Undervolting? a more powerful motor for more speed.

[The S Man]

I suppose what I am trying to do is get my bike up to around 25mph for off road use, as cheaply as possible (£200ish), with the least hassle. Plus, being able to revert to road legal quite quickly and simply.
My latest (and probably dumbest) thoughts are.....
If I just connected a 48V 1000W motor into my existing 36V 250W setup without changing any wiring
would the bike work at all.
If reverse overvolting works (undervolting?), I would hope that a 1000W motor at 48V gives approx. 32mph then only supplying 36V would give 32 x 36/48 which would be 24mph. Mileage between charges is not that important, hopefully at least 10 or so!
This would then leave me the option of further upgrade to battery, controller etc. when funds allow or building a complete off road bike altogether.

 

[Alan Quay]

reverse overvolting

In a word, no.
To expand, NOOOOoooooo!

 

[trex]

The speed you can achieve depends on two factors: the maximum output of your controller and the efficiency of your motor at the maximum speed. For example, if your controller can output 15A at 36V (usually printed on the label of the controller) and your motor has 60% efficiency, the mechanical power is approximately 36V * 15A * 60% = 324W. You can use the motor simulator chart at http://ebikes.ca to look up how fast your bike can go with 324W, that's about 20 mph.

 

[Deleted member 4366]

When you undervolt, you lose torque as wll as speed. Hill-climbing won't be very good. Why not just get a motor that's designed for what you want?

 

[Alan Quay]

The speed you can achieve depends on two factors: the maximum output of your controller and the efficiency of your motor at the maximum speed. For example, if your controller can output 15A at 36V (usually printed on the label of the controller) and your motor has 60% efficiency, the mechanical power is approximately 36V * 15A * 60% = 324W. You can use the motor simulator chart at http://ebikes.ca to look up how fast your bike can go with 324W, that's about 20 mph.

This assumes that efficiency is linear across the RPM of the motor.

It is not.

 

[trex]

60%-70%: that's estimated efficiency of a 1000W direct drive motor at around 20mph.

 

[Deleted member 4366]

It'll be higher, though, if you undervolt it.

 

[Swytch Bike]

When you undervolt, you lose torque as wll as speed. Hill-climbing won't be very good. Why not just get a motor that's designed for what you want?

I would echo this, you're better off choosing a motor designed for your needs and matching your battery voltage. All motors are designed to a particular motor constant which determines torque and the top speed at a certain maximum voltage. Any good supplier/manufacture will be able to build a motor with the right motor constant to give you thr performance you want