Planning first ebike. Need some advice

Dougt

100 mW
Joined
Nov 23, 2014
Messages
48
Location
San Diego, CA (& Wash DC area)
Hi Everyone,

Planning my first ebike build. Been reading these forums for a month now, and I'm sure some of the answers are already here somewhere, but some are a matter of opinion based on experience and goals, so I would like feedback that takes my goals and build concept into account.

A) My background: Engineer with good electrical and mech. skills. Access to test equipment, tools, friends w/ nuke/aerospace cert tech welder & some machinists. Used to road bike 7000+ miles a year and race cross country mt bike, so have decent bike handling skills and in-traffic experience. Have gone over 50 mph on steep road downhills many times (full tuck). No motorcycle experience. Enjoy building stuff, hate repairing stuff. Would rather build my own ebike than buy a used Stealth Bomber or such

B) My goals:
1)budget about $4k (USD). Quality build, but not insane. aka Strong, safe, reliable. Can spend more if needed, but thats my target
2) Usage: 95% road / 5% dirt. Dirt only hard pack trail to cut between roads, maybe pop a curb or two at low speed. No jumping, but should be able to survive average pothole at 40mph. My body is too beat up to do any serious off road stuff anymore,

3) desired performance
i) 40+ mph capable (for a few minutes for fun), most time at 25 mph.
ii) acceleration: don't care much, as long as it doesnt overheat getting to top speed
iii) capable of mild 6% grades for 1 mile before overheating. Very short (100 meter) 9% grade. Any speed
iv) range 18 miles at 25 mph
v) battery to last 800-1000+ cycles

4) practicality
i) charging simple...no separating or removing pack to charge or balance. 4 hrs ok.
ii) doesnt scream ebike to casual observers from distance. Don't want cops to take interest

C) my concept
1) frame: ??? havent decided between hard tail, FS, or rigid. road use means dont need suspension - cost savings? strength? safety? availability? Seems most ebike frames are FS and expensive ($1500).
i) front shock ?, strong with good tire clearance. Since road use, big travel not needed.
ii) brakes 203mm hrdraulic with E-cutout, front and rear. Tektro Dorado. Stopping really important to me.

2) motor: crystalyte fast wind (40100) or cromotor. Allows for future upgrades, rather do it right the first time. drawback wide...need special frame. torque with big dia tires a problem?

3) wheels:
i)rims 21" motorcycle. Strong, and want MC tires so no flats. Equiv tire diam to 26" mt tires?
ii) tires: prob Shinko 244 Dual Sport Front - Rear Tire - 2.75-21
ii) front hub ????

4) battery:
i) 20s 72v 20 ah. havents decided on chemistry. will make pack myself. have spot welder.
ii) charger: use two 10s balance chargers in series. (iCharger 1010b+) Use isolation power supplies on each to allow this. rewire/upgrade to custom coonectors for simplicity and idiot proofing.
iii) bms: none? need one if balance charge every time? will fuse battery.

5) controller: 60a? 72v? 80v?

6) gears: single speed ok. only plan to pedal in emergencies or for appearances sake. Prob geared to pedal 70rpm at 15 mph.

D) Questions:

1) frame...front suspention only ok or asking for trouble at high speed? any ebike frames with good triangle battery capacity? or use DH frame, but I prefer the clean look, assembly convenience, and added strength of ebike frames though. I'd prefer not to spend $1500 on a frame, $450 on a front fork and $350 on a rear shock for on-road use seems overkill and wasteful. I definitely want to put batteries in the triangle - no racks. maybe the E-kross frame with cheaper suspension components? opinions?

2) suspension:
a)fork: inexpensive, low travel, but strong and clear 3" wide tire + brake? suggestions? used ok. suggestions?
b) rear shock/spring (if full susp): again don't need much travel for road use. Suggestions?

3) batteries: suggestion for cells to build 72v20ah that can source 3C without sacrificing cycle life. Desire 700-1000 cycle life.
a) I'm thinking the panasonic NCR18650PF in 20S8P. They are 10 amp each and good cycle life...expensive though.
b) I see cells for half the price on alibaba, but are they likely fakes? suggestions for reliable sourcing?
c) i assume I can use two 10S iChargers in series if I run them off isolated powr supplies, but not sure if motor controller truly looks like open cicuit during charging. Anyone done this? (I will have beefy wires for each bank, esp the first and last, and charging at 8 amps is plenty fast for me.

