Specialized Stumpjumper conversion recommendations

General Discussion about electric bicycles.
raylo32   10 kW

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Re: Specialized Stumpjumper conversion recommendations

Post by raylo32 » Jul 23 2021 7:47am

I looked into that a while back and couldn't find any of the common providers making hubs for thru axles. Not to say they don't exist but if they do they are hen's teeth and probably $$. One thing to consider with your bike... the way the down tube is arranged there is a ton of room inside the triangle and the CYC pro and I believe also the new Stealth have a mounting option that puts the motor above the down tube. That would provide the ultimate clearance and keep the motor out of the dirt and mud spray. I am still waiting to see more Stealths in the hands of users but the Pro is a solid bit of gear so I expect they will be fine. I may be converting a ti gravel bike in the future and the Stealth will be in the running for sure... although not so much because of the extra clearance since that is not an issue for a gravel bike.

I am itching to take my Stumpy out to one of our rocky trails but even with added straps I am still not thrilled with the battery mounting for that kind of riding. Usually I need the big battery because I ride to and from the trails... but I may get one of those smaller rectangle batteries and a bag to use when I drive to the trail head and just bash around the trails.
tomolry wrote:
Jul 23 2021 7:30am


Now to figure out the motor. Can some verify a rear hub is a no go with thru axle?

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Re: Specialized Stumpjumper conversion recommendations

Post by Hillhater » Jul 23 2021 8:12am

For best bike balance and handling for trails, off roading, and serious downhill, pet the battery in a backpack with a flex connection down to the mid motor.
After 15 mins you will forrget you have a backpack and just enjoy a really light ebike ! :bigthumb:
This forum owes its existence to Justin of ebikes.ca

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Re: Specialized Stumpjumper conversion recommendations

Post by raylo32 » Jul 23 2021 8:18am

But backpacks make me sweat even more than I already do. I hate backpacks. Part of my roadie background, I suppose. Now I DO wear a backpack when I take the Stumpy or TSDZ2 Cannondale on a beer and wine run. No getting around that... and it isn't very far.
Hillhater wrote:
Jul 23 2021 8:12am
For best bike balance and handling for trails, off roading, and serious downhill, pet the battery in a backpack with a flex connection down to the mid motor.
After 15 mins you will forrget you have a backpack and just enjoy a really light ebike ! :bigthumb:

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Re: Specialized Stumpjumper conversion recommendations

Post by raylo32 » Jul 23 2021 8:23am

But if I can find my old MTB backpack and want to try this can you point to an example of the "flex connection"?
raylo32 wrote:
Jul 23 2021 8:18am
But backpacks make me sweat even more than I already do. I hate backpacks. Part of my roadie background, I suppose. Now I DO wear a backpack when I take the Stumpy or TSDZ2 Cannondale on a beer and wine run. No getting around that... and it isn't very far.
Hillhater wrote:
Jul 23 2021 8:12am
For best bike balance and handling for trails, off roading, and serious downhill, pet the battery in a backpack with a flex connection down to the mid motor.
After 15 mins you will forrget you have a backpack and just enjoy a really light ebike ! :bigthumb:

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Re: Specialized Stumpjumper conversion recommendations

Post by Grantmac » Jul 23 2021 10:36am

Backpack battery is one option. Custom to fit the frame is another, especially if you keep the power and battery small.

Definitely don't do a rack mount battery and hub motor, you might as well ride one if the dinosaurs Chalo posted.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 23 2021 10:47am

Grantmac wrote:
Jul 22 2021 11:34pm
I actually think the Stumpy frame is ideal, but not for a BBx based build. For a X1 Stealth or possibly Lightest (once they ship) it's about perfect BECAUSE you can put the motor and a decent sized battery inside the frame.

Also they use a BB30 bottom bracket which you can now get very nice freewheeling cranks for via the trials community.
Grant, what is an X1 Stealth? I'm assuming a Luna brand, but I only see some kind of rigid bike with "stealth" in the title. I looked for something they're preparing to release perhaps, but didn't see anything with that name. Something new? We are talking about mountain bikes, right?

