Drivetrains & Batts to sustain Long Uphills

Sorry if I opened a topic already discussed or over discussed. Hey admins, if there is a topic where this issue is well discussed please show me the link and delete my topic. A topic resuming present day situation should be useful, discussing openly the painful truth. At present day battery technology all e-bikes can be no more than commuting bikes? Can not be used for real trail or traveling?

Many of us are accustomed with gas enduro bikes, we take for granted one thing that most electric drives CAN NOT do right now as it seems. Some engine producers have thermal protection included in their design but the issue is to have something capable of doing the damn thing not stopping the bike after a few miles when thermal limits are hit.

I am quoting here a designer: ''Hubs are great on streets, can be tuned for low hill climbing but on longer technical uphill trails can easily hit thermal limits. I am stating the results of a few years and almost $100k in experimentation. I know all about the inefficiency and waste of the capitalist structure. When people see a big travel bike, some are going to push its limits. That bike .. is a great example of this. I see big travel, fat knobbies, and I think, that would be a blast to fling down some hills. Being an engineer though, I know for a fact that the hub motor simply can't handle some of the uses the styling and other components suggest. Consumers aren't aware of this stuff and will beat these bikes into the ground. A large percentage won't ride hard but they'll read the critical reviews of the guys that do.‏''

Also geared engines seem to better use the energy contained from batteries, another big question is - what is the longest uphill your drivetrain can sustain? A friend of mine who built 2 bikes in Austria says that he can do no more than 20kms of trail with 1400m of altitude difference with 2! batteries. So we have the ebikes, looking nice and the mountain in front of us. For what uphills can be used the present day ebikes? What uphill range can sustain a good battery, what uphills can sustain the best engines? 6-15% grade mountain, forest trails for how long??

How many kms/miles up a 6-15% mountain trail can go your bike without hitting thermal limits of having the battery finished?


‎11‎:‎33‎ ‎PM
can your present drive train sustain LONG TECHNICAL UPHILLS without quickly hitting thermal limits?

While I can't answer your question with an anecdotal firsthand response, I can perhaps steer you in a useful direction. Your question has two components, thermal limitations and energy storage.

"Long, technical uphills" are currently outside the mainstream of what I have seen in the ebike community, perhaps partly because of the challenges you've highlighted. Another very important set of variables is the speed at which you would want to climb such hills, and how much weight you want to carry up. Assuming we are still talking about bicycles, we could want to travel the same human powered speed, to several multiples faster. If you want an electric motocross bike, the design would be markedly different. How fast is your friend in Austria going? What percentage of the required total energy was the cyclist providing?

Hub motors designed to fit in bicycle wheels are limited in thermal management designs, due to the small diameter of the non-rotating, fixed interface with the vehicle. They also are not ideally suited to minimizing unsprung weight for technical trails run at high speed. You can solve this problem by using modified design parameters, such as a larger non-rotating interface diameter, or a traditional inboard motor system that can be cooled more easily with air or liquid. There is no shortage of high-power-density electric motors to choose from, although acquiring them in small or single quantities could be challenging. Thermal management of dense, high power applications are the same between petroleum engines and electric motors - the benefit being that electric motors have an order of magnitude less waste heat product to deal with. You either cool them with air or liquid.

The primary consideration of most all electric vehicle design is energy storage density. While the drivetrain can make more efficient use of that stored energy, we can not yet match the density of petroleum fuels, so you need to consider we are using something with < 300 Wh/kg (lithium polymer) vs. > 12,000Wh/kg for gasoline (most of which is used for heating the air). You must need less energy storage in your application for current technology. How far do you want to go? There is progress being made on this storage limitation, but the available technology exceeds the needs of the general ebiking community today. Corner cases, such as a specific need to travel at high speeds up steep grades for long distances, will require waiting on better density, or better creativity.

