Bafang Ultra Motor 620 on Old Technology?

[traderfjp]

Hi,

I'm new here but eager to learn. I have a Surron with a 5000w motor and it's single speed with one chain. The bike is fast and can climb hills like it's no bodies business. I do miss shifting. I can get it up to 45mph and it's fun to drive. Why do powerful motors like the Ultra need so many gears - is it about PAS?

I just ordered a Biktrik Juggernaut Duo 2 step over with a Shimano 9 speed Altus setup ( 11-34T), KMC E9S chain. The bike has the Ultra 620 motor and thumb drive, cadence and torque sensor with no governor so it should do about 35mph. Which is nice to have. I really wanted a full suspension bike but I have the Surron and will mostly be out with the wife on tame trails and pavement anyway.

When I was a kid 45 years ago I had a bike with Shimano gears and while I'm sure there has been tons of advancements the concept of gears, cogs, derailer and chain seem to be familiar. I feel like we are taking a powerful motor that chugs out 160nm of power and hooking it up to bike gears that really aren't designed to handle this much power. Am I wrong? If I'm careful will I be able to keep the change from jumping off or damaging my cassette? There is a shifting sensor that is suppose to pause the motor during a shift but I read that this is not fool proof and yo u still need to be careful. Are CVT and geared hubs better solutions? Did I buy old technology. Part of me loves the idea of the CVT tranny.

What upgrades might I want to consider in the future to make the drivetrain as robust as the motor? Bike Specs

 

[AHicks]

Many of us are NOT having any issues with high wear anywhere in the drive train. If you find yourself on the smaller gears (like the 11t) often, they don't handle the Ultra's power well. There's just not enough chain contacting the teeth on that gear to absorb large amounts of power (or shifting mistakes). If you don't require gobs of climbing power available on the bigger gears, a larger chain ring would be a good solution. That would leave the 11t intact if you needed it, while avoiding continuous use of it. Issue depends on your cruising speed....

The shift sensor works pretty good on my bike, but I've been shifting without one for a LONG time, so I find myself pausing even with the shift sensor.....

I have no experience with IGH's, but the scuttlebutt is that they may not be quite up to the task of holding the Ultra's power. Love the idea of a belt drive though.

Last, I've found the Ultra to be a huge torque monster that's very forgiving/friendly. My casual riding style allows it to accelerate from a stop in 5th gear while pulling very low wattage (say less than 250w). When pulling low wattage numbers like that, there is no, or very little stress anywhere. Point being, there's no issue starting in the mid range gears as long as you aren't in a hurry. Dropping to 1st or 2nd not necessary under those conditions...

Knowing this after riding it a bit, I find there's really no need for even the 9 speeds a lot of them come with. 10 and 11 speeds are way overkill. If I were replacing/rebuilding my drive train, I would likely go 7 speed. That would offer me plenty of shift range, while allowing for much sturdier chain. A much sturdier setup with very little/no downside. Because of all the available torque, there is no need here to keep the Ultra in a narrow power band - which is the only way to justify 9 speed plus drive trains.

Geez, those thoughts in mind, congrats on the new bike. Betting you're going to love it! -Al

 

[theemartymac]

I had wear issues on my Ultra originally, but found most of it seemed to be related to the setup and how I used it (High-speed commuting >40kph). I swapped my chainring to move the chain down the gears a couple of spots and keep off the small cogs, and it's been perfect since. I've almost tripled the mileage of my second chain/cassette over the original, and I ride it much harder and faster than the typical user. So, yes, there is potential for increased wear, but for typical riding, don't fear the ultra.

And you don't NEED those extra gears with the power of the Ultra, but it does allow you to get it right in the sweet spot for speed and cadence a little easier than if you just had say 6 speeds. But honestly, I only use maybe 4-5 gears out of my 9 with any consistency, so if it was a 6 speed with the right spread, I wouldn't have any cause to complain..

I agree an internal geared hub would be great, and if they ever build one that can take the power of the Ultra or an equivalent motor and is tunable for my usage, I'd probably be first in line throwing my money at a salesman.

 

[scrambler]

This is a catch 22 on bikes with a single power train but two power sources, a motor, and human pedaling.

Human pedaling requires multiple gears, so when the motor shares the same drive train as pedaling, it has to have internal gearing that can work with these pedaling gears, and as a result, it cannot handle all the power and speed efficiently on a single gear.

On bikes with a dual drivetrain like the LMX, or SEM or BoxxBike, the motor can use a single appropriate gearing, and the pedaling side has its own multiple gears

 

[Ken M]

This is a catch 22 on bikes with a single power train but two power sources, a motor, and human pedaling.

Human pedaling requires multiple gears, so when the motor shares the same drive train as pedaling, it has to have internal gearing that can work with these pedaling gears, and as a result, it cannot handle all the power and speed efficiently on a single gear.

On bikes with a dual drivetrain like the LMX, or SEM or BoxxBike, the motor can use a single appropriate gearing, and the pedaling side has its own multiple gears

I've been saying this exact same thing for quite some time but no one seems to accept that this is true. It's simply not technically possible to optimize both human and motor via one drive train but the powers in the industry do not want that to become common knowledge.