4) Controller: handle 60amps, 72V. suggestions? dont need regen, but may want flux weakening if not much cost added (20% more $ ok).
a) its not clear to me that a controller will limit its current to its current or temp rating. - adjustable? How do I make sure I don't blow up my controller? suggestions for sources?

5) motors...ok the ones I've speced are overkill and restrict frame selection, but I rather start with more in case I want to upgrade.

6) wheels: Will lace myself for proper dishing. The 21" MC rims have same tire diam as 26" MB. I know people frown on large diameter wheels, but I don't care about big acceleration and prefer the front wheel stays on the ground. And I think normal sized tires will draw less cop attention. Contrary to what ive read, frame stress should be the same, because if you motor puts out 150 n-m peak torque, then it doesnt matter how far away the reaction force (tire/ground interface) is, the frame or torque arm will see 150 n-m. A bigger wheel means the bike will accelerate slower, and the motor need to work harder for the same lower speeds or on hills...right? The eBike similator says I can do my combo. comments?
a) BTW I love the similator, but wish it had a feature that showed the total heat deposited into the motor and/or contoller to get to a certain speed. Since the simulator says I can be at max throttle at max speed (41 mph) for 40 minutes before overheat, then that implies that I should have no prob getting up to max speed as long as I dont go full throttle at <5 mph.

I know there are many more components, but those seem to be the major ones.

Thanks in advance for any guidance,

-Doug
 
You're looking for higher speed than I have. Went with the BBS02 but I'll probably do a hub motor next year for fun. Mine does 18-20 mph up hills and 30 mph on downward slopes. That's fast enough for me in City streets.

Went with 29er store bike with front shocks and hard tail. For suspension (rear end comfort), I added a Suntour NCX SP-12 seat post suspension. Boy does that make a difference on city streets [youtube]HFEeC1dkzbc[/youtube]

Having a soft tail eats up energy and if you're doing a hub motor, the unsprung weight is a LOT higher than without the hub.

Got the battery from Paul at EM3EV.com. He's a good resource and they are less expensive if you can wait for the build/ship time.

Haven't had any stability issues at higher speeds with the bicycle front suspension (used to be a Flying Qualities Engineer).

Good luck with the build
 
Don't build a bike for 40 mph unless you want to ride that fast regularly. Just ride a regular bike down a hill for occasional jollies. This is not internal combustion power we're talking about; surplus power isn't just there for the taking. You have to spec the whole system to provide it.

As an engineer, you understand that going 40 mph packs more than 2-1/2 times as much kinetic energy as going 25 mph, and the power required to sustain those speeds is probably a bigger ratio than that (though subject to variation in the motor's efficiency curve). Every extra watt of motor and controller and every watt-hour of battery comes with tradeoffs-- weight, packaging, effects on handling, reliability, wear, cost, etc. I suggest not trading off enough of your bike's virtues to get 40 mph if you won't often be riding that fast.

With your budget, you might be able to afford a 25 mph bike and a 40 mph bike. I'd start with the slow one and sharpen your skills and preferences before taking on the fast one. That way it will come out cheaper and better.
 
scfoster: thanks for the feedback. Ya rear suspension eats energy when changing acceleration and on bumpy roads, but I see most igh power bikes here use them.

And yes, its a lot of unsprung mass, but going mid-drive adds a lot of complication at high powers. Started with that concept, but decided for road riding, it was too much, do now looking at hub drive.

I will definitely consider a seatpost shock if I go hardtail. I used to think they were a gimmic, since it ruins pedaling efficiency and form, but for an ebike, they make more sense.

________________

Chalo,
It's true that a 40mph bike is probably not necessary, but frankly, I want one. Same reason people buy muscle cars or whatever, 99% of the time you can't even hit the throttle due to traffic and such, but that 1% of the time just puts a big ol smile on your face.

There are long sections of my commute where I could go 40 mph safely without much fear of traffic, cops, or upsetting regular cyclists. With saddle time and confidence, I could start doing that.