Long distance cross-country traveling is already quite possible on electric bicycles, the primary limitations are formal infrastructure. There have been numerous examples of extreme long distance coverage by members of this forum. Since you are posting in the Motor Technology section, if you primary concern is the motor, I can guarantee an electric motor matched to the design goals can exceed any useful performance metric of a petroleum counterpart in this application.

I used to melt down a hubmotor pretty regularly, pushing them too hard for too long up a steep trail. Up to 15% grades, about 4 miles is the turn around point I use now. Much less for grades above 15%. But that applies only if 90% of the trail is not so technical that you can't ride up it at 15 mph. You don't need to fear a short 25% grade, with plenty of pedaling. But ideally not more 15% after that really steep part.

Really bad stuff, so rocky and staircase like you just can't ride it fast, you can fry your hubbie in a mile easy. You can also fry a motor pretty quick on the flat too, if the sand is deep, or the turns so tight you constantly brake/throttle, ending up the whole ride in the 30% efficiency zone or worse.

It's pretty much known now, that if you can't ride up it at 12-15 mph because of the turns or the rocks, you need a mid drive you can gear down to 5 mph crawl up the hill.

Battery use up a hill is so variable, it's impossible to say shit without a watthours per mile number to work from. But with hubmotors, going up moderately steep stuff, 60 watthours per mile is not uncommon. A big powerful hub motor, even more.

So calculate your battery size needed based on 60-70 watt hours per mile, or more. A 48v 15 ah battery gets me about 10 miles of ripping the dirt up, and longer rides just lead to crashing a lot near the end of the ride when I got tired. So even though I might have more range on the bike, I tend not to use it.

The best trick is to avoid all trails built for horses, mules, and hikers. Also bulldozer roads to log or mine. If possible, ride a loop that goes up the easier way, and take the rock staircase on the downward leg.

You need to build or buy an electric trial motorcycle. Slow technical does require a mid drive with lots of power.

Gas Gas TXT E electric trial

I do not mean THAT technical, no hard enduro no trial.
Look at this bike - great design - looke at these trail - no more than 1 hour uphill, that is the limit for this bike, 40v11a if I am not wrong, lots of pedalling and small engine.
https://www.youtube.com/watch?v=73W0INTb8tE
The idea is to be able to go up at low speed not high speed, but long uphill trails, and not just one mountain up than down.

Using currently available tech, a mid-mounted motor and some gear options would be ideal for those conditions.

BTW, those conditions are nothing compared to the big mountains and real desert trails. That BHT bike would be smoking within a mile or two on the desert trail I take to town, on my pedal only bike.

In Colorado, the regular hike/bike trails have sections like those in the video, one after the other, up and up, and up. Sometimes, it's a 12 mile push to the top that takes three hours to earn a 20 minute ride down. That's a different type of riding though, less park like, and usually shuttled. A lot of the guys that want 8" travel $5k+ ebikes only want them to avoid the shuttle. Selling less capable versions to those in cities is likely going to encourage urban freeriding, which will get e-bikes banned quickly if it becomes popular. I guess my point is that if someone is going to build a bike that looks like a downhiller or trail runner, and it can't do long extended uphills or steep technical trails, it might as well have 3" travel and skinny tires for the street. Not that urbanfreeriding isn't fun...

Also, I can't imagine the dh looking ebikes at a dh park, in the beginning I guess.... It's bad enough dodging the weekend warriors as is, either sitting sideways across the trail right around a blind corner at the bottom of a speed run, or in a pile at the bottom of drops... They start coming up backwards, and people are going to get killed. Parks will have to make alternate shuttle trails to get back up.

