Improve low-end torque with more teeth on the Bosch motor sprocket?

Mike leroy

Active Member

By changing the number of sprocket teeth, without updating the gear ratio in the Bosch firmware, would low-end torque improve?

I do not want to go faster. I want greater uphill climbing power in hills above 10% grade.

I do not know the Bosch Algorithm details. My guess is more teeth would result in the motor perceiving sensor input differently. More teeth is a slower cadence RPM. You must push harder, so the torque sensor might register greater force. The combination might cause the controller to supply more torque?

I appreciate any insight you can provide. I do not know how to calculate the outcome from adding more teeth to the motor sprocket.

I am software developer with firmware experience.

 
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opimax

Well-Known Member
This is not your personal blog , please behave in a responsible matter and delete your excessive self centered posts to your self important view of thermal imaging!
 

Mike leroy

Active Member
You
This is not your personal blog , please behave in a responsible matter and delete your excessive self centered posts to your self important view of thermal imaging!
i am unclear whether you want the thread removed, or just the reference to my post? I removed the reference to the post.

I apologize if I offended you. Perhaps, I got too excited over something that feel is very insightful, or used the wrong tone.
 

opimax

Well-Known Member
The thread , IMHO is fine, contains much information just not to my interest but this a community so it's great to share but the multiple post pointing to it, to me , are self serving and not needed.
 

Mike leroy

Active Member
Just to clarify, the reference contains more detail concerning my reasoning.

I am not selling anything or promoting a product. I have no personal gain.

I live in an area where the hills are all 10-20% grade. I want to carry 25-50 pounds of food, 2 miles from the store.

I did not want to belabor the thread with this level of detail.
 

Chris Nolte

Well-Known Member
You can change the sprocket size, but the motor is tuned to a specific sprocket so it is possible to get an error if it's not configured right. For most peoples cases it doesn't cause an issue. I would just use a taller gear in the rear, I would try to ride the bike if you have one available for test rider though. I think you'll find they have plenty of low end torque.
 

Mike leroy

Active Member
You can change the sprocket size, but the motor is tuned to a specific sprocket so it is possible to get an error if it's not configured right. For most peoples cases it doesn't cause an issue. I would just use a taller gear in the rear, I would try to ride the bike if you have one available for test rider though. I think you'll find they have plenty of low end torque.

If it helps, this link points to a map of the area I plan to ride in. The grades are keyed to the blue numbers in the Rohloff Gear Ratio table that appears on the map.

http://electricbikereview.com/commu...ciency-test-route-0aredwood-city-ca-png.2093/
 

Ann M.

Well-Known Member
@Mike, unless you want to blow warranty, why chop into the Bosch motor? We have plenty of hills with 10% gradient in the Austin TX area and the mid drive bikes generally do better than the 500 watt hub motor systems. If you want to go the overpowered route, look at some larger wattage aftermarket kits, like the Golden Motor 1000watt 48V or talk with the guys at electricrider.com. They're located in San Angelo TX (have an actual shop, not just internet stuff) and have a lot of experience outfitting regular bikes as well as heavy duty work bikes and other multi wheel exotica with a variety of over 1000 watt systems. You might want to look at one of their hill climbing special systems if it seems that the off the shelf ebikes won't hack it for you. There are a lot of options out there for specific applications like yours.
 

Mike leroy

Active Member
Ann,

I like your suggestions. CA has a 1kW legal limit, higher than the federal 750W limit. I also like 48V because the battery is future-proofed, more acceleration, better heating characteristics, etc... I can believe the electrical system will generate adequate torque.

My primary goal is to understand how to calculate or estimate Bosch low-end torque and speeds. The Rohloff website is completely transparent in this regard. The blue highlighted cells indicate physical limits. I know which hills are beyond my ability.

For example, if I fall into the 200W column, will the Bosch unit simply assist me into the 300W column?

(Link Removed - No Longer Exists)

I can infer how Bosch works. I may be unfairly underestimating, because my estimates lead me to believe 350W may not provide a significant benefit. I will struggle more on a bike than walking or running. I can run uphill with 10 lbs in my fanny pack -- strength training.

If the parameters are transparent, I can adjust wheel size, gear ratios, etc... I simply hate being in the dark. Feeling blind due to uncertainty makes me doubt.

I have done a complete analysis, including mapping the above table grades to actual streets I run each week.

Perhaps, you can tell me why I am underestimating? I have explained my reasoning in a scientific and transparent manner:

http://electricbikereview.com/commu...camera-reveals-ebike-just-right-for-you.1259/
 

Ann M.

Well-Known Member
Hi @Mike leroy , a little digging shows that Bosch does have an alternate 14T cog, but the internet is vague about whether that option is available or an aftermarket option that the Bosch repair centers or your local ebike shop can do. I'm contacting Bosch now to see if there's more detailed specs for you. Believe me, as a techie scientific type myself, I get where you're coming from. Let you know as soon as I hear back from them.
 

Mike leroy

Active Member
Hi @Mike leroy , a little digging shows that Bosch does have an alternate 14T cog, but the internet is vague about whether that option is available or an aftermarket option that the Bosch repair centers or your local ebike shop can do. I'm contacting Bosch now to see if there's more detailed specs for you. Believe me, as a techie scientific type myself, I get where you're coming from. Let you know as soon as I hear back from them.

Thank you. The last time inquired, a year ago, that was not available to the public. I think it might make pedalling easier, but generate less torque.

I would be very grateful if you could find out from Bosch how many NM are needed for each percent grade at wobble speed(9mph) at 275 lbs total load. I weigh 175 and a bike is probably another 50 lbs. I want to transport 50 lbs of groceries 2 miles from the store.

My guess is ~10NM per percent grade. In other words, a 70NM motor is designed for a 7% grade.

My area is a 10% grade, which is steeper than Bosch designed for, which is very reasonable from a global standpoint.
 
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Ann M.

Well-Known Member
Looking at BionX's D-series 500 watt kit, they spec it up to 50Nm which having ridden is way more than you need to climb a 7% grade. BTW haven't heard back from Bosch yet; would like to know more, too.