Does speed effect range?

[e-bike mike]

Volts X Amps = Watts. Watts is a measure of work. To move a bike with rider from point A to point B requires a certain amount of work, which could be expressed as X Watts. Since the only real variable in going from A to B at different speeds is increased air resistance as speed increases, will going slower significantly increase range? Let me explain, I know that a gasoline engined bike's gas mileage can be incresed significantly by going slower. Is this also true with an electric bike, or is it simply a matter of work regardless of speed?

 

[Ypedal]

speed above 30 kph has a great effect on range... absolutely...

I can take my A2B metro to work at 30 kph . aprox 5 kms, and use 1.5 ah ( 36v ) = 54wh

If i use my 100v BMX going 65 ~ 70 kph and burn thru 2ah at 100v = 200 wh ! :wink:

 

[ZOMGVTEK]

Yes. The impact is extremely significant.

The slowest speed your can go, is often the most efficient.

 

[Miles]

Since the only real variable in going from A to B at different speeds is increased air resistance as speed increases, will going slower significantly increase range?

Air resistance increases by the square of the speed. That's the problem - it's nothing to do with propulsion method....

 

[dogman dan]

Some real world range data. Includes pedaling, but not much more than 50-100w of human effort. Includes riding in all 4 directions, and up and down hills, to get an average range. 48v 15 ah lifepo4 battery.

30 mph range 20 miles 1000 to 1200w

25 mph range 23 miles 600-800w

20 mph range 30miles 400-600w

15 mph range 39 miles. 150-300w

By 15 mph, the pedaling effort is propotionally more. So 100w added to 200w is a lot more added human power. So the range really jumps at the slowest speeds. You can pedal 10 mph for 100w or less.

 

[Sacman]

You mean Watt-hours not just Watts right Dogman? :wink:
Those power consumptions sound pretty resonable.

 

[amberwolf]

I'm pretty sure those would just be plain Watts.

 

[JennyB]

Air resistance increases by the square of the speed. That's the problem - it's nothing to do with propulsion method....

Actually, air resistance increases by the cube of the speed, so to go twice as fast you use eight times the power for half the time, so energy expended overcoming air resistance increases by the square of the speed.

i'm wondering though - if you are happy to maintain an average of say 20 mph for a long hilly ride, is it actually more economical to ride an ebike powerful enough to let you get close to that on the long climbs, because it means you don't have to ride so fast elsewhere to make up the time. any real-world figures on that? :?

 

[Miles]

Air resistance increases by the square of the speed. That's the problem - it's nothing to do with propulsion method....

Actually, air resistance increases by the cube of the speed, so to go twice as fast you use eight times the power for half the time, so energy expended overcoming air resistance increases by the square of the speed.

Nope. Air resistance (as in drag) increases by the square of the velocity. The power to overcome it increases by the cube because your going twice as fast... Anyway, as we both agree, energy expended overcoming air resistance per distance travelled goes up by the square, so that's the determinant for range

 

[Sacman]

Now that I think about it, Dogman was relating speed with rate of power consumption so Watts is right. I stand corrected... thanks AW.

Volts X Amps = Watts. Watts is a measure of work. To move a bike with rider from point A to point B requires a certain amount of work, which could be expressed as X Watts.

It's been a while since I've been in college but I'm sure I still remember the Physics pretty well.
Watts is NOT a measure of work...
Watts is an instantaneous RATE of work being expended. (look it up in Google or WikiPedia)

To answer your questions...
Does speed effect range? YES
Will going slower significantly increase range? YES

But it looks like you definitely understood that air resistance has a lot to do with it. And as Miles explained it's a resistance that grows exponentially the faster you go. So you'll need to expend more power at a higer RATE to overcome that resistance. And finally Dogman gave his real data of power consumption rates (in Watts) that you need to expend at the different speeds.

Now since you only have a finite amount of energy stored in your battery. The less energy you waste on overcoming wind resistance ... the more useable energy you have to travel farther.

 

[JennyB]

Nope. Air resistance (as in drag) increases by the square of the velocity. The power to overcome it increases by the cube because your going twice as fast... Anyway, as we both agree, energy expended overcoming air resistance per distance travelled goes up by the square, so that's the determinant for range

I stand corrected, but I'm still interested in figures relating to the other question.

I'm wondering though - if you are happy to maintain an average of say 20 mph for a long hilly ride, is it actually more economical to ride an ebike powerful enough to let you get close to that on the long climbs, because it means you don't have to ride so fast elsewhere to make up the time. Any real-world figures on that? :?

 

[Miles]

I'm wondering though - if you are happy to maintain an average of say 20 mph for a long hilly ride, is it actually more economical to ride an ebike powerful enough to let you get close to that on the long climbs, because it means you don't have to ride so fast elsewhere to make up the time. Any real-world figures on that? :?

I'd say so. It's usually better to maintain an average speed by having the ability to increase the speed of the height change component. Rather a lot of variables, though...

 

[Ypedal]

Now since you only have a finite amount of energy stored in your battery. The less energy you waste on overcoming wind resistance ... the more useable energy you have to travel farther.

On the flip side, if you have a known amount of energy to use, and know how far you need to go, making use of as much energy as you can in the shortest amount of time = bigger ev gin !

 

[miro13car]

Sacman,
I was just about to post about Watts NOT being measure of work when I saw your post.
It seems there is misunderstanding of power versus energy on this forum when.
From time to time I read about somebody clearly confusing energy with power.
Power is a rate at which energy is converted from one form to other,
Like in electric motor where electric energy is converted to mechanical energy.
Did you see those posts about motor "producing " Watts?
How people got that ideas?