Until someone goes crazy and designs a 300mm diameter, composite, air core, quad rotor, axial flux, force cooled motor with machined windings and figures out how to make a controller that applies the correct high intensity radio frequencies to silicon graphene based vaporwarium cells to get them to self regulate voltage and current discharge rates, I think we're stuck with using some mechanical means to expand the design limitations of current tech. :wink:

Here are a couple of threads about gearing/drivetrain options that you might find interesting.

http://endless-sphere.com/forums/viewtopic.php?f=7&t=67112
http://endless-sphere.com/forums/viewtopic.php?f=30&t=47930

Just like you don't take a smoke spewing crotch rocket riding the trails, with an electric you still have to choose the right tool for the job, and you haven't sufficiently defined the job. ie total load (bike and rider), desired speeds (top speed along with minimum speed on the highly technical and challenging stuff).

Batteries have reached the stage where there isn't anything that an ICE can do that an electric can't do better, though long range at high power will be a bit bulky and expensive in terms of the battery pack.

ErnestoA said:

Here are a couple of threads about gearing/drivetrain options that you might find interesting.

http://endless-sphere.com/forums/viewtopic.php?f=7&t=67112
http://endless-sphere.com/forums/viewtopic.php?f=30&t=47930

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Both threads are flawed in their basic premise.

Like the Gas Gas, you are needing to look at mid drive if you will be riding up steep hills at 5 mph.

But as said above, we know nothing of your trails. Where I live, they call it the rocky mountains for a reason. Trails are so steep and full of boulders you simply cannot hang on to the bike at 15 mph going up them. So a hubmotor in 26" wheel fries itself. Those same trails are open to motorcycles, but nobody rides them twice! They want to ride faster.

Same grade with a 20" wheel and enough power to ride it at 15-20 mph or more, and it becomes a question of how much battery can you carry.

If you can ride 15 mph up your trail all the way, it won't be any different from roads I've ridden, 10 miles of continuous climb at 8-10% grade. That a hub motor can do easy, even only 800w will do that if you pedal enough to maintain 15 mph. Maintaining at least 15 mph up really steep grades will simply take a bigger hub motor. You can do it slower in a 20" wheel though, if the rocks allow a small wheel.

Lots of very interesting mid drive bikes with at least 800w coming in 2016. Bike shops will soon be full of mid drives. Extra battery capacity can be packed in a knapsack, if no other way works. Rear rack carry does suck, but a tiny 48v pack weighing less than 8 pounds won't affect handling that badly. Or a pack that small can be carried on the handlebars pretty easy too.

The key thing about mid drives, is you better select the right gear. Pick too tall a gear for the trail combined with your power level, and it can be about the same as the hub motor. Like a hub motor, a temp gauge could help a lot. When you see that temp suddenly spike, you are flogging the motor at too low rpm.

Again I am not talking about hard enduro or trial. In the Carpathians there are many trails, used for lugging, the idea is to TRAVEL, the question is how far can you go without thermal limits or finishing the battery.
I quess the new Bafang 750 would be enough with 120Nm, lower 'power' watts means also longer range with same battery. Energy efficiency needs to improve many many years before we can en ebike making 200km trips in the mountains. So I would like to see links to ebikes to make a table, list. For each bike real range examples - made so many miles/km, this altitude difference, on trail with this engine and this battery, and real uphill examples - so many miles/kms on a 6-12 degrees uphill ...

Cool, it sounds like you are OK with staying in the low speed/low power realm of bicycles, which means we can focus primarily on the hills/grades/slopes - i.e. the inclined plane. These grades simply help us lift us (and our bicycle) away from the earths surface (well, sea level I guess), our primary enemy is now gravity! Good thing we have Netwon's 2nd law to help us with the basics. What we need to know is how much energy is needed to lift us up, up, and away! Well, we can approximate 10 joules to lift 1kg by 1 meter. To lift 125 kg, by 1 meter - 1250 joules. Say we want a 1000 meter climb in altitude - 1.25 MJ (Mega-joules) are required. We know that 1 (Wh) watt-hour is 3600 joules. So 1.25MJ means we need to have 347.2 Wh of energy with which to do our work, at 100% efficiency. Watt hour is handy, because that is our common way of measuring battery capacity.

