Choosing A Mountain Bike To Electrify – Part 2

This is a continuation of Choosing a Mountain Bike to Electrify – Part 1 Suspension

Frame material-

most e-bike gurus prefer steel frames over aluminum. Why? Steel is stronger and does not fatigue the same as aluminium. Aluminum fatigues and snaps and breaks. At high speeds this can be fatal. Remember most mountain bikes were designed to be pedaled at maximum 20mph. An e-bike can be considerably faster than that. Most e-bikes can go 20mph without pedaling, and some can go over 40mph. Also hub motors put a lot of stress on the drop outs of the bike. If you install a front hub motor you must make certain that your forks at least are made from steel, or that you use steel torque arms to compensate.

Also because of all the weight the electronics add to an electric bike, the few pounds of weight saving you get by using aluminum over steel is not a big deal, and should not be a big factor when choosing a frame.  Surley is a high end frame producer which builds all their frames in steel and are extremely popular in the eibke community.


Surly Big Dummy Cargo Bike Electrified

Folding mountain bikes

The Montague because of its folding characteristics has been a popular mountain bike to electrify.  If being able to fit your bike in a trunk of a car, or store in the corner of your garage..maybe a Montague is for you.

Montague Folding Bike

Brakes –

Brakes are a huge consideration on an electric bike. Many electric bike gurus will preach do not build a high powered e-bike without disc brakes. I agree with this. If you buy a bike to convert with v style brakes or coaster type brakes, you can expect you are going to have to spend money later to upgrade. Upgrading to disc brakes on a bike that was not designed for disc brakes in the first place may mean that you will need to buy a whole new bike just to go with disc brakes.

The bike above has some strange characteristics. 20″ wheel, suspension forks, and high power 600w bmc motor and cheap aluminum suspension forks. For safety it has bb7 mechanical disc brakes and steel torque arms on both sides of the fork.

Disc brakes are not only highly effective, luxurious feeling  and low maintenance when compared to v style brakes, on e-bikes they are often a safety necessity. Remember on an e-bike you will be able to climb hills you normally would not be “inclined” to pedal up. WHen going back down a hill on a steep grade, cheap brakes can  overheat, not function enough, or outright fail.  Cheap brakes  can also make your hands really tired by having to grip super hard.

Whatever frame you convert remember the manufacturer did not intend it to be an e-bike, and its braking system was built according to the purpose of the bike. If you buy a downhill racing mountain bike, guaranteed it will be outfitted with beefy disc brakes (probably hydraulic). On the other hand,  if you buy a single speed  beach cruiser, by definition a bike designed to cruise at slow speed on level ground, it will more than likely have nothing more than a rear coaster brake and therefore would be  a bad candidate for e-bike conversion without modification.

Also remember you cannot add disc brakes to a bike frame later that was not designed to be outfitted with disc brakes.
Not all disc brakes were created equal.

Hydraulic disc brakes are the nicest brakes for e-bikes.  It sounds like I am being lazy but it is a real nicety when you can stop a speeding bike with just 2 fingers. When riding downhill for long lenghts of times with mechanical disc brakes my fingers do tend to get tired. Also hyrdraulic brakes require less maintenance then mechanical brakes and are less exposed to the elements. The drawback to hydraulic brakes besides for the initial expense is it is a slightly difficult process to bleed the brakes, and bleeding brakes will be necessary every year or two, but there are plenty of youtube videos on this process to  assist you.

Avid Elixir Brakes

The good news is because disc brakes are bicycle technology they are made in huge numbers in Chinese and Taiwan factories so you can get quality hydraulic disc brakes for an affordable price.

For example, Avid Elixer brakes bikes, one of the finest sets of hydraulic disc brakes currently on the market, can be found brand new on ebay for under $300.  Avid Juicy 7 brakes, last years top of the line Avid brakes can be gotten for even cheaper, especialy if you can settle for used.

The best option if you are converting a bike is to find a used bike which already has nice hydraulic brakes already installed.

Bicycle Gearing
The cheaper the mountain bike, the cheaper the shifting components. Although rickety shifting is annoying, it is not as big of a deal on an electric bike as it is on a conventional mountain bike because the motor is doing a lot of the work you would usually be doing in the lower gears.

A hub motor bike effectively takes a lot of the stress off the pedal drive train of the bike.

The most important part for an e-biker is that he has a super high gear for pedaling when going fast. However this gets tricky because no off the shelf mountain bike shifting system is made for   pedaling at 35+ miles an hour. So if you are running a high power set up and want to pedal assist the bike, you need to plan to modify your gearing.

Gearing is sort of a complex equation…but I will just break it down for you simple. On a high powered electric bike, for your highest gear you want the biggest sprocket possible on the front, and the smallest possible sprocket on back. THe highest tooth count on the back, and the lowest tooth count on the back.  This gets tricky in the standard 3 ring cranksets which usually do not come stock with a extra large sprocket.

You can solve this by running a single huge sprocket on the front. The problem is it is hard finding extra large sprockets for moutain bikes. Most downhill mountain bikes come with a larger front sprocket because they were designed for going fast downhill.  Another option is  buying a  specialty cassette for your rear sprocked from  on the back with an extra small 11 tooth gear for high gearing.
One of the sleekest solutions to this problem is relplace your bottom bracket and front derailleur with a planetary shifting system made by Schlumpf.

