Hello everyone, I am not sure if this is the right place to ask this question. If not sorry for that.

I have a Btwin 120 folding bike. It has 6 speed at rear wheel. Is it possible to convert it to 9 speed? What parts do I need to change, if it is possible?

Welcome. Several issues at play here.

Your present 6 speed rear will likely have 126mm hub spacing. A 9 speed will have 130mm spacing, so no, they are not compatible.

If you were to replace the wheel with a hub that has 130mm spacing, you'd also need to replace the 6 speed shifter to a 9 speed.

Are you looking to 9 speed to get higher or lower gearing, or simply more gears? Higher or lower gearing might be accomplished by a different freewheel than your current 6 speed. That's where I'd start.

Hello and thank you bargainguy .


I use my bike regularly for about 20 km a day, Sometimes I feel I need more gears than 6 when I climb hills especially. I love my bike, I don't want to buy a new one.


I have searched a bit and learn that I need to change many parts, but I am confused and don't know which parts will be compatible with my existing Btwin. For example, will I need to change my rear wheel entirely, or changing the hub is enough? Do I need a freewheel or cassette?

Your 6 speed cluster is a freewheel, not a cassette.

If you need lower gears than you presently have, the most cost effective solution might be to replace the freewheel with one that has lower gearing. Much depends on your present rear derailleur and whether it could handle the change. For ex., if your present 6 speed cluster is 14-28, you might be able to run a 14-30, but not much more if at all.

This is the paradox of cheaper folding bikes. Often equipped with low-rent parts that don't lend themselves well to upgrading. The choice of a 6 speed freewheel is evidence of cost-saving. Better folders have cassettes and wider-range gearing.

To get in excess of 7 speeds, you'll need to change to a freehub system with a 130 mm hub width. I've done this a couple of times on vintage steel frame bikes but not on a folder. The folding bike may be more of a challenge, due to shorter chain and seat stays. You'd want a shop to evaluate that.

What is the gear size range on your current freewheel? As mentioned above, it may be simple to change to a different freewheel. You can usually add a couple of teeth in the lower range without needing a new derailleur. Chain length may be an issue.

What you seem to need is not more, but lower gears for climbing hills. The simplest and cheapest solution is a 6 speed freewheel with a large cog that has more teeth. You would have to determine if your rear derailleur is able to accomodate a larger cog and a longer chain. If your derailleur won't work with a larger cog it would have to be changed. Next cheapest would be a 7 speed freewheel with a larger big cog. This would require a new 7 speed shifter that would be compatible with your derailleur. Again, you might require a new derailleur and you would also need a new chain. 9 speeds would mean changing your rear wheel. Changing a hub means completely disassembling the wheel which is time consuming and would cost more than buying a complete wheel. Again you would need a new shifter, chain, perhaps a derailleur and a cassette to fit your new wheel.

Do you use your highest gear a lot? If not, by far the simplest solution to get lower gearing is just get a smaller chainring.

Many thanks friends, now I better understand what I need...

Thanks to the ebike boom, you can now get 9-speed freewheels. So a new hub/wheel might not have to happen.
However, several of the issues already mentioned remains.
Hub width, available gear ratios, new chain, new shifter.
Also, 9-speed freewheels have the weakness that caused cassette hubs to be invented - risk of axle bending/breaking.

As others have said, the easy change is going from a 6 speed to a 7 speed freewheel.

You’ll need to know your current freewheel. If the smallest cog is 14t and the largest is 28t. Then going to 13-34 freewheel will give you a little bit higher end and about 20% lower gearing for climbing. You might have to get a 14-34 if the 13-34 can’t be found. Don’t get a Megarange where the jump is 24 to 34.

I saw a BTwin Hoptown model with a Tourney rear derailleur. Depending on the exact model, I think it will handle a max cog of 34t. This is important because you only need the freewheel and a 7 speed shifter, and most likely a new cable.

The main difference between a 7 speed “freewheel” and a 9 speed “cassette” will be 11t and an another extra cog; and a lot of cost. You’ll still be limited to 34t for climbing.

John

A 6 speed freewheel with a bigger large cog is even easier, no need to change the shifter

That’s true, unless it is a Mega with a 24-34 jump.

I understand the rational, especially touring with a triple, as an ultimate bailout gear for someone whir aren’t needs it. But I find that gap to be so enormous, and momentum sucking, for most climbing.

John

I checked my rear cog, it is 14-28. I found followings which all are cassettes:

Shimano CS-HG20, 7 gear 12-34
Shimano Altus CS-HG31, 8 gear 11-34
Shimano Acera CS-HG200-9, 9 gear 11-34

Smallest cog will also help me improve my speed which is good for me.

I cannot find a freewheel example, which means I need to change my hub, derailleur, shifter etc. And need to find a good local shop to do it for me.

https://www.ebay.com/itm/38428243417...QaAs5JEALw_wcB

​​​​​​https://www.amazon.com/ZUKKA-Freewhe.../dp/B098DYL6JT

​​​​​​https://bankruptbikeparts.co.uk/prod...-shimano-gears

Thanks [MENTION=28167]dedhed[/MENTION]

The first thing you should do is to yank out the rear wheel and measure the frame drop out spacing. In this day and age I am guess even a 6 sp freewheel bike will have either 130 or 135mm spacing.
Also- take pictures of everything and post them.

Thank you icemilkcoffee , I measured it, the width between rear wheel's axe's connection points of the frame is 130mm. My rear wheel's hub has 28 holes on it. I cannot post any pictures because of my membership level.

Good. 130mm means you can change to a common 8-10 speed Shimano or Shimano compatible hub.
Now what crankset, derailleurs and shifters do you have? Some of these will have to be changed as well.

I ended up following equipment:

Shimano Tiagra FH-RS400 rear hub
Shimano Altus Cs-Hg31-8 11-34T rear cog
Shimano CN-HG40 6/7/8 Speed Chain
Shimano Altus RD-M310 rear derailleur 6/7/8S
Shımano Altus SL-M315 Shifter 8S
Shimano Acera V-Brake front and back

After that I also needed to replace front hub with one which is 113mm length. Previous was 122mm length. I changed it because the chain was coming off the front cog when İ changed the gear from two to one on hills.

Now it goes faster and easier to climb hills.

Thank you all for helps and opinions.