Increasing mid-drive's acceleration with bicycle parts only

Jul 22, 2018
49
0
London
#1
As in the subject line, I'm looking for ways to increase the initial acceleration without touching the motor, controller or battery. Not interested in top speed, just bigger 'oomph' when launching at traffic lights. Currently using BBSHD on a 29er bike on 2.3 tyres with 42T lekkie and 28T low gear on rear cassette. I have thought of the following options:

a) buying new rear cassette with 34T or ever 40T low gear
b) changing rear wheel only to 26inch on 2.5-2.7 tyre
c) both of above
d) replacing front ring with 36T lekkie, but chainline most definitely will be messed up and that option is least preferrable.

What's your opinion on this?
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
871
371
Basildon
#2
You can't really do anything on a crank drive bike. Assuming that you start only in first gear, you can get more torque by using a first gear with more teeth, a chainwheel with less teeth or a smaller back wheel. That torque will only last until you engage second gear, when you're back to where you started because second gear with a smaller wheel or chainwheel will be the same as your old first gear with whatever else you had before.

Sensible options are to increase the current that the controller allows or the way it ramps up in the settings, lose weight from yourself or strip off all the unnecessary weight from the bike. Each 1kg saved gives you approx 1% more acceleration.

If you're experiencing acceleration weakness with a BBSHD, there's probably something wrong with the settings.
 
Jul 22, 2018
49
0
London
#3
lose weight from yourself
:D

All I'm looking for is a little more acceleration on a first few yards, I'm happy with further acceleration as it already is. Just not sure which way is most effective, surely all of them combined, but if I was to try out just one which one would you start with?
 

soundwave

Esteemed Pedelecer
May 23, 2015
8,762
338
#4

Woosh

Trade Member
May 19, 2012
10,085
2,378
Southend on Sea
wooshbikes.co.uk
#6
As in the subject line, I'm looking for ways to increase the initial acceleration without touching the motor, controller or battery.
you are going to waste your money on this.
The acceleration is proportional to the square root of power, inversely proportional to the total weight of rider + bike.
you can't increase acceleration by changing the front to rear gear ratio.
The only way to mechanically increase acceleration is to store up inertial energy of a rotating mass and release it to help with the initial push.
 

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
7,595
908
The European Union
#7
You must be quite heavy?

My GSM accelerates away from the lights faster than all but the motorbikes and nervous young men in cars with loud exhausts. That is a 250W motor putting out +600W (at the rear wheel) and in 42:24 ratio. It is faster than most two stroke mopeds over the first 10 meters.

I think I would have problems keeping the front wheel on the ground with a BBSHD. You don't want to go to very low ratios because with bike tyres either they stick and the front wheel goes skyward or you will spin the wheel. I spin the rear wheel on the trike in the wet using 26:40 and it doesn't have a motor...
 
Nov 28, 2018
172
90
#9
"The only way to mechanically increase acceleration is to store up inertial energy of a rotating mass and release it to help with the initial push".

Never mind jet-packs.
We were promised flywheel powered bikes! I want my flywheels :p
 
Jul 1, 2018
79
27
Michelmersh SO51
#11

Ajax

Esteemed Pedelecer
Feb 2, 2008
305
6
#12
Most mid drives don't have accessible controllers.
If it has a controller it must be accessible. It might be harder to get at than a normal controller but it must be accessible, unless its welded in.
 

Woosh

Trade Member
May 19, 2012
10,085
2,378
Southend on Sea
wooshbikes.co.uk
#13
If it has a controller it must be accessible. It might be harder to get at than a normal controller but it must be accessible, unless its welded in.
the maximum current is now set by programming, not changing the shunt. Most internal controllers on CD motors are potted in silicon compound to protect them against water ingress.
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
7,003
404
55
West Sx RH
#14
Programming and solid state mini components is the main reason mid drive controllers are so small and unless you are a skilful electronics expert then very little chance of upgrading.
 

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