48V vs 72V

Hi!
I'm allready feeling that my 48v battery is not going to last that long for me, i have an obsession with going faster and faster.
Currently looking into upgrading to 72v battery and controller.
(my rear DD hub will take 72v with no problem)

You guys that have swapped from 48 to 72, how much more top end speed and acceleration did you guys get?
Is it worth it?
I live on the country side with long straight roads that my current top speed of 50km/h with (80-90% battery) isnt enough ;/


best regards

Hello there,

this sounds like a job for the Grin motor simulator. (just find a motor that closely matches yours):
http://www.ebikes.ca/tools/simulator.html

Potentially the hub and wires can run 33% cooler at 72v . make sure you invest in regen braking these days it's very simple it just requires an ebrakes and a regen controller and it's safer and cheaper than regular brakes.

A motor's speed is directly related to the input voltage. So if you get 50kph from a 48 volt battery, you can say you get 1.041666 kph per volt. So figuring out your speed after increasing the voltage is simple math.

50kph / 48volts = 1.04666 kph/v
72 volts X 1.04666 kph/v = 75 kph

or even more simple,
72v is 50% more than 48v, so your speed will be 50% more.
50kph X 1.5 = 75kph


That's in theory, In reality, motor speed is linear, wind resistance is not. Expect wind resistance to take a bite out of that 75kph. Figuring that out needs more info than we have here, but you should be able to hit 65 to 70kph.

If you keep the amp limit the same, then the power difference will be be the same 50% more, same as the speed. It will accelerate with 50% more torque.

Great info!

Yeah if im able to hit 60-65kph i will be a happy man.

Right now im able to ride a whole week to work without charging. and i have a 48v-12,5ah battery.
And when im charging im charging at work on fridays.

so i guess that a 72v with 17-20ah shuld be enough for my application, maybe 25ah

No, 72 volts is way too fast for an ebike in my opinion. You risk a lot by going that fast. 48V is the max and is far safer.

Its not a linear relationship, because of increased wind resistance at higher speeds. 75% more volts will result in roughly 75% more RPMs when the wheel is unloaded (held up in the air), but on the road it might be 40% more speed.

Above 30-MPH, aero mods can have a significant effect on top speed and battery efficiency...

Yes, go 72 volts. Ignore the person above who says it's dangerous. How dangerous it is depends on your skills, vigilance, protective gear, and the mechanical condition of your bike as well as your awareness of that mechanical condition. In other words it's highly variable and if you understand the risk and think you're good for it then get going!

And it depends on the winding if your motor... Sometimes it takes 72v to get a slow motor to spin up to a respectable rpm.

But it you have a janky conversion of a terrible to start with POS bike, with a battery high on a rear rack, and a flimsy fake suspension fork with mushy brakes, then any decent speed will seem unsafe.

The frames of bicycles weren't designed to hit potholes at 30+ mph. That's just too fast for an ebike. Should you get in an accident and be injured, your insurance might not cover you.

There is a kernel of truth in what Lester says. But its not a one answer fits everybody thing.

Typically, a 72v 40 amps bump up from 48v 20-25 amps, will get you into the 40 mph club. You gotta up your amps along with your volts, to overcome that wind resistance. 3000w can get you 40 mph. Upping the amps can be very hard on your battery, so plan on higher discharge rates, rather than bargain basement cells.

Hooning around the streets of most cities at 40 mph, with bike tires and average brakes is dangerous. Lester is dead on right about that.

Starts with no car expects you are going 40 mph, so getting crossed by a car pulling into your path increases exponentially. Then, there you are, going 40 mph into some steel, with inadequate brakes, and even if you got great brakes, your contact patch is still a third the size of a motorcycle. Yer screwed. Grabbing brakes won't help a bit, so you better be good at skidded turns, typically diving to the curb and doing some nice starfishing on concrete sidewalk. Calls for good body armor. You can also just find yourself with the wrong wheel off the ground, hitting manhole cover bumps or potholes on no suspension bikes at 40 mph. Can you do a 40 mph stoppie? Maybe you can, but most cannot.

That's all pretty grim. But on the other hand,, having 40 mph capability does not mean you are inexperienced enough to think you can ride around like that ( always at 40 mph) safely in a city.

So it all depends,, on your riding skill level, on your traffic, and your common sense not to become another lemming on a two wheeled vehicle.

