BBSHD recommanded gear ratio

[CroqueMr]

Hi, I have a BBSHD on my bike, I would like to know what's the recommended gear ratio to save battery and controller.

I can only change the gear ratio by switching the chainring.

My setup is:
- 48V 30A Battery
- 11-34 9Speed Cassette
- 26" Wheel (26 x 2.15 Schwalbe Big Ben)
- 42T chainring (can switch this part)

I would like to have a max speed of 30mph / 50kmh

What chainring should I take ? I think 38T will be a good choice but I am not sure.
Moreover If I change my battery to a 52V one, am I going to save battery and preserve my controller ? I burnt 3 controller (2 BBS02 / 1 BBSH) in a year

Thank you.

[stts]

waste of time

[CroqueMr]

For max 30mph with that 11 sproket, you could go down to a 30T chainring. The most efficient cadence is between 60 and 100 rpm. The 30 would get you about a 60 rpm cadence and would be lots easier on your controller. You may need an adapter to make those fit on a Bafang. You must have some wicked hills to be smoking controllers like that.

thank you for the reply

I am not sure about this chainring, it seems way too low to me.
If we take a cadence of 80rpm
Max speed kmh= 80 * 30/11 * 26*2,54*pi = 45243cm/m = 27kmph = 16mph

[stts]

waste of time

[Retrorockit]

Sheldon browns bicycle gear calculator. Generally select gear units as mph#90rpm, unless you want some other value. That's a brisk spin for most people. 80 is more relaxed.

https://www.sheldonbrown.com/gear-calc.html

My own bike is very much like yours. 26x2.15 Big Ben + tires. BBSHD. I'm running 8 speed 11-40t cassette. I'm running a flat 50T chainring. but my top speed is 36mph. I can cruise at 30-32mph.
50x11t is a little long and has no inset for chainline. I would go with 48t to get the chainline.
The reason you see smaller cogs advised is the BBSHD can run up to 140rpm. So on throttle it can go fast with smaller gears. If your going to be pedaling then normal bicycle gearing rules still apply.
You can get an adapter to lower your derailer to run wider cassettes.
https://www.sevendaycyclist.com/sun-...lleur-extender
Then you can run an 11-40, or 11-46t cassette.

https://sunrace.com/product/csm993-9az/

A long cage 3x9 speed MTB derailer can handle 1x9 at this range. I'm actually running a shorter mid cage derailer at 11-40t range. I also welded up a longer derailer hanger that is not as long as the hanger+adapter.
With the wide cassette you will have the long , and the short gears with the big chain ring. The BBSHD actually works better with the wide gear splits.
You can enter 3 chainrings at Sheldon brown and compare them side by side.
11-13-15-18-21-24-28-34-40

https://www.amazon.com/Sunrace-Cass-Csm980-11-40-CSM980-9AX0-NS0-BX/dp/B071JNRPS8/ref=sr_1_6?crid=1ZJ8F3WE0U83O&keywords=Sunrace+CSM983&qid=1668790199&s=sporting-goods&sprefix=sunrace+csm983+%2Csporting%2C178&sr=1-6

[Retrorockit]

MPH @ 90rpm with 26x2.125 tires.
42t 46t 48t
26.5 29.0 30.3 11t
22.4 24.6 25.6 13t
19.4 21.3 22.2 15t
16.2 17.7 18.5 18t
13.9 15.2 15.9 21t
12.2 13.3 13.9 24t
10.4 11.4 11.9 28t
8.6 9.4 9.8 34t
7.3 8.0 8.3 40t
The forum removed all the spaces form the chart.

[Retrorockit]

It's funny AZ and I ride completely different bikes in completely different situations, yet when you do the math we have the same top gear.

[AZguy]

I've run 38-44t rings and can hit over 30mph with any of them.. I can barely keep up with the cadence with the 44t (on 11t rear cog) so if you want to pedal at 30mph, going to need at least that

However riding at 30mph continuously will *eat* battery - if trying to go any sort of distance at 30mph better have a really big battery if that's the plan...

[CroqueMr]

When you say "I can barely keep with the cadence" do you mean shadow pedaling ?

Battery consumption is not an issue I lived in Paris, I only need to ride 5-10km max every trip.