If I remember correctly, you're somewhat anti-mid-drive conversion for actual mountain biking...or have I confused you with someone else? Regardless, I kind of get that because I had little hope of this application working very well. I see you're from BC. You see me often joke about "not-for-Red-Bull-Rampage" riding on some of my posts. While poking fun a bit, I do want people to know this type of conversion is not up to some of the shenanigans that the Fro Riders like Wade Simmons, Schley, and Tippie were up to in your neck of the woods by any means, but let's be serious...who is?...LOL!

However, I'd have no qualms about riding a good all mountain or enduro framed bike with a mid-drive on Porcupine Rim in Moab for example...if it were still legal to ride the whole trail anymore. In my best and younger years of riding there on very good bikes, there were always those three, maybe four or so spots where mere humans had to get off the bike because of crazy tight squeezes or like that step-up near the end where you cross the dry creek bed. Obviously there are riders who can tackle some of those features...I've been with them on some of our trips there...but they are not the norm. Even my skill level at my best was a little higher than "the norm". The highest percentage of "mountain bikers" out there are not going to be "sending it" like Simmons and Schley...me included...and a good, solid full suspension frame that will accept a mid-drive will be more than adequate for some decently serious trail riding.

On your mention of an X1 (enduro?), I don't think I'd mind one of those at all. However, I'd have to be into it by about $4K when it was over. A no-holds-barred bike for me would be a Santa Cruz Bullit emtb, but the money is out of the question. Already having an older Nomad in pristine condition with some high dollar components already attached was an easier pill to swallow and give a try. Heck, if I found it to suck as a trail bike, I'd still attach the motor and battery to one of my other bikes and make something more urban for grins. A BBSHD is a hoot just for fun no matter what you put it on. I've mentioned before that I work at a Trek and Specialized shop. I get to ride both of their emtb's, and they are impressive. My Nomad/BBSHD isn't that far removed from those with good programming, and I still have money in my pockets. Plus, I have a throttle when desired and way more power when desired. Some who poo-poo using a good framed mid-drive MTB setup as a decent off road bike are missing out on some fun. Oh...and tell Wade Simmons hello. :mrgreen:

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Re: Specialized Stumpjumper conversion recommendations

Post by efMX Trials Electric Freeride » Jul 23 2021 11:57am

CYC X1 Stealth (NEW) : viewtopic.php?f=28&t=110305
some ride & sk8 videos:
metacafe.com/channels/NATAS666DAMIEN
http://www.youtube.com/natas666damien
i have nothing for sale.. :)

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Re: Specialized Stumpjumper conversion recommendations

Post by HrKlev » Jul 23 2021 12:01pm

tomolry wrote:
Jul 23 2021 7:30am

Now to figure out the motor. Can some verify a rear hub is a no go with thru axle?
No problem using a hub motor motor on a through-axle bike! Wouldnt want to mount in inside the wheel, though. Sounds like a bad idea for offroad use.
20210716_210222.jpg
20210716_210222.jpg (3.66 MiB) Viewed 297 times
Looks like there's more than enough space in a Stumpjumper frame to mount a battery pack. Just get yourself a 3d printer and get creative 😁
Hubdrive as middrive, with torque sensing EMTB build: viewtopic.php?f=6&t=107622

6x6 conversion: viewtopic.php?f=34&t=109567

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Re: Specialized Stumpjumper conversion recommendations

Post by Grantmac » Jul 23 2021 1:27pm

I'm very PRO mid-drive and ANTI hub motor for off-road use actually.

What I am against is loosing ground clearance and having a motor hit obstacles first.

As was just posted the X1 is a mid-drive from CYC which has just started shipping.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 23 2021 5:03pm

Grantmac wrote:
Jul 23 2021 1:27pm
I'm very PRO mid-drive and ANTI hub motor for off-road use actually.

What I am against is loosing ground clearance and having a motor hit obstacles first.

