suspension post it replaced. As with a classic English bike, when I'm not pedaling, I put most of my weight on the pedal at bottom dead center, almost like standing on one leg. On a bump, the crankshaft rises about half as far as either wheel, and my leg absorbs the bump like a spring. For a speed bump, I bring the pedals level so I can absorb the bump with both legs and both pedals. I usually maintain light contact with the saddle. I did this with a straight seat post, but it works better with the layback because the seat is farther aft of the crankshaft.

Improved pedaling is another benefit I didn't anticipate. I'd depended on motor assistance even for a 1% grade. Now I prefer to handle even a 2.5% grade without the motor. The ankle is about 7" behind the ball of the foot. If the seat was 6" behind the crankshaft, at top dead center, the ankle would be approximately under the hip joint. The ankle has a limited range of motion, so when the knee is bent back that far, the heel will be several inches above the pedal. Pedaling was like doing deep knee bends. With the layback, I don't have to bend my knees so far.

The brace didn't allow the post the be inserted more than 8" into the frame tube. I clamped it that way because it put the seat at the same height as before. After a week, I raised it an inch. I liked it even better. A week later, the post had bent perhaps 4 degrees. A bulge had formed on the back of the post where it exited the tube in the bicycle frame. It was probably the cumulative effect of hitting bumps, and it would get worse. Because of the bulge, I could no longer insert it all the way to the brace. I was going to buy a new one and accept the fact that I couldn't adjust the height.

Then I realized that a plywood brace could support my layback at any height I chose. My Radrunner frame has rails a few inches below the seat. I drilled corresponding holes in scrap plywood. I sawed the board off so the holes would be semicircles to fit over the rails. I removed the seat, clamped the layback an inch higher than before, put the board on the rails, traced around the end of the layback, and drilled a hole for it. Then I sawed off the board to make a sort of triangle. I chamfered the hole to match the way the post expands just past the seat clamp. The seat clamp holds the board on place.

It works. The tight fit on the layback holds the board so securely that I haven't even fastened it to the rails. By drilling holes in another board, I could change my seat height, but it seems just right. The seat looks level, but it's tilted forward. There's no need to touch the ground from the seat, but by sliding forward, I can straddle the seat with both heels on the ground. By sliding back slightly, I can coast with one knee straight but not locked, the ball of my foot on the pedal, and the sole level.

Riding that way, if I want to put most of my weight on my foot in anticipation of bumps, slightly extending my ankle will take most of the weight off the seat and the handlebars. It looks as if the layback would put most of my weight on the back wheel, but this shows that in my normal posture, my center of gravity is approximately over the crankshaft. For hard pedaling, I lean forward more to move my center of gravity ahead of the crankshaft. Before taking a hand off the bar, I sit back to bring my center of gravity aft of the crankshaft. Moving one's center of gravity is automatic.

The geometry between the crankshaft, the steering axis, and the seat is similar to that of a classic English touring bike.

[wkindred]

the instability you mention i find odd.

i've had a radrunner 1 since april 2020 that both my son and i ride. i'm constantly telling my son to get his hands on the grips during our rides since he like to ride hands-free. during one of our rides he actually was able to ride no hands for over 3 miles on winding trails - longer had i not been nagging him, i'm sure.

[Altema]

Have you had a mechanic check your head bearing adjustment? I used to build bikes, and the Rad is the first bike I had that would wobble when hands free. The frame and suspension geometry is partly to blame, but it goes away after a head tube adjustment. Weight distribution also plays a role. With nothing on my rear rack, I can ride one hand or no hands for miles. When I am carrying weight, such as my second battery or cargo, it wobbles due to oscillation and there being less proportional weight on the front wheel.

However, even in the worst case scenario with the rack loaded up, the bike is still very stable and I can still comfortably ride one handed. I ride it quite a bit on mountain bike trails with hairpin turns. One of the trails I've ridden is below, with two miles of turns, and it was actually a bit boring on my Rad.

[handlebar]

the instability you mention i find odd.

i've had a radrunner 1 since april 2020 that both my son and i ride. i'm constantly telling my son to get his hands on the grips during our rides since he like to ride hands-free. during one of our rides he actually was able to ride no hands for over 3 miles on winding trails - longer had i not been nagging him, i'm sure.

I'll compare a rider's upper body to a floor lamp in the back of a truck. Depending on the height of the lamp and the size of the base, it could wobble badly on bumps. I sit tall enough that two days after my Radrunner arrived, I dented my helmet trying to ride into the garage. The layback gives me a longer base. 

As a teen on the way home from the swimming pool, I'd ride my English bike down a steep hill with a stop sign at the bottom. Why put needless wear on the brakes? With both hands holding the corners of my towel behind my head, I'd let it pop open like a parachute. I was always impressed that it slowed me down so well. With good seating geometry, my legs kept me stable so that I could steer with my weight.

Now I'm more responsible. Instead of lifting my hands off the bars, I use thumbs and forefingers to make rings around the grips. With the layback seat, I can make a game of not letting the handlebar bump my fingers. My feet keep me stable.

[handlebar]

Have you had a mechanic check your head bearing adjustment? I used to build bikes, and the Rad is the first bike I had that would wobble when hands free. The frame and suspension geometry is partly to blame, but it goes away after a head tube adjustment. Weight distribution also plays a role. With nothing on my rear rack, I can ride one hand or no hands for miles. When I am carrying weight, such as my second battery or cargo, it wobbles due to oscillation and there being less proportional weight on the front wheel.

However, even in the worst case scenario with the rack loaded up, the bike is still very stable and I can still comfortably ride one handed. I ride it quite a bit on mountain bike trails with hairpin turns. One of the trails I've ridden is below, with two miles of turns, and it was actually a bit boring on my Rad.

Thanks. The steering works freely with no slop.

"Laugh In" used to play a clip of an old man toppling on a tricycle. That's how I felt with the stock Radrunner. If my weight wasn't stable with respect to the bike, of course my steering wasn't stable. A u-turn is a good test because steering sharply will cause inertia to push your body forward and to the outside with respect to the bike. After two months of daily practice, u-turns were still big and clumsy. I'd need a burst of throttle to get out of trouble. The layback fixed the problem.

On Youtube, more than one Radrunner reviewer said he preferred to slide back to sit on the passenger seat. I wanted to be high enough to pedal. The layback lets me sit back and high, and my center of gravity is normally over the crankshaft.

Because of the layback, I had to mount my 12 x 17" crate farther back so that now it extends several inches aft of the rack. It will hold 35 pounds of groceries. I use a bungee cord to mount a second crate on the first so I can buy more. I haven't noticed a difference in handling with all that weight hanging off the back. (I keep trying to remember to take it easy on speed bumps with groceries. Back there, they bounce much higher than my crankshaft, and groceries don't have legs to serve as springs. I'm amazed that I haven't broken any eggs.)

The photo was taken before I got the layback and moved the crates aft. It was also before I found an old-fashioned mirror that shows full-sized images.