Specialized Stumpjumper conversion recommendations

tomolry

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Howdy. I have the same bike as in this video and would like to do a conversion:

https://www.youtube.com/watch?v=7qO1Yuj3sH4

However, there are few issues with this frame. One is that due to the frame shape a mid drive motor will need to hang down causing loss of ground clearance. Also I'm not sure a read hub motor will work due to it being a thru axle (?).

The other issue is the I don't think I can find an off the shelf battery suitable for mounting on the frame (want a longer range than the under-seat shown in the vid). I was thinking of using a stem mounted rear rack I already have (link below) to mount the battery. It's weight limit is 20lbs and seems very solid, but wonder how it will hold up. I'm 57 and I'm a pretty tame rider, but I still want to be able to take it on somewhat technical single track.

https://www.amazon.com/dp/B002T5GHNI?psc=1&ref=ppx_yo2_dt_b_product_details

Looking for any thoughts or recommendations. Thank you!
 
I just did a conversion on a 2003 Stumpjumper XC. I went with CYC X1 Gen 2 because this motor has a torque sensor and provides outstanding clearance and has power to spare, especially for MTBing where one is often constrained by terrain from really going too fast. But it will roll along at 45 mph on throttle on flat pave even on soft knobbies if you want to and have the battery for it. A bit noisy... but that's the tradeoff for the clearance as opposed to BBS or TSDZ2.

The motor install fits easy peasy but as you say the battery is an issue. No room in the triangle for a shark pack. So what I did for now was to add several rivnuts to the underside of the down tube to install the battery mount. But I don't think that is really strong enough especially if you are riding rocks and such. So I always wrap the battery to the down tube with a couple of velcro straps... could use duct tape if you leave the battery in that bike for charging.

On my bike there is plenty of clearance for the battery installed this way, even with full fork compression. Not sure about yours. You would need to mock it up to be sure.

CYC_Installed.jpg
 
Thanks for the reply, raylo32. I like the motor recommendation, but not the price. :)

What do you think of the seat stem rack mount for the battery? I'm afraid the underside of the down tube would be an issue when the front shock compresses fully. Was thinking of putting a 15lb weight on it and taking the bike of some rough terrane to test it out.
 
You're correct, ground clearance will be an issue, as well as the 73 mm BB (can't use a jam nut). Additionally, the chainstays may be designed such that the right side of the motor won't "nest" acceptably. Battery mount should work, but I would insulate from vibration with some foam (JMO, as I've done the same thing).
 
Seat stem rack would probably be OK for a small battery but I'd be reluctant to put a full size shark or somesuch on it for serious technical riding. They say 22 pound capacity and these batteries are only about 10 pounds but the dynamic loads when you hit bumps will be much higher. Same issue I face with my under down tube mount. I have done some good singletrack with it but not any big rock gardens... yet. I guess it really depends on how and where you will ride and how heavy your battery is. I also wonder how such a high battery mount would affect handling. I picked up a car battery at the parts store and rode it home once upon a time on an old pedal MTB with rear rack and it felt very ungainly. But that was a very heavy battery.

My other bike has a TSDZ2 and I'd be inclined to try that on a MTB before a BBS. It has plenty of power and a torque sensor... plus is it smaller and lower weight than a BBSHD so slightly better clearance and cheaper, too. Not as much power as the CYC or BBSHD but really has plenty. Just IMO and experience.

tomolry said:
Thanks for the reply, raylo32. I like the motor recommendation, but not the price. :)

What do you think of the seat stem rack mount for the battery? I'm afraid the underside of the down tube would be an issue when the front shock compresses fully. Was thinking of putting a 15lb weight on it and taking the bike of some rough terrane to test it out.
 
raylo32 said:
CYC_Installed.jpg

Well you have a decent fork on there but you need a longer travel fork. I just fixed the same situation on my bike by installing a downhill fork. It can be quite dangerous if you compress the front fork all the way and it bites down on the tire as you will go over the handlebars. Don’t ask me how I know this 😅
 
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 said:
Additionally, the chainstays may be designed such that the right side of the motor won't "nest" acceptably.
 
tomolry said:
Howdy. I have the same bike as in this video and would like to do a conversion:

https://www.youtube.com/watch?v=7qO1Yuj3sH4

However, there are few issues with this frame. One is that due to the frame shape a mid drive motor will need to hang down causing loss of ground clearance. Also I'm not sure a read hub motor will work due to it being a thru axle (?).