Using the speed and power to cross busy streets and intersections quickly and safely is priceless. But if you need more than 1000w or so to do that, time to find safer routes around your city, or just be more patient about getting across those big streets. 1000w gets you same acceleration across an intersection as cars. But leaving them behind can be a safe way to get through that nasty left turn on a big intersection too.

Raising the voltage generally makes the throttle more "touchy" and difficult to control at low speeds. This makes the bike "jerky" and harder to ride. This depends on the controller, torque type throttles are better, but most controllers don't have those. This leads to a more difficult to control bike that really wants to accelerate hard and go fast. Test rides with inexperienced riders often result in crashes. It may seem funny but these accidents can cause serious injuries and damage. Take care.

1500W is only 33% more jerky than 1000W. it's not voltage related, it's the bms and controller watts output.

It would be good to have a turbo switch on the throttle for easier control, a couple of diodes on the voltage feedback controlled by 1-2 switches can easily make a throttle with 2-3 power levels. with IC's that would be an object the size of a coin that you can place beside the throttle and send the throttle output through it.

lester12483 said:

The frames of bicycles weren't designed to hit potholes at 30+ mph. That's just too fast for an ebike. Should you get in an accident and be injured, your insurance might not cover you.

Click to expand...

If your conversion is done on a beefy downhill bike, then yes, it is designed to hit potholes (and rocks and logs and jumps) at 30+. But its def not for everybodys frame or reflexes.

Plus, the OP is out on long straight country roads.... so city potholes and traffic seem like less of an issue.

Motor: Magic pie2 (internal controller)
Battery: 16S Lifepo4 (52V)
Speed tailwind: ~45km/h
Power: ~1000W

Upgrade to external Lyen 12fet controller
Added 3-speed switch so no no jerky at slow rides.
Battery: 22S Lion (79V)
Speed without wind 60km/h
Speed tailwind 74km/h
Power: 2700W (Programmed Lyen 32A limited)

Voltron said:

lester12483 said:

The frames of bicycles weren't designed to hit potholes at 30+ mph. That's just too fast for an ebike. Should you get in an accident and be injured, your insurance might not cover you.

Click to expand...

If your conversion is done on a beefy downhill bike, then yes, it is designed to hit potholes (and rocks and logs and jumps) at 30+. But its def not for everybodys frame or reflexes.

Plus, the OP is out on long straight country roads.... so city potholes and traffic seem like less of an issue.

Click to expand...

Country potholes are worse but less frequent.
Do not go that speed on a Walmart bicycle, buy a good brand name bicycle, full suspension downhill is perfect.

30 mph is a piece of cake for basically any bicycle out there. Those are human power speeds (in a sprint) for anyone reasonably athletic. Just know how long it takes to stop. You shouldn't be hitting obstacles unaware either, so idk why people are going on about massive potholes. If you can't swerve to avoid a pothole at 30 you're either not paying attention or you're not in control of the bike.

zzoing said:

Potentially the hub and wires can run 33% cooler at 72v . make sure you invest in regen braking these days it's very simple it just requires an ebrakes and a regen controller and it's safer and cheaper than regular brakes.

Click to expand...

A commonly shared misconception, including by myself years ago, but the motor actually ends up with exactly the same average current in the winding for any given power and speed. When operating from a higher voltage battery it just means the mosfet is switched on for a shorter period to ramp up the current in the motors winding Inductance before it switches off and let's the current and field flyback into the body diode to complete the buck converter circuit enabling the phase current to be identical despite initial starting pack voltages being different.

Easy to avoid a pothole at 30 mph that you see. If you don't see it, the bike should handle it with minimal damage at 30 mph or less. Riding at night, slow down is good. Even at 30 mph, cars will think you are going 15, and pull out in front of you. with some riding skill, ( or maybe just practice crashing) the 30 mph crash is much more comfy than the 40 mph + one.

Re the twitchy throttle.

Bumping to 72v 40 amps does make it much harder to control the bike at very low speeds. Meaning like, 5 mph through the crowded sidewalk place. A park, boardwalk, flea market, etc. But its fine for typical street riding, where you won't want 5 mph much, you want 20 mph much quicker. Three speed switches can help solve that.

But IMO, once you go to 5000w or more, then yeah,, its not only twitchy throttle, but sometimes just hard to keep the front wheel on the ground so you can steer at all. Above the 40 mph mark, its going to be much more like riding a motorcycle, and you will need or at least want that motorcycle stuff, stout brakes, bigger and stronger tires, body armor, etc.

