Geared motor on tough off-road terrain - wrong choice?

[Samd]

Of all the bikes I own, mid or hub (geared or large DD) there is something very special about a light and tight geared hub at about 1300 watts that cannot be matched by the other two.
A big DD hub is wonderful but heavy. A middrive is light but finicky. The gearmotor is a punchy beast.
I've burnt a few BPM's in overdoing it as lots of others have, but it's the WRX impreza of the ebike world.

 

[flat tire]

It's very simple. If you want performance (and handling) for off road riding, you need a mid drive.

DONE, and DONE.

 

[Samd]

You'll need to back your argument with facts.

Facts are I have three mids, two big DD and two geared bikes. They are all as separate from each other as sportscars, hummers and buses.

A gearmotor is damn fast on singletrack. A mid is slowed by continuous ratio adjustment.


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[flat tire]

Well, any ebike that goes even slightly fast (and is sufficiently sturdy) will be rider limited when hauling ass on trails. Skill is by far the most important factor unless your bike is dead slow.

The mid drive has the best weight distribution and a GIGANTIC reduction in unsprung mass on the rear. That's why the handling is better, other things equal. Full stop, boom, there is no substitute for performance, and the unsprung weight deal is HUGE offroad with any kind of suspension since the ground tends to be rough. The mid drive also offers variable gearing (if you use something like an 8fun) so you can get very good advantage for steep climbs without stressing the motor while also having the capability to stretch the bike's legs on the straights. A geared hub will be ok at one and suck at the other since it has a fixed ratio.

Need more evidence geared hubs suck ass? They're not even silent, which is the biggest thing I love about my own hubmotor.

 

[Samd]

A 3.2kg bpm really doesn't impact the metacentricity any more than a bbs. And if you are going to take big drops a bbs spindle will bend.

Any evidence that a mac and a 3077 sine wave isn't silent?

If you are worried about cruising at top speed on single track you're not doing single track.

And as for ability i ride my different bikes with the same skill. Geared is quicker by an order of magnitude. Even with some automation on gear changes.

My first two bikes were middrives twelve years ago. I have a BEng Mech. And I live in a very skills-rich mountain biking region. Where gears rule the roost.


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[flat tire]

Metacentricity, huh? I'd ask where you pulled that word from but I have my suspicions. First, though, let's talk about unsprung mass. The wheel, the part that actually has to contour the ground while your suspended bike and body float above will have a much easier time doing its job if there's not whole motor weighing it down and adding in a bunch of inertia. Unsprung mass aside, changing the position of 3.5 kg on a really light e bike (with that small of a hubmotor it's hopefully pretty light) will significantly affect handling if your options are putting it inside the rear wheel versus in the middle of the frame. If you don't think it is / don't notice the difference from a hub bike versus a bike with light wheels offroad then you're not riding at even a remotely decent pace.

Now, for motors with equal power, the shifting issue is irrelevant because you could leave the mid drive in the same ratio as your hub and have equal acceleration with much BETTER handling. Or, you could shift a little, and probably go faster...

 

[Samd]

Mate I appreciate the entry level overview of unsprung weight but a quick scan of my credentials might put me well north of that. In fact similar scenarios of system dynamics were the basis of my undergrad thesis many years ago.

These days I take a decent fee to carve up high end DH and freeride bikes then fit a variety of powerplants to suit specific conditions around the globe.

Here's a bike based on the legendary Norco Shore pulling about 1350 battery watts.

On a few local singletrack runs its pretty fast mostly on account of the superior rear end. I can't take big drops due to the middrive spindle.

Here's another custom framed bike based on the equally legendary GT Fury. On most local runs it would be a good three to five mins faster despite the single swingarm. Almost precisely the same wattage. Proper crankset too.

There's also a logical flaw in your last assertion. You're confusing power with torque. Kinematics don't work the way you have incorrectly asserted there.

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[flat tire]

You mean your bottom bracket is breaking? You better find some better stuff. As far as your undergrad thesis, it obviously wasn't very good or relevant if you don't understand that mid drive is THE configuration you want for off road riding. Besides that, who cares about a thesis written in undergrad anyhow?

All kidding aside, I'm confusing nothing about "kinematics". Power is power and we are using GEARS to turn that power into torque. Power is torque * RPM so when comparing 2 motors one motor can make more RPM less torque the other can make more torque spin slower and as long as the power between the 2 is the same we can put down an equivalent torque at the wheels, which is what actually accelerates the bike, with THE MAGIC OF GEARS. Someone who wrote a "thesis" shouldn't have trouble understand that the gears are the equalizer. Powerband is another factor but with 2 pm brushless motors of equal power and optimized controller settings, I wouldn't expect much difference there...would you?