Good points on the cost, but its a matter of priorities. Looking at ebike simulator: having a 25 mph bike with 36v40ah at 100% throttle vs a 72V20ah (ie same batteries but different config) running half throttle at the same speed...both give the same range for the same motor. So the battery cost seems constant, but the 72V bike has the option of going faster if desired. Agree the motor, controller, bms, and charger will be more. I'm guess total of +$300 motor, +$100 controller, +$100 charger, so maybe $500 more, or 15% increased build. Worth it to me, since I have more money than time in this point of my life. Glad you made me look at that again though. I did already tone down my original build thoughts..was going to do a 55mph bike, but then decided the hassle of 100+ V batteries and deathwish speeds weren't really worth it to me, in risk, hassle, and money.
 
My advice would be to make your ebike inconspicuous. Don't have any wires hanging out or having your bike look like a birds nest. Make it look neat and clean looking.

Do what you can to make it look like a regular bicycle. This will avoid potential problems with thieves and police.

Buy 2 kryptonite U locks if you don't have them already.

Remember to post pictures of your bike here when your done building it.

:idea:
 
Yeah, looking normal is not a bad idea.

So, how do you do that flying along at 40 mph? Everybody will look at you like this. :shock:

Since a 40 mph ebike in most places is a completely illegal vehicle, perhaps it's time you just got some motorcycle experience?

My scoffing would be completely different if you said 90% dirt, 10% street. But for a commuter, you'd be better off to build a 30mph bike. Much lighter, much less costly, close enough to "normal" for bikes to slip under the cops radar, not get complaints having the cops actually looking for you.

No reason your second build next year can't be completely aimed at off road, and 40-50 mph. You'll have almost $2000 in your budget left over to get started on it. You can take that bike to the dirt, or the racetrack, or sneak it out at dawn sunday mornings when the streets are empty and cops are getting their coffee.

One last option that may appeal. Use a controller that will run on 48v or 72v. Then you can ride 99% of the time at 30 mph ish. but the bike can be capable of 40 mph with the addition of a 24v battery to your normal battery.
 
You don't say where you live, but let's consider it is OK to ride a fast ebike in your town. Here it is, and I can tell you it is the best mean of transportation and a very fun toy to ride off road. I find it safer to have better acceleration and being able to ride faster than cars in town.

Your budget is OK, some will say you can build cheaper but I say it is a little tight for a performance ebike. Some will say 40 Mph is too fast, but I say build for 50 if you think 40 is OK. I build most of my bikes to do 60 Mph, but rarely ride faster than 50. Your bike will have to be handling like a motorcycle, built on one of the very best frames and equipped with the best components that you can afford. Building a performance machine on a cheap frame with cheap components is suicidal, or plain stupid. Go for the cromotor, it is much better than any Clyte.
 
Welcome to ES****Do this before your first post or now (it's retroactive)*****
Please go to the User Control Panel, select Profile, and then enter your city, state/province, and country into the Location field (country minimum) and save it. Once done, your location will appear in every post so you won't have people asking where you are ever again. This will help people help you. Example: Wylie, TX, USA. or just USA, but country as a minimum, and country is the most important. There are many cities with the same name all over the world. Without knowing what country you are in it's hard to make any recommendations. Thank you.
 
If you want a reliable and easy to charge battery, go for lifepo4 with bms of course. All you need to do is plug the charger and let the bms do the job
 
Much does depend on where you live. Mostly I scoffed building a faster more expensive bike, because it really sounded like you would only actually ride it that fast very seldom.

Plus depending on where you are, cops may pay more attention to you than other places. For example, in one city cops may just ignore you driving at full traffic speed in the lane till you are actually lying in the road bleeding. In another, they may be laying there looking for a motorized bike to bust for riding on a bike trail.

Situations vary so much with enforcement. But if your town is like Mad Rhinos, then by all means go for it. And by all means take his advice to use only the very best, nearly motorcycle quality components. A weak floppy frame is the worst when you pile on power and battery weight.

