Power=Speed

[furcifer]

I'm curious what this community is finding in terms of power and speed.

I've been riding e-bicycles for several years now and apparently my experience has been slightly underwhelming. I have both hubs and mid-drives, a couple BBSHD's and a "1500W" hub.

I have now heard claims that motors in this range will do 40-80 km/h. In terms of watts, claims of 80km/h from 2000W are out there.

I'm running +3000W to a BBSHD and in my experience it will move my 100kg frame on 26" wheels comfortably 40-45km/h. If I push it, on flat level ground with a fully charged battery maybe 60 km/h.

On the highest gear, with the wheel off the ground I believe I can get the wheel spinning 95 km/h. That's with a 42t/11t drive.

But that's literally a velocity going no where, which is a scientific oxymoron.

This inquiry comes about as a result of my recent discussion on FB, and a community speed radar. I thought maybe I was going faster than my display read and that's why I'm not getting these speeds. Turns out according to the calibrated radar my display is spot on. I've done some test runs and the sign is accurate.

tl;dr - what do you feel are the speeds a 1000W, 15000W, 2000W and 3000W ebike can achieve on a routine basis.

 

[amberwolf]

If you want to see how the power relationship works, I recommend experimenting with the http://ebikes.ca/tools/simulator.html
with all your various riding conditions.

Speed is determined by a number of things, of which power is only one. The others you can see in the simulator as you experiment with different motors, controllers, batteries, wheel sizes, gearing, etc.

 

[ZeroEm]

Could say most but some would be more accurate match the Motor (windings/gear reduction), battery (voltage/amps), controller and wheel size to get the desired speed and power.

Have a 1500w DD leafmotor and it does 53 kph without speed limiting. Set my trike up to easily do 28 mph. Now the same setup and change out my winding from 7T to 4T and it will do 77 kph or 48 mph. It would be limited by the 40a setup. Could upgrade to higher amp battery and controller say 60a-80a then 84 kph or 52 mph. But I have a trike and have less drag than upright bikes.

Sorry you have been slightly underwhelmed. What do you think will make you happy.

Though there was a survey on members rides with power and speed.

 

[DogDipstick]

If you want to see how the power relationship works, I recommend...
Speed is determined by a number of things, of which power is only one.

I wholeheartedly agree.

Load is load, a given and set force. Well enumerated.

While you guys are comparing unloaded RPm.. Check out this one!

This bike was heavy and reached 55mph loaded... on an 8kW controller and a powerful pack. 4T motor. 134lb bike.
My bike is lighter and reaches 59mph on the same battery and the same 4T motor. On a 4.5kW controller. 100 lb bike. Figure that one out.


https://www.facebook.com/jeanpaul.rosse/videos/4375012112529084/?idorvanity=2137184879932374

 

[ZeroEm]

Your Whours for kms

 

[BalorNG]

Technically, record for human power (and a wee bit of 'gravity assist', 0.6% decline) is 140 kmh.
Aerodynamics trumps everything except UPhill, but making something that will go 100 kmh on 300 watts is challenging not only technically, but will end up extremely impractical.
I've seen test of fatbikes that go only 40 kmh on 1000kw of power.

Your real-world performance will lie somewhere between those extremes.

 

[classicalgas]

Based on the few comparative tests I've seen, a full fat (over 3" wide) tire has almost twice the aerodynamic drag at 20mph that a 2" MTB tire has (given similar tread patterns) It's much easier to find a relatively smooth tread design in a 2" wide tire than a 4" wide one, as well, and tread pattern has an effect on aero drag.

Why worry about tire aero?

The top of your tire is moving twice as fast through the air as the rest of your bike is, and aero drag goes up as a square of speed (2x as fast =4X the drag)

In short, before throwing a bunch of money into more power, look at your aerodynamics.

 

[classicalgas]

So far as direct experience, my semi fat (3" tire) will do 40-45kph on 800-900w. That's with the tires at less than max rated pressure, and bars that put me in a typical MTB, "leaned foreword but not crouched" position. If I trigger the dropper seat post and assume a more "boardtrack" position, I pick up a couple mph. Can't peddle that way, though.

 

[E-HP]

If you want to see how the power relationship works, I recommend experimenting with the http://ebikes.ca/tools/simulator.html
with all your various riding conditions.

Speed is determined by a number of things, of which power is only one. The others you can see in the simulator as you experiment with different motors, controllers, batteries, wheel sizes, gearing, etc.

