Can I make this mountain bike do 50MPH?

[EdwardNY]

I would like to know if I can convert this mountain bike to an E-bike that can do 50MPH. Bike is aluminum.
I am trying to get an idea at what I am looking at and how much it would cost.

I would like it to hit a top speed of 50MPH. It will be for the street and sometimes going off road through grass or dirt roads.

Can you tell me what motor, batteries, and anything else I would need to do the conversion. I have read alot on the forum but it is hard to know for example what motor (model number) I should get and what exact batteries I should use.

I would like to keep my budget under $2500 if that is possible. Cheaper is better of course.

Thankyou, and if you can recommend parts to use that would be very helpful.

 

[amberwolf]

Can? Sure. You can make anything go as fast as you want if you spend enough money on it.

Should? Poke around ES for the various fast-build threads and read up on those, and you'll get some ideas of limitations and suggestions for components, etc.

 

[EdwardNY]

amberwolf, thanks for the reply. I continue to read old posts but I seem to only find people who want to go max speed 25-30MPH.

 

[icecube57]

Do a fork swap spring swap front and rear disc brakes and a decent torque arm you have potential.

 

[cohberg]

You'll need something in the ball park of >= 24s to get there with a dd hub. Here are some suggestions for rear hub, batteries, and controller. You'll also need torque arms and a big disk up front.

As someone who has done / can currently do 50 on a bike, its not practical or safe. The frames and forks were never designed to go that fast: the smallest pothole and you are going flying.

 

[icecube57]

You'll need something in the ball park of >= 24s to get there with a dd hub. Here are some suggestions for rear hub, batteries, and controller. You'll also need torque arms and a big disk up front.

As someone who has done 50 on a bike, its not practical or safe. The frames and forks were never designed to go that fast: the smallest pothole and you are going flying.

35 is respectable and a good target rather than 50.. 40 tops... Im on 20s Im happy

 

[cohberg]

35 is respectable and a good target rather than 50.. 40 tops... Im on 20s Im happy

Well, its always nice to know that your bike can do 50. There are always going to be those stretches of road (not public of course :wink that you could hit that safely. But yeah, I agree 35-40 is a good first target goal. Heck, you could probably achieve that with the stock 48V controller that that comes with the kit i linked (@ 63V | 15s that is).

 

[amberwolf]

amberwolf, thanks for the reply. I continue to read old posts but I seem to only find people who want to go max speed 25-30MPH.

Perhaps you might want to use the search function with one of the terms you are after:
http://www.endless-sphere.com/forums/search.php?keywords=50MPH
which brings up a number of threads discussing such speeds on a bike, and motors capable of doing it, and/or what it would take to do that kind of speed, energy-wise, etc. (as well as discussions of why it might or might not be a good idea)

There are also a number of bikes (and trikes) built specifically to go much faster than 50MPH, including various race bikes. You can search up the race threads and see what the winners used. (and some of the 2nd/3rd/etc placers were fast enough to meet your goals, too).

It is not quite as easy as "here's the parts lists, bolt 'em on and go".


A few non-electric pointers:

Stopping from those speeds (without destroying the brakes, tires, or wheels, or crashing you) is probably going to require significant upgrades to the bike.

Suspension needed for anything but a perfectly smooth road at those speeds is probably going to cost a pretty penny for bicycle stuff, even used.

Tires that can keep you on the road in anything but a straight line will also be needed.


A few electric pointers:

Power required to get to and maintain such a high speed will be very high. It is many times more power needed to go 50 than 30, and several times more power from 20 to 30, etc. There are online calculators you can use to determine the power levels you will need.

This either means very expensive batteries and a large pack of them, or shorter range (possibly much shorter) with a small pack or cheaper batteries. Cheaper batteries tend to not have the C-rate needed to deliver high power without many parallel cells, which means a larger pack, because you already may need many series cells to get the voltage for such speeds (if you use direct drive).

It also means a motor that can handle that high a power continuously, either as-is or venting or otherwise cooling it enough to sustain this power without damage.

It also means the same for a controller.

 

[Chalo]

You certainly can make that bike go 50mph; I have my doubts about whether you will like doing that enough to make it worth the effort and expense and compromised operation at more normal speed.

If you have any hills on roads near where you live that are especially long and steep, I suggest you go visit one, and see if you can attain 50mph on your bike. Most people find such speed on a bicycle to be enough of a white-knuckle experience that they would not do it in traffic on purpose. If highway speed subjectively feels twice as fast on a motorcycle as in a car, well, it feels about twice as fast on a bicycle as on a motorcycle. Consider for a moment what you'll have at stake if stuff breaks from being pushed so much harder than it was meant to be.

