Money D

I've procured two full susp mt bikes on which to perform a DIY ebike conversion, one for me one for the wife.
Mine is a 2014 Spec Stumpjumper FSR Elite 29er XL - I'm 6'5 270lbs. I've mtb'ed since the days of DaleRider here on MTBR. I was thinking mid-drive BBSHD. I'd hate to build this and be unhappy with the power. My concerns are which battery and where to put it? I'm concerned about the motor hanging a little low, but I'm getting older and won't be jumping logs much.
The wife's is a 2006 C'dale Prophet. It has mostly XT with "Dual Control" shifter/brake combos. Are these shifters compatible with the 7 speed cassettes the rear hub motors run? The wife is 5'7 and skinny, but doesn't MTB much (hence getting the diy ebike to foster passion?) I was thinking rear hub (can't do front do to the Lefty fork) 500 watts would probably work since she is light and it would be cheaper. But I keep reading that rear hub conversions are tricky/difficult and wonder if I should just get a mid-drive. Location of the battery is another problem, as the shock of the prophet takes up most of the triangle. Rear rack sounds like the best idea here.

My bike will be used for actual mt biking as well as fun with the family/easy rides. The wife's will mostly be easy rides, with some logging roads thrown in.

Thoughts? BBSHD with a 48 or 52v 20ah battery for me? Rear hub or mid-drive for the wife? Motor and battery spec recommendations?

Thanks in advance.

cat0020

If your designated riding is NOT going to be serious trail mtb, maybe just consider buying complete ebikes instead of DYI with your existing mtbs.
It will save you lots of time & effort to have complete ebikes that suits your riding needs, instead of compromising your existing mtbs, make them into something that don't quite suit your next riding needs.
I've built my own ebike with my Balfa 2-step nearly a decade ago into ebike with power/motor that I thought I needed, but it just became much heavier & did not perform well on the trails that I used to ride on.
I took off the conversion and converted it back to just plain mtb and it was much more enjoyable ride.

If your budget allow, I would recommend going with complete ebike purchases rather than converting existing mtbs.
Get something that is designed from ground up to be an ebike that suit your riding purpose, whether it be casual or competitive level riding.
BTDT with the wife's cycling desire.. my wife is just happy to be out with me regardless which bike she's riding.

2old

The BBSHD is a bulletproof system (AFAICT and based on the three BBS02's I've converted) and the XL frame should have enough room for a downtube battery. Your challenge might be getting the motor to "nest" on the right side of the frame since it appears as though "your" chainstays flare out. I've converted only hardtail frames so can't predict. The conversion of your wife's bike should be pretty straightforward. I would suggest a BBS02 instead of the rear hub since the bike will handle much better. Again the seatstay configuration may be a consideration.

Doc_Wui

Those two frames are not suited for the strap-on batteries usually seen on converted ebikes. You'll ruin the lines, if you care about looks., Given that they are expensive frames, seems like you can afford dedicated trail ebikes.

Pop N Wood

Have to agree with 2old here. Seems like BBS02's or BBSHD's would be a better option than hub drives. The conversion will be a fraction of the cost of a "factory" bike and IMO look considerably better then most of those.

Not sure your wife's shifters will work with a rear hub motor unless the shifters have the same number of speeds. Not an issue with the mid drive, you can run the same rear gears and derailleur.

Not sure where I would put a battery on either bike. One option is placing a battery in a backpack. Pretty common to do, they sell long power cords, and more convenient in a way. Other than that you might be looking at the underside of the down tube with multiple velcro straps to keep everything in place.

Your bigger problem right now might not be where to put a battery, but where to find one. I notice Luna is pretty much sold out of everything.

chas58

7 and 8 speeds have the same chain size and cog spacing. Above that and your indexing will be off.
You can get a hub motor that uses a cassette (instead of a freewheel), and you can put 9-11 speed cassettes on there.
The biggest issue may be just making sure the motor fits in the dropout of a high end bike. Hub motor axles are oversized (and flattened on 2 sides), so they aren't gonna fit everything.

Leisesturm

Agree. He will have no choice but to wear the battery on his back. The C'dale should have enough clearance underneath the DT to hang the battery there. And since so much effort is being expended to preserve some bikelike handling for both machines, a mid-drive is the preferred motor choice for both. I would recommend the torque sense TongShen TSDZ2 for the Mrs. because it is easier (more intuitive) to ride. Not as robust as a BBSHD but it should probably work for the intended usage profile.