Since we are working on an inclined plane, the hypotenuse (distance) traveled is merely a function of how high we want to lift our bicycle into the atmosphere. If we have our perfect electric bicycle with no losses and have 350 Wh in our battery, we could travel 4.8 km at a 12 degree slope (21.3% grade), or do the same work in 9.5 km on a 6 degree slope (10.5% grade). Our primary concern is how high we want to lift ourselves. We can experimentally find our efficiency constant by traveling a short distance on our vehicle on a similar grade, to find out how many watt-hours will be lost to friction, heat, etc - as well as how much energy our food will provide us for the journey through our legs.

We can carry 500-1500 Wh comfortably on a bicycle, more if necessary. The more you add, the more work needs done to carry the extra up the hill - so adding 1000 Wh does not get you 1000 Wh more work!

edit: added % grade <> slope equivalents

Ebike range is a theory, that proves in extremes. On the same terrain, some rider will do 40 Km per charge with a bike, and another will do 10 Km with the same bike, weight and charge.

Until you know your own avg power usage, you can't define your range. You have to rely on theory, yet that can come pretty close if you can define and calculate all factors that are affecting power usage and losses.

No matter how range is important to you, the bike that you build must be able to climb the trails that you ride. If you count on yourself helping the bike to climb, it will fail the day you won't help. So, calculate the power it will need to climb the steeper sections without your help, that would be your minimal power set up target. Then, you will notice that you have enough power at hand to drain your battery pretty fast, and it will be up to you to dose watt you are using for the range that you plan.

I totally agree, and the more variables you can fix, the better a comparison can be made. A database of conditions/consumption would be useful when planning a build for the analytically inclined. The theory just helps us ballpark what is within the realm of possibility - and it handily combines with a cycle trip elevation map, which gives you total meters climbed on route. Really, a repository of GPS CA Analogger plots along with bike information such as weight and build info would go a long way.

kd8cgo said:

We can carry 500-1500 Wh comfortably on a bicycle, more if necessary. The more you add, the more work needs done to carry the extra up the hill - so adding 1000 Wh does not get you 1000 Wh more work!

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This is a great point that too many designers/inventors miss. There seems to be a positive feedback loop in e-drive design in the form of more power means more weight, which means more power is needed.

Since 68% of people's average commute is less than 20 miles, 76% drive a car, alone, 76% of mountain bike riders ride less than 20 miles on average, and after 20-25 miles of hard trail riding, most dirt bike riders are worn out, it would seem to make sense to me to develop the lightest possible machine that can reliably do all three. This means 15-25 ah of battery 3-5kw of max power is all that's necessary to cover a large portion of people's transportation and entertainment/exercise needs. This can be mounted on a sub 75lb machine, using drivetrain tech that's already available, and proven reliable. As battery tech improves, which it will, range can be improved by simply swapping out the old tech cells for new ones. As motors and controllers develop, they can also be swapped out and the transmission can eventually be removed and replaced with more battery.

http://www.statisticbrain.com/commute-statistics/
http://forums.mtbr.com/passion/average-ride-distance-426200.html

Sure, some people have got themselves into a position where they have a 90 mile commute, or can handle pounding the trails all day. They're such a niche usage group that auxiliary battery packs or heavier/more complicated machines could meet their needs for now. I know the general public tends to focus on range but they just repeat what they're told and buy what they're sold. When I used to commute on my ebike, I'd get to where I was going close to as fast as, or sometimes faster, than friends in cars and gas bikes. They never cared what my range was. They just wanted my bike. They just didn't want to pay much for it because it was less than visually stunning.