You don't have motorcycle experience, but surely you are aware how fast you go down if you push speeds and the load bike tires are carrying. You say you are too beat up to ride off road. So do use a motorcycle tire on your flyweight motorcycle. Bike tires will have you laying it down too much if you build a really high speed e bike.

I still think you'd be better off to build a daily rider that runs on 48v most of the time, for speeds in the low 30's mph, but can be ridden at 72v when you want a thrill. Or buy an actual motorcycle, that you can ride with full license and insurance. What if you hit a pedestrian at 50 mph, while riding your presumably illegal street vehicle?
 
No bicycle is going to be safe hitting a large pothole at 20mph, much less 40mph. Not the fat tire bike I'm building up or any motorcycle I've ever ridden. Potholes and light vehicles just don't work at speed. Other than that, you can build a bike that does the rest for as little as $800 or as much as you want to spend. A $280 48V 1000W conversion kit will do what you want with a 72V controller and 20-24s lipo battery pack. I've got 3.5 years and over 15K miles on mine without a problem, and it can do 30mph all the time and hit 40+ mph if needed for short distances without burning up the motor. Still you might want to consider one of the 3000W motors that will cruise forever at 40mph. Should be able to build one of them up for under $2K. And half that if you know what you're doing.
 
I strongly recommend having suspension on your bike if your going to ride over 20 mph. The front forks could break due to the weight.
 
You want to make sure your brakes are up to the task. My rig has disc brakes but the stopping power is still nowhere near as good as my abs motorcycle brakes at 30pmh. I have to keep that in mind when commuting to the office. I keep the speed down unless the road is clear and there's fair warning of things jumping out in front of me.
 
wesnewell said:
No bicycle is going to be safe hitting a large pothole at 20mph, much less 40mph.
We live in a different world I guess, or you just don't know what is DH riding and what it feels to ride a good DH bike on the street. The large pothole at 40 Mph, even when I can avoid it I go for it most of the time just for fun. In fact, on the street I miss the terrain challenge that I have in the mountain, and I would find it boring if it wasn't for the stupid car drivers who are making it somewhat unpredictable.
 
We must have a different definition of a large pothole. Hit some of the ones around here at 40mph and there won't be anything left of your bike. Large is 3' or more in diameter and 4" or more deep and sharp edges. Not concave, but holes.
 
Thanks you all for your feedback. I VERY much appreciate it!

I decided that all my goals aren't compatible, and to make some compromises. The main one being that the bike will obviously be an ebike, as I'm considering using the "E-kross" frame if we can work out the transaction details.

The reason is I really want to build a high performance bike. For me, if I'm going to go through the effort of a build, I want it to be kinda badass, but not necessarily insane.

As for legality, it is definitely illegal where I plan to ride, California, but I can make it have a "legal" street mode by using a CycleAnalyst with dual settings (one full capability, the other limited to 20mph and 750W) and a key switch to go between the two. I could possibly argue the case with a cop, especially if the key for full performance is out., but if they see me cruising at 35 mph on the flat, I will have to eat a ticket. The real deal is I know the roads and trails and where I can get away with it and where I can't.

As for pot holes, in Southern Califonia they are rarer and smaller than in places where they get more precipitation and freezing temps. I have gone over many a pot hole at 30 mph on 17 lb racing bikes with 18mm wide paper thin tires on radially spoked rims. Never went down and usually only had to true the wheels. Granted, none were monster pot holes. I do want to run motorcycle rims & tires if possible to avoid flats, but can't find any reasonably priced front suspension forks that clear 3" wide tires and fit 1-1/8" headsets (most are for tapered headsets).

Anyway, thanks again for your feedback.
 
wesnewell said:
We must have a different definition of a large pothole. Hit some of the ones around here at 40mph and there won't be anything left of your bike. Large is 3' or more in diameter and 4" or more deep and sharp edges. Not concave, but holes.
That is the kind I bunny up giving a short burst of throttle just before :D
I ride 40 Mph in mountain trails, where a 4" deep pothole is about the smallest obstacle that you can encounter, the kind you just fly over without a blink of an eye. A bike with 10" suspension travel is made for riding fast and hitting hard, even with a hub build (that doesn't make the best jumpers), taking a 3ft drop on the flat is perfectly smooth.
 
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