Comments/Critique on Prospective Build

T

TlfT

100 µW
Joined
Mar 23, 2014
Messages
7
Location
Ridgefield, WA
Hi All, been lurking here and soaking up some fantastic knowledge.

I am 31 and a long-time MTB and Touring rider. New to the Ebike realm.

I am planning to build a bike for ~$3000 to be used as an on-road commuter and all-around joy. My budget is high, so please help me fill it :lol:

Right now I am planning on:

From EM3ev:
--- 50V26.5Ah Li-NCA triangle pack ( seemed to be the best pre-assembled combination of range, power and portability I could find )
--- Infineon 40A controller (12 FET IRFB4110)
--- CycleAnalyst CA-DPS computer

-Lightning Rod's upgraded GNG mid-drive kit ( many thanks to LR for putting this together! )

-CroMo Rigid MTB with 29" tubeless wheels (which are very reliable IME, save weight, no flats, run low pressure to soak up road chatter); 2.4" 630g semi-slick tires and beefy Hydro brakes (which I will modify to ebrakes)

-Thinking 11-36t cassette and 32t-48t front chainring ( maybe both a 32t and 48t, depending on if I can fit 2 ?? )


What do you guys think of investing in a $70 Silica Welding Blanket to throw completely over my rig when storing/charging in my concrete garage? Its rated for molten metal and working temps up to 1800 degrees F. Is looking for complete 'airtight' coverage overkill, should I just go with scrap metal ?

My biggest question is gearing. I want to give myself the best opportunity to pedal-assist at as high a speed as possible. What do you all think I should do?

Any Comments or Criticism is greatly appreciated, Thank You for this Fantastic Community!
 
Hi and welcome..
Sounds like a nice set up. I'm not an expert by any means so I'll leave the finer points to someone more knowledgeable :)
With regards to gears, (depending on how hilly your area is) you'll find that you travel so much faster that you'll spend most of your time in the top end. If in doubt get bigger gears! A road cassette could be good if you're in arelatively flat place, as would be a 52t on the front, The 29s will help a bit. Speeds of 40-60kph mean the 36t on the back won't get much use! However I don't know what hills you have out the back....have fun
 
I can't comment on controller motor compatibility. But 40 amps is a BIG controller. I know for a fact the battery will like less. Maybe not 20 amps, but 30 maybe? Still 1500w, enough to be perky, and through the right gear, it should wheelie.


I find bringing my battery to a safe place to charge to be much better. But that is NOT the unsafe to charge battery type. Nevertheless, don't charge in the newspapers to be recycled pile, or lean the bike next to the gas can. :mrgreen:
 
a 40-amp controller with a 26 amp-hour battery will run at less than 2C discharge rate, so it should be fine. I run a 40-amp controller on a 10 amp-hour battery and it has no problems. Sounds like a good setup that will give you decent power and range.
 
Duh, I missed he was buying one that big. Yeah, that one will handle 40 amps.
 
At $3000 budget, get a torque sensing assist, like a THUN sensor or similar. I personally don't have one, but have heard good things about it's feel used in conjuction with electric assist.

Edit: erm, a THUN may be a wrong pathway in conjunction with a mid-drive, others can chime in on it. But from what I can tell, should be able to make it work via the CAv3.
 
That's my sort of build spec! my build 2 linked below was similar, a mid drive but with 18s 75v and a 40a controller, the changes I would make to your spec would be to bin the granny ring, you will never need it or use it!! Your gearing with a 48t 11t top gear and 29" wheels should be fine with that setup. On the road you will find yourself in that gear most of the time, you may want to set the chain line up to reduce the chains angle in the higher gears as that is where it will spend most time and reducing the chain angle helps with smoother power transmission and gives the chain an easier life. It might be wise to keep the front changer as this can act as a guide to prevent the chain from getting pulled off the side of the front chainwheel when under power in the top or bottom gears, mine needed it.
 
Thank you very much, fellas!

As per gearing:
There are some hills where I live, but they are just rolling hills without any extended climbs. I can muscle them on a 32t front chainring and a 26t rear cog on my rigid karate-monkey with 32c touring tires. Maybe I will take your advice, Tench, and just go with an 11-34t and 48t with a chain guide....or maybe an 11-24t and a 34-52t, to get cleaner closer-ratio rear shifts and give myself a chance to keep up pedaling at speed. I imagine I just have to ride the thing and see how things work out rpm-wise with one of LightningRods' larger BB sprockets (he offers 64-93t, a WIDE range). Gearing advice is very much appreciated, though! I am flying blind!

Just an aside, I stumbled on SRAM's new 7-speed DH-oriented 10-24t rear gearing built for clean double/triple shifts and using a super stiff threaded driveshell interface which allows a 10t ... looked promising until I saw that it was $1000 for just the shifter, derailleur and cassette!! wtf ( I budget less than one tenth of that! ) worth a look for kicks though.

 
Sounds like one hell of a ride.

For reference:

With my 48T Front gear and 11T rear gear on 26" Tires, I can get 32 MPH.

I also developed a gearing spreadsheet so you can play around with the numbers. - I find a pedal cadence of 70-80 RPM comfortable.

Link to Excel file below:

http://1drv.ms/1g2gYSX
 
I have found that a 52 tooth front chain ring is an absolute must for casual long rides.
 
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