The Schlumpf high speed drive gives you an ultra high gear up top, and a low bottom gear, allowing you to pedal your e-bike at speeds of up to 50mph and at the same time getting rid of the  front derailleurs, sprockets and shifters.

Above you will see a 20 inch wheeled bike with a front wheel drive high powered bmc geared motor up front. Normally this bike would be geared way too low considering the small diameter tires. However the Schlumpf compensates for this and it is possible to pedal assist this e-bike all the way to 40mph.  Also this bike  has a 8 speed Sturmey Archer, giving this bike a total of 16 speeds without a single derailleur and a perfectly clean chain line. This bike came stock as it is without the schlumpf and the electric bike components.

The stealth fighter uses the Shlumpf high speed drive system, and no other shifting system…so just one ultra high gear and one low gear. This is a nice solution on a high power electric bike because you  should only need the low gear when your motor or battery dies. Check out the ultra clean chain line accomplished in the Stealth Figher because of the Schlumpf up front

Stealth Fighter with schlump = 2 speeds and incredibly clean chain line

Pictured above is the author with a great lesson in Bicycle gearing and how it has progressed through the years. This is an original high wheel bicycle made in 1888, one of the first bicycle designs. The idea was that this 52″ wheel allows the pedals to go directly to the wheel giving a 1:1 ratio. This is the cleanest drive imaginable with no sprockets, gears, chains, or other mechanical parts to get in the way of the efficiency of the pedal rider to the ground. This 52″ wheel at 1:1 gives the same gearing as a modern mountain bike in a middle gear at 2:1.  Modern gearing can allow ratio’s up to 5:1 with very little efficiency lost. With the advent of modern mechanics and better engineering involving bicycle gearing, the high wheeled bicycle became obsolete.



Especially if you are planning to put a beefy hub motor on a bike you want your tires and wheels to be high quality.

Remember the considerations for choosing an electric bike tire are completely different than for a regular bike. Read our in depth story regarding e-bike tire selection here.

If you are buying a used high end mountain bike to use as your conversion frame to e-bike, more than likely the mountain bike will come with knobby tires. changing out these knobby tires to something more electric bike worthy should be a priority after you read the article above.

A word about spokes

Ypedal's Crystalyte hub motor laced with beefy 12 guage spokes

Especially running a powerful hub motor you will notice your spokes will come loose and your wheel will be out of true very quickly and need to be tightened, and sometimes the wheel re done by an experienced wheel builder. This adds hassle to owning your e-bike. So we recommend you start with very thick guage spokes….12 guage is really sweet for a hub motor over 500 watts, but not all rims can accommodate spokes that thick.  Use as thick of spokes as you can manage.  No matter which spokes you choose, expect to pay a dollar a spoke to either buy spokes or have existing spokes cut or to order new spokes (about the same price). Also expect to pay as much as $100 to have an experienced wheel builder install your hub motor into the wheel, which is a tricky task. Be warned…Not all bicycle shops will agree to build a hub motor into a wheel. If you can get a bike shop to do a hub motor built into wheel  job for $50 or less consider yourself lucky.

Rims and Wheels

In general the wider the rims the better for a electric bike build. Downhill bikes and even fat tired sand bikes make great e-bike candidates because of their extra wide rims.  Bicyclists buy rims to be lightweight and strong, for an electric bicycle rider all that is really important is the strength and width of the rim. Because lightweight isn’t a big factor for an e-bike you dont really need expensive rims but they look nice. Also remember if the rims on the bike your are selecting do not have 36 holes you are going to have to buy a new rim to accomodate the hub motors. All hub motors have 36 spoke holes.

Regarding wheels. IF you are converting to hub motor, remember you will have one extra wheel since the hub motor serves as the wheel on one tire. Many people decide to keep this wheel around in case they can easily  convert their e-bike back to a pedal bike if they decide.

seat –
comfort and styling should be your main concerns because as we have stated before weight is a non issue on an electric bike.  Conisider a suspension seat post for the ultimate in comfy if you have $ to burn.

Thubbuster suspension seat post

Book racks-

Front racks or rear racks are a big plus on an e-bike because of the capacity to mount a battery. Some racks even come stocked with a beer opener like the electric fat bike pictured.  For racks they don’t get any better than pictured….topeak rear rack as well and center triangle pouch as well.


Selecting a pedal bicycle to electrify is half the fun of building an electric bike. Also it is critical that you pick the right donor bike to serve the function of a safe and effective electric bike. Hopefully this article and the part 1 choosing a mountain bike to electrify will give you an idea where to start in the seemingly endless selection you have of new and used bicycles as possible electrification candidates.  The most important part is you select the right bike for the bike of your dreams the first time….or end up like a lot of us always chasing the better and more ideal e-bike and have a fleet of e-bikes in your stable. My advice is if you think you are going to become fanatical about electric bike riding,  or even ride a lot…it is better to spend the $ now on a used donor bike, then upgrading later. Word to the wise.

Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.


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