BBS02 Top Speed

[Rickidoodah]

Could anyone help me calculate the theoretical top speed of a BBS02 conversion please.
I'm looking at the BBS02 750 watt version.
The bike I'm looking at converting has a Shimano Nexus 8 Speed hub with a 20 tooth sprocket.

 

[brightonebikes]

Other factors required.
Wheel size? Tyre size? Number of teeth on front chain ring?
I have aBBS01 250W set up with an Alfine 8 with 16 tooth sprocket and 42 tooth chain ring on the motor. 26x1.35 Marathon plus tyres at 65psi.
Top speed is about 30 on the flat.
Put a 52 tooth chain ring on and I guess it could push beyond 40?

Sent from my E5823 using Tapatalk

 

[Rickidoodah]

T

Other factors required.
Wheel size? Tyre size? Number of teeth on front chain ring?
I have aBBS01 250W set up with an Alfine 8 with 16 tooth sprocket and 42 tooth chain ring on the motor. 26x1.35 Marathon plus tyres at 65psi.
Top speed is about 30 on the flat.
Put a 52 tooth chain ring on and I guess it could push beyond 40?

Sent from my E5823 using Tapatalk

Thanks for the reply, I was going to say I had a 44t chain ring but then realised the BBS02 has its own chainring and O didn't know how many teeth it had.
I would be using 26" wheels with 1.9 or 2.1 tyres.

 

[brightonebikes]

Maybe have a play with this?
http://www.machars.net/bikecalc.htm


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[Deleted member 4366]

You can gear a crank-drive as high as you like but the higher you go, the less torque you have, so you get to the point that wnen you change to top gear, there's not enough torque to maintain that speed, so you'd slow down.

Assuming that you set the controller to 25 amps and that you have a 48v battery, power from the battery would be 1200w, which would equate to about 900w at the back wheel. You need 1000w to maintain 30 mph on a mtb-type bike, so with perfect gearing, the top speed would be 28 mph, though more downhill and/or with the wind behind you.

A motor makes it's maximum power at about 75% maximum RPM, so the perfect gearing would be 28 mph at a cadence of 75 in top gear.

Now you need to do some sums based on what you've got.

 

[Deleted member 4366]

According to Sheldon brown, the Nexus 8 has a top gear ratio of 1.615. If you had a 20T sprocket, 44T chainring and your crank turning at 75 RPM, the wheel would turn at 266.5 rpm, which is 20 mph for a 26" wheel. You'd therefore need a smaller rear sprocket, bigger chainwheel or both.

Speed at peak power would go up to 25 mph with a 16T sprocket and 27 mph with a 48T chainring as well.

Note that these speeds are all at maximum power. The motor will continue to assist to speeds 33% higher, but with less power. That means 27 mph, 33 mph and 36 mph, although you'd have virtually zero power at those speeds.

If it were my bike, I think I's use an 18T on the back and 44T on the front. That will just reach 30 mph downhill with the wind behind you, but have good power round about 22 mph. I think 16T is a bit small for that much torque, so it'll wear out pretty quickly and start slipping.

 

[anotherkiwi]

I obtained 45 km/h at a cadence of around 75-85 with an unrestricted GSM "250W" running at 37 V x 17 Amps = 629 W (470 W at the wheel) on flattish ground. That was in 5th and 6th gear not top - 46:11 is beyond me these days on all but downhill or with strong wind in the back

I am now converted to the idea of a 12S 44.4 V battery (you win again d8veh!), I just need a controller that can handle both 37 V and 44.4 V batteries. One with an LVC set to 36.5 V would be perfect! And bluetooth...

 

[Rickidoodah]

Thanks for the replies everyone. I appreciate it.

 

[tommie]

similar spec here....

BBS 02, 48v 750W,
Alfine 8 IGH,
26" wheels, Battery supposedly 13aH, 48V
controller sat at 22amps,
46 chainwheel and 18 rear cog,

full throttle on flat ground approx 25 mph,

could change gearing for more mph but i really value its climbing ability more.

 

[DavidSWP]

As others said, bigger chain ring and smaller rear spocket. I have a Nexus-8 with 15t sprocket and a 46t chain ring. 44t, 20t is really low gearing with a nexus-8 and would be a hill climbing rather than speed setup.. I still feel assist going at around 34mph going down hills. It will still go up a 1 in 5 hill in the lowest gear with pedalling effort like going up a very slight incline. Not a BBS but similar crank motor.

I'd probably put an even bigger chainring on but I was not able to find a track chainring in above 46t with the BCD I require (110). I'm not sure what BCD the adaptors you need to fit a normal chainring onto a BBS take. I'm not sure if anyone mentioned that you need an adapter?

Maybe I am being anal because people say that you can use normal rather than 'track' chain rings with a nexus and either 1/8" or 3/32" chains. But I like to stick to 1/8" with a track chainring as it should theoretically provide more traction and make the chain less likely to come off.

 

[nemesis]

You can gear a crank-drive as high as you like but the higher you go, the less torque you have, so you get to the point that wnen you change to top gear, there's not enough torque to maintain that speed, so you'd slow down.

Assuming that you set the controller to 25 amps and that you have a 48v battery, power from the battery would be 1200w, which would equate to about 900w at the back wheel. You need 1000w to maintain 30 mph on a mtb-type bike, so with perfect gearing, the top speed would be 28 mph, though more downhill and/or with the wind behind you.

A motor makes it's maximum power at about 75% maximum RPM, so the perfect gearing would be 28 mph at a cadence of 75 in top gear.

Now you need to do some sums based on what you've got.

What speed would the BBSHD be capable of with a 48v 17ah battery,there are videos on youtube of bikes doing 45mph on the flat with this setup or would you need 52v,the rider is pedalling.
He has one of those cycle analysts on the bars to show the speed is accurate.

 

[Fordulike]

What speed would the BBSHD be capable of with a 48v 17ah battery,there are videos on youtube of bikes doing 45mph on the flat with this setup or would you need 52v,the rider is pedalling.
He has one of those cycle analysts on the bars to show the speed is accurate.

As others have mentioned, depending on software, chainring and final cog ratio, 45 mph is achievable.

BBSxx's are happiest when the motor is spinning fast, so don't be surprised if it goes bang, running at these speeds.