Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

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fladam   1 mW

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Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by fladam » Jul 22 2021 12:45pm

Hi there, I bought an ebike which came with a standard 7 speed rear cog. The front derailleur originally had a 3 cog set up due to the motor being a rear hub.

I since swapped out the hub motor for a mid drive Bafang BBSHD (no front derailleur). I changed the rear hub wheel for a regular 26" wheel. Now I want to increase the gearing so that I can climb hills without necessarily using the motor, as my battery doesn't have substantial range.

How many gears can a 26 "rear wheel fit on a standard frame. I realise that a new screw on freewheel is limited to about 10 gears. I will have to probably buy a new wheel and add a cassette to take it up to 11 speed, which will mean buying a new derailleur and shifter.

Is this prudent? Any advice welcome please.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 22 2021 1:06pm

Bad idea. Higher gear count sprockets and chains are narrower, quicker to wear out, and easier to break. BBSHD has an enormous appetite for these parts, and the more gears you use, the more expensive the consumables are.

Be realistic about how low a bottom gear you really need, and use the lowest number of cassette or freewheel sprockets that will give you that ratio. That way you will get improved lifespan, less adjustment, and lower cost replacement parts. With a mid drive, you won't want as many different ratios as a pedal cyclist anyway.
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ccihon   10 mW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by ccihon » Jul 22 2021 1:33pm

I don't think freewheels (screw on) are readily available or work with anything over 8-speed - and even those are rare. The vast majority of freewheels available new are 6, 7, occasionally 8. You are correct in that if you want 9, 10, or 11 speeds you will likely need a cassette-based system.

Chalo is the bike expert here - I think one point to remember is that more sprockets means more steps, but not necessarily more gear-inch range. More steps in the same width requires narrower spacing and narrower chains. Regardless of whether your are using a 7-speed freewheel or a 11-speed cassette, the smallest sprocket is likely between 11-14 teeth, and the largest, between 28-34. Maybe can get a bigger climbing sprocket if thats what's needed, but more steps in between won't help. You may want to look at a smaller chain ring up front to climb more easily.

I motorized a recumbent trike (heavy, hard climber) that originally had a mtb triple up front mated to a 9-speed cassette. The DD motor I chose was screw-on freewheel only, so I thought I would lose something going to that. Turns out the range is similar, and in fact I also need fewer gears total when used with assist. I do miss the cassette system for one other reason - I need to find a quieter freewheel, as the one included with my hub motor sounds like a swarm of bees at speed.

fladam   1 mW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by fladam » Jul 22 2021 4:55pm

Thank you all for your valuable insight. I will look more into the necessary ratios before adding a high count sprocket.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 22 2021 6:37pm

ccihon wrote:
Jul 22 2021 1:33pm
I don't think freewheels (screw on) are readily available or work with anything over 8-speed -
https://www.sunrace.com/en/products/freewheels-e-bike

These are more nicely made than run-of-the-mill freewheels. 8, 9, and 10-speed models all use customary Shimano spacing.
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ccihon   10 mW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by ccihon » Jul 22 2021 7:43pm

Those look like something I could maybe use... Would the "stack height" of a nine speed be taller than the 7? Not sure how much room I have between the current small ring and the axle shoulder. It's on a 9C clone motor, and the whole rear dropout width is already wider than the original hub and cassette that was on the trike.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 23 2021 12:07am

ccihon wrote:
Jul 22 2021 7:43pm
Would the "stack height" of a nine speed be taller than the 7? Not sure how much room I have between the current small ring and the axle shoulder.
8, 9, and 10 speed cassettes (and freewheels) all use the same overall spacing, which is 4mm wider than 7 speed spacing.
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fladam   1 mW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by fladam » Jul 23 2021 3:24am

That is very interesting. You wouldn't need to buy a new wheel for its hub, but the question is how can a 8, 9 or 10 speed freewheel fit if the spacing is the same? I mean would there be enough axle space between the swing arms?

Thanks for the link.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 23 2021 10:24am

fladam wrote:
Jul 23 2021 3:24am
That is very interesting. You wouldn't need to buy a new wheel for its hub, but the question is how can a 8, 9 or 10 speed freewheel fit if the spacing is the same? I mean would there be enough axle space between the swing arms?
You have to add 4mm of spacing to the axle and dropouts (or spring the dropouts open 4mm more to install the wheel). Then you have to increase the wheel dish to compensate, or else let the wheel run off center in the frame. For some frames this is more plausible than for others.
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2old   100 kW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by 2old » Jul 23 2021 6:36pm

Luna (probably others) has a 30 tooth front ring for the BBSHD. This will lower the ratio considerably and with a 28T or 34T rear should provide a low enough gear. I've had one on my BBS02 equipped hardtail for years and it has functioned perfectly.

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E-HP   100 MW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by E-HP » Jul 23 2021 7:50pm

2old wrote:
Jul 23 2021 6:36pm
Luna (probably others) has a 30 tooth front ring for the BBSHD. This will lower the ratio considerably and with a 28T or 34T rear should provide a low enough gear. I've had one on my BBS02 equipped hardtail for years and it has functioned perfectly.
Looking at how the 30 tooth mounts on the BBSHD, it might be challenging to get to the 34T rear and still maintain a usable chain line.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 23 2021 9:00pm

E-HP wrote:
Jul 23 2021 7:50pm
2old wrote:
Jul 23 2021 6:36pm
Luna (probably others) has a 30 tooth front ring for the BBSHD. This will lower the ratio considerably and with a 28T or 34T rear should provide a low enough gear.
Looking at how the 30 tooth mounts on the BBSHD, it might be challenging to get to the 34T rear and still maintain a usable chain line.
This.

