Replacement cassette question

[Phil_P]

Hi,

My folder with 20" wheels currently has 6gears. The cassette fitted is a shimano mf tz20 which I understand is a 14 - 28 t cassette.

The bike has 3 modes and on medium setting I can just about keep up on the flat but in high assist mode or downhill I am just peddling air. So far I have not needed to change down by more than 1 or 2 gears for any of hills around here I need to climb.

My question Is can anyone recommend a replacement cassette that would maybe give me a smaller ...say 11 t top gear ?. Is this sensible or should I look to increase the main chainring which I guess is also possible but I have strutted to find a 51t single chainring set - I think my current chainring is 44 or maybe 48t.

Any advise would be appreciated as I an very much a novice about such things.

Regards
Phil

 

[flecc]

This is a universal folder problem due to the 20" or 16" wheels. A larger chainring/chainwheel is the best solution. Available cassettes are very limited and even an 11 or 12 tooth small sprocket won't lift things much and would wear very fast.

In my case I changed a 48 tooth chainwheel to a very large 60 tooth chainring and spider since I like pedalling a bike to high speeds down moderate slopes, but you might not want to go that far:

 

[Jeremy]

I had the same problem. My 20" wheel electric folder has the same Shimano rear freewheel (it isn't a cassette, BTW, it's a screw on freewheel). Being a freewheel there are a limited range of replacements. I've fitted a Stronglight single 50t chainring and crankset, which is as large as I can go and still fold the bike without the chainring bashing on the ground, but the gearing still isn't tall enough.

As I don't need the 28 low gear at all, I've just bought an 12-18 freewheel to try. These aren't made any more, I believe, the one I've bought is old stock from the 1980's, which is around the time when freewheels were being swiftly overtaken by cassettes, with their much wider range of ratios and number of sprockets.

I'm waiting for it to arrive, so don't know for sure if it will work. In all probability it won't index, as it's pre-indexed gears, but it does have the correct thread for the hub (not all freewheels have the same thread, although some are sufficiently close to fit OK).

If you want to explore doing this, then the two companies that made small sprocket 6 speed freewheels seem to to be Regina and Sunrace. Shimano are reputed to have made a very short production run of them, but these seem rarer than hens teeth. There is an extremely nasty (but not very cheap) 7 speed wide range freewheel available from the Chinese company DNP, but in my experience DNP make their stuff from material with all the structural properties of soft cheese, so I couldn't in all honesty recommend it.

There is a seller on ebay that has some old stock Regina Extra close ratio freewheels with English threads (which are compatible with the ISO thread on the hub motor), welcometothebikeman. A search of his items for sale may find another one of the old stock freewheels that I've bought, for around £30 delivered.

Jeremy

 

[Phil_P]

Hi and thanks for the advice. I think the best bet would be to try larger chainawheel. I have a new stronglight 51t (5083) so I just need to buy a spider and give that a try. I expect I could then increase upwards if I find that is not enough.

As I said I am a novice But at least I now know I have a freewheel and not a cassette thanks for putting me right on that one.

I had not considered the additional wear on a much smaller rear sprocket.

Just need to source the right spider and make sure I can either fit the existing or get a new chain guard.

Will let you now how I get on.

Regards
Phil

 

[flecc]

at least I now know I have a freewheel and not a cassette thanks for putting me right on that one.

That's if your bike has a rear wheel motor Phil, they can only use freewheels. If a front motor and normal rear derailleur, it's a cassette.

This is because the thicker 12 mm motor spindles are too big for the standard cassette core which is for standard 10 mm bike spindles.
.

 

[Jeremy]

That's if your bike has a rear wheel motor Phil, they can only use freewheels. If a front motor and normal rear derailleur, it's a cassette.

This is because the thicker 12 mm motor spindles are too big for the standard cassette core which is for standard 10 mm bike spindles.
.

It's definitely a freewheel. The Shimano TZ20 is a screw on 6 speed freewheel, not a cassette; as I said, it's the same freewheel as came fitted to my folder.

Jeremy

 

[flecc]

Thanks Jeremy, I was posting on the general principle of course and hadn't looked back to Phil's first post.
.