As was just posted the X1 is a mid-drive from CYC which has just started shipping.
OK, glad I got to see that. That dual chain setup is totally outside my wheelhouse. Are those problematic in any way as far as rough off road use? Pure speculation on my part, but that drive chain looks every bit as exposed as a BBSHD. I'm a dirt motor guy. Almost no one runs a dirt motor off road without a skid plate. Obviously those skid plates are bike specific. This is one of those elements that all bicycles with mid-drive motors used for off road should have, but I understand that's not realistic for all applications. The Trek Rail 7 demo bike we have at the shop, has a thick, rubberized kind of cover on the bottom of the frame below the motor...a very good idea.

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Re: Specialized Stumpjumper conversion recommendations

Post by HrKlev » Jul 23 2021 5:30pm

TNC wrote:
Jul 23 2021 5:03pm

OK, glad I got to see that. That dual chain setup is totally outside my wheelhouse. Are those problematic in any way as far as rough off road use? Pure speculation on my part, but that drive chain looks every bit as exposed as a BBSHD. I'm a dirt motor guy. Almost no one runs a dirt motor off road without a skid plate. Obviously those skid plates are bike specific. This is one of those elements that all bicycles with mid-drive motors used for off road should have, but I understand that's not realistic for all applications. The Trek Rail 7 demo bike we have at the shop, has a thick, rubberized kind of cover on the bottom of the frame below the motor...a very good idea.
Never tried a bbshd before because if the lack of torque sensor. Did run a tsdz2 which is smaller, and it got a lot of beating over rocks and logs. That is not what killed it, though.

I've never hit the motor in picture, the main chainring has gotten a few hits, but its still in decent shape. I did get a big stick in the chain at one point, so I had to loosen the chain and retighten it, but no biggie. Should probably make some kind of guard, but as long as its working, Im too lazy.
Hubdrive as middrive, with torque sensing EMTB build: viewtopic.php?f=6&t=107622

6x6 conversion: viewtopic.php?f=34&t=109567

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Re: Specialized Stumpjumper conversion recommendations

Post by 2old » Jul 23 2021 6:40pm

raylo32 wrote:
Jul 22 2021 9:43am
I ran into that issue converting my Cannondale F1000 with TSDZ2. The solution is simple, just add a couple mm of spacers to move the motor case away from the stay. BBS installs face the same issue and they sell the spacers as installation accessories.
2old wrote:
Jul 22 2021 9:36am
Additionally, the chainstays may be designed such that the right side of the motor won't "nest" acceptably.
Problem for me was twofold. First, the distance of the right crankarm from the chainstay already favored the right side by 10 - 15 mm, and this exacerbated the problem, and secondly it didn't allow me to use the jam nut to hold the motor on. I just used a different frame since there were a bunch in my "parts" box.

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Re: Specialized Stumpjumper conversion recommendations

Post by 2old » Jul 23 2021 6:54pm

TNC wrote:
Jul 22 2021 10:55pm
tomolry, if you intend to do any real mountain biking, that long curve at the intersection of the downtube and bottom bracket will kill your ground clearance with a mid-drive. And I'm not referring to just hardcore off road stuff. Mid-drives are likely the best choice for off roading as you get to use your rear cogset, and the center of gravity is much better. Also hub motors affect unsprung weight fairly detrimentally as far as the suspension goes.

On suitable frames, you need one that has a direct, straight line from the headtube to the BB like raylo's pic. This gives the best fitment for a BBSHD or BBS02. I admit to being biased toward these two motors for actual off road us due to their power and the ability to be easily programmed to fit a specific rider's needs and conditions. I use a BBSHD on a long travel, Santa Cruz Nomad. The beauty of these longer travel, big hit bikes is they are super forgiving and very competent on gnarly terrain. Their weight actually becomes a positive with a motor, as you get more stability in rough terrain.

On 2old's comment about the 73mm bottom bracket being an issue, I'm not sure that's a general issue. My Nomad has a 73mm BB, and the main locking nut and jam nut fit perfectly. On a lot, maybe most of these conversions with the 68-73mm BB, you often need to go to something like the Luna Eclipse 42T chainring setup to get a good chainline.