The other issue is the I don't think I can find an off the shelf battery suitable for mounting on the frame (want a longer range than the under-seat shown in the vid). I was thinking of using a stem mounted rear rack I already have (link below) to mount the battery. It's weight limit is 20lbs and seems very solid, but wonder how it will hold up. I'm 57 and I'm a pretty tame rider, but I still want to be able to take it on somewhat technical single track.

https://www.amazon.com/dp/B002T5GHNI?psc=1&ref=ppx_yo2_dt_b_product_details

Looking for any thoughts or recommendations. Thank you!

Definitely sounds like you’re looking for a mid drive since you do actual mountain bike riding. I run a hub motors but I don’t do any serious mountain bike riding on my E bikes. there’s definitely limitations with a heavy hub motor with off road use especially if you plan on jumping.

For your battery sounds like you need a custom built battery to fit the frame. I know you mention you’re trying to keep this budget but the battery is going to be your biggest expense.
 
LOL... yes! Been there and done that, but not from a fork compression issue. I really need a longer travel bike front and rear. I had this bike around and it was still in good shape so I converted it. But to really explore the motor's potential in the rough it'd be nice to have at least a 150mm bike with some fatter tires. My rear travel is only 70mm.

Eastwood said:
raylo32 said:
CYC_Installed.jpg

Well you have a decent fork on there but you need a longer travel fork. I just fixed the same situation on my bike by installing a downhill fork. It can be quite dangerous if you compress the front fork all the way and it bites down on the tire as you will go over the handlebars. Don’t ask me how I know this 😅
 
Good discussion here on battery size for mt biking...https://endless-sphere.com/forums/viewtopic.php?f=28&t=111282

The consensus is that a ~8ah battery is sufficient for most riders and most rides. Going with a big (15ah+) battery adds considerable weight and cost.

Not sure how much time/effort you want to spend on the conversion, but I believe the 8ah will fit in your frame with either a custom bracket or a frame bag. It's also less than 6lbs, so realistically you could put it on that seat post rack and be fine (notwithstanding the quality of the rack). There's plenty of people who run batteries in a seat post bag, and the rack would have arguably better CoG. I wouldn't take it to Whistler but if you describe yourself as a tame rider, it's probably workable.
 
raylo32 said:
LOL... yes! Been there and done that, but not from a fork compression issue. I really need a longer travel bike front and rear. I had this bike around and it was still in good shape so I converted it. But to really explore the motor's potential in the rough it'd be nice to have at least a 150mm bike with some fatter tires. My rear travel is only 70mm.

Eastwood said:
raylo32 said:
CYC_Installed.jpg

Well you have a decent fork on there but you need a longer travel fork. I just fixed the same situation on my bike by installing a downhill fork. I do quite a bit of off-road riding but nothing too extreme It can be quite dangerous if you compress the front fork all the way and it bites down on the tire as you will go over the handlebars. Don’t ask me how I know this 😅

I can understand wanting more travel for off-road use. That was another motivating factor for the downhill fork in my situation. Also just increased my rear travel by fabricating new suspension linkages that allows for a longer rear shock, much better now off road. The factory shock was around 160 mm eye to eye, The new one is 230mm eye to eye.
 
COAR said:
Good discussion here on battery size for mt biking...https://endless-sphere.com/forums/viewtopic.php?f=28&t=111282

The consensus is that a ~8ah battery is sufficient for most riders and most rides. Going with a big (15ah+) battery adds considerable weight and cost.

Not sure how much time/effort you want to spend on the conversion, but I believe the 8ah will fit in your frame with either a custom bracket or a frame bag. It's also less than 6lbs, so realistically you could put it on that seat post rack and be fine (notwithstanding the quality of the rack). There's plenty of people who run batteries in a seat post bag, and the rack would have arguably better CoG. I wouldn't take it to Whistler but if you describe yourself as a tame rider, it's probably workable.

But in his situation he does actual mountain biking so putting a battery up high in the back will throw off the center of gravity for the bike. If he put it inside the frame it would be much better for off-road use and handling in general. But yes I agree 8lb battery should be good for seat post mount But maybe not so much for actual Full suspension mountain bikes.
 
im running a tsdz2 with a 9.6ah cheap chinese pack made with ncr21700t. had it on a stumpjumper hardtail before and it was great off road. the battery weighs 5 lbs and was like 120 dollars. I got it from the seller and Aliexpress and made it custom for me. I know most people won against the cheap blue brick batteries But so far it's worked out well. results may vary. now have on a marin hybrid and just did 30 miles on the road with 45 battery left, averaging 18.3mph. I found that on the road and off-road battery usage tend to be roughly equal for the amount of time though not miles, So I would say you could probably expect two hours from decent seat bag style battery with 8ah on a tsdz2
 
Manbeer said:
im running a tsdz2 with a 9.6ah cheap chinese pack made with ncr21700t. had it on a stumpjumper hardtail before and it was great off road. the battery weighs 5 lbs and was like 120 dollars. I got it from the seller and Aliexpress and made it custom for me. I know most people won against the cheap blue brick batteries But so far it's worked out well. results may vary. now have on a marin hybrid and just did 30 miles on the road with 45 battery left, averaging 18.3mph. I found that on the road and off-road battery usage tend to be roughly equal for the amount of time though not miles, So I would say you could probably expect two hours from decent seat bag style battery with 8ah on a tsdz2

Got a link to that? I paid more than 3x that for my 8ah off ebay from an american seller.
 