42T (or 40T with whatever Lekkie mounting solution) is the smallest that makes sense. Why folks would knacker their chainline with a 30T, when there are cassette sprockets up to at least 51T, is perplexing.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

fladam   1 mW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by fladam » Jul 24 2021 3:03am

Thanks for all your help :) :)

2old   100 kW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by 2old » Jul 24 2021 8:03am

Chalo wrote:
Jul 23 2021 9:00pm
E-HP wrote:
Jul 23 2021 7:50pm
2old wrote:
Jul 23 2021 6:36pm
Luna (probably others) has a 30 tooth front ring for the BBSHD. This will lower the ratio considerably and with a 28T or 34T rear should provide a low enough gear.
Looking at how the 30 tooth mounts on the BBSHD, it might be challenging to get to the 34T rear and still maintain a usable chain line.
This.

42T (or 40T with whatever Lekkie mounting solution) is the smallest that makes sense. Why folks would knacker their chainline with a 30T, when there are cassette sprockets up to at least 51T, is perplexing.
I've been running the 30T Luna with an 11 - 32, 8-speed rear for three years without difficulty, excess wear or any other problem. Doubt anything would be different with a "34'. Looks like individuals don't like Luna (fine, probably there are other products), look for imaginary problems or trust the experiences of those who don't know how to set up a drivetrain.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 24 2021 10:39am

2old wrote:
Jul 24 2021 8:03am
Chalo wrote:
Jul 23 2021 9:00pm
42T (or 40T with whatever Lekkie mounting solution) is the smallest that makes sense. Why folks would knacker their chainline with a 30T, when there are cassette sprockets up to at least 51T, is perplexing.
I've been running the 30T Luna with an 11 - 32, 8-speed rear for three years without difficulty, excess wear or any other problem. Doubt anything would be different with a "34'. Looks like individuals don't like Luna (fine, probably there are other products), look for imaginary problems or trust the experiences of those who don't know how to set up a drivetrain.
It probably helps you understand the effects of bad chainline to work on lots of different bikes every day. Some people let their bikes fall apart underneath them but never see a problem until the bike stops working entirely.

Bad chainline isn't an imaginary problem. It causes power loss, excessive wear, poor shifting, chain drops, and inability to turn the pedals backwards without snarling the chain. The is no amount of "setting up your drivetrain" that compensates for it. The chainring goes in the middle of the cassette, or you get problems in some gears.

Running in the 30-11 gear all the time doesn't constitute bad chainline, though. It unnecessarily tears up your bike for other reasons.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by 2old » Jul 24 2021 6:06pm

Chalo wrote:
Jul 24 2021 10:39am
2old wrote:
Jul 24 2021 8:03am
Chalo wrote:
Jul 23 2021 9:00pm
42T (or 40T with whatever Lekkie mounting solution) is the smallest that makes sense. Why folks would knacker their chainline with a 30T, when there are cassette sprockets up to at least 51T, is perplexing.
I've been running the 30T Luna with an 11 - 32, 8-speed rear for three years without difficulty, excess wear or any other problem. Doubt anything would be different with a "34'. Looks like individuals don't like Luna (fine, probably there are other products), look for imaginary problems or trust the experiences of those who don't know how to set up a drivetrain.
It probably helps you understand the effects of bad chainline to work on lots of different bikes every day. Some people let their bikes fall apart underneath them but never see a problem until the bike stops working entirely.

Bad chainline isn't an imaginary problem. It causes power loss, excessive wear, poor shifting, chain drops, and inability to turn the pedals backwards without snarling the chain. The is no amount of "setting up your drivetrain" that compensates for it. The chainring goes in the middle of the cassette, or you get problems in some gears.

Running in the 30-11 gear all the time doesn't constitute bad chainline, though. It unnecessarily tears up your bike for other reasons.
Three years without a problem trumps all your hypothetical verbiage. The bike isn't coddled since all my off road riding involves hilly terrain.

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Chalo   100 GW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by Chalo » Jul 25 2021 12:15am

2old wrote:
Jul 24 2021 6:06pm
Three years without a problem trumps all your hypothetical verbiage. The bike isn't coddled since all my off road riding involves hilly terrain.
It's not hypothetical. It's my experience of repairing many thousands of bikes in varying states of decay and abuse. As I pointed out already, some folks can't tell their bike is in distress until the wheels refuse to turn. For all I know, you are one of them.

I've cleaned up the aftermath of bad chainline more times than I can remember or count. I've also had to remedy bad chainline on my own BBS02, and my buddy's BBSHD, and that Conference Bike I set up with a BBSHD, etc, etc. I didn't fix these things because they hurt my feelings-- I fixed them because the bikes didn't work right until I did.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

2old   100 kW

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Re: Increasing the Gearing on a cheap 7 speed ebike Samebike LO26

Post by 2old » Jul 25 2021 11:13am

I've got chain checkers and the tools a home mechanic needs to build many, many bikes from frame up. Also, not a lightweight, but 180 at 6'1'. I've ridden this bike for six years with one change of "cassette" (the first was 11-17-28 in 8-speed spacing so the chainline was basically straight in any gear, although only in the "17"). You can cite whatever you want. Guess what? It's BS to me since I know what works.

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