Pedal Assist - need more speed

[RooneyRider]

I need some advice from the experts - all of YOU! I just bought a Yuba cargo bike and had some local specialists here in L.A. add a 2000W motor so that it can really replace my car for the 10-mile roundtrip from home to grocery, drigstore and other stops. The pedal assist works great up to 17 MPH and then goes to mush because the motor is too powerful for the crank sprocket. I want to pedal at 25+ MPH to conserve battery juice, but can't. Can anyone tell me what size crank sprocket I need to get so that I can peddle assist at 20 - 30 MPH? Thanks!!

 

[indianajo]

My yuba bodaboda has 52 front & 11 rear available. That allows me to pedal up to 23 mph which is as fast as my Mac12 motor will go. Younger people may be able to spin crank faster than me, I'm age 70. Muscles can retain strength but stiffen up after age 63.
You need to count the teeth on the rear sprocket to achieve even that ratio. Last I checked yuba was selling a single front crank 10 speed rear shimano mid drive setup electric bodaboda. I wouldn't have bought that; I pedal myself unless the wind is >12 mph in my face or I'm over 25 miles already. I have 32 42 52 front crank, 28 to 11 rear sprockets. 8 speed rear sprocket, so my first chain lasted ~5000 miles. 10 speed chains are thinner.
Weren't you the guy in introductions that had a mid bucket bike with 20" wheels? You'll need a much faster ratio than 4.7 to 1 to go 25 mph with those wheels. Mine are 26".

 

[RooneyRider]

I put the question to Yuba a few days ago, but they haven't replied. I suspect they won't reply because I altered the bike away from how they designed it to be used. But thank you for the detailed information! That sends me in the right direction. I have 20 inch wheels, but today was my first post.

 

[indianajo]

Yuba wouldn't tell me the measurements of the child shelf, 11 months before I bought. They wanted me to ask the facebook group. I'll post on facebook right after I develop an intense desire to listen to the lies of Pres. Putin & Foreign Minister Lavarov. The dignitaries who you can tell they are lying because their lips are moving. Besides facebook wants my birthdate to join. The can have that by paying a private detective, I'm certainly not going to give it away. Yuba is not helpful even before the sale, but the bike was top quality, and fits my short legs. Better than expected too, with all the welded in bosses for accessory mounts and the tapped 5 mm holes all over the back end. The SRAM shifters are great! no adjustments.

 

[harryS]

Facebook wishes me a happy birthday every 1/1/60. They don't audit your birthday. I'm getting a $250 class action settlement here in Illinois because someone sued their facial recgnition scheme, which requires permission in our state. That's one benefit of F/B, beside being able to connect with old girl friends, of which I had none,

Anyway, 20" wheels? A good combo is 52T/11t, If your frame can fit the bigger crank, 56T is possible,

 

[RooneyRider]

Thanks very much, Harry. I want to use pedal assist full-time to elongate battery life. Happy riding!

 

[PedalUma]

Here is how you can figure out gearing. It does not account for factors such as weight and wind.

Sheldon Brown's Bicycle Gear Calculator

A JavaScript calculator for analyzing bicycle gearing

www.sheldonbrown.com

 

[RooneyRider]

Thanks much. It's quite complex, but i'll give it a try.

 

[PedalUma]

It seems complex at first but it is precise. First count the number of teeth on the chainring. Then count the number of teeth on the smallest and largest cogs of the rear cassette of gears. Have your tire size ready to plug in to the calculator. Crank arm length does not seem to matter because it is so small a difference (170mm or 175mm). Put Cadence at 80 and look for Mph.
Just ask if you want further help with input or with interpretation.

 

[RooneyRider]

I took another look and it appears to be just for manual bicycles - which makes sense. I'm trying to figure out what setup of gears I need that will allow me to peddle assist at 25 - 30 MPH with my 2000W motor.

 

[PedalUma]

Try a 42-T chain ring from eBay. Clearing the frame is a factor. Google how to measure your BCD. This is how far the ring bolts are from the center of the chainring. It will be a number such as 130mm. Narrow/Wide chainrings are nice. Place your order.

 

[harryS]

MAnual or electric, the calculator still computes the pedal cadence. I like this calculator. WIth 52:11. you have to pump 80 beats a minute to go over 20 mph on 20" wheels.

Bicycle Gear Cadence Speed Table | BikeCalc

Calculate cycling cadences at a specified speed given chainring, sprocket, tire and wheel sizes.

www.bikecalc.com