My new Custom GMAC build

linklemming

Well-Known Member
Just starting a thread for my latest ebike project.

Its going to be a 52V, Grin Technologies build using a GMAC 10T motor, CA3 and PhaseRunner with a 52V Panasonic Battery I got from luna about 1.5 years ago.

My ebikes so far:

2018 Bulls Evo 27.5+ Brose Motor Hardtail eMTB - Love the bike, great offroad, 20mph speed limit
52V Bafang BBS02 conversion of a 1994 GT Zaskar - HATED the PAS, despite aftermarket tuning.
52V TSDZ2 conversion of a 1994 GT Zaskar, MUCH better than the BBS02(feel wise) especially with the opensource software I ran(which I actually modified). In the end, mechanically, the TSDZ2 is a POS and I threw it in the trash at about 1k miles.
2018 iZip Moda Brose Motor Speed Pedelec - lovely bike, takes some effort above 23mph or so (but well worth it).
2018 Juiced CCX - Setup more as a gravel bike (removed all accessories and added MTB tires). Its fast but crude, if I could run fatter tires on it I would love it....I still like it ALOT.

So Im looking for a bike faster than my CCX but with fatter tires. Initially I will use my old 26 inch wheel GT zaskar (baby steps). Eventually I will go with a surly Ogre/ECR or Bridge Club frameset targetting 2.6 to 2.8 tires

I have ordered everything from Grin
GMAC 10T with 26 weinman 24mm ID rim (not my first choice for a rim but I didnt feel like building a wheel and finding 36h rims can be a REAL PITA..I tried)
ERider Torque Sensor/BB (no holes in BB required)
Phaserunner
Cycle Analyst 3
Throttle

The overall order from Grin was about $1200 us.

I had planned on 2 orders from Grin, First the motor/wheel build and then everything else.

This has turned out to be very expensive shipping wise. The cheapest shipping for the rear wheel/motor was about $95(Thats what people usually charge to ship a whole bike) My subsequent order of the CA3/Phaserunner/Torque Sensor/Throttle was $31 for shipping.

If thats what GrIn charges, so be it. Just want to let others know what to expect and perhaps combine all items to reduce shipping costs.

I will provide more updates as I get things and start the build.
 
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Timpo

Well-Known Member
😁
Microsoft Teams add on SW - Spiceworks Advertising
 

Deacon Blues

Well-Known Member
I have a new ebike (Cannondale Topstone Neo Lefty 3) and I have another new ebike coming in December (fingers crossed), but I still have a hankering to do a DIV build.
I really like Grin products and would buy pretty well exactly what you bought. I even have a great old commuter bike to convert (1990 Rocky Mountain). The only thing holding me back is my old bike has rim brakes and I wonder if this will offer enough braking power for an ebike that will be able to cruise at higher speeds.
The other option is to look for a used, newer bike with disc brakes.
 

JES2020

Active Member
I have a new ebike (Cannondale Topstone Neo Lefty 3) and I have another new ebike coming in December (fingers crossed), but I still have a hankering to do a DIV build.
I really like Grin products and would buy pretty well exactly what you bought. I even have a great old commuter bike to convert (1990 Rocky Mountain). The only thing holding me back is my old bike has rim brakes and I wonder if this will offer enough braking power for an ebike that will be able to cruise at higher speeds.
The other option is to look for a used, newer bike with disc brakes.
I was worried about my rim brakes too, but I am able to come to a stop with the tires skidding along the ground. I don't think you can get any better stopping than that. I have cantalever brakes vs v brakes, so unless you have an issue with your grip I would say try it with your brakes. You can always add disks if you have issues (provided your wheel will accept them).
BTW I can go about 30 mph on my bike.
 

linklemming

Well-Known Member
I have a new ebike (Cannondale Topstone Neo Lefty 3) and I have another new ebike coming in December (fingers crossed), but I still have a hankering to do a DIV build.
I really like Grin products and would buy pretty well exactly what you bought. I even have a great old commuter bike to convert (1990 Rocky Mountain). The only thing holding me back is my old bike has rim brakes and I wonder if this will offer enough braking power for an ebike that will be able to cruise at higher speeds.
The other option is to look for a used, newer bike with disc brakes.
You might be able to convert to disc brakes, I did it on my Zaskar about 10 years ago.

For the front, just buy a new fork with disk mounts. When my zaskar wasnt my primary MTB anymore I put on a rigid disc fork. I bought a suspension fork awhile back (rockshox reba) that had both canti and disc brake mounts.

For the rear, you could use the A2Z adapter. I used this for over 9 years on my Zaskar. Its big, bulky and fiddly but works
a2zadapter.jpg


I knew this could cause problems with a hub motor so I recently got an adapter specifically for the Zaskar
discadapter.jpg


I still might have fitment issues, we will have to see
 

linklemming

Well-Known Member
I was going to initially build up on a new surly frameset (BridgeClub/Ogre/ECR/Troll) but they are really hard to find given the covid crisis...especially in Black. There was also the issue of having to build my own rear wheel(I recently sold my park wheel truing stand, knew I would regret that) and then there is the issue of finding a 36h rim(needed for GMAC) for plus size tires.

So initially I will get it running on this bike. Whats funny is back when I got this bike, I ran flat bars, no rise stem and no headset spacers (we used quill stems back in those days). Things change over the years. The early GT zaskars like this one that were built in california were known to be bulletproof. That being said, it saw 7 years of hard trail use and 17 years of easier gravel riding(including 2 ebike conversions) and I will eventually get a new surly frame.

I debated putting 27.5x2.4 wheel/tire on this bike but it would have reduced standover by about an inch.
gt-zaskar-pic.jpg
 
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linklemming

Well-Known Member
I have been doing alot of research on frames for this build, thought I would share some thoughts/insights and such.

