Choosing an Electric Mountain Bike – Part 1 Suspension

February 27, 2012
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One of the first questions you should ask yourself when buying an electric bike, or choosing a base mountain bike for a conversion to electric, is what kind of suspension you want on the bike. The basic 3 choices are: No suspension, front suspension only, or full suspension Here are 3  examples of bikes I own.

No Suspension:

This bike has 4 inch fat tires that serve as an inch of suspension. The look of the bike without front suspension forks is clean. I enjoy riding this bike, on the road, on the sand, and on trails. (read Electric Fat Bike Creations)

Front Suspension only:

When you have no rear suspension its possible to have a triangle battery bag (this one made by falcon) which is the ideal place for the battery.

Full Suspension:

This bike is full suspension, and has no room for the battery in the triangle. Therefore this bike has the traditional rear bag for the battery. The problem with this bag is it does not ride with the suspension so the battery gets a rough ride. I have ruined many batteries riding on this bike off road, so now use it for on road only…and the high quality suspension is total overkill for regular road riding….lesson learned.

 

 

You also need to ask yourself how are you going to be riding the bike. D0 you live in Boulder Colorado and want to traverse mountain trails? Or do you live in Junction City Kansas  and want an e-bike to go to  buy groceries in the day and traverse the local bar scene at night?

If you are with the majority of electric bike riders you are a commuter, using your e-bike in replacement of a car or regular bicycle to get to places close to your house instead of walking, pedaling or driving. (read Dogman’s Commuter Builder Primer)

So if thats the case how much suspension do you want or need for common e-bike road applications?

Suspension definately makes for a more cozy  ride. The better the suspension the cushier the ride. But suspension is not a no-brainer, it also comes  with some  drawbacks.

 

Pros and cons to suspension:

Pros

  • Suspension is fashionable and the in thing for around the town mountain bikes
  • hurts pedaling efficiency
  • makes for a more comfortable ride
  • makes the bike look more expensive and eye catching
  • allows you to go up curbs over bumps easier
  • because it is mass produced you can get quality suspension for pretty cheap
  • suspension makes the ride easier on battery by smoothing the bumps.
  • on an electric power bike  the extra weight and loss of pedallng efficiency does not make a big difference
  • appeals to the gadget freak inside most men

Cons

  • less room in frame triangle for batteries
  • harder to mount rear rack on rear supsension bike
  • adds weight to the bike
  • adds expense to the bike
  • not as clean looking in some applications
  • makes the bike more expensive looking at a bigger target to steal (bike thieves love full suspension bikes)
  • more components to upkeep
  • In case you are deciding to go with a front wheel drive hub, it is not safe to mount front wheel drive motors to front suspension bikes
  • Harder to find smoking deal on used mountain bike with suspension

Suspension Mountain Bikes on the Cheap

Suspension mountain bikes are easy to come by these days and are not as expensive of a commodity as they use to be. If you do end up with a suspension mountain bike, and are doing an electric bike build around it here are some things to consider:

Where are you going to put the battery?

Most full suspension bikes have much smaller triangles then there hart tail counterparts. So the triangle is usually out for battery mounting in a full suspension frame.

Rear Rack mounting- mounting a rear rack on the bike is a common thing to do.  However a full suspension bike is not as easy to mount a rear rack because the rear end is floating. Also you have to make sure the travel of the rear wheel does not come up and hit your battery. Therefore the battery weight if mounted on the rear will more than likely be higher than on a hard tail bike, where you can ride with the back rack just an inch from the tire.

There is a big drawback to mounting a battery pack on a seat post style rack like this topeak system (insert picture)

For one thing the battery pack is pretty high above the rear wheel…this is to allow the rear wheel clearance  so it can move up and down freely when going over bumps. However because the weight is so high you feel the weight much more than when it is lower. For example this bike would be hard to lean down and get on.

Also this is a lot of weight for this type of rack to carry. A typcical lithium battery weighs 10 pounds. From my experience with this kinds of racks, the rack comes loose a lot and swivels annoyingly from left to right..especially getting on an off the bike.

It is possible to build a rear rack that moves along with the suspension..sort of a floating rear rack. Basically the rack connects to the rear swingarm and pivots where it connects to the seatpost so effectively the rack is not suspended and does not move when the suspension flexes. Here are some pictures:

The pluses to this system are great. You are able to lower the battery weight as close as possible to the rear wheel, or mount on side bags along side the wheel so center of gravity is lowered.  The rack is able to mount solidly so more weight can be  carried without the “jankiness” of the seat post rack. The look of this rack is much nicer, looking more like a part of the bike than a weird extension. The drawback is simple..the weight in the bag is “non suspended” meaning the battery pack is now riding its weight direct with no suspension on the rear wheel. This makes your landings somewhat harder, and also makes for a bumpier ride for your batteries.  No matter how well i have strapped the batteries down in the bag, I have still managed to ruin battery packs riding off road with rigidly mounted rear battery bag.

