RadRunner Plus Chainring upgrade - stock to 60T

[ElectricRides]

I thought my experience while upgrading my chainring would help out some people who are thinking of switching out their stock 48T RRunner+ to something else.

Part 1 (install)
https://www.youtube.com/embed/Ir87_5xBwAI

Part 2 (ride)
https://www.youtube.com/embed/UuIMLkLPVF4

Thank you!

[Radio Runner]

Interesting, My RR has a 130mm bolt circle diameter. I would have used a crank puller to make the job easier but maybe you didnt want to buy one. ( ouch my knees)

I think that chain will be two short now for the low gears and a new one may not be long enough with a 60T up front and a 34T in back. You may have to mate two together with a chain tool.

[Altema]

I need to do this. Rad made it just right for 20mph, but nothing more!

[tacomanatx]

I need to go the other way w/ my RadRunner, the single speed set up is a bit aggressive for the hills in my hood.

[Radio Runner]

I need to go the other way w/ my RadRunner, the single speed set up is a bit aggressive for the hills in my hood.

No kidding. I geared down to 50t in front and 17 in the back. Pretty significant reduction.

[handlebar]

I need to go the other way w/ my RadRunner, the single speed set up is a bit aggressive for the hills in my hood.

No kidding. I geared down to 50t in front and 17 in the back. Pretty significant reduction.

A traditional way to state bicycle gearing is the equivalent diameter of a penny-farthing wheel, pedaled directly. (Another way is meters per pedal revolution, which would be inches multiplied by pi and divided by 39.37.)

When Raleigh announced the Sturmey Archer gearshift in 1902, second gear was 53 inches because that was standard for a single-speed bike. I believe a Radrunner is geared to 75". No wonder I use the throttle to get underway. Naturally, it's challenging on hills.

Raleigh soon changed its sprockets to 66" for second (about like Radio Runner), 50" for low (climbing hills with about the same gearing as a single-speed), and 89" for high (which I used except on hills and to get underway).  Aft seating, about 14" behind the bottom bracket, made it possible. (I increased the distance 2 more inches by flipping the seat clamp.) In 1891, Charles Terront made history by completing a 743-mile race 9 hours ahead of the next fastest. It caused a sensation for his revolutionary Michelin tires, but the aft seating of his Humber was surely a factor. It increased the power he could deliver to each revolution of the crank.

The rack on my Radrunner made it easy to brace a layback seat post with an 8" equilateral triangle of plywood, so that I could move the seat back 7". I did it for safety.  A rider braces his upper body on the triangle formed by the seat and hand grips. With the seat only 20" behind the steering head, my weight was too close to the narrow end, at the seat. If your upper body isn't well braced against inertia, your steering will be unstable. My steering was so rickety that even with weeks of practice, I had trouble making a u-turn on an 18-foot road. The layback put my weight nearer the center of a longer triangle. I could make a u-turn on a 10-foot driveway.

There were other benefits I'd forgotten. One was a longer power stroke, the reason Raleighs had such high gearing. When a pedal is at top dead center, you need to push it forward, not down. With forward seating, your knee will be bent well past 90 degrees. That puts your quadriceps at a mechanical disadvantage. Besides, pushing the foot forward with the knee bent so far will entail lifting the knee at the same time the glutes are pushing the knee down to keep pressure on the pedal for traction. Your muscles will be fighting each other, meaning wasted energy, knee strain, and muscle strain, all for little gain. You probably won't do much pushing until the pedal direction is mostly down. That means a shorter stroke and less power per revolution.

With aft seating, your knee will be bent about 90 degrees at top dead center. Your quadriceps have a better mechanical advantage, and you can push your foot forward without fighting downward pressure on the knee. Forward thrust on the pedal means backward thrust on you. I tilted my seat forward as a brace, as I'd done with my Raleigh 50 years ago. The tilt of a Raleigh seat was a way to tell if the rider pedaled well.

Longer power strokes  increased the torque I could deliver. (Generally, I'll climb a 4% grade without the motor, and 150 watts is adequate help on a 6% hill near here.) More efficient use of leg muscles meant that circulation of sugar and oxygen, not leg muscles, were my limit. I might not know I'd been exercising until I dismounted and noticed I was breathing faster and more deeply than a couch potato.