An electric motor will give stronger acceleration at any given watt input if its free speed is lower. So a motor that maxes out at 30 to 35mph will be more spirited for any given battery and controller than a motor that uses the same peak wattage to reach 50mph. And it will run much more efficiently at typical bike/moped speeds.

In the bicycle world, only a dedicated downhill bike with unusually slack angles and relatively long suspension travel, or a motorpace bike (which is unsuitable for e-conversion), will feel well composed at 50mph. A cross-country MTB like yours, or a loaded touring bike, would be passable, but it is outside its intended "flight envelope" at such speed.

You can make your bike behave better at speed by lacing up some very robust wheels with heavy tires for it. The gyroscopic stability of heavy wheels has a steadying effect as speeds climb out of the human power range. And heavy duty wheels are less likely to turn into Pac-Man shapes when you encounter a pothole or piece of road debris at 50mph. Ditch the knobbies unless you are riding on soft dirt, sand, etc.; off-road tires have highly impaired traction and handling qualities on pavement, which becomes a bigger issue the faster you go.

I suggest building your bike up to reach 30 or so mph on 48V, with a controller that can accept at least 72V. Then you can ride it a while and assess whether you really want to go that much faster. All you'll have to change for higher speed will be the battery, though you may decide you also want to change some other things to make the bike safer and more manageable.

Chalo

 

[NeilP]

You'll need something in the ball park of >= 24s to get there with a dd hub. Here are some suggestions for rear hub, batteries, and controller. You'll also need torque arms and a big disk up front.

As someone who has done 50 on a bike, its not practical or safe. The frames and forks were never designed to go that fast: the smallest pothole and you are going flying.

I can often jsut do it with 20s LiPo, 24s LiPo every time.
When people talk of how many series, check the battery chemistry referred to, LiFePO4 will have different voltage at 24 s than liPo, and the more in series you go the greater the difference will be.

My spec is 24s LiPo 20Ah pack with Lyen 18 FET controller, and Xlyte 5304 motor, if you go with a higher windign motor like a 5305 or 5306 you will easily make 50 on 20s or less.

Torque plates or better still clamping axle 'grips ' are better at these levels . I snapped myu axle last month
http://endless-sphere.com/forums/viewtopic.php?f=3&t=40785
see the torque/axle clamps I built

go for hight regen to save the brakes, but that does take it out ont he axle

bigger disks better..180mmpluss

 

[Rodney64]

Yes it will but when doing those speeds you need good brake's. I have just set my 3580 kit up with 24s lipo and will easily do 50 mph but it will only do it for short periods. Today I commuted to work 46 kilometers return (4 22.5 9 amp hour zippys) but to do this trip to and from work you need to pedal so this means 35-40 kmh top speed.

Might be worth looking for a second hand down hill frame with good brakes. Cars pulling out in front of you are the main issue.

Rod

 

[hjns]

50mph ? That's like 80km/h. Yes, you can do it. No, like it is now it wouldn't be safe.

For that speed on the flat, you need indeed around 80V and a nice big DD hubmotor. Cromotor would certainly be powerful enough. Crystalyte X5 and HS models come to mind. Fast wind 9C as well. Anything that can give you 2 to 4kW. Think about $600 for the motor and you can't go wrong.

Same for the controller. You need someting that goes up to 100V (giving a buffer for voltages spikes) and 50A. In that range there is quite some choice. Think about $250 and you will still have money left for stuff like throttle, ebrakes, wires etc.

If you have RC experience, go for Lipo, otherwise stay with LiFePo4. Think big, at 80km/h you are spending a lot of energy (25-30Wh/km) so in order to have any range at all (say 25km) you will need at least 1kWh. That is heavy and expensive. Think $800

Now put that all on the bike as it is, and it goes 80km/h if you accelerate very slowly. If you want to stop, using the current brakes will stop you from that speed in about 100 meters. Better upgrade to large disc brakes. Not necessarily hydraulic, BB7 do just fine. If you want to accelerate a bit harder the axle of the motor will spin out of the dropouts, so you definitely need torque arms on both sides, and even that will probably not be enough. Think of changing the rear swingarm in such a way that you will have real 5mm steel torque plates that grab the axle from at least three sides.

With the first hole in the road, your front fork will bottom out. Probably best to change to a DH fork. Think $600.

Hope this helps. I don't do 50mph usually. Too dangerous. 40mph is a nice topspeed as well, and keeps you in line with the cars in town.

 

[Rodney64]

My bike I purchased it in parts. 600 for marzocchi 888 forks. If you do buy down hill forks they use a 20mm hub so when purchasing your new front wheel keep this in mind. I learnt the hard way buying a 10mm hub first. The problem with disc brakes is that you not only need to buy the brake but a new wheel as well. This is where the cost starts.