Battery choice and location is one of the biggest decisions on a conversion. I'm a backpack battery guy, and it works great for me and serious trail riding. A lot of people are not in favor of this system, but it works great for me.

One other often mentioned snafu with a mid-drive is ground clearance for real off road. I thought this would be the biggest headache trying to ride with one of these...bashing the motor, etc. It's rocky on the trails I ride here in west Texas. Just today I was marveling how well the BBSHD on my Nomad clears rocks and small ledges. With only a little attention to proper line selection, this hasn't been the issue I thought it would be. In fact, my Nomad has about a 1/4" more ground clearance than the Trek Rail 7 emtb we have as a demo bike at the shop. I'm running an 8" dual crown DH fork and have 6.5" at the rear with a coil DH shock. It probably increases my ground clearance in a good way. The trail I was on today is one I helped open and build since 2000. It has names like Rock Canal, Triple Diamond, Rock Bridge, Troy's Revenge, Jacob's Ladder, Buck Creek's Revenge, and on, and on. Those names are not for simple obstacles on the trail. This is a rocky, rough single track. My Nomad has been doing just fine out there despite these crazy zigs-and-zags through odd, uneven rock obstacles. No one is more surprised than me. It's been a hoot.

I only go into some detail on all this to try and convince those who are really going to do more than smooth, winding single track to get a bike with some travel like an all mountain or enduro level bike. These bikes that allow good fitment of a mid-drive and really shine on a decently rough trail. While I will not claim that mid-drive conversions are going to make good Red Bull Rampage rides, they are capable of way more than I would have expected.
There's absolutely no way to use the "jam" nut on a 73mm BB with a BBS02. It has been reported repeatedly and I've observed it on several frames.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 23 2021 6:59pm

The lack of torque sensing on the BBSHD has not been an issue once properly programmed for my riding style. It's pretty impressive how responsive one can get the power delivery dialed in fit one's preference. I've also ridden our shop's Trek Rail 7 demo bike. The Bosch torque sensing motor is impressive, but I've gotten very close to that with the BBSHD. With 9 levels of programmable pedal assist, you can get all kinds of input intensity. One main benefit is the separate throttle. There's nothing like it when you start to stall in a rocky climb, and the throttle maintains your momentum. I don't have to use it a lot, but when I do it's a real benefit.

And I in no way poo-poo other types of motors. Choices and competition make all these products better and more refined in the long run. And that's the interesting thing about these bike forums. A place like MTBR is more hardcore off road, but most of these ebike forums cover such a wide array of bike, trike, quad, etc. that it's hard to keep up. Not everything crosses over, and that sometimes gets confusing at to what works best for what application. It's still neat to see all the different options even when they won't apply to my specific use.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 23 2021 7:05pm

2old, I'm referring to my BBSHD, not the 02. Still on the 02 or HD, the jam nut is not an actual requirement. It does make for a cleaner looking install, however.

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Re: Specialized Stumpjumper conversion recommendations

Post by Grantmac » Jul 24 2021 10:26am

TNC wrote:
Jul 23 2021 5:03pm
Grantmac wrote:
Jul 23 2021 1:27pm
I'm very PRO mid-drive and ANTI hub motor for off-road use actually.

What I am against is loosing ground clearance and having a motor hit obstacles first.

As was just posted the X1 is a mid-drive from CYC which has just started shipping.
OK, glad I got to see that. That dual chain setup is totally outside my wheelhouse. Are those problematic in any way as far as rough off road use? Pure speculation on my part, but that drive chain looks every bit as exposed as a BBSHD. I'm a dirt motor guy. Almost no one runs a dirt motor off road without a skid plate. Obviously those skid plates are bike specific. This is one of those elements that all bicycles with mid-drive motors used for off road should have, but I understand that's not realistic for all applications. The Trek Rail 7 demo bike we have at the shop, has a thick, rubberized kind of cover on the bottom of the frame below the motor...a very good idea.
Not generally problematic any more than the chain wheel on a regular bike.