[Retrorockit]

I ran the gear chart at 26x4.7 inch tires and got the same top speed as my 50x11 top gear..32mph@90rpm. So it's about a 6 tooth offset.

[AZguy]

When you say "I can barely keep with the cadence" do you mean shadow pedaling ?

Not exactly, I mean really pedaling... 99+% of the time on my BBSHD build I'm pedaling hard... I *never* "shadow" pedal...

At 30+mph the pedal cadence is getting really high though, more than 90 to 100rpm which is getting to my old disabled leg limits..

[CroqueMr]

Thank you for your reply

I thought my gear ratio was wrong and causes damage to the controller because my motor died on my first ride after 5km with my stock un-programmed BBSHD, and I burnt 2x BBS02 controllers before.
But the issue is deaper : The core motor burned, All phases are shorten....
I bought the motor a month ago on Aliexpress I hope the seller will be fair and repair my motor for free.

Do you know what could have burned the motor ? Can a defective rotor burnt the stator ? I would like to know If i need to change the rotor and the stator or only the stator. ?
Thank you

[Retrorockit]

Most of us in the US avoid Aliexpress. We use US vendors who but directly form Bafang in bulk, and have some leverage with the Chinese on our behalf.
Luna is one of them and the sponsor of this forum.Luna's focus on offroad kits has made them experts on the BBSHD. In EU that option probably doesn't exist..

[stts]

waste of time

[CroqueMr]

Good news, The seller will cover the reparation.
Bad news I can not open the core motor to see the damage by myself.

[Retrorockit]

I've run my BBSHD for 3 years with no issues. Due to strong headwinds here it's not uncommon for me to run at 1100W or more for extended periods at 25mph into 20mph winds. I have a 24Ah,40A battery that can support this. i've had no motor trouble at all. Since you've had this with more than one motor I suspect something else is wrong. Since I've never had to fix anything I haven't got a clue what it could be. My ride to lunch and back is 22miles. 30-35mile rides are common.
One thing I do know is when Volaatge drops Amperage goes up at the same watts output. Maybe too small wiring? ust a guess.
Since you're in Europe maybe some component is rated for the 350W limit that's common there? Grin Technology in Canada makes some powerful bikes.
They're all about hub motors, but know what they're doing.

[CroqueMr]

I think I received a defective BBSHD, the core wiring burnt during my first trip. Some guys drawing 3000W on the core motor, mine burnt with a stock controller. I think it's a manufacturing defect on the wiring.

A 350w BBSHD does not exist, every version of this motor is not street legal in EU.

I did not have any issue on the BBS02 core motor. I only burnt 2 controller and I know why, the starting current was too high. I bought a BBSHD to have a more resilient controller

[Retrorockit]

I'm aware of people running these at higher power. That's why it's shocking to burn one up at 1500W.
Perhaps start another thread on this issue. I'm not sure gearheads like me will be much help with this.

[Retrorockit]

The motor may be more efficient and run cooler at higher RPM. You could drop down a couple gears when throttling and get the same speed at higher motor rpm. You will still want the higher gears for when pedaling. No matter what gear you have the BBSHD will run into a wall somewhere around 35mph on a typical bike.

[CroqueMr]

Thank you for your answer. I also notice the same thing, I will definitely switch to a smaller chainring.

[73Eldo]

My questions is do you pedal or are you almost always throttle only? Then if you were to pedal what speed are or would you be pedaling? Slow, normal, fast, or can't quite keep up fast? For throttle only fast to too fast seems to be the ideal gears vs. ground speed ratio. That has been my experience and what others that seem to have not had issues seem to be doing also. The people I have talked to that have been burning things up have not been able to answer that question and say they don't usually shift gears.

[CroqueMr]

On my BBS02 I don't have a throttle, and I shift gear.
On my BBSHD I used the throttle on a low gear when it burned, but I had a default on the BBSHD core.

[Retrorockit]

Pedaling for 30mph I need 50x11t or 50x13t gears. 48x11t or 48x12t would be in the middle of that range also. Those might be better choices.
Throttle I can use 50x15t or 50x18t but can't pedal that fast. 5/8 or 6/8 of my gears.
For over 32mph 50x11t is needed. It's my run for your life gear to get off of 45mph roads I don't want to be on. I don't use it very much, but it's nice to have.