Originally Posted by
joejack951
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.
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.
Originally Posted by
CliffordK
Thank you! At 90 pedal rotations/min I should be able to help at about 35mph with this.
Originally Posted by
deapee
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!
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.