Help! Help and advice with cassette choice needed.

[MikeFB]

Hi all,

Just bought a Woosh Bafang G06 fat kit for my fat bike with 26" wheels.

I'm about to order a 7 speed cassette for it. But need help on deciding which to get. The Bafang G06 hub requires a cassette and looking at my options I'm getting confused!

The bike is currently fitted with a Shimano MFTZ21 7 speed 14-28T freewheel, a single 44T front chainring and Tourney rear derailleur.

The bike will be used 30% on the road, and 70% on trails. There are quite a few hills around me, but I can pedal quite hard if needed and have got up some steep hills with the fat bike without a motor (just).

I believe that the following are my options?

Shimano CS-HG200-7 12-32T

Shimano HG41 7 Speed 11-28T

Sunrace CSM63 7-Speed 11-28T

SRAM PG 730 7 Speed 12-32T

Does anyone know if the above are suitable/compatible and given that they have different cog sizes to the current freewheel will I need a different chain length and if so what/how do I go about making sure I get the correct length?

Opinions/advice would be much appreciated as this is my first rear wheel build, plus I have never changed a rear cog setup before, so am quite confused about what to get.

Images of the G06 hub (9 spline) and current freewheel if it helps:

 

[sjpt]

An 11-28 will give a higher top gear than you currently have; allowing you to go faster for the same pedalling speed. Do you use the highest gear at the moment much and feel as if you would like higher still? You might want a bit higher when you have the motor helping too. Same length chain should do fine.

A 12-32 will give lower bottom. It sounds as if you can just cope with your current lowest gear, and that will be easier with the motor so maybe you won't really want a lower one. You will need a slightly longer chain. In the lowest gear you may be going so slowly that the motor is rather stressed; hub motors don't like going too slowly. I expect that one is wound to go fairly slow; Woosh will advise on that. It will also give a higher top gear, just not as high as the 11-28.

I'm at an age where I prefer low granny gears so I'd certainly go for the 12-32, but I suspect you'll be better off with the higher 11-28,

 

[Woosh]

you'll need one 3mm spacer or two 2mm spacers with the 7-speed cassette.

 

[Nealh]

Personally I would put a 8/9 spd cassette on it and change the shifter, and opt for a better low gear. A 34/36t low gear then becomes an option.

 

[vfr400]

Don't use your existing freewheel. The top gear will be too low. I recommend you use an 11/32 cassette.

As above, you have the option to go up to 9-speed if you change your shifter and derailleur. There are often some used ones on Ebay because a lot of people changed 9-speed to 10 or 11-speed.

 

[Woosh]

he's got 4" tyres, 11T would give him 30+mph derestricted.
I know the controller is good but still at risk of overheating.

 

[vfr400]

he's got 4" tyres, 11T would give him 30+mph derestricted.
I know the controller is good but still at risk of overheating.

If he pedals like the BMX guys in the world championships. I have 11/53 on my road bike. That's 25% higher. anyway, he can always use the next gear down when he's not going downhill. he doesn't have to stay in top gear all the time.

 

[Woosh]

the tyre circumference of my fat bike is about 2.35m.
if he pedals at 80 RPM, his speed would be 2.35m * (44T/11T) * 80 * 60 /h = 45kph

 

[vfr400]

the tyre circumference of my fat bike is about 2.35m.
if he pedals at 80 RPM, his speed would be 2.35m * (44T/11T) * 80 * 60 /h = 45kph

That would be about right then. Mine does 32 mph or 51.2kph at 80 rpm. That's without a motor.

 

[Nealh]

Don't use your existing freewheel. The top gear will be too low. I recommend you use an 11/32 cassette.

As above, you have the option to go up to 9-speed if you change your shifter and derailleur. There are often some used ones on Ebay because a lot of people changed 9-speed to 10 or 11-speed.

I totally over looked the derailleur but they can be had quite cheaply as well.
He can't use freewheel any way on the hub.

 

[Andy-Mat]

He can't use freewheel any way on the hub.

Just to improve my knowledge, why is that?

Andy

 

[peter.c]

free wheel has a thread and screws on

 

[Bonzo Banana]

ETC do a 11-34T 7 speed cassette. ETC I think are a brand of moores and large (something like that) who are an importer. I think the cassette maybe a sunrace. There seems to be a couple of versions one has a big gap between the granny gear and the next smallest cog and others seem to have a more even gap. I think more recent versions have had the big gap, something like 34T to 24 or 26T. It's an all steel cassette and pretty decent quality I would say although thinking about being only 7 speed means there is more space for thicker stronger cogs. Don't rely on the image of the cassette shown where sold as you may get a slightly different spread of cog sizes inbetween and as the jump is so wide you may not actually like it that much because there is no 28T cog. Personally I think its a great option to give wide gearing on a 1x that uses a 7 speed cassette, a jump of 24T to 34T would be fine for me. It's a great bailout gear if your battery has run out of charge and need to get the heavy ebike home.

I've seen it for sale, Amazon, ebay, Tredz and I'm sure many other stockists.

 

[Nealh]

Just to improve my knowledge, why is that?

Andy

The G06 has cassette splines and not a screw thread.

Did you not look at the pics in #1, then again as you put your rotors on the wrong way you likely wouldn't know the difference .

 

[Bonzo Banana]

Just to improve my knowledge, why is that?

Andy

There is a good wikipage here about the two different types of cogset. The image below shows why freewheel hub axles are so much weaker and prone to bending as there is such a long distance between the bearings and the dropout on the driveside. Although some would argue that the freewheel is better because each time you replace a freewheel you also get a fresh ratcheting mechanism but the freewheel is definitely a cheaper weaker option and freehubs can last a very long time. As a heavy rider myself I always have to go with a freehub. I've bent quite a few freewheel hub axles in my time by overdoing pavement drops onto the road or just hitting potholes.

