New Drivetrain, need help
 

Hi guys,

I have two high powered ebike builds and I am having trouble sourcing some upgrades. I have one bike that has a 3000w nominal mid mounted battery that uses the drive train for momentum. The chain and cogs are not able to hold up unless the power output is lowered using the controller. Anyways I want to install a much sturdier chain and cogs even if I have to do a single-speed setup. I can't find any info on this type of upgrade.

That previous bike was for my father. My bike on the other hand can reach speeds of about 45mph and I use a DD motor. I want to be able to pedal around 30-40mph range. My wheels are 22" and my 12t x 52t setup is not at all useful above 30mph. It looks like if I change to an 80t cog for my front then I'll be able to have a nice cadence for 30-40mph. Does anyone have a link to an 80t chainwheel that is for sale?

TLDR:
1.) Any ideas on sourcing a motorcycle chain/cogs that can attach to a standard bicycle?
2.) Any ideas on sourcing a 80t chainwheel?

Thank you,
Al

If youre pushing out more power than a regular bike drivetrain can handle, then youre ALSO pushing out more power than a regular frame and fork is built to handle. And that you're probably reaching speeds regular brakes aren't meant to deal with.

I'm NOT helping you get that contraption on the road.

Especially brakes. You are in "test pilot" territory, good luck.

No you're wrong. I've got a full steel enduro frame that I'm adding the components onto. I've got a nice downhill fork with dual hydraulic brake mounts on it as well. So dual hydraulics for the front, single hydraulic caliper for the rear. All 3 have 240mm rotors. Both of my wheels are Excel rims with 2.75" 2ply DMV rated road tires.

Here is my frame:
Qulbix Raptor 140 Bicycle Frame Kit

Here are my hydraulic brakes,
Front: TEKTRO BRAKE SYSTEMS
Rear: TEKTRO BRAKE SYSTEMS


This is not a bicycle, this is more of a moped and substantially more sturdy than one. I would appreciate your guys' help finding the right parts for my bike.

Which chain and cogs are you currently using? The most durable bits will be single speed track bike parts (1/8" chain and compatible chainring and freewheel). If you want multiple gears, I'm not sure what to tell you other than try to keep the chain in contact with as many teeth as possible using big chainrings and big cassette cogs and probably a maximum of 7 speeds.

Some folding bikes use massive chainrings (IIRC around 60T). 80T would almost certainly be custom. Do you have any friends with a CNC? If not, how much are you willing to spend to make something custom? I can help you get there but it won't be cheap making a one-off.

There is a 70T chainring on E-Bay for a reasonable price.
Bikingreen 70T BCD130 Recumbent Chainring CNC 7075 Road Fixie Black TT Track | eBay

I think I had seen an 80T for sale by various trike & small wheel bike companies, but generally quite expensive.

As a person that's just reading along for understanding/learning, can you clarify this? If a battery is rated at 3000w, which is amperage times voltage, how does this correlate to knowing that the motor is powerful? Couldn't you have that same battery with a less-powerful motor? A couple posters seemed to know that the motor was powerful, and I'm just curious how they knew this without it being mentioned. I do see your mentions of top speed, which can be hit at a fairly average power output with the gearing mentioned. Was it the mention of 80t/12t that infers the power being discussed here. Thanks!

I appreciate the offer but for now I don't want to spend the money on that. Perhaps eventually I'll go all out for the upgrade but for now I just want something close. Right now I've got a 1/8" bmx chain with a front 3 speed 44-32-24t, rear 12t. Mine is DD hub and the pedal assist would only add my leg strength so probably <500w? so durability really isn't an issue. My father's 3000w mid drive build on the other hand I'm worried about. My brother has a 1500w mid drive and it has already damaged his 11t rear cog pretty badly and the controller isn't even releasing full torque right away, more of a 70% then 100% after 2 seconds when full throttling. I'm thinking I'll have to make sure my father has a solid steel cassette with like 17t for his smallest cog or something. Then just do a larger front crankwheel to keep the max speed up there. As you said the more teeth on that little cog in the back the better hopefully.

Thank you! At 90 pedal rotations/min I should be able to help at about 35mph with this.

Ah sorry to be confusing. My terminology got fudged. I meant the motor is a mid mounted 3000w motor. So that rating means it should be able to run up to 3000w, ~72v at 42amps, forever without overheating but it can handle spikes a lot higher which will cause it to overheat quickly. The battery is 72v nominal. Batteries use some form of a BMS(Battery monitoring system) that limits maximum discharge. My father's battery is 72v nominal and the bms allows a continuous 50amps and allows a peak of 70amps. You're right, a smaller motor will simply draw less amps and can be used with packs that allow bigger amp outputs than necessary. Generally larger amp hour packs have a larger safe amp output that won't strain the batteries. If you look at batteries online you'll see they'll have a continuous amp rating.

The 45mph is what most likely tipped people off that it was a powerful setup. An ebikes ability is mostly based off of the battery since even if the motor can't handle a high continuous wattage it can at least handle high wattages in small bursts with cool down time in between. If the motor isn't a regular hub motor and instead a geared hub then the internal gears may be shredded under heavy loads. Usually heat is the main issue.

12t and 80t are what cog sizes I want to use for my pedal drive-train. So one full circle of my pedals would rotate the chain by 80 links and since the rear wheel has a 12t cog it will rotate 1 time for each 12 chain links. 80/12 is my pedal rotation to tire rotation ratio. My rear tire will rotate 6.66 times for every 1 rotation of my pedals. Since my rear tire is 22" diameter and 80-90 pedal rotations/min tends to be optimal you can plug all the numbers together to find the speed you can get dependent upon the cog ratios. I want to be able to assist my bike at 25-35mph since that is a good speed for me so I was looking to see if anyone on this forum had some insights on where to source parts.

Thanks for the informative response...I really appreciated that.

Your questions would be better answered on a moped forum, nothing to do with bike mechanics. The components you ask about are not bicycle parts. You might ask to move this to Ebikes but even there it would be a stretch.

An 80t chainring would be quite vulnerable, too. Perhaps you should start over, using 36" tires?

Thread moved from Bike Mechanics to Electric Bikes.

The guy at electricbike-blog (dot) com has done a lot of rear hub testing with high power motors. Possibly one of the 3spd Internal Geared Hubs (IGH) will work for you with a single speed straight shot setup chain. Take a look around his site if you haven't already. Straight talker, because he's been there and done it... until it breaks!

I had to replace a front worn out chain ring on my Giant LaFree, but they no longer made them. What I did was cut down my old worn out chain ring and weld a new one to it. Problem solved. If you can source the correct ratio and size drive parts, you can always weld them to the old bike parts. Or, run double chains for more strength.

Moped chains and gears are really quite big, probably larger then what is needed.

1) SRAM will have released an e-bike specific drivetrain by Interbike (end of September).
2) I think that your only hope is a Schlumpf drive (look at endless sphere for a reference).