Another thing I don't understand about current/near future offerings is the sacrifice of reliability and capability in favor of range and efficiency. I'd definitely prefer an 80% efficient machine that can go anywhere and is reliable as a rock over a 95% efficient machine that could let out the magic smoke or break in half at any moment. My current project, that I will unleash on the forum soon, once it's more than a pile of parts, tools, and ideas, has seven belt drives which seamlessly combine the ev and pedal drives, and a CVT that can be used by both...lol... If it only goes ten miles per charge, at first, on pack alone, without factoring in solar charging/supplementation on the fly, or pedaling, that's fine with me, as long as it can do those ten miles reliably, in the toughest conditions.

The point is, right now, we have motors, controllers, and transmissions that are super efficient, powerful enough to handle any road or trail, and super reliable and cells that are pretty dang good. The cells are only improving and the motors, controllers, and transmissions don't care where the power comes from so it makes sense to me to put the best drivetrain components we have into the most reliable and versatile frames we can produce, and just design everything so all major components can be upgraded as the ev industry advances.

Well, now that you defined your hills slightly better, they are NOT what I would call steep or technical. I see no particular problem with long rides if the terrain is that easy. It sounds more like moderate trail to me. Still damn steep to pedal up, but not hard at all for a good off road ebike.

Sorry if I misunderstood, but I live in real mountains, where if you say steep and technical, I think shit an Iceland rock crawler still struggles on. You gotta see rocky mountain mine roads to believe them.

If the grade is mostly under 10%, then there is no reason a hubmotor running about 1000w can't climb them more or less infinitely. As I have said, and will keep repeating, keep a 26" wheel hubmotor turning at 15 mph or better, and you won't overheat unless something is broken in the system.

At that rpm, you will still heat up good, no doubt of that. But if the weather is not too brutally hot, the motor will reach an equilibrium temperature that is below the danger zone for hub motors. If that equilibrium is below 200F inside the motor, it won't even brown the windings, but 250f can be tolerated by a hub motor for a long duration.

But if already running 250F, it won't take a very long steeper section to pop that motor to 350F, where the halls die. This is where you just must have a thermometer inside the motor, so you can look at that 1/4 mile of 20%, and decide if you need to smoke a joint and let the motor cool before you tackle it or not.

The rest then becomes a matter of how the hell you carry enough battery to go that far, on a nimble trail bike. Obviously the solution starts with the very most energy dense and lightweight battery you can find. But if the trail is truly technical, you will be screwed trying to carry 30 pounds of battery. I would say carrying 1500wh would be about the max, weighing perhaps 20 pounds, located as low and centered as possible.

Oh, that much battery low and centered, how the hell do you still pedal now? The compromises begin! So perhaps 15 pounds of battery in the middle of the bike, and the rest on the handlebars or something.

Ok, so lets say you manage to pack 1500 wh on the bike and it still handles tolerably well. Call it 70 wh per mile on the uphill, and figure you pedal it back down motor off. You should be able to do at least that good, if the grades are more like 8% on 90% of the climb. That's about 20 miles you should be able to climb uphill, stopping only to cool the motor some either before, or just after the steeper bits. If you let speed drop for a steep part, or just a lot of turns, then you will have to stop to cool from time to time. But if you can really maintain 15 mph, you can go pretty much till the battery runs out.

This jibes very well with what I have done on my local hills and mountains, getting at least 10 mile runs out of 750 wh packs. I have to stop sooner, because very little of my local trails will be less than 12% grades. mostly about 15% with steep bits up to 25% for very short sections. In general I can maintain at least 12 mph up the 12% stuff. Not so efficient rpm by then, but still where the temp isn't spiking so fast it overheats in 10 min. I can make it 5 miles or so to the top, then turn around. I could keep going, if I cooled the motor. Carry water, and soak a rag to drape on the motor when you stop to cool.

The bottom line though, is you must have a thermometer in the motor to ever find out what the effects are, where you ride, how you ride, in the weather you ride in, and for your weight. When you gotta stop, you must or you will smoke a motor. But why stop when you don't have to? That thermometer will tell you when you must stop.

dogman dan said:

Sorry if I misunderstood, but I live in real mountains, where if you say steep and technical, I think shit an Iceland rock crawler still struggles on. You gotta see rocky mountain mine roads to believe them.

