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Great article about selecting the proper chainring for a mid-drive ebike

richj8990

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https://electricbike-blog.com/2017/0...the-first-try/

This guy has done it all --- commuters, trails, mud, snow, with many different DIY e-bikes. He basically says for dirt try 42t first, and if that's not good enough for climbing you can go down to about 36t, but below that, you'd better have some really wide tires to take the torque or things may start breaking (especially with his 2500+W motors!!!).


Some interesting snippets:

My Little Bronie – (42T/34-11T/26″) BBSHD with Ludicrous controller 42T Luna ring and a 9-speed cassette with 34-11T range and normal 26″ rims with 2.25″ tires. I don’t care about this bike so it’s the one that gets thrashed on when I go on trips. It sucks pedaling uphill when the battery dies, but this ebike shreds the trails and you can still pedal along at 30mph.

For different mid drives, there are a plethora of aftermarket chainrings out there in a variety of different sizes. The biggest appeal of the 42T Lekkie and 42T Luna chainrings are that they are big enough to completely surround the secondary reduction gear and move the chain line back towards the bike by over 2 centimeters. That might not sound like much, but I assure you, when dealing with adding a mid drive a cm is a lot of offset. The best case scenario is to have the chain-line line up with the middle of the cassette, but that rarely happens. Most of the time it is farther away from the bike and lines up with the higher gears. While this is fine for commuters, it sucks for trail riding machines and deep snow bikes because you spend almost all your time in the lower granny gears.

For 20-24″ wheels and a normal cassette, the 42T is a good bet. For 26″ wheels and a normal cassette I generally use a 34T-36T chainring although the 42T can be made to work if you’re not running fatty tires. For 26″ fat tires, 27+, 29er or 29er + tires I would go with a 30T-34T depending on the tire diameter. Bigger tire diameter means go with the smaller chainring. For any IGH system, I would start with a 42T chainring or smaller then adjust the speed/power range by swapping out the rear cogs, you might have to get a super large cog from ebay but using a 42T chainring will give you the cleanest chain line which is super important with an IGH. I really like the CS-S500 cog ($13 on ebay) which comes in 18T/20T sizes (the 20T is a safer bet). For CVTs you can also use the 42T chainring and experiment with cogs sizes, for a 26″ tire you’ll probably settle on the 22T like I did. Be aware that the power limit for keeping your CVT under warranty is only a scant 250W.
 
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Nurse Ben

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This is total nonsense!

You pick your gears for the terrain you ride, wheel size factors in but it’s no where near the most important variable. A 42t chainring is worthless on a mountain bike unless you’re riding on the road.

Ebike or non ebike, gearing needs are the same. Just because you have a motor doesn’t mean you can push bigger gears. Most people riding ebikes are not that strong; hence the use of an ebike, so their output and gearing needs won’t be that different from a fit non ebike.

Now in your case, a 2500 Watt ebike is not allowed on any mtb trails, only ORV or motor vehicle roads, so tall gearing might be acceptable.
 

Gutch

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^Agree. 2500w motor says it all. My ebike performs better at a higher cadence in a lower gear.
 

Nurse Ben

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Took my wife on a steep and technical climb up a gas line right of way, she was struggling both to pedal and to start from a standstill, got her to gear down for a faster cadence and she was not only better able to continue riding, she was also able to start more easily.

Even with assistance, gearing matters.

Rarely (never?) do I want avyaller gear, but I often wish for a lower gear.
 

hikerdave

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I have a 34 tooth chainring that’s perfect for me mountain biking but just a little too small for my daily commute. Bike came with 38 tooth setup for forest roads.
 

richj8990

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She couldn't gear down by herself? hmmm

This is exactly why the author says if a 42+ chainring doesn't help for climbing, you get a smaller one. And why he also talked about wide-range cassettes in back. I didn't ever read him saying that gearing didn't matter. Did he say that? The whole article was about chainrings and gearing.
 

Nurse Ben

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It's nonsense, no amount of back pedaling will change that, the gearing you're proposing/supporting is completely unusable on a mountain bike.
 

BCsaltchucker

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good post

though I find I do just great with the stock 32T on my Powerplay. On my regular non e trail bike I run a 26T in the front (on my non e hardtail used in AZ it is a 30T). This is for coastal BC gnarl.

I thought the 8 speed cassette on the Powerplay would not be enough selection. But in reality it is plenty. The extra power lends a little more momentum so I am just not gearing down as much for the sudden short steeps like I do on my other bikes (which is where the 26T chainring suits my needs)

So the needs of gearing for eMTB are different and generally much less fussy than for non-e MTB. IMHO. Kind of like how gasoline dirt bikes only need 5-6 speeds
 

KenPsz

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Curious where did you get the information for your claim in bold? Since that is a pretty bold/broad claim you have there.

I agree that you pick the gears you need but that depends on many factors. Weakness might be one factor but I doubt it is the blanket reason.
 

richj8990

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Ken, if someone presents an apple, and someone else refutes that apple with an orange, then you just ignore it, no sense in arguing past each other.
 

KenPsz

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Oh come on you can't take the fun out of a forum like that!

Plus is it is a rather condescending comment which is more of my point than anything else.

But you have a fair point.
 

Nurse Ben

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No data, but it does figure that ebikes would be more attractive to less fit riders, ie if you’re fit enough to ride without a motor then why would you buy a bike with a motor.

So maybe the average biker isn’t as fit as the average non ebike rider, but just as there are non fit non ebike riders there are also fit ebike riders.

I’ve got a Shuttle in my garage and a Smash, trails out my backyard, but I’ve only ridden the Shuttle once, whereas I ride the Smash most days; the Shuttle is my wife’s, but it fits me too :)

Kinda dumb conversation for educated adults, but it is winter, prime season for mincing words ;)

On a bright note, at least you got one non ebiker that is pro ebike :)
 

KenPsz

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I would just disagree with you that ebikes are more attractive to less fit riders, I like them because I hate climbing. I can climb just fine it just is not fun and biking is supposed to be fun. I do know people that love to climb and I just don't understand that idea.

On another note: I saw posts of yours in the fat bike forum so I know your a cool guy if you are a fat biker!

Now I just need to mix my two loves and I would be happy. An electric FS fat bike now that would be sweet. Although figuring out the gears would be a PITA. :)
 
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