The strength of the X1 or Stealth is they can be mounted inside the frame. Also on a 29er the chain wheel is pretty small.
Because of the chain secondary you can also play with the gearing much easier.

The downside to them is they rely on a kinda crappy bottom bracket if you want torque sensing and they are a bit louder than the BBx series at similar power levels.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 24 2021 2:53pm

Grant, that's an interesting motor for sure. I read up on what's out there at the moment, and I'll keep my eye on this option. The impressive stuff was in regards to alleged efficiency and power. I'm sure I missed it somewhere, but do you recall the weight of the motor and its necessary components?...not with battery. I'd like to see quite a few in use and hear the feed back on how they work for off road.

This is both the interesting but sometimes confusing thing about most of the ebike forums. Feedback comes from so many venues of use and abuse that you really have to sift through info that fits the riding type and application your looking for. That's not really meant as a complaint...just kind of the nature of ebikes.

I just did another lengthy off road ride this morning and really appreciate the BBSHD's performance. But being a dirt and street motor guy too, I appreciate new and better technology when/if it comes along.

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Re: Specialized Stumpjumper conversion recommendations

Post by Grantmac » Jul 25 2021 3:17pm


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Re: Specialized Stumpjumper conversion recommendations

Post by raylo32 » Jul 25 2021 6:05pm

I read this all the time from BBS riders, but no matter how you program them whatever assist level you ride in is just an on/off switch that provides a fixed assist power. It is a very awkward way to ride a bike.
TNC wrote:
Jul 23 2021 6:59pm
The lack of torque sensing on the BBSHD has not been an issue once properly programmed for my riding style.

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Re: Specialized Stumpjumper conversion recommendations

Post by Chalo » Jul 25 2021 6:58pm

raylo32 wrote:
Jul 25 2021 6:05pm
I read this all the time from BBS riders, but no matter how you program them whatever assist level you ride in is just an on/off switch that provides a fixed assist power. It is a very awkward way to ride a bike.
I didn't find it at all awkward when I had a BBS02, just as I don't find it awkward to use throttle only on my current bikes. Steady power is what e-motors do best. Turning on a constant power assist by turning your feet over makes both intuitive and ergonomic sense to me.

What I do find awkward is torque sensing that lags pulses of motor power behind the application of pedal power, like the TCDM/Cycle Analyst setup I tried on a pedicab we built up. When that dude mangled his sensor pulling out the bottom bracket for maintenance, I think he may have done himself a favor.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 26 2021 12:36am

raylo, I'm not getting your take on this. In your reference to the on/off switch aspect, technically that may be true in the way the PAS works, but in actual practice the power delivery is smooth if the parameters in the tuning are done correctly...or at least programmed in a way that fits one's preference. A gas engine spark plug(s) are basically on/off switches, but timing and other parameters make them work just fine. I think you may be over exaggerating the issue.

On your description of "awkward", I would agree on my first off road trail ride on somewhat challenging terrain, it was a herky-jerky mess. A mess, but I could still ride it without hitting a tree or launching off the trail. But that was not too difficult to program out after about three sessions. Where I ride I could not hit some technical sections with an awkward power delivery.

raylo, I don't know your personal experience with a BBSHD. I would guess that if you had one, you programmed it in some form. All I can say is that mine works extremely well. You say you read all the time from BBS riders that they achieve smooth power delivery after programming. Maybe there's a reason for that. I will admit that I expected mediocre performance at best. I've been super pleased. I will not badmouth torque sensing motors...at least the Trek and Spec versions we've sold at the shop. In particular we have a Trek Rail 7 that is a really good emtb. It works. But I just can't find much to complain about on my BBSHD.