But I do think its quite possible to safely ride a 3000w bike, 72v 40 amps, in a city. Possible, but maybe not likely. :wink: It depends on your ability to control yourself. FWIW, I gave up motorcycles for decades, because I had repeatedly proven I could not control my throttle hand.. I was in deep shit for a time, getting tickets for 90 mph in a 25 zone, and such. So think about your ability to ride safe, before you go to the 40 mph club.

Isak.svensson said:

Great info!

Yeah if im able to hit 60-65kph i will be a happy man.

Right now im able to ride a whole week to work without charging. and i have a 48v-12,5ah battery.
And when im charging im charging at work on fridays.

so i guess that a 72v with 17-20ah shuld be enough for my application, maybe 25ah

Click to expand...

I have built a qulbix with QS205 and cycle analyst setup
under the CA settings i restricted to 2000 watts and i reached real 60 kph.. with 3000 watt 70kph in Forest.

The thing is that im not going to ride in my Town nor at busy streets.
I just want to get from A to B a bit quicker wich is mostly on a contry dirt road. I have to cross a intersection but i have to stop there and wait for the cars to pass.
I hear all of you guys arguments about that is exponentially more dangerus to be going 65-70kph than 50-55kph that im going now. For protection i have helmet, glasses and gloves.

I have a hardtail mtb with 203mm discbrakes allround. Really nice bike with good components. 3500$ bike new. The bike i have no worries nor disbelife in.

My plan was a 72v battery 40amps. And a Kelly controller.
That would be plenty.

But now when i am reading all you guys experienced talk im now in a status quo..

Don't bother. Your target performance is low by the standards of many of us on ES.

I believe that performance is a factor of safety, if the bike and rider are good to handle it. I personnally, had not been passed by any car in years, and would never go back to the time when cars were passing me without any care many times a day. Build the performance that you like to ride, and use adequate frame/components that are suitable to make it safe to ride that performance.

MadRhino said:

I believe that performance is a factor of safety,

Click to expand...

I really couldn't agree more. If you're going to ride the bike on the street, it is HUGELY safer to be able to keep pace with or stay ahead of traffic vs doing "bicycle speeds" and having everyone blow by you. Even if there's a bike lane it's still really sketchy going slow.

MadRhino said:

Don't bother. Your target performance is low by the standards of many of us on ES.

I believe that performance is a factor of safety, if the bike and rider are good to handle it. I personnally, had not been passed by any car in years, and would never go back to the time when cars were passing me without any care many times a day. Build the performance that you like to ride, and use adequate frame/components that are suitable to make it safe to ride that performance.

Click to expand...

So you are basically saying that with a cartine performance that in a situation say keeping up with a car, that is doing 30mph or 40mph. If needed to do 40mph is a 72v battery to keep up with the trafic you therefore should buy a 72v battery and the components to go that speed? ( sorry for my English btw)

But in my case i dont need to keep up with trafic, i just want to go faster and get more Power up some hills i have. But the safety factor in my case is the bikes capacity and my own skill basicly.

To be real, and honest. My bike in the current state is doing this job without any issues or problems.
But im a tuner, I have always tuned my cars and mopeds/ Motobikes and want to explore the World in Electric bikes. That the main reason i want to do this uppgrade.
Also i dont want to get hurt or injured during it. Its a hard decision.

I just want to thank every singel one of you guys that has provided me with great info!

The better you tell us how you ride, the better our advice can fit your needs.

Go for 72v 40 amps for sure. You can ride to razor edge of your skill level and the bikes capability on dirt, and come up bruised but laughing from any crash. You will soon memorize that part of the trail/ road you can't do full speed on. As you crash, or nearly crash on the first trips, you will know the route and what speed to ride even at night. You are going to have some real fun now.

We just see the opposite quite a bit here over the years. Guy rode a bike 15 mph as a child, coasted faster a few hills but did not live in mountains, and never owned a motorcycle.

Now he builds a 30+ mph bicycle for city riding, and in a week or two, he's in the hospital. Often as not, a car gets in the way, brakes get locked up, and nothing much happens till he hits the steel. Very common till you get used to riding in traffic at speeds nobody thinks you can go. Riding an e bike 30-40 mph in the city takes more concentration than flying. The other aircraft are not trying to kill you so hard when flying.

Off road though,, let it rip to your personal limits. Same as if you owned a dirt motorcycle.