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.
 

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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.
 
Maybe start with a better Stumpjumper.

dscf9710.jpg


stumpjumer+85.jpg


SWBEAST.JPG
 
So Chalo...you're the guy who broke into the Specialized Museum and stole Sinyard's prize possessions? :mrgreen:

Are those actually yours or some file footage? Classic!
 
TNC said:
Are those actually yours or some file footage? Classic!

Found on internet.

I did own a 1989 Stumpjumper Comp that I bought new from a local bike shop. It was my first ill-fated experiment with drop bars (experiment with ill, fetid drop bars?) I put it on a Greyhound bus one day and never saw it again.

The community bike shop where I work restores and sells a surprising number of these bikes.
 
circa 90's era that are 22" frames with not much breathing room down there, maybe thats Chalo's style of frame but I don't mind 19" frames like the last pic judging by the top tube to the top of the 26" wheel. Also another clue is the fork tube, how far away the top bar is from the down tube bar.
 
tomolry said:
Looking for any thoughts or recommendations. Thank you!

That frame is perfect for a custom battery. I have an old stumpjumper here - never did the full conversion, but I designed a battery. With 2 thick side plates held together by 6-7 68mm m4 spacers, you can clamp in any waterproof battery pack in the triangle. Best build one yourself using half holders to squeeze in more cells. I can't find the mockup right now, but I remember beeing impressed by the number of cells you could fit.
 
I have a specialized FSR that also had the frame that could not carry a battery in the triangle, as well as an older Y frame giant. The option is pretty much, to carry the battery on a rear rack, but minimize the weight. It can help a lot to add a strut to the seatpost rack, bracing it back to the bottom of the seatpost. Bolt right through the frame and the seatpost. I have had cheaper bikes seat post break right off from carrying 15 pounds on a post rear rack.

Bear in mind, if you want to ride like its not carrying a battery back there, don't motorize it. But if your riding is not fully balls out, like descending twisty trails at 25-40 mph, you can still get a reasonably good ride out of a battery that only weighs 8 pounds back on that rack. I used to run a 52v 10 ah lipo set up, and could still handle good enough to descend tricky trails at the speeds I was comfortable with in the first place. Like 15 mph down the hills, or up. I just didn't want to kiss the cactus and sharp rocks out there. And on a 4x4 road with more room for error, 25 or 30 mph downhill was fine.

But stick a 15 pound battery back there, and it sucked balls for off road, single track trail riding.

At one point wanting more range per trip back to the house, I put another 5 ah on a handle bar mount. It did not balance out and handle better, but it sure beat putting 12 pounds on the back. A backpack is another option to carry a bit more weight, but in my desert climate, I never even liked carrying a hydro pack back there. I put water on the frame mounts for bottles.
 
OK... perhaps dating myself, but I remember these bikes. I even have one of that vintage but from Trek, bought in 1988 or 1989. A classic Trek 8000 one of the first aluminum frames. That was my original MTB and it has seen duty here in MD and on trips to Montana, Colorado, California and then it got consigned to my parent's house in FL for me to ride on visits. Then it got caught in Hurricane Ivan in 2004. I recovered it from the debris pile and I still have and use that bike to this day. I use it here mostly on the C&O towpath where we take the dog in his trailer out for nice rides and lunch. The bike still has the same BB and headset that it had when it was submerged under 8 feet of seawater in the storm and they still operate perfectly. They are sealed bearing units that I used to replace the OEM loose ball parts that had previously worn out. I will probably never convert this bike to electric. In any case that bottom bracket would be beyond difficult to extract.

DSCN0679.JPG


Trek_8000.jpg



Chalo said:
Maybe start with a better Stumpjumper.

dscf9710.jpg
 
Thanks for all the replies. Regarding the rear stem mounted rack, I tried it out with 2x5lb plate weights. For the type of riding I to it seemed fine (the most air I ever get would be about a foot or two). I'll probably add a shock cord on each side and also the near the rack mount going up to the seat just in case.

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

20210722_131933.jpg
 
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