Cogset - Wikipedia

en.wikipedia.org

 

[vfr400]

There is a good wikipage here about the two different types of cogset. The image below shows why freewheel hub axles are so much weaker and prone to bending as there is such a long distance between the bearings and the dropout on the driveside. Although some would argue that the freewheel is better because each time you replace a freewheel you also get a fresh ratcheting mechanism but the freewheel is definitely a cheaper weaker option and freehubs can last a very long time. As a heavy rider myself I always have to go with a freehub. I've bent quite a few freewheel hub axles in my time by overdoing pavement drops onto the road or just hitting potholes.

Cogset - Wikipedia

en.wikipedia.org

That's true for bicycles that have 9mm or occasionally 10mm axles, but most electric motors have much stronger 12mm axles or even 14mm. In 10 years on this forum, I've never heard of someone bending their motor axle, and free-hub motors only became common in the last couple of years.

 

[Andy-Mat]

There is a good wikipage here about the two different types of cogset. The image below shows why freewheel hub axles are so much weaker and prone to bending as there is such a long distance between the bearings and the dropout on the driveside. Although some would argue that the freewheel is better because each time you replace a freewheel you also get a fresh ratcheting mechanism but the freewheel is definitely a cheaper weaker option and freehubs can last a very long time. As a heavy rider myself I always have to go with a freehub. I've bent quite a few freewheel hub axles in my time by overdoing pavement drops onto the road or just hitting potholes.

Cogset - Wikipedia

en.wikipedia.org

Firstly, thanks to you and the others who answered my query.
My first e-bike was a free hub, and the reason that I know this, was that after about 10,000 KMs or so, I had to replace the cassette.
My current bike, has not got so many miles (or KMs!) on it, and up to now is running fine, and I have never taken it apart.
One of the things about e-bikes with hub motors, is that the stress on all the components in the drive chain, is far far less than a mid motor bike. So IMHO, the possibility of bending the axle must be significantly reduced for bikes with hub motors.
The only time I ever had an axle damaged, was on my last pushbike, that fell over to the right, and it actually BROKE the axle in the middle..... It took a long search around to find one that fitted, that was also a freehub style.
Thanks again for the very clear drawings.
Andy

 

[MikeFB]

Thanks guys for the replies and info.

Looking at my options, I think I'll go for a 11-28 7 speed and get some spacers for the moment and keep everything else as it is and see how that goes. They're not expensive, so if that doesn't work out I may go the 8/9 speed route and change everything while going for better derailleurs and shifters etc at the same time.

 

[Bonzo Banana]

That's true for bicycles that have 9mm or occasionally 10mm axles, but most electric motors have much stronger 12mm axles or even 14mm. In 10 years on this forum, I've never heard of someone bending their motor axle, and free-hub motors only became common in the last couple of years.

To be perfectly honest I wouldn't disagree with you, I can see motor hubs have better axles, you still have the issues of poor alignment of threading on the internal thread of freewheels and on the external thread of the hub itself which can give freewheel wobble, you also have limited high gearing and the fact freewheels are now pretty much the cheap end of the market so fairly poor quality and light duty. Freewheels dominate the sub £200 bike market. BMX bikes have solid axles and single speed freewheels and get loads of abuse but then often have hardened chromoly axles. The main issue of bent axles is with un-hardened solid steel axles or for snapped axles quick release axles. Mountain bikes especially hardtails are notorious for bending rear axles even for models ridden by young light children when fitted with freewheels. One of the main criticisms I have of ebikes fitted with freewheels is they use the low grade 8 speed or more freewheels often produced by low quality Chinese brands which are short life and don't have consistent shifting because the tolerances of shifting are so tight yet the freewheels wobble so it can be a pain to keep them shifting reliably even as a 1x setup. These are the sort of low cost ebikes you get on aliexpress but you do occasionally see them at retail in the UK, I think groupon have sold them in the past. For me it has to be a freehub and cassette for so many reasons.

 

[vfr400]

To be perfectly honest I wouldn't disagree with you, I can see motor hubs have better axles, you still have the issues of poor alignment of threading on the internal thread of freewheels and on the external thread of the hub itself which can give freewheel wobble, you also have limited high gearing and the fact freewheels are now pretty much the cheap end of the market so fairly poor quality and light duty. Freewheels dominate the sub £200 bike market. BMX bikes have solid axles and single speed freewheels and get loads of abuse but then often have hardened chromoly axles. The main issue of bent axles is with un-hardened solid steel axles or for snapped axles quick release axles. Mountain bikes especially hardtails are notorious for bending rear axles even for models ridden by young light children when fitted with freewheels. One of the main criticisms I have of ebikes fitted with freewheels is they use the low grade 8 speed or more freewheels often produced by low quality Chinese brands which are short life and don't have consistent shifting because the tolerances of shifting are so tight yet the freewheels wobble so it can be a pain to keep them shifting reliably even as a 1x setup. These are the sort of low cost ebikes you get on aliexpress but you do occasionally see them at retail in the UK, I think groupon have sold them in the past. For me it has to be a freehub and cassette for so many reasons.

I used freewheel geared motors for many years over thousands of miles. I never had a problem with any of them. Also, I worked in an ebike shop for over 10 years as their mechanic, and I never had to adjust or reset anybody's gears except on folding bikes when they bent the derailleur by putting the bikes in the car the wrong way up.

Considering all that and that the majority of rear hub-motored ebikes have freewheel gears, and the number of people reporting shifting problems on this forum are virtually non-existant, I would say that your concerns are unfounded. In fact nearly all those reporting shifting problems have cassette gears and mainly at the higher end of the scale. You can do a search and see for yourself.