Questions about bike gearing?

[nukezero]

I'm a newbie with bikes so I have a few questions regarding basic bicycle gearing.

I have a Electra Townie 21 speed with a 28/38/48T front chainring paired with a Shimano 14-34T mega range rear gear drive. I really like the power when I use the 48T and 14T to get high speed. So I am assuming the math is: 48/14 = 3.42 ratio. So that means, for every 1 revolution of my legs, the rear tire is turning 3.42 times?

So now onto my Motiv electric bike, it only has a 44T chain ring in the front. The rear has a 16-24T but I am planning to change that to a DNP Epoch 11-28T because I want more top-end speed and I want to catch the crank. So if my math is correct, 44T / 11T = 4.0. That means, with this setup, I will get a even faster higher speed than the Electra Townie and I don't need to bother with upgrading the front chain ring to a 48T?

I realize that even if I put on a DNP 11-34T mega Range, I still won't get the lowest gear ratio of 28T chainring/34T megarange like the electra.

My goal is to maximize the top end without degrading existing hill power and keep costs low.

Thanks

 

[teklektik]

A bit ago I upgraded my Mundo to a Shimano FC-2303 crankset with 52/42/30 chainrings and chugged out a little spreadsheet to see the ratios.

Here's a snap of the spread updated with your freewheel/chainrings so you can get an idea of how the ratios will work out... I don't have the Shimano freewheel included, but the Shimano 14T cog is between the DNP 13/15 cogs for the purposes of comparison...

The DNPs seem to have the same 6 small cogs - only the 7th differs. I know this is true for the 28, 30, 32 versions and am assuming it's the same for the 34...

 

[cal3thousand]

I'm a newbie with bikes so I have a few questions regarding basic bicycle gearing.

I have a Electra Townie 21 speed with a 28/38/48T front chainring paired with a Shimano 14-34T mega range rear gear drive. I really like the power when I use the 48T and 14T to get high speed. So I am assuming the math is: 48/14 = 3.42 ratio. So that means, for every 1 revolution of my legs, the rear tire is turning 3.42 times?

So now onto my Motiv electric bike, it only has a 44T chain ring in the front. The rear has a 16-24T but I am planning to change that to a DNP Epoch 11-28T because I want more top-end speed and I want to catch the crank. So if my math is correct, 44T / 11T = 4.0. That means, with this setup, I will get a even faster higher speed than the Electra Townie and I don't need to bother with upgrading the front chain ring to a 48T?

I realize that even if I put on a DNP 11-34T mega Range, I still won't get the lowest gear ratio of 28T chainring/34T megarange like the electra.

My goal is to maximize the top end without degrading existing hill power and keep costs low.

Thanks

Looks like you have it figured properly. With that setup, you will lose some low end climbing ability, but will gain some top. (17% if my calcs are correct)

 

[nukezero]

Okay great, thanks a lot. Does anyone know if the quality of the DNP Epoch is good?

I just bought this DNP Epoch and my local bike shop told me he doesn't recommend it and insists me to return it. He says it's one of the strangest freewheels he's ever installed previously on a customers bike and it had problems. But I'm thinking isn't this what cellman sells for his ebike kits too?

Are the DNP's that notoriously bad?

 

[Chalo]

Does anyone know if the quality of the DNP Epoch is good?

It's crap; it is well known to break early and often. Since Shimano's 11-34 and 11-28 freewheels went out of production years ago, there has been no decent quality thread-on freewheel with an 11t high gear.

Note that power comes from force at the pedals times the speed of the pedals. Therefore a higher gear usually gives you less power, if you are turning it slower than you would a lower gear. A good rule of thumb is that if you're pedaling less than 90rpm, you can make more power by pedaling faster. Above a certain point, turning the pedals faster makes less power because force at the pedals falls away faster than rpm increases. But 90rpm is regarded as close to optimum for most people.

A 48/14 high gear turning at 90rpm with a 26" wheel yields 24mph. So you'll need a higher gear than this only if your electric bike goes faster than 24mph in circumstances where you'd like to pedal along.

You might like the feel of turning the pedals slowly, but don't mislead yourself into thinking that you are producing more power just because you are pushing against firm resistance.

Also, 11t sprockets are inefficient and dramatically increase chain and sprocket wear. 13t is mechanically much better for your drivetrain. If you feel you need a higher gear, consider using to a crank with bigger rings, such as a 30-42-52 "road triple" or a 39-53 "road double".

 

[nukezero]

Damn. Okay I already cancelled the order on the 7 speed DNP freewheel. The only other freewheel I can get is the Shimano MF-HG37 Tourney 13-28T which is 1 tooth less than my 14-28T 6 speed. But the gains will probably be minimal but I would get 7 speed right?

44/14 = 3.14
44/13 = 3.38

That's a 7.64% gain. That's probably not much.

 

[nukezero]

I guess my only choice is to go to bmsbattery, buy the 500watt cassette bafang BPM and rebuild the wheel with that? Then I can slap on a 7,8, or 9 speed cassette with a 11T shimano.