Good bike to build? Specialized SX Trail

Looking at building my first DIY e-bike conversion on a Specialized SX Trail. Full suspension with 6" of travel on both ends. Purpose will be flowing single-track, gravel roads, and family pavement adventures. I've MTB'd off and on since the early 90s. I'm an ex FB player, 6'5 270. I was thinking BBSHD mid-drive and a battery under the down-tube. I'm a noob to ebike, can someone look at the BB pics and tell me if I need an adaptor or this will be - pull the BB, insert the BBSHD? And the 68-73 will be the correct size? And are those the tabs that people have to grind off? I'm not above doing it, I just need to know which ones? Thanks in advance.

Need a more up close picture of the crank side chain tensioner.

Good enough?

Here's a couple more of the chain tensioner.

OP, that's an aluminum frame, correct? I was looking at the paint chips on the BB shell and was just wanting to make sure. Are those "official" ISCG tabs on your frame for the chainguide? A fellow named "geosped" on this forum had ISCG tabs and removed the necessary material to make his application work. He would be a good source of info for that. I believe there are even some pics on this forum showing the issue.

Your downtube to the BB angle looks good and straight, so that contributes well to mounting the motor. To achieve the best chainline for the rear cassette, many have to go to a Luna Eclipse 42T or so chainring. Sometimes that chainring interferes with the chainstays on the swingarm, so that would have to be considered.

You might need to decrease the travel on the front shocks so the wheel doesnt hit your battery when mounted under the downtube- maybe build a mockup out of cardboard to check clearance.

also if there's any sideways play in the rear swing arm the chain may come off as there's a lot of torque on one side. might want to replace bearings / bushings if there is.

TNC said:

OP, that's an aluminum frame, correct? I was looking at the paint chips on the BB shell and was just wanting to make sure. Are those "official" ISCG tabs on your frame for the chainguide?

Click to expand...

Thanks for the reply.

Yes, all Aluminum frame.
No idea if they are official ISCG tabs.

My BBSHD is arriving in a week. I need to buy a battery/charger. Thinking 52v and somewhere between 10 and 20Ah as I usually don't ride more than 1.5 to 2 hours. Anyone know of any good deals currently?

I went and road an older Santa Cruz V10 yesterday. Unfortunately it was setup for a 140lb guy so it felt like a pogo stick, hard to tell if that much travel would just feel completely unlike a trail bike when setup for me.

Any other opinions?

slm9s, yes it's hard to give specific advice on what kind of bike people need or want. I will say this as far as BBSHD installs go, you don't have to worry that much about the weight of the bike like our pedal-only applications. That SX Trail is an awesome candidate for emtb. You mention "flowy singletrack", and in a pedal-only application this bike would be overkill. However, don't worry about that with a BBSHD. Also the 26" wheel deal won't be an issue either, I don't care what the 29'er only crowd screams...LOL! That actually is more of a feature on a pedal-only bike, but a 26'er doesn't suffer as much when you mid-drive one. I have a BBSHD in an '08 SC Nomad which is a bit in the same category as the SX Trail, and it has been an absolute hoot on aggressive trail and even just plain dirt road riding.

Back to your project, your frame does have "official" ISCG tabs. I know geosped here on the forum has trimmed his tabs on a big hit MTB to work with a BBSHD. He had more of an issue with the less common, wider, BB shell size. Your pic there appears to be the more standard 68-73mm size, so you should have no issue once you address any issue with the tabs. If your chainstays will clear a Luna Eclipse 42T chainring, you should achieve an optimum chainline. It was perfect on my Nomad. This is the lowest gear chainring you can install on a BBSHD, and it still allows my Nomad to achieve 40.8 mph in the 11T rear cog. If you've mountain biked before, you will find the torque of the BBSHD allows much less shifting and not require all the incremental rear cogs of the 11 and 12 rear cogsets. I'm running an 11-50, 9-speed rear cogset, but I could have easily gone with the 11-46 cogset instead. There is amazing torque available in this motor, and unless you're trying to start out or climb in the really high rear cogs, you won't hurt this motor and controller. I bring this up because your rear cogset looks like it may be quite small...perhaps?

On the battery, this is an area of application and preference that can be all over the board. I use a 52V, 17.5AM setup in a backpack. Others want smaller battery packs on their frame somewhere. The problem with some full suspension frames is battery location on the frame. You'll have to assess what works for you. My battery will power my bike for a good, long ride without battery anxiety...LOL!https://endless-sphere.com/forums/download/file.php?mode=view&id=298495

Here's a pic of mine for some reference.

slm9s, I forgot to mention that depending on how aggressive your mountain biking is, you can also beef-up the motor mounting with stabilizing plate to insure the motor stays put. Here's a pic of my plate, and here's one of the Luna chainring for reference. Sorry for the purple...LOL!...but in this market that was all I could get.

Hey, I notice the Titec Berserker saddle there. Man, that's a classic. I used one of those back then. slm9s, can you expand on the older Santa Cruz V10? I have an acquaintance looking for one of those for a BBSHD application. Can you PM any detail on it or just post it here. If it's a sale that has a link, please post if you can.https://endless-sphere.com/forums/download/file.php?mode=view&id=298497

TNC, thanks for the great reply.

I have a 46 and 44t chainring on the way, I couldn't find a 42 in stock when I ordered. I just pulled the trigger on a 52v 16ah battery for the downtube. I made a cardboard model to make sure the tire wouldn't hit it. Not the prettiest solution, but like you said options are limited.

Sorry, the V10 sold. I was really considering getting it and trying to make it work for me, but I was too late.

And yes the Titec Berserkr is still my favorite saddle. I've acquired 5 or 6 over the years, but a couple have failed - it was the plastic getting brittle, not my Hugh Jass!!!

Be careful with grinding off the iscg tabs, it appears they have doubled up their use as the flange onto which the down tube welds. Removing them would damage the frame badly... It's a lovely bike, don't kill it

I'm not convinced the bbshd is a good match for that frame, but since you've already ordered it I guess you'll find out and tell us soon enough.

I'd be inclined to go hub motor on that frame (only hesitating because those sx trails were a bit rear triangle snaptastic... This was usually for people sending them off large jumps though).

Thanks for the tips guys. The BBSHD came and this frame is so burly/reinforced at the BB that the motor wouldn't fit even if I ground off the tab.
I had grabbed a cheap 48v 1500w rear hub kit and battery off craigslist and the install went smooth and I'm loving it. On road is a lot of fun and even off road actual mountain biking is going well - still getting used to such a heavy bike. I might be looking to upgrade the controller and battery for a bit more torque and speed.
Thanks again!

I had difficulty with an aluminum frame BBS02 for my wife too. Finally built on a traditionally-designed one (no funny bottom bracket or stay curves), and it went together nicely.