Help! Best conversion kit for GF 29er Full-Suspension bike?

[kripski]

What would you recommend? I am converting my full-suspension 2008 Gary Fisher Hifi Plus 29er into an affordable and clean looking all-terrain rear hub-motor ebike, but I am discovering several major challenges. The internal frame triangle is small and will only allow for a battery max height 3.25 inches. There is another water bottle attachment under the down tube but the battery will get more exposed to the elements. Below the tube also cannot allow for a tall battery. From what I read I would want a 1500w rear hub motor for ample off-road power, I live in a area with lots of hills so power is key. All the 1500w ones I see only allow for a 7-speed cog setup and my bike has 9-speen cog. Is this an issue? I have little to no room to mount a controller so I was exploring motors and batteries with built in controllers?? It also appears that off-road enthusiasts prefer a thumb throttle because a wrist throttle can be difficult to manage while hitting roots etc. This is becoming a real challenge to build. Are you aware of any conversion kits that would works for my bike out of the box?? Aiming for 35+ mph and over 25+ mile range. Need your help...
Adam

 

[motomech]

W/ the BIG wheels, "all-terrain" aspirations and high speed goals, you probably would be better served w/ a mid-drive system.
Certainly, a 1500W hubbie and a "bottle battery" won't cut it.
You would need a BIG hub motor w/ lot's of battery.
You might want to research some of the builds here.

 

[amberwolf]

The rear sprockets you just need to swap for your actual unit, taking off your old wheel and putting on the new. If you have a cassette, then get a hubmotor that supports that. If yours is a thread-on type, then get that kind of motor. Etc. If you can't, and can't get the right kind for the new wheel, then you may need to change your shifter and derailer out for one that will work with whatever you can put on the wheel.

To help you solve some of your issues, along with others you probably haven't even thought of yet, I'd recommend doing as much reading of various other builds with similar needs / problems as you have time for.

You may also want to go to
https://www.ebikes.ca/tools/simulator.html
and read the entire page to learn what everything is and how to use it, then play with different setups and situations to see how they perform, so you can be sure that what you want to do will work with the stuff you already have or what you plan to get.


But here's some things to think about:

35MPH+ is likely to take upwards of 50-60wh/mile to sustain, on flat ground with no winds. So to go 25miles+ you'd need at least 25 times that, so say 25 * 60 = 1500wh. That's a fairly large battery, especially if you have space constraints. It might mean having to carry two paralleled batteries to get the range you want. I have a 2000wh battery that is around 35lbs, so you're probably looking at 25lbs+ of battery, depending on type.

Now...batteries lose capacity (and range) over time, and also sometimes you run into detours or headwinds/etc that can significantly impact your needed range/capacity. So it's a good idea to add 20%+ to your known needs to allow for these things. So you might need at least 2kwh.

Since you have lots of hills, it's going to take more (possibly a lot more) capacity to do what you want. It may take a lot more power to do it, too, so you may need a bigger motor to maintain 35MPH+ up those hills, and this may mean an even bigger battery to handle the extra power to give the same range.

For instance, if you have a 10% grade hill, and something like the H3548 motor and a 40A controller at 72v, it would take about 2kw to just maintain about 28mph (fastest that could do on a hill lke that). The power usage goes up to about 100wh/mile, and will overheat the motor in about 5 minutes.

https://www.ebikes.ca/tools/simulator.html?batt=B7223_AC&cont=C40&axis=mph&autothrot=true&throt=100&hp=0&grade=10

Let's assume that half your route is going up such hills, then your average wh/mile goes up; divide both the wh/mile numbers by two and add them, you get about 80wh/mile average. So you would need at least 25 * 80, or 2000wh, which if you add a good margin to is now up to 2500wh. So now you have about 40lbs of battery on the bike.

You may also need a bigger motor to handle the power without overheating, especially if you need to maintain 35mph up those hills, becuase you'll need a bigger controller to do that, too (which will then also increase your power usage, which means needing an even bigger battery, etc).


So...at some point you end up with something as big and heavy as a small motorcycle, but with a frame that can't handle that weight, and wasnt' designed for those speeds either in it's wheels or it's brakes, suspension, etc.

At that point, you're better off actually getting a motorcycle, that's designed to do what you want.

 

[dogman dan]

Hmm, to solve some of those problems I've had with off road e bikes for more than a decade, I just bought a honda. Its nice, to have better float in deep sand. The honda climbs hills that have melted motors on my e bikes. And I can ride it for several hours before the gas is gone. The e bike runs out waaay sooner, then has to take hours to charge for another ride.

However,,,, I did not say don't build an e bike. I said all your goals are easier to get from a honda.

What I did, was swap my rear shifter to a 7 speed, and run a fairly light, fairly affordable planetary gear hub motor. The battery carries on a rear rack, that mounts on the seatpost. Then the rack is braced with additional struts back to the frame. That battery has to be pretty small, usually I pack only about 10 ah. Multiple batteries can help with that second ride, but you end up circling back home a lot.

I get a tolerable ride, though I do have to lean into the bars some to balance that battery back there. Not a lot, just enough to get that front traction back enough to not crash over and over. Do that on the honda too, when needed by the terrain. My bike is an old Y frame, so nothing carries on the frame, 2005 giant. But absolutely, the max you can carry back there is 48v 12 ah or so. Any more and you wreck your handling too much to stand it, and start crashing a lot. A smaller controller can cram into a tighter space, under your seat, or something like that. I often put them just in front of the battery, on the rack, or rack mount.

 

[Balmorhea]

The internal frame triangle is small and will only allow for a battery max height 3.25 inches. [snip]

I live in a area with lots of hills so power is key. [snip]

Aiming for 35+ mph and over 25+ mile range. Need your help...

Your speed, range, hill climbing, and battery constraints are not compatible with a hub motor. To make a hub work, you’ll have to give up on either top speed, range, or steep hill climbing capability. Or you’ll have to get really creative about mounting lots of battery, and overload the bicycle with more weight than it’s competent to carry. In the unlikely event you succeed in hitting all your performance targets with a hub motor, your bike will be loaded down like a pack mule with expensive batteries (and a big controller, and a heavy motor).

You can get what you want from a BBSHD mid drive, though. It requires a lot more maintenance and consumables (mainly chains and cassettes). And it rewards good shifting technique, to keep the motor running in its high efficiency range. if you go that way, consider switching your shifter to 8 speed so you can take advantage of cheaper and more robust chains and sprockets.