 

[Samd]

Yes. Yes you would expect a lot of difference across two totally differently constructed brushless motors.

Whats with trying to win an argument by trashing my thesis as if I know less that you, are less experienced, and moreover - using capitals?




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[Dauntless]

Whats with trying to win an argument by trashing my thesis as if I know less that you, are less experienced, and moreover - using capitals?

e. e. cummings would be on your side.

 

[flat tire]

Yes. Yes you would expect a lot of difference across two totally differently constructed brushless motors.

Whats with trying to win an argument by trashing my thesis as if I know less that you, are less experienced, and moreover - using capitals?

In brushless motors, torque ramps to peak fast from zero RPM, plateaus and then falls off. The torque curve will be SIMILAR between 2 brushless motors of equivalent power output once you equalize the torque output with gearing.

This is not about your knowledge relative to mine or anyone else. Don't assume I'm attacking you personally, I'm not. I don't know you and I'm only responding to incorrect information. You are advocating in favor of chassis arrangements that are widely known to be suboptimal for, uh, at least the last 60 years if not basically the entire history of motorcycles. To restate, the importance of reducing unsprung mass and centering your CG are not even SLIGHTLY new concepts, nor are they in the LEAST bit controversial.

As for my use of capitals, that is as much a stylistic choice as anything. Don't let it freak you out.

Anyway, if your thesis is relevant, let's see it.

 

[Samd]

Sure. It was centred around resolving harmonics in sprung trailing masses. Directly relevant.

Let me keep it simple and visual. Without capitals and smart arsed passive aggressive taunts.

If you are going to attempt to resolve the vertical harmonics of the total system by focusing on that tiny little box at the right you're using a copy-paste argument that died out a few years ago.

You may as well insist the rider takes a dump before heading out in order to get optimal performance.

Note the lack of capitals in order to bully my point. Or in your case, outdated opinion.

On second thoughts I was just browsing new posts and saw your call for comments on what its like to ride drug-f*cked.

I think we're done here.


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[flat tire]

Yes, that paper sounds quite relevant.

There are no taunts or threats here. Please do not fear my capitalized words! I will recommend not getting bent out of shape, no matter the ultimate truth. It is not worth it, life is too short 8)

Your sketch that makes it clear you would want to centralize as much mass as possible. Your heavy bike frame is suspended, and the heavier rider is VERY suspended with his legs. The mass being suspended is significant because the more you allow mass to not interfere (cause sharp transitions, fight) with the ground the better the wheels will be able to keep a consistent contact and the more grip you will have. The wheels are NOT suspended; save for a very little give in your tire, they are forced to either follow the rough patten of the ground directly or float, losing you grip. So, it is very much to your advantage that these wheels have as little mass as possible! The joke about the rider taking a dump doesn't make sense, because the fact that the rider taking a dump is very unimportant is not because his evacuation probably has a small mass, but instead due to the fact that it is placed in a suspended organ on a suspended human on top of a bike with suspension. In there is basically the best possible place you could put 1KG (or whatever) while the wheel is the WORST POSSIBLE place.

Do you disagree?

Let's simplify all this arguing. With equally good motors and other things equal, a mid drive configuration is going to give you better handling over a hub drive configuration of the same power. There is no reason to have significant mass (a motor) in non-ideal places when it can be avoided without any real compromise.

Do you disagree?

 

[nutnspecial]

Samd, this is even more ridiculous than arguing about persistant contrails not happening in another part of the world due to an advanced understanding of thermodynamics lol. What in the world are you trying to argue- of course sprooooong weight is critical to offroad ride, and if a freakin geared hub is a ferrari (or whatEVer), then what the heck is a single reduction middrive? Lol.

 

[Punx0r]

Sam, give it up It's a case of a little learning and the confidence of fools...

Flat-tire has been a vociferous instant-expert of every subject he's touched since his recent coming to this forum. As you've observed, he also smokes a lot of weed.

 

[nutnspecial]

Lol, looks to me samd is just trying to boss/push someone around, as I've seen you do too punxor.

There's so much wrong Sam's definition and follow thru of this argument about geared vs middrive I don't even feel the need to call it out.

Basically geared hubs are great and simple and snappy. Not too heavy, but the weight is still in the wrong place, the hub is susceptable to shocks of offroad, and the gearing is inadequate for the slow steeps, when compared with a typical 500-1000w middrive. Let alone the Tangent.