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Yep, everybody misunderstood, I guess.
Different riders having various interpretations of 'steep' or 'technical', we should define:

-A steep trail is one that you can hardly climb on your feet.

-Technical is when it is difficult not to put a foot on the ground on rough sections and tricky corners.

Long steep technical means this to me:
https://www.youtube.com/watch?v=FLVpoH8M-j0
but the opposite direction.

Taking my hardtail down that sucka sometime before I die, possibly right before! lol

MadRhino said:

-A steep trail is one that you can hardly climb on your feet.

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Ha, that would exclude just about every street in the world. Sounds like a dirt bike centric definition

A more bike oriented definition might be, a steep uphill is one that the majority (50%) of bikers have trouble pedalling up, maybe 15% grade. A very steep uphill is one that only the top riders (5%) can pedal up. Somewhere north of 25% grade?

tln said:

MadRhino said:

-A steep trail is one that you can hardly climb on your feet.

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Ha, that would exclude just about every street in the world. Sounds like a dirt bike centric definition

A more bike oriented definition might be, a steep uphill is one that the majority (50%) of bikers have trouble pedalling up, maybe 15% grade. A very steep uphill is one that only the top riders (5%) can pedal up. Somewhere north of 25% grade?

Click to expand...

I defined 'A steep trail' for we were talking trail.
A steep street is one you can hardly pedal, I agree.

Alex Imreh said:

How many kms/miles up a 6-15% mountain trail can go your bike without hitting thermal limits of having the battery finished?

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Not sure how useful this is as a data point, but I did a quick ride this morning from the coast to the top of a local hill, 1214 gain that ranged from 6 to 20% grade (started out flat though). I used 177wh out of 770wh in my battery, and I pedaled to get a workout.

I have a bafang mid drive and the motor was warm, not hot at the top. I believe it could keep climbing until the battery was flat or about 4x further, 17mi and 4800 foot gain.

Of course coming down used practically nothing so I ended up about 20wh per mile total

For sure, mid drive (ridden in the correct gear) for the win. But a few hundred feet of 20% is still doable with fairly mundane hubmotors, like a larger geared motor and 1000w.

Likely your mid drive does the same thing more efficiently, so that's important for what he wants, a long ride on the hilly road or trail.

But if he only needs to get up grades of 10% or less, and it's not so rocky or twisty you can't climb it at 13-15 mph, he'll get up it without smoking a larger geared hub motor easily.