I think of power and torque as outputs and power is an offset to load, and speed is determined by voltage, but can be the influenced by one or all of the others. When I play with the simulator, all other factors being equal, I've concluded that increasing voltage is the single input that when increased, results in an increase in torque and acceleration along the entire curve, in addition to an increase in speed and power. Efficiency suffers a little at equivalent speeds, which is the trade off:
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_52_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=25i&mass=110&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_80_0.05_24&wheel_b=25i&mass_b=110&hp_b=0

You could increase current to as much as the motor can take, and it will smooth out the kinks in the torque, power, and efficiency curves, but has no impact on speed.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_52_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=25i&mass=110&bopen=true&cont_b=cust_400_800_0.03_V&motor_b=Leaf%205T&batt_b=cust_52_0.05_24&wheel_b=25i&mass_b=110&hp_b=0

If you eliminate the load (wind drag, rolling resistance, grade), and keep all else equal, the power needed to overcome the load drops to zero, letting the motor run at the designed speed. None of the curves are affected, just where the top speed intersects.
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_52_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=25i&mass=110&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_52_0.05_24&wheel_b=25i&mass_b=110&hp_b=0&frame_b=cust_0_0&autothrot_b=false&throt_b=100
You can achieve the same speed by leaving the drag and resistance alone and setting the grade to -12.2%, which is a fairly steep descent:
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=cust_52_0.05_24&cont=cust_70_200_0.03_V&hp=0&axis=mph&frame=mountain&autothrot=false&throt=100&grade=0&wheel=25i&mass=110&bopen=true&cont_b=cust_70_200_0.03_V&motor_b=Leaf%205T&batt_b=cust_52_0.05_24&wheel_b=25i&mass_b=110&hp_b=0&frame_b=mountain&autothrot_b=false&throt_b=100&grade_b=-12.2

 

[ZeroEm]

Thx, The half fenders make sense to me now. Cover the high speed part of the wheel.

by classicalgas » Dec 26 2022 9:07pm

Based on the few comparative tests I've seen, a full fat (over 3" wide) tire has almost twice the aerodynamic drag at 20mph that a 2" MTB tire has (given similar tread patterns) It's much easier to find a relatively smooth tread design in a 2" wide tire than a 4" wide one, as well, and tread pattern has an effect on aero drag.

Why worry about tire aero?

The top of your tire is moving twice as fast through the air as the rest of your bike is, and aero drag goes up as a square of speed (2x as fast =4X the drag)

In short, before throwing a bunch of money into more power, look at your aerodynamics.

 

[BalorNG]

Note that 'tire rotating twice as fast' affect *surface* drag/friction drag, while *shape* of the tire (shape drag) is moving against the flow with speed of the bike... not spokes though! Wheel covers/aero spoke wheel can save you considerable watts, but first you want to fair yourself, because rider accounts for 80+% of overall drag, especially if your position on a bike is not that of TT or recumbent bike.

I'll be experimenting with that next year... hopefully.

 

[E-HP]

Note that 'tire rotating twice as fast' affect *surface* drag/friction drag, while *shape* of the tire (shape drag) is moving against the flow with speed of the bike

In this context, is the surface drag still an element of wind drag, or considered an element of rolling resistance/rotational drag?

 

[BalorNG]

Note that 'tire rotating twice as fast' affect *surface* drag/friction drag, while *shape* of the tire (shape drag) is moving against the flow with speed of the bike

In this context, is the surface drag still an element of wind drag, or considered an element of rolling resistance/rotational drag?

Wind drag of course.
Rotational drag is due to very different mechanism (tyre hysteresis and lubrication drag in bearings)
Also, 'surface drag' is also called 'viscous drag' and like all aerodynamic phenomena goes up with square of speed, not linearly, and while drag goes up squared, power to overcome this drag goes up *cubed*.

 

[Bbbbrass]

I'm curious what this community is finding in terms of power and speed.

tl;dr - what do you feel are the speeds a 1000W, 15000W, 2000W and 3000W ebike can achieve on a routine basis.

I'm new and have very limited experience (only 3 E-bikes ever ridden, and only mine more than 2 short rides). That said, I get 48kph out of 1000W. This is a 26 wheel, total load just over 300LBS. Tires are 2 inch knobby. My experience with golf carts and other electric motors is that watts=speed, but you need a good amp & voltage meter to actually see what watts you are pushing.

 

[amberwolf]

My experience with golf carts and other electric motors is that watts=speed,

The relationship is more complicated than that; if you experiment with the http://ebikes.ca/tools/simulator.html using different systems, voltages, controllers, motors, wheel sizes, gearing, etc., you can see how the relationships work.

This was posted early in the thread as well:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=118649&p=1745231#p1743448

but you need a good amp & voltage meter to actually see what watts you are pushing.

A "watt meter", like the many cheap RC wattmeters, or computers like the Cycle Analyst from Grin Tech, or other coulometers, would be easier to see power usage, as they display wattage directly rather than having to do math on voltage and current from separate meters.

(they also measure and display both volts and amps, and usually monitor Vmin, Amax, and sometimes Wmax, all of which are useful in diagnosing problems).

 

[k2orbust]

To add my data points, my recumbent with GMAC hub motor (slow winding, 26 inch wheel, 52V battery) cruises at 50 km/h using about 1200 watts from the battery. If I turn up field weakening in the BaseRunner controller it can sustain 60 km/h on the flat but pulls more like 1800 watts. In practice I don't ride that way because it hurts range and I don't want to wipe out going that fast!