Okay i just read about IGHs for a couple days solid, and i'm disappointed.
It seems the only IGH i could use is a 3 speed, i found some specs on the Shimano Alfine 8 that showed it can only take 60nm. Shimano says the 5 speed is 50% stronger, that means it's rated ~90nm if true. I can't find any rating on the 3 speeds but a wild guess would be 120nm.
But we have 120nm of motor power already before i start pedaling. Then maybe we add 80nm peak. We may hit 200nm on this IGH's input and it probably wouldn't have a long life.
So basically if you want a reliable experience with an IGH then you are looking at a Rohloff or '3x3 nine' for >$1000 and adding another 3lbs to the bike and also getting some % lower drivetrain efficiency for the privilege.
It doesn't make any sense. I could buy ~10 years of 11t sprockets and other drivetrain parts for that price.
How can we just put a honker of a chainring on here instead?
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I have two sets of mid mount plates. I could use the second set as a replacement for the inframe mount bracket and gain 60mm of extra length at most. But we are going to dock ourselves 12mm because this midframe mount adds about that much and we gotta account for that.
Let's call this + 48mm unit a mid-long mount.
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If we put a 60T on the bike ( let's just imagine ) and use a mid-long mount, we just barely miss clearing a 60T sprocket and having a strong 60T to 12T. Going from a 11T to 12T/13T motor sprocket wouldn't give us enough added clearance to make this work.
If i were to retain the inframe mount plates then i could cascade these 3 plates and have a total ~60mm of rise. and make the 60T -> 12T thing actually work. This configuration may lack lateral stability so i think it'd be wise to also create a solid front mount like Nervagon has.
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52T is easy street and considering we probably need to upgrade from a 11T motor sprocket to 12T or 13T, then the mid-long mount should be able to clear at least a 56T. The frame should be able to clear it too with the narrower BB than stock.
With a 11T lowest cassette gear and some aggressive pedaling i should be able to hit the top speed of 35mph i desire.
In the gear with 14T, i should hit the maximum legal ebike speed, which is the speed i prefer to cruise at >90% of the time. perfect!
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Can we actually go 35mph with high intensity pedaling and stock power?
This motor's burst wattage is 25A x 48v = 1200W.
By using a 52v battery we should have a burst power of 1300W.
Let's use the Shengyi SX2 ( highest efficiency geared motor RN ) as a model of the lightest considering the lightest is supposedly ~90% efficient. This should at least give us an idea of the watt requirements of that speed.
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Yup.. just below 1300w burst power limit at 35.5mph, and we can pedal harder if the lightest is is -2% efficient as this.
On a 29er with a 10T lower gear you could just fit a 46T to a mid mount to hit this same speed.
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But you may get tired of disposable 10T chainrings and eventually want to move up to my mid-long mount and 56T chainring + 12T lowest cassette sprocket.
I'm glad i can at least get the kind of gearing that would max out the drive without resorting to anything exotic!