 

[Goathead]

Know your bike . . .
Is it prone to "death wobble?" And at what speed?
http://en.wikipedia.org/wiki/Speed_wobble

 

[dogman dan]

Yes, there you hit the actual issue right on the button. Is your bike stiff enough from side to side to avoid a death wobble, or tank slapper.

I have a pair slightly cheaper, but very strong looking bikes that arent. The frame tubes are just too thin walled to have great lateral stiffness. So they get a bit prone to high speed wobble at about 35 mph. I ride the crap out of them in the dirt, at 25 mph with no problemo. But I gave up the idea of making one go really fast. So in the end, your bike is going to have to be evaluated for that by yourself. We can't just look at it and say definitely yes or no for 50 mph. Build it, and see, and if it's sketchy you'll be able to look down and see that frame bending like a noodle as you ride. Then you shop for another bike.

There are a few reasons why the 50 mph club doesn't have that many members. I could claim to be one, but my bike hit 51 mph on a slight downhill, and only got to about 45 mph coming back up the hill on the return run. Not good enough for real membership. My economy build will not sustain that kind of power for long either. If I try to ride it's true speed, 47mph, for very long at all I will surely melt the motor.

50 mph is just simply across the line from the cheap 40 mph club build, and into where you really do need big motors, big controllers, and big budget. $2500 shoud do it if you don't wise up and buy a real custom frame designed for such a bike. The cheap 40 mph club budget is more like $1500 max.

To find the 50 mph club members, one place you find some of them is in the racing threads. Even those not in the USA take interest, then look for thier build threads in pictures section.

Then there are the legal issues. You say you want to ride the street with this. Look up what the fines are in your locality for riding a homemade, uninsured, unregistered motorcycle, then evaluate the attitude of the local cops. Particularly, do they know you? Even hate you? Can you afford the ticket and loss of the bike?

The cheaper 40 mph club bike is your starting point. And in fact, the 25-30 mph bike should be the starting point for most people. I don't know how much riding skill you have, like motorcycle experience, or how good you are at making stuff you'll need like good torque controll devices.

My standard advice is to start out with a fairly cheap, but fastish rear hubmotor kit with a dd motor. 1000w 48v kit from Yescom usa assuming you are in the USA. Get RC lipo batteries from Hobby King, and build yourself a 15s, (63v fully charged) bike with the stock kit and controller. Get your torque plates sorted out. Find out if the frame is stiff. You should hit 30 mph, fairly fast for bicycles, and the limit for safe riding of many.

Then begin to volt up. A 72v 40amp controller is fairly cheap, and a few more lipos not expensive. Now you are in the 40 mph club. It might be plenty. Remember, you are still on bicycle tires. My 47mph bike can wear out tire in one day on the racetrack. You might be happy enough at that speed on that bike. Then you can make the decisions that cost real money. The $1000 or so you have left can buy a hubzilla/ cromotor. But at the point you go cromotor, you should be thinking of much stronger frames than a typical bicycle. You might be ready to go fully custom at that point, with small rear wheels running scooter tires or moped tires. You'll need an even higher voltage controller that costs a lot more, and the battery just keeps getting bigger, heavier, harder to carry and more expensive. From 40 mph to 50 mph, it really starts to cost for every mph more.

Bottom line, 50 mph club on purely "bike stuff" is really pushing it. You start doing things like twisting your axle into two pieces, melting smaller motors, having tires wear out from heat from the inside rather than tread wear.

So try the much cheaper 40 mph club build first is my advice.

 

[Goathead]

Done the "death wobble" bit at 50+ on a bicycle . . . Wouldn't wish it on an enemy . . . VERY frightening.

Sustained 50 MPH will also require a much bigger battery than one might think . . . air resistance is what it's all about from about 18 MPH on up. And that resistance increases to the square of speed, -- as does the kinetic energy which you must dissipate to come to a halt, whether by braking or some other way . . .

That all being said, think big . . .
http://www.bloodhoundssc.com/car.cfm

 

[MadRhino]

If you have the balls, just ride it at that target speed on a downhill road. You will understand why this bike is not suitable for this kind of performance. You could upgrade the components to make it ride better at that speed, but it is not stiff enough to ride good with the added weight and torque of a powerful motorization.

Start with a good bike if you plan that kind of speed. Used downhill racing frames can be found for a good price off season. Even starting with the best bikes, one need to build strong and buy high end components to make an Ebike that is safe to ride that speed.

 

[mvly]

50mph safely on only $2500... probably not. No offense, but your bike does not look like it can take 50mph. It is better to over engineer in this case just to be safe.

