Converting a 9 speed to a SS

[rich c]

I'm like the idea of fixie ebikes (with enough motor power it makes great sense) but I'm going to bring up something no one seems to be mentioning. When you do a fixie with a mid-drive motor you are locking yourself into a gear ratio that dramatically reduces the torque transmitted to the rear wheel (this is where hub drives shine because at high speed they are more efficient and all the torque is directly applied to the rear wheel). It's simple math...let's say you ride with a 48T front and a 16T rear fixie ratio, only 1/3rd of the motor torque is every utilized. This is why mid drives are much much better for mtn biking and climbing then they ever will be on urbam mobility bikes.

You do know that a true fixie does not have a freewheel right? Can't imagine pedaling to the rpm of the motor all the time! Better not have a throttle!!!!

 

[Ken M]

I definitely wasn't talking about non-freewheel fixies. I like the screw on fixie sprockets with their own freewheel/clutch. There is some very high end brands making these and they are very reliable and robust. The screw on fixed cogs you are referring too would not be appropriate on any ebike.

 

[TForan]

I definitely wasn't talking about non-freewheel fixies. I like the screw on fixie sprockets with their own freewheel/clutch. There is some very high end brands making these and they are very reliable and robust. The screw on fixed cogs you are referring too would not be appropriate on any ebike.

I thought all fixies were non free-wheeling. And I agree without power, I'm screwed ! I just think when you have the power of the Ultra, you can overcome shortcomings in gearing. Bike will be back on the road tomorrow. Hopefully .

 

[Ken M]

I thought all fixies were non free-wheeling. And I agree without power, I'm screwed ! I just think when you have the power of the Ultra, you can overcome shortcomings in gearing. Bike will be back on the road tomorrow. Hopefully .

I thought all fixies were non free-wheeling. And I agree without power, I'm screwed ! I just think when you have the power of the Ultra, you can overcome shortcomings in gearing. Bike will be back on the road tomorrow. Hopefully .

The Ultra has plenty of torque to overcome gearing issues but keep in mind that in reality gearing looses equate to an inefficiency. In other words, if only 1/3rd to 1/4th of the motor torque is transmitted to the rear wheel it's pretty much the same as any other inefficiency in the drive system.

I don't think anyone has any charts that provide a direct way to compare overall efficiency of hub motors to mid-drives but my guess that somewhere around 12mph and above hub motor drive systems have an efficiency advantage which is never discussed in the ebike industry because mid-drives dominate the dialog.

One of the reasons I'm a big fan of DD hub motors is that at the speeds they are inefficient a rider is very efficient - it's not a huge effort to get a bike to 12mph and then engage motor assistance. In reality only a throttle ebike can be ridden like this. Most people associate a drive systems performance based on how we feel the acceleration for a standing start. If you have a 10+ mile commute and spend a high % of that ride above 12mph this is something that really is tangible.

 

[TForan]

I tried a hub and it overheated and cut out on me on a steep hill. All I'm saying if I only use one gear out of nine, why have the other eight , when there is advantages of the single gear. Less slack, perfect chain line, etc. And I sure don't want the weight imbalance and rear flat tire hassle of hub drives. Why hubs were brought up , I have no idea.

 

[Ken M]

I tried a hub and it overheated and cut out on me on a steep hill. All I'm saying if I only use one gear out of nine, why have the other eight , when there is advantages of the single gear. Less slack, perfect chain line, etc. And I sure don't want the weight imbalance and rear flat tire hassle of hub drives. Why hubs were brought up , I have no idea.

Not sure what the power rating was on the hub drive you had earlier and most current hub drives have temperature sensing to prevent overheating. Really any hub motor drive system not capable of a full 750W will be under-powered / under-specified for hilly riding. I just brought up hub motors because they are more efficient in single speed applications like this string was about.

When urban / street riding I find it somewhat unbelievable that any rider would really notice the difference in handling between a mid-drive and a rear hub motor. My guess is that your belief the weight imbalance impacts handling comes from the expectations of e-mtn bikes which do suffer a performance impact - the higher unsprung weight will impact how well a rear suspension keeps the rear tire on the ground and in extreme cases the handling differences are relevant and noticeable.

There is so much industry marketing on mid-drives, most ebikers have been convinced they are superior on all ebikes and if someone owns one they will defend that decision. I actually own both mid and hub drive ebikes so I just try to objectively focus on the merits of each. The gearing & speed stuff I brought up is real (ie not misleading or biased marketing).

 

[TForan]

Not sure what the power rating was on the hub drive you had earlier and most current hub drives have temperature sensing to prevent overheating. Really any hub motor drive system not capable of a full 750W will be under-powered / under-specified for hilly riding. I just brought up hub motors because they are more efficient in single speed applications like this string was about.

When urban / street riding I find it somewhat unbelievable that any rider would really notice the difference in handling between a mid-drive and a rear hub motor. My guess is that your belief the weight imbalance impacts handling comes from the expectations of e-mtn bikes which do suffer a performance impact - the higher unsprung weight will impact how well a rear suspension keeps the rear tire on the ground and in extreme cases the handling differences are relevant and noticeable.

There is so much industry marketing on mid-drives, most ebikers have been convinced they are superior on all ebikes and if someone owns one they will defend that decision. I actually own both mid and hub drive ebikes so I just try to objectively focus on the merits of each. The gearing & speed stuff I brought up is real (ie not misleading or biased marketing).

The hub/mid drive debate is humorous to me. It's like a religion to some of you guys. I'd ride either one, if it suited me. Have you tried a mid with the Bafang Ultra ? I originally was interested in the Hyperfat 1000, but it wasn't easily available , so I bought the Biktrix.

 

[Ken M]

The hub/mid drive debate is humorous to me. It's like a religion to some of you guys. I'd ride either one, if it suited me. Have you tried a mid with the Bafang Ultra ? I originally was interested in the Hyperfat 1000, but it wasn't easily available , so I bought the Biktrix.

I'm drive system and religion agnostic. I just think each drive system has it's strengths and weaknesses and rarely are those really considered.

I really like Ultra and you are correct that it has enough torque to over-come the gear ratio losses but the result is added complexity inside the motor to allow the rotor to spin faster which is then that is just lost back thru the gearing of the bike at the higher speeds.

The ideal way to utilize an electric motor on an ebike is how the old Izip express did it where the motor and human drive systems are mechanically separate. The were onto something but they never really perfected the rear differential hub (anyone who has ridden an Izip Express will understand this).

 

[TForan]

I just got my new battery and rode around the block a few times and I think I'll leave well enough alone. I forgot how much fun this bike is. It just flat out works. I would suggest to anyone to give a Bafang Ultra equipped bike a spin , if you get a chance. Or if you are ever in Traverse City or nearby, come ride my bike for a hour or two. I've had dozens of performance cars and MCs, but this is more fun than any of them.

 

[Off road all day]

So you're planning on getting rid of all the gears except the highest gear?

I don't see the problem with changing gears. You said you use it because it's there, but what's the problem with that?

Chevrolet Corvette Z06 can accelerate 0 to 175mph in 1 gear.
(According to Top Gear, I'm sure it's still on YouTube)

So no, Corvette only needs 1 gear because of massive torque, but I don't necessarily see the benefit of getting ride of all the gear selections.
If you find shifting gear that bothersome, then maybe don't shift as much but I honestly don't see the benefit.

not massive torgue, actually the opposite, increase torgue decrease speed. increases grunt, It's actually low torgue and high horsepower that gives the Z06 the rabbit effect.