There is a lot of info from you that I have to read carefully, thank you. I changed the title of the topic - no more technical, steep, just ''Long Uphills'' but to be more precise probably I should say between 10%-20%
http://www.alke.com/electric-vans-calculate-slope The engine should help enough to be able to ride short steep portions without walking.
10% 5,71 degrees all electric vehicles
15% 8,53 degrees all electric vehicles
20% 11,31 degrees Alke' electric vehicle
As a reference I think about 2 models - the Bultaco Brinco and the BHT bike.
Brinco was intented to have a 2-2.5kW engine at 33kg now it seems to have 39kg total weight, the battery is an 8kg 1.3wh liion, the engine .. becuase of hot Spanish summers hmm is still in testing, maybe they will not keep the first choice - Crystalite... https://ibikes.wordpress.com/2015/06/09/bultaco-brinco/
Yes temperature management is a must, Golden Motors have this function, the engine will stop when too hot. It would be nice to be able to choose this temperature, to have warnings, and of course to be able to follow the temp on the LCD. Keeping the speed at 15 mph or better could be difficult as trails can have corners to take and some technical parts so it does not seem to me the right solution.
I am not talking about short commuting, and not talking about doing up and down trails, a normal use implies travels up to 150-200km per day, so 50km up (plus 50km down) is the minimum range for me, in order to make a small decent travel in the mountains. The ideal thing would be to be able to go up 80-100km to have a total range up to 200km.
I tried today a Bosch system ebike, something like this http://www.centurion.de/de_de/cms/112/e-bikes_emtb , we have a Bosch factory here in my city. The factory people told me about a 60miles minimum range that could go up to 200km, I intend to read about the Bosch ebikes range.
''A more bike oriented definition might be, a steep uphill is one that the majority (50%) of bikers have trouble pedalling up, maybe 15% grade. A very steep uphill is one that only the top riders (5%) can pedal up.'' The idea is to travel on such uphills with average phisical condition, with small effort, without too much effort, with the help of the engine.
One quick ride to the top of a local hill is not traveling, it is just going to the hill next to your ''house''/camp. Travelling is going from one location to another each day. Now the discussion could get interesting if we could carry in the backack high quality foldable solar panels to charge batteries from the sun. But that's not yet realistic..
I am new to this ebike thing, for the moment I can see as a solution the BHT houte couture bike with a Bafang 750w 120Nm engine and a battery up to 1kwh or more - total weight under 40kg.
http://www.szbaf.com/en/components/component/motor/mm-g01500dv.html
But with such a battery the bike will not look anymore so skinny as in these pictures - https://ibikes.wordpress.com/2015/06/20/hagop-torossian/ With a 12kg battery this bike could be still under 40kg total weight, it could climb up to 3-4 hours ie up to 7-8 hours of riding per day, quite a good travel. And it could be still pedalled on flat roads after the battery is finished, without engine help.

With an efficient setup, in offroad conditions, plan on 50-60 watt hours per mile on average, on road, 18-25wh. This will give you an idea of how much battery capacity will be needed to get the range you're after. I've found that in hard riding, 1ah/mile can be expected. On average, with some pedal assist, my old bike would get closer to two miles per amp hour of battery capacity in mixed conditions of street/trail, uphill/downhill.

The Bafang will do the job but it's not going to do it fast. You also lose the lower front gears with it which means that riders won't be able to effectively pedal assist on the steeper hills.

Another thing to consider if the bike is going to have big travel. Stay away from square drive bottom brackets, which is what I've seen come with most commercially available solutions. They just aren't strong enough for the big drops and jumps that people are likely to try on a long travel bike, sporty looking bike like the BHT or Brinco. As far as I'm concerned, all of the commercially available options out there are best suited for on road commuters and shouldn't be put on bikes with big suspension and knobbies. It's like putting a 50cc air cooled 2 stroke on a DRZ400. If the rider is knowledgeable about the mechanical/electrical aspects of the bike and pays attention to how its used, it could get them around if they adjust their riding style accordingly. Most consumers however, don't even like to think about shifting gears and aren't going to consider things like heat buildup and efficient speed ranges. I really think that a custom setup will have to be developed for an offroad capable, reliable ebike.

Bottom line is, if you are on more moderate grades, and you are overheating a hub motor, then you have it overloaded.

When I said most any hubbie could do it, I was assuming a total weight well under 300 pounds. So this can become a problem, if you intend to carry 30-40 pounds of batteries. If your total weight gets heavy enough, then you'd have to increase the wattage to keep the speed up going up steeper hills, which means a faster use of the battery, which means increasing the wattage to keep the speed up, which means adding more weight. Like putting two mirrors facing each other, infinity.

So again, mid drive for the win, since it can crawl up those hills slower, on less watts, and not smoke itself.

How you carry a shitload of extra batteries on the bulltaco or similar bike, that's a dilemma unless you are willing to tow a trailer or wear a backpack.

For street or graded gravel dirt riding up and down mountains, I welded myself a full suspension longtail bike, and put a big fat hubmotor on it. It will climb a huge mountain pass with 8% grades easily at 15 mph, even when loaded to 400 pounds. That bike is easily able to carry 2000 watt hours (actual usable) of battery capacity, weighing up to 50 pounds.