 

[allen-uk]

It's not just folders, Phil, it's a question many ebikers ask (including me). I like 'pedalling air'; nice phrase.

One day ebike manufacturers will modify the battery/downtube area so that we CAN have multiple front chainwheels and gear shifting, hopefully.

Me - I slowed down a bit, I suppose, and got used to easing off the pedals at 16 or so mph, changing down on the power setting to middle, and so on, in order to keep a reasonable cadence. But I think that as I get fitter/faster/etc, I might think again about changing the size of the chainwheel.

Allen, Wisper 905se

 

[jbond]

There is an extremely nasty (but not very cheap) 7 speed wide range freewheel available from the Chinese company DNP, but in my experience DNP make their stuff from material with all the structural properties of soft cheese, so I couldn't in all honesty recommend it.

Shame about this. There's a couple of US and one German source for these in 7sp 11t-30t and 11t-32t. It seems like a good solution with a 48t front except for the quality issue.

 

[Andrew harvey]

Freewheels with 11 tooth sprockets were sold by Shimano, but they were discontinued some years ago. The cycle reps who visit me tell me they had a tendancy to fail, most freewheels do not go smaller than 14 tooth for structural reasons it seems.
The smallest commonly available cassete is a 7 speed below that you are almost always looking at freewheels, except on really old bikes that had a hybrid type. These hybrids use a freewheel body with a cassete arrangement on top so you could change your own sprockets.
Inspired Cycle Engineering make their own 9 to 32 tooth 9 speed cassetes but you need a special driver to take them, price with a back wheel....... around £200 pricey but a lovley bit of kit.

 

[Phil_P]

Hi,
I have decided to go for a larger chainwheel as Flec suggested. Not quite so extreme (i didn't find any 60t models) and I had a new spare 51t already. Found some new FSA vero 130 BCD spider/crankarms for £22 incl postage on eBay and some chainset bolts for £8.

Do I need anything else....I have a crank removal tool already.

Many thanks for all your help

Phil

 

[flecc]

The 60 tooth one was a French Zenith one that Highpath Engineering happened to have in stock Phil.

Highpath often manufacture these larger sizes to order when needed, but that's not cheap of course.

52 tooth is about the largest commonly found, though I remember Shimano listed a larger one, 56 tooth I think.

Just the crank removal tool is needed, plus the Allen key for the spider bolts. You may need to trim the chain alignment afterwards by using spacers on the spider bolts to get a good between small sprocket to central rear sprocket chain alignment.
.

 

[piotrmacheta]

Will it ever be possible to have an electric hub that takes a cassette? Is it just a matter of someone doing some design or is it that there isn't enough room - could the spindle not be made smaller?
I was just interested really as it seems such an obvious way to go and I would love to have one.
I run a 12-32 (I think) freewheel with a 52 front chainring on my trike and although it's about right I could do with a couple of lower gears and a higher one.

 

[flecc]

The standard bike spindle is 10 mm which is too small to have a hole in it to feed in wires to a motor, so motors use 12 mm spindles usually which are to large for the cassette core.

Now we have side plate entry cables on some motors, it may be possible to have 10 mm spindles. However, internally geared motors are wide so the overall spindle width may be a limiter in some cases, though the narrower direct drive motors might not have a problem with that.
.

 

[Phil_P]

Hi,

Fitted the 51t chain wheel I already had and it has made big difference. I still think that I could go for more so will continue to hunt down a bargain on eBay but for now it works a treat and I can keep going up to about 17 mph.

I went for a ten mile ride today and everything felt nice and smooth and after a little tinkering with the gears these all now select perfectly.

l Have ordered a chain guard as the old one would not fit with the new cranks. I think a 60t would be perfect but as already discussed in these posts is a bespoke item that will no doubt come at a premium. I am a lesiure cyclist usually just bumbling around the Norfolk countryside at 10 mph so it's not really a big deal for me.

So I have fitted the larger chainwheel , added a computer and a holder for my iPhone. Fitted a cat eye rear view mirror which is also great. Now I have just to fit the chain guard when it arrives and a find a nice bag to go onto my rear carrier and then I will be ready for my day trips around norfolk in the spring / summer sunshine

thanks to all for your advice and guidance

Regards

Phil