 

[Ypedal]

Has everyone missed my wh claim?

 

[dogman dan]

I just wasn't suprised by it. I've seen 100wh/mi on my CA. But that wasn't speed, it was a wicked hill.

Yeah, I was trying to show how the typical watts used at higher speeds just takes off.

All those numbers were from the same 48v 15 ah ping. Somewhere around 900 wh in it.

 

[sangesf]

Volts X Amps = Watts. Watts is a measure of work. To move a bike with rider from point A to point B requires a certain amount of work, which could be expressed as X Watts. Since the only real variable in going from A to B at different speeds is increased air resistance as speed increases, will going slower significantly increase range? Let me explain, I know that a gasoline engined bike's gas mileage can be incresed significantly by going slower. Is this also true with an electric bike, or is it simply a matter of work regardless of speed?

It depends on the speed...

If you're talking the difference between 16mph and 10mph, then not much of an effect..
If you're talking 20 to 16mph, a tiny bit more....
If you're talking 25-30 to sub 20mph, then quite a bit.
If you're talking 30+ and sub 20 then A LOT!

From real world experience, I know using a dual 36v 15a controller/motor setup (dual 36 25ah batts) if I average 20mph I get 80+ miles.. If I average 18mph I get about 90.. If I average 16mph, then I get 100+.

These figures go down about 10-20% if I have a slight wind against you and over 30% if I have a good wind against you.
(As Is the 'vice versa' holds true as well - as I've gone 116 miles with wind behind me and averaging between 18-20mph)

I've also ran numbers using a 48v 35Ah (similar WH and 48v 20a controller) battery averaging 25mph and only getting 60 miles.

 

[John in CR]

"Does speed effect range?"

Yes, but not as much as the physics of wind resistance would dictate. That's because our systems typically will run more efficiently at higher rpm.

 

[dogman dan]

That's true, and why I don't have data for less than 15 mph. It seemed like it was dumb to go any slower with a hubmotor that wants to go 25 mph.

But the efficeincy at 3/4 throttle gained by less wind resistance is worth it, if you are trying to get home on a pack with less charge than normal. Below half throttle, you really may be entering an area where you may be getting a bit more, but it may not be worth it to go quite that slow.

Sure, 80 mile range vs 100 mile range, but either one is a dang long day in the saddle. 100 miles at 16 mph. Not if I can charge a few hours at 50 miles. Rather ride 4-5 hours and charge for two than ride for 8 hours.

 

[docnjoj]

This is why Velos with good streamlining are really efficient at speed, but they suck going up hills because of the extra weight of the shell.
otherDoc

 

[dogman dan]

Right, and even just a normal recumbent bike tends to get much better wh/mi, at the same speed.

All my data is from the worst possible areo, sitting up straight, panniers hanging out, coat a flapping. Speed really hammers an upright bike covered in cargo bags.

 

[Kingfish]

In Brief:

• Most common ebikes can manage 20-25 mph, and wind (drag) created by this speed does not have a significant effect unless you are going cross-county. Aerodynamics on the bike has some effect.
• Generally speaking it takes about 50% more power to go from 24 mpg to 32 mph, and at that speed wind/drag is significant for ebikes. Aerodynamics has a much larger effect on distance.
• It takes roughly 50% more power to go from 32 to 40 mph. Aerodynamic styling is required to reduce noise, improve performance, and stay warm/dry in nasty weather.

That given, external factors such as wind (beyond that created by travel), road conditions, and grade all contribute to limiting or extending distance over time. Good planning and well-thought faring design can make the most of the potential. On my road trip last summer heading north along the coast I figured out that the headwinds picked up about Noon, so I made a point to get up before dawn and got on down the road before it sapped my potential.

I frequently calculate Power (P) as:

• P = τ ω; Torque * Angular Velocity, or as
  P = IV; Current (Amps) * Volts.

In this context Power is typically measured in Horsepower with the former, and in Watts for the latter; for Electrical Power it is preferred to measure it in Watts or kW.

The mistake I often make (as I am reminded by the vigilant) is mixing my Watts with Watt-Hours.

Though I consider myself smart (arsed), I am indelibly flawed & quite human just the same…
~KF

 

[sangesf]

I'll have to run a real world test tomorrow..
I usually average around the 20mph mark (18mph min-23mph max) and get to my favorite Starbucks (10.2 miles away) in about 45-50 min given stop lights, etc.
The other day, I pulled WOT the entire way averaging 25mph (23mph min-27.8mph max) and got there in 30 min...

I didn't think to record m/Ah or WH/m, but guess what I'm gonna do tomorrow..

(I know it's not quite the same, but I'll see if the extra speed along with more wind makes a difference...)

I'm curious to know if going slower (hence taking more time and more time = more WHs) is better than going faster (Hence less time, but more Watts)

 

[dogman dan]

Faster is better of course, if your battery will last. Slower is better, if it means you make it there.

Somewhere in between is my favorite speed, around 20 mph. Allows me to enjoy the view, which is at least half the point of riding in the first place. At 30 mph, I'm just looking at asphalt, trying to spot a broken bottle in time.

 

[migueralliart]

I'll have to run a real world test tomorrow..
I usually average around the 20mph mark (18mph min-23mph max) and get to my favorite Starbucks (10.2 miles away)

Is this the Starbucks that's right off the I-95 (okeechobee)?