I initially wanted to use a newer MTB frame but most newer MTB frames use thru axles which are not compatible with rear hub motors at this time. There is also the issue of chainstays widened to allow bigger tires, the trend of really short chainstays and many frames not supported a front derailler since they are intended for a 32t or so 1x setup.

Getting a frame to support at lease a 1x 42t non boost chainring seems challenging.

Luckily Surly lists chainring size compatibilities for their frames, 2 frames allow a 42t 1x non boost chainring, the Ogre(27.5+ to 29) and the Troll(26 but can technically fit a 27.5x2.4). You cant find an Ogre anywhere and it doesnt look like they will offer it in black in 2021. I found a troll but not sure I want that frame. Supposedly surly will be getting their 2021 frames in mid november.

Both these frames would/should well with a BBS02 or BBSHD with minimal spacers and chainline issues. I had a BBS02 and never really liked it but was considering playing with a BBSHD with Phaserunner Controller in the future.

Other frames I have considered are the Surly Bridge Club and ECR. The ECR is quite a bit heavier (most non ebike builds are 33+lbs) but is built like a tank, probably the best frame if I like this ebike setup. Not sure what chainline issues I might encounter but I can always buy a wide range cassette and just not use the lowest gear,
 
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Edrummer

Member
Here’s a thru axle Gmac from Grins website
 

linklemming

Well-Known Member
Here’s a thru axle Gmac from Grins website
Im not interested in a front hub motors, if they ever make that for a rear hub motor Im all onboard, thats also not a GMAC
 

Deacon Blues

Well-Known Member
If the bike I was converting had regular (for lack of a better word) axle I'd go with the GMAC. If it had a thru axle I'd go with the All-Axle Ready-To-Roll kit, which can be mounted front or rear. I think both can be built to put out plenty of watts.
The price of these kits rises quickly when you start ordering the upgraded parts.
 

AHicks

Well-Known Member
My plan, prior to actually going Ultra mid drive instead, was to build a GMAC using a new donor e-bike. Plans here were for a RAD Rover, because I know I can strip it down to what I need, and sell the unneeded parts at a pretty fair price pretty easily. This was done a couple of seasons ago with the MAC 12t converted RAD City I still have (recently taken over by the wife), that I still love dearly. Original direct drive rear wheel, and ALL RAD electrical (other than the battery), were sold for 600 (as a complete "kit") if I remember right, making the price of the donor bike pretty reasonable in the grand scheme of things.

If you look at a similar GMAC project, starting with a RAD Rover purchased at Black Friday pricing, then selling the unused parts, and adding on the entire price of the GMAC kit (1200 or so), you have a pretty reasonably priced bike that will really deliver! Heck, thinking about it, I may still do something like that!

I would want disk brakes for back up purposes, even knowing full well the GMAC is capable of locking up the rear wheel.

In any case, will be following your project with interest. -Al
 
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linklemming

Well-Known Member
Well today was christmas, unfortunately santa got stuck in the chimney :cool:

The wheel and parts arrived and were very well packaged
IMG_20201019_154001837.jpg


Here is a pic if the built wheel
IMG_20201019_154336977.jpg


The bad new is the this wheel is not going to work on this frame due to the disc brake adapter which interferes with the torque arm mount.
IMG_20201019_193438437.jpg


Not sure what Im going to do at the moment, every easy option seems blocked either technically or covid parts supply. I will update when I make decisions on how to move forward
 

linklemming

Well-Known Member
No need to go into all the details but I decided to go with a new Surly Troll frameset(very hard to find one in stock). I searched craigslist, ebay and every avenue I could find and 26inch disc brake compatible frames(new or used) are rare. That being said, the Troll is a tank that can carry 355#(designed for bikepacking) so it will be a good candidate for an ebike.

I didnt want to go with 26inch but wanted to use the bike I posted earlier(which isnt going to work). I dont want to buy all the tools to build my own wheels so Im going to stick with 26inch wheels for now. Bummer that its next to impossible to get tires greater than 2.4(2.6 would be ideal). There are the Maxxis DHF which I have on another bike and are awesome but this bike will see about 30% pavement so I will be going with 2.23 smartsams for now.

Lots of compromises, just want to get something on the trail ASAP.

Will post more updates/pics when I start building up the frame
 

opimax

Well-Known Member
Sorry to hear of the issues. I am confused on wheel size . The nice looking already built wheel is 26 were you going to use different size on the front or different sized tires or relace a different rim?
 

linklemming

Well-Known Member
I originally wanted to run a 27.5 rim with about a 30mm inner width so I could run a 27.5x2.6 tire. I was hoping to put these on a surly ogre, ecr or bridge club frameset. Out of all these frames, I could only find an ECR.

Grin doesnt offer a GMAC prebuilt wheel with a rim that width in 27.5 so I was looking at making my own wheel or having one built locally. I sold all my wheel building tools a year or so back (I knew I would regret it).

Since I had a existing 26 inch MTB bike/frame I thought I would just convert to that 'first' and hash out all the details before commiting to a new frameset with larger wheels. So I ordered the GMAC with a 26inch rim with about 24mm inner width (not ideal but close enough). Due to the fitment issue with the GMAC and aftermarket disc brake adapter, this wont work. FWIW, I also bought a new 26inch front wheel with a wider rim so now have two new 26inch wheels 😀

So the option would be to go with my new 26inch wheels with a 26inch surly troll frameset, or get/build 27.5 wheels and go with the ECR. The troll seems like the easiest path for now.

Not what I originally wanted but so many roadblocks in what I want to do. All my other ebikes have larger wheels with larger wheelbases, maybe having a shorter wheelbase 26inch bike will be a good addition to my ebike quiver.