Also, I didn't hear single reduction (parallel or otherwise) mentioned/compared. Those are "where it's at" imo- and think BZH and LR are bringing them to public attention with the LMX and those new Raptor builds.

I also wanna understand this comparison of busses and hummers and sportscars more :wink:

 

[flat tire]

No expertise here, guys, this is really basic stuff and if you take the time to read and understand my posts you will see that. Much like Samd's undergrad "thesis", my other meanderings on this forum are not relevant to this discussion on chassis configurations...my claims will either stand on their own or not.

To clarify so there's no confusion, YES, geared hubs can be ridden off road successfully. BUT, a geared hub configuration is technically inferior to an equivalent mid drive in terms of off road handling for all the reasons described above which are clarified and concentrated in my last post. If you don't understand what I mean by something, ask, and I will illuminate.

 

[Samd]

But the thing is Flat Tyre - they're not.

You haven't addressed the shifting delays (makes them slower). I don't see any electric drag cars or even a Tesla p90d with a gearbox.

And you haven't addressed the rear wheel dynamics. You've only cited that they're an unsprung issue in the vertical direction. They're not. Feel free to drop the equations of motion below and take the derivatives. 130kg up front doesn't care about 3kg more trailing it. Its a fallacy.

And nutspecial you should probably let the chemtrail conspiracy junk go man. They're a hoax.

If you want to play the anti-academic route thats fine. Come back when you own a couple of each type of bike and you can wheelie the geared one.


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[flat tire]

You haven't addressed the shifting delays (makes them slower). I don't see any electric drag cars or even a Tesla p90d with a gearbox.

There's funny, it's just a few posts back:

Now, for motors with equal power, the shifting issue is irrelevant because you could leave the mid drive in the same ratio as your hub and have equal acceleration with much BETTER handling. Or, you could shift a little, and probably go faster...

The Tesla doesn't need more than one ratio (it does have a gearbox) because it has overwhelming power and torque available at all reasonable speeds. When we can say the same about the power of an ebike motor, it becomes significantly heavy and you would incur a GIGANTIC handing penalty, especially offroad, by putting it in the rear wheel. Mid drive is the only reasonable option.

And you haven't addressed the rear wheel dynamics. You've only cited that they're an unsprung issue in the vertical direction. They're not. Feel free to drop the equations of motion below and take the derivatives. 130kg up front doesn't care about 3kg more trailing it. Its a fallacy.

Lighter wheel has less inertia, is more easily able to conform to the terrain, giving you more grip. The extra weight in the back will also make the bike understeer more. It's not rocket science. The handling characteristics of a hub vs mid drive are EXTREMELY noticeable to me and I'm not even that fast of a rider. Since you say you ride and have experience on both configurations, I can only conclude that you're either dreaming or you have about as good a grasp on riding as you do of the subject matter at hand.

So to recap:

Mid drive:

Pros:
--centralized mass
--reduced unsprung mass
--variable gearing easily avaiable

Cons:
--more complicated to install
--variable gearing not easily available over a certain power level


Geared hub:
Pros:
--Easy to install
--Simpler
--Easier to find in high power levels than bolt on mid drive kits

Cons:
--significant increase in unsprung mass
--screws up the bike's balance, makes it understeer more
--no variable gearing without making things rather complicated, heavier and / or more fragile and more expensive

 

[nutnspecial]

It's not rocket science.

Apparently it is . . . to some :| Seriously good on you for continuing, I don't see how Mr Sam is deserving of the logic and well formed argument.

And nutspecial you should probably let the chemtrail conspiracy junk go man. They're a hoax.

I didn't say it. You did. Also, I like that's all you have to retort to me. . . .
Please stop arguing about nothing Sam (or just for argument sake - some might say), and pushing your <self perceived> weight around. If you were as claimed, these perceived 'attacks' by flat tire would roll right off your back, and you'd not be so thin skinned (and illogical) in arguments. You'd patiently make your point instead of condescension coupled with the poorly made and sometimes rhetorical points.

So what is it? Geared bikes are better offroad for some applications and people? Sure, why not- I'll give you that. You like them better? Same. That's the extent of this argument imo, and you're doing nothing but flatulate it with ego. Of course less sprung weight is better. Is 8-10 lbs extra a deal breaker? Not for people that don't ride the bike real hard, I guess. Is a single ratio @ ~1kw enough to give good starts and climb decent hills? Maybe when your idea of 'good' and 'decent' differs from what a serial middrive can do, or a single reduction mid with a big motor.

Short story: please use this supposed authority/superiority you have not to act like an asshole. :lol:

 

[flat tire]

I don't see how Mr Sam is deserving of the logic and well formed argument.