Types of mountain bike frames:

When searching for a mountain bike frame keep in mind the different types. Mountain bike types are defined by how heavy duty the suspension is..here is a break down with an estimate of the weights:

Downhill – 40 pounds
AM (All mountain) –  35 Pounds
Cross Country Around 30 Pounds
Rigid (no supension) – 30 pounds
El Cheapos – 40-50 pounds

What follows is a desciption of all the above types of mountain bikes:

Downhill – Massive frame and massive suspension. Usually 8 inches worth of suspension travel in front with double crown forks (see in picture below) and 5 inches in back.  Designed for 20 foot drops and serious mountain trail riding.  Also downhill bikes, because they are meant for serious downhill riding, usually come with good quality disc brakes, preferably hydraulic.

Downhill bikes are not meant to be pedaled long distances on flat ground. They were designed to be taken up to the  top of a mountain on a chairlift and then bombed down.

You can find incredible deals on downhill mountain bikes used, because serious riders are always upgrading to this years bike.

The drawback to downhill bikes is they are much heavier than the other types of bikes. A typical downhill bike weighs 40-50 pounds…Although this seems heavy it is only 10-15 pounds heavier than a typical mountain bike. Since most electric bikes weigh from 60-100 pounds, the added weight probably wont make a big difference.

Because of their ruggedness and cushy suspension downhill bikes make great candidates for electric bike builds. Also they usually come standard with hyrdraulic disck brakes with 8 inch rotors, perfect if your thinking about riding your electric bike at top speed.  In addition these bikes usually are epuipped with wider than usual tires…2.5 inches rim is a standard for a downhill mountain bike frame allowing for a tire up to 3 inches wide. Downhill bikes weigh from 35-45 pounds depending on their ruggedness and quality. Downhill bikes can cost as much as $8,000 brand new utiitlizing components that are both high quality and lightweight.

To see a prime example of a commercially avaialble downhill bike, scroll down and see a picture of the Stealth Bomber. Also read our review on the Stealth Bomber here:
https://www.electricbike.com/stealth-bomber-review/

It is possible to find a great deal on a used downhill bike on craigslist or ebay. The Ellsworth Rogue pictured below was picked up on ebay for $2500, a bike that the original owner just a few years earlier spent 8k on.

 

AM (all mountain)

All mountain – usually 5.5 inches of suspension on the front, and 5 in the rear. Basically AM bikes were build to bridge the gap between down hill bikes and xc bikes. They usually have single crown front forks (instead of double) and 6 inches of travel (instead of 8).  They are build a little less sturdy and are thus a little lighter than the downhill frame. Generally  a quality all mountain bike weighs 32-35 pounds.
Cross Country – (most common) standard 4 inch front suspension fork, and 4 inches in rear or no suspension in rear. These bikes are made for all purpose.

Rigid Mountain Bike

No suspension  at all.  This is the most veratiile bike for the elecric bike builder. With no suspension you can use the entire space inside the triangle for mounting your battery. Also rear rack is no problem  to mount since the rear triangle is stationary. There are less components to wear and to take care of.

El Cheapos:
If you want a good source of an El Cheapo mountain bike frame, look no furthr than your local walmart. Budget minded e-bike riders have been converting to electric with hub motor kits cheap mountain bikes from walmart for years. Walmart bikes mountain bikes have the appearance of being descent bikes but are usually of very cheap quality. The suspension is so cheap its almost better going without it entirely or gong with a cheap with just a front suspension so you can utitlize the entire triangle if you need it to mount the battery somehow. To see a good example of cheap mountain bike frame, look to some of the budget electric bike offerings like the izip made from currie:

Finding a Used Mountain Bike Based on Suspsension

If you are planning to build an electric and are looking for a used mountain bike to use as a base bike, first choose a category of bike you want from the list above, and then search away. There are so many used mountain bikes available that you will probably be overwhelmed on which one to pick.

Here is a tip for people shopping for a used high end mountain bike for their e-bike platform. It is overwhelming to pick a brand of mountain bike to search for. It’s much easier to pick a front fork and search for the bikes used with that front fork.

For example I found my used turner RFX frame by searching my local craigslist for “Fox 36 Talas” and found a number of high end bikes selling used with this fork including my Turner. The fork sells for over $1000 new, but you can find complete used bikes with this fork in the $1500-$2000 range. Generally if a bike is equipped with a high quality  front fork, all the other components are  high quality as well.

Riding a high quality suspension electric bike

My Turner RFX electric bike  (green bike pictured above) is a real nicety to ride. It feels cushier than any electric bike I have ever ridden. It goes up street curbs as if they were not there. I soar through golf courses at night, and the nice front suspsension makes me feel confident that if I hit an unseen bump I am not going over the handlebars. The suspension is adjustable from cushy to firm, and I prefer to ride my electric bike cushy. The suspension really comes into play obviously when off road riding, riding trails that normally would be jarring on one of my non suspension bikes, my Turner eats up the bumps as if they are not even there. THe bike feals more stable when off road then a non suspension bike, and the bike is in many ways a joy to ride. Among the biggest drawbacks is the bike is expensive looking, and since I ride in a city environment (San Francisco) I always have to keep in mind the threat of bike thieves when I arrive at my destination. Also because the bike cost me so much to build ($2000 just for the actual bike used with no electric components) I am always afraid of getting a part stolen, or worst the entire bike. When I ride, add 5-7 llbs for high quality locks I am forced to carry in case I decide to stop and leave the bike unattended.