1) Get big motor (Cromotor, x54, or HS). HS3548 is only good at 50mph for a short burst. My HS3545 takes a long time to get to 50mph on flats w/o head wind or backwind.
2) Get a good torque arm. Your current bike's dropout will not do.
3) Make sure you get rear drive. Please none of those front motor crap
4) Go Lipo if you want to save money. And make sure your bike is balance. i.e. battery should be in the triangle area
5) Get some good tires. Maxxis Hookworm, Big Apple, or Crazy Bob
6) Get some good rims and 12G spokes build for your motor.
7) Get a good controller. Lyen 18FET 4110 is minimum. Some would say 12FET with beefed up traces will do, but you are just killing your controller.
8) You will need at least 74V or more if you want to get to 50mph and sustain it.100V is ideal to keep current low. And if you are using the cromotor, you will need 100V.
9) You will need disc brakes at minimum. Preferably 203mm rotors just incase.
10) You better have a decent Front/rear Shocks. And yes you will need Full Suspension, but your bike is already Full Suspension. Just beef it up a bit.
11) Get yourself some motorcycle jacket and motorcycle helmet.

12) Know what you are getting yourself into.

If you build an ebike for 50mph, you should really use it up to 40 or 45mph at most. If you really want to go 50mph, then build one that will go 55mph or 60mph.

So I take it you are really aiming for 40-45mph max.

 

[HumboldtRc]

It's funny reading this thread when I'm working on making my next 4wd mountainboard go 50mph+ probalbly closer to 60mph. That last mountainboard I built goes 40mph, and I built it for Laird Hamilton (the pro big wave suffer). He must already be used to 40mph, now he wants one that can do 50mph+!!!! It is going to be insane!

 

[John in CR]

All of my ebikes will do 50 or more, and my latest does 65mph on the highway with a fresh charge with voltage sagging to 75V. My first ebike only did 30mph and it felt the least safe at speed of all my bikes. For me at least, a normal upright bike just doesn't feel right at high speed due to the short wheelbase and high center of gravity. The only stock bike I would feel comfortable riding at 50 or more would be a downhill or freeride bike. They're made stronger to take big impacts and their geometry is set up with a more slack head angle for more stability at speed and to be able get your COG lower and more rearward for heading downhill at speed.

I'm heavy at 250lbs, so even a stock DH bike isn't enough for me, so I customize my bikes to give them a longer wheelbase and lower saddle. Here are some of them to see what I mean:

This is my primary ride right now, which feels just fine at 65mph, though I rarely exceed 50-55, because it's just too windy
View attachment 2

I've had my nearly 4 year old cargo bike, Blue, up to right at 60mph on a long stretch of highway a couple of times


LFP had this bike, Red, up to 61mph when he was down 2.5 years ago

 

[Chalo]

It's funny reading this thread when I'm working on making my next 4wd mountainboard go 50mph+ probalbly closer to 60mph.

Russian roulette seems more stylish, and doesn't take as many people to clean up afterwards.

 

[el_walto]

Have you ridden a bike at 50mph? I'd highly suggest you keep your max speed under 30mph. Have you ridden a bicycle at 30mph? I wouldn't push it any faster than that on bicycle tires.

 

[Chalo]

bigger disks better..180mmpluss

The disks he's got now are over 560mm, and heavy enough to soak up a bunch more heat, and made of a material with more heat capacity and conductivity and higher wet friction coefficient than stainless steel, and strong enough to get bumped on things without getting bent beyond repair. I'd say all he needs is careful setup and a good set of pads.

Chalo

 

[Punx0r]

A lack of castor on the front wheel does seem an issue. I notice at 30mph on my cheapo bike if I take one hand off the bars, they start to oscillate gently (thankfully not in an increasing way).

I guess you could mod the front dropouts to increase castor and/or add a steering damper, but it seems like a band-aid solution.

Is there not inherent lateral frame flex in rear suspension bikes, on account of the pivots?

 

[Punx0r]

The disks he's got now are over 560mm, and heavy enough to soak up a bunch more heat, and made of a material with more heat capacity and conductivity and higher wet friction coefficient than stainless steel, and strong enough to get bumped on things without getting bent beyond repair. I'd say all he needs is careful setup and a good set of pads.

Chalo

Now, I've attempted to stop from 50mph using rubber rim brakes, so I don't want to say it's impossible. However, I'm not convinced.

You don't see many cars/motorcycles/aircraft/trucks etc using cable-operated rubber brake pads. Rim brakes need pads with a high coefficient of friction because they have feck all clamping force. And they still don't work if wet, or if they've melted.

I certainly appreciate the argument that good rim brakes beat shite mechanical disc brakes (I've experienced it), but I don't see how this is relevant here.