It's not so much for Sam's benefit as for the benefit of all the people who will read this thread later. I want them to learn the right things

If you were as claimed, these perceived 'attacks' by flat tire would roll right off your back, and you'd not be so thin skinned (and illogical) in arguments. You'd patiently make your point instead of condescension coupled with the poorly made and sometimes rhetorical points.

Yeah, pretty much.

 

[Samd]

You'll need to address the reasons why the gear white bike is faster on several segments of single track than the mid driven Norco, or your points are just opinions. Your declaration that middrives are always better is incorrect.

To quantify the unsprung mass impact, its a little under 3% for a BPM. The constant gear shifting is a higher penalty.


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[flat tire]

You'll need to address the reasons why the gear white bike is faster on several segments of single track than the mid driven Norco, or your points are just opinions.

Maybe your geared hub is more powerful. If the bikes accelerate equally quickly then the only reason the mid drive would be slower on your single track is if it's mounted on a worse bike, or has a worse rider. If the rider on the mid drive HAS to shift all the time just to be close to the geared hub, then obviously that motor isn't as powerful. If the bikes accelerate just the same and rider skill is equivalent, then the bike with the better handling will have the advantage. You keep talking about having to shift all the time so I'm really suspicious that your geared hub is way more powerful than your mid drive. Can you clarify for us, if the ratio on your mid drive is set to the same top speed as your geared hub, which one accelerates faster?

Your declaration that middrives are always better is incorrect.

They're not always better. For example, maybe someone only needs one specific ratio and doesn't want the hassle of a mid-drive build. In that case a geared hub could be a good choice. For performance, other things equal, a mid drive will always have better handling than a hubmotor due to mass centralization and reduced unsprung weight.

To quantify the unsprung mass impact, its a little under 3% for a BPM. The constant gear shifting is a higher penalty.

The vast majority of the bike's mass is suspended. Really, this point you either don't understand what unsprung mass is or you're being disingenuous. You're comparing a wheel weighing a couple kilos with one weighing what, 8 kilos? Even when we add the weight of the swingarm, the tire, and whatever other unsprung crap there is in the rear that's a doubling of rear unsprung mass...not a 3% increase. We don't need to do math, though, you can just go ride some trails. Try to push yourself on that geared hub and you will find the understeer I'm talking about.

And for the fifth time, with equally good motors, you won't NEED to shift the mid drive. The shifting will just be icing on the cake.

 

[Punx0r]

Saying "less unsprung mass is better, therefore mid-drive is better" is a gross over-simplification. You can't judge the overall suitability of a system based on one axiom.

On technical subjects some people know what they're talking about and some people think they know what they're talking about. The latter tend to draw sweeping conclusions based on a single factor, while the former have the knowledge and experience to arrive at the best compromise that works in a real-world application. This is usually non-ideal in most or all factors. That's what you pay an expert for: google will tell any idiot in 10 seconds that "unsprung mass = bad for handling", the expert can tell you whether or not this is relevant in a given application.

 

[Alan B]

There are many factors aside from unsprung weight that make the geared hub a poor choice for tough off-road terrain. It can work but it has many disadvantages.

A mid drive in the right gear doesn't have to shift to equal the geared hubmotor. They can be essentially exactly the same, given the same power. The mid drive has the option of shifting to yield improved torque or speed over the fixed geared hubmotor.

I often ride my mid drive that way, in one gear. A middle gear that will both lift the front wheel and reach good top speed. Why shift when it isn't necessary?

The mid drive has the option of changing the gearing to match the terrain. The geared hubmotor is fixed into one gear which is a compromise between torque and speed.

The mid drive motor can be much better cooled than the geared hubmotor due to a number of physical factors. The geared hubmotor subjects its gears to higher temperatures due to the thermal path and proximity of the small total volume and narrow packaging format.

The geared hubmotor makes fixing flat tires a greater chore with a heavy wheel, torque arms, motor wiring and nutted axles. The mid drive has standard light wheels and quick release axles. Wheel swaps are easy.

As the gradient increases the mid drive can be downshifted to produce more torque per amp. The geared hubmotor's torque per amp rating is fixed and i squared r losses get very high when very high torque is needed. Geared hubmotors are not competitive on really steep gradients as they overheat.

In summary, geared hubs work well, but when the going gets really tough they lack the flexibility of the mid drive's ability to adapt gearing ratios to the task. Changing tires is more difficult.

How much these differences matter depends on your needs. Tough off-road, as stated in the title, would seem to favor the mid drive choice.