Suspension seat posts-

A nice alternative to suspension is a suspension seat post which have evolved recently and are now being produced by several manufacturers.

The idea is on a non suspended bike to absorb the bumps oftentimes a rider needs to stand up. IF you have a suspension seatpost with 2 inches of travel small street bumps can easily be absorbed without having to lift your butt.

Suspensions in commercially available Electric Bikes

Optibike
Optibike’s founder has strong connections with Fox Shocks, and uses shock suspension for all their bikes.  The optibike currently uses the Fox talas 36 (or 32 on lower grade bikes)  a $1000 front shock with 6 inches of travel. On the rear . Note that the optibike is an extremely well balanced electric bike, ideal for trail riding and a high quality suspension makes perfect sense on this set up. Also note that the optibike can cost up to $15,000 depending on the options.

 

 

 

Stealth Bomber

The Stealth Bomber has a motorcycle style rear suspension in the back giving you a whopping 9 inches of travel.  It comes  stock with a no name bargain fork called the RST-R1.  This is a descent fork that looks good, performs well, but is know to be heavy (8 pounds)….but a few extra pounds wont make much of a difference on a 120 pound electric bike. For $1200 extra you can upgrade to the White Brothers Groove 200 which is a little bit lighter and better performance. Notice that the Stealth Bomber uses a double crown fork, which will give you 8 inches of travel. The Stealth Bomber is the equivalent of a Downhill mountain bike frame with a gigantic battery mean to hold a gigantic wad of lithium battery. The Stealth Bomber is made to go off some serious jumps…not that you would want to given how much this thing weighs and more imporantly how much it costs. Steatlh bombers start at $10,000 and depending on the options and shipping costs can set you back up to $14000.

The Blacktrail Bt-01

The blacktrail is a 80 thousand dollar bike without suspension. Blacktrail uses a carbon fiber fork custom designed for the bike. What is interesting is why did german engineers decide to go for a custom hard fork on this bike, instead of using a readily available high end mountain bike fork instead?

The reason is that the blacktrail was designed as a commuter bike to be ridden on the road. Even at 60mph, the speed that the blacktrail claims to hit, suspension is  not necessary on a road bike.

Also the non-suspension fork has a clean look adding to the blacktrails already impressive styling.

The Blacktrail is proof that suspension on an electric bike is purely optional.

Continued in part 2: Other components click here to read


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.

10 Comments

  1. Do you know of any examples of a tweel being used? Wouldn’t that give some suspension advantages?

  2. thanks

  3. First of all, many thanks for your site which is an incredible source of inspiration and information. Would you recommend a top of the range DH bike with a custom made electric propulsion (DYI approach) or a stealth fighter/bomber? I already own a 2000W system with a BMC v4t Hardtail mounted on a Cube carbon hardtail (16 kgs for the bike + 3.5kgs for 750W in my backback). Unfortunately, I suffer too much on enduro tracks around my place and want to go with dual and long travel suspension. Shall I just transfer my components to a good DH bike or go with the stealth bike? Many thanks in advance for your answer. Kind regards and congrats for all your hard work.

    • If you can afford it a Stealth Bomber/ fighter is very nice. THe frames are custom made to have the battery protected within.

      If you build it yourself put a lot of thought how you will protect the battery pack from shock of jumps etc. Battery packs can get ruined quick on a DIY home bike.

      Hope that helps.

      • Excellent write up. One thing I do want to address though.. Front hub motors are ok on front suspension bikes as long as it is steel …. Granted I realized very few bikes use steel front forks… It is the aluminum and magnesium forks that break… Certainly correct me if I am wrong, with care

  4. Thanks for the write up, very informative. Quick question regarding the frame material, I can hardly find any mountain bike with steel frame other than those cheap ones. Will Bafang BBS02 and EM3EV frame pack battery be OK on an alloy DH bike?

  5. Mounting battery above the back wheel is pure folly. The rear wheel already weighs a ton on a decent hub motor wheel, add the weight of the rider plus battery? That’s a lot of weight for the rear of your bike meaning balance for the riding experience is way. Batteries should always, without fail, be mounted in the triangle. Less shock to the battery and much better ride balance.

    • Well, kinda. My last cross-country bike had the battery mounted on a double deck rear rack. It handled well. I would say that putting the battery in the triangle is “greatly preferred,” but won’t be as absolute as you about the need to do so.

      • The real point here, HS, is that the lower the center of mass, the better the handling of the bike. That the triangle is the only area available, and mass on a rack over the back wheel is subject to shocks and trepidation, “greatly preferred” seems to make great sense.

  6. Downhill bikes usually have 8″ of rear travel, not 5. Also, you might want to add in the freeride bike. It is like a downhill bike (7-8″ of rear travel and just as heavy), but easier to pedal.

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