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Re: Specialized Stumpjumper conversion recommendations

Post by raylo32 » Jul 26 2021 7:27am

Sorry, I am not trying to convince you. Just trying to inform any serious riders looking to add an e-bike to their fleets of pedal bikes like I did who may not understand what PAS is and that is it unlikely to be how they think an e-bike would or should work. IMO, PAS is simply not acceptable. As always, YMMV and as long as you are happy...
TNC wrote:
Jul 26 2021 12:36am
raylo, I'm not getting your take on this. In your reference to the on/off switch aspect, technically that may be true in the way the PAS works, but in actual practice the power delivery is smooth if the parameters in the tuning are done correctly...or at least programmed in a way that fits one's preference. A gas engine spark plug(s) are basically on/off switches, but timing and other parameters make them work just fine. I think you may be over exaggerating the issue.

On your description of "awkward", I would agree on my first off road trail ride on somewhat challenging terrain, it was a herky-jerky mess. A mess, but I could still ride it without hitting a tree or launching off the trail. But that was not too difficult to program out after about three sessions. Where I ride I could not hit some technical sections with an awkward power delivery.

raylo, I don't know your personal experience with a BBSHD. I would guess that if you had one, you programmed it in some form. All I can say is that mine works extremely well. You say you read all the time from BBS riders that they achieve smooth power delivery after programming. Maybe there's a reason for that. I will admit that I expected mediocre performance at best. I've been super pleased. I will not badmouth torque sensing motors...at least the Trek and Spec versions we've sold at the shop. In particular we have a Trek Rail 7 that is a really good emtb. It works. But I just can't find much to complain about on my BBSHD.

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 26 2021 9:43am

raylo, there's no "sorry" of any kind that needs to be attached to your statements. This is a discussion and often opinion forum, and the more info the better. As long as civility of some level is observed, there is seldom an absolute for every rider, for every ebike, and every condition. As I stated before, this is one of the sometimes confusing things on these ebike forums. I come from an exclusively off road MTB venue while others come from all manner of emotors and ebikes. I may work at a shop and ride a bicycle, but all experiences do not overlap.

raylo, if you don't mind, like I asked grant on another post, what is your main form of riding and what kind of bike(s) do you ride? To me, this tends to provide a better understanding of where each of us is coming from.

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Re: Specialized Stumpjumper conversion recommendations

Post by HrKlev » Jul 26 2021 1:00pm

Its seems like its quite personal how people want to get around. Im with raylo here, a cadence sensor is not how I want to ride the tecnical terrain on a pedal bike. I did also start out with cadence based pas, and spent a good while trying to tune it. But there is no way around relying on the throttle to get around the technical stuff, and that ruins the whole bike experience for me. I'll rather take the dirt bike and skip the pedaling, then. I have a throttle on my MTB's, but I very rarely use them for anything else then walk assistance instead if pushing the bike.

For cruising down the road, I really enjoy cadence based pas on my heavy DD hub bike. So smooth!

A badly tuned or laggy torque sensor I can only imagine to be the worst of both worlds.
Hubdrive as middrive, with torque sensing EMTB build: viewtopic.php?f=6&t=107622

6x6 conversion: viewtopic.php?f=34&t=109567

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Re: Specialized Stumpjumper conversion recommendations

Post by TNC » Jul 26 2021 2:51pm

HrKlev, from your post I take it that you also ride a dirt motor. I'm curious as to which throttle system for the mid-drive that you use. I was able to live with the universal Bafang thumb throttle, but the twist grip throttle put me back at home as a dirt motor guy. Like you, I rarely use the throttle. However, in those occasional, critical spots where an unexpected stall out starts to occur or just a step-up that isn't going to happen with pedal-only, the throttle is a pleasure.

On your statement that "there is no way around relying on the throttle to get around technical stuff", I think that may depend on the rider and what they're able to do with PAS only. I'm fairly new to emtb's but not MTB's. I notice the more I ride this mid-drive Nomad, the more I get used to what PAS is capable of vs. my old pedal-only routine. Depending on how one has the program tuned, and which display level one selects, the PAS is pretty effective if you're in the right rear cog...that part not being any different from pedal-only off roading.

Of course it would be pretty presumptous of us to think our individual riding preferences, bikes, and components would fit every rider out there...LOL! We know better. Rider skill, age, and type of bike all come together to make the options all over the board.

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