Increasing mid-drive's acceleration with bicycle parts only

Jul 22, 2018
45
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
476
129
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
45
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
8,626
285
#4

Woosh

Trade Member
May 19, 2012
9,811
1,861
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
7,523
790
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
119
49
#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
72
26
Michelmersh SO51
#11

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