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[Farfle]

I am putting together a CAD file for a 4130 18T 8M polychain front sprocket to fit the 1" keyed shaft on the 13-16 bikes. (CAD for this is much harder than you think, as its a custom tooth profile to make the small radius work)

I am wondering if I should open this up into a group buy to bring the price down. Right now My cost is $70/ sprocket in qty 10. You would be left to source the belt and rear sprocket (OTS zero parts) unless there is enough interest in a turnkey kit.

Be warned, the 18T sprocket will drop the S/DS top speed by a few MPH, and SR/DSR owners will drop a dozen MPH and become MUCH more feisty.

Also, the 18T is below Gates recommendation for minimum diameter, so the belt might actually wear out this century.

Let me know if you all are interested

[liveforphysics]

I can vouch that Farfle is legit, figured out what it took to do the small radius sprocket profile right, and I will be running the 18t sprocket for my own DSR to be a wheelie-machine! :-)

[Arlo]

I can also vouch for Farfle   I have a few motor that need these.  If we can get the numbers up it will help get the cost down who's in? 

[Farfle]

Thanks guys!

Here is the sprocket as it sits. I oversized the set screw hole to replace the anemic 2.5 mm set screw with a 4mm setscrew. Its also 4130 chromoly instead of cast iron and should last a good while. (although those in wet/salty climates will want to hit it with a rattle can before install).

[Kocho]

Are the rear sprockets interchangeable b/w '17 and older models in terms of mounting to the bike?

[Farfle]

I believe so, but I will check.

[BrianTRice@gmail.com]

This is really cool. Since I have a couple of spare belts and not much need for torque, I'll take a pass, but I'll try to help if I can since I'm nearby.

Can I offer you some CAD files of my own or figure out how we can collaborate on that aspect?

[laramie LC4]

Are the rear sprockets interchangeable b/w '17 and older models in terms of mounting to the bike?

this is the real question. if you can't fit a bigger rear sprocket on pre'17 bikes then this is all for not...

laters,

laramie 

[Say10 15FX 16FXS]

70 bucks is less than a similar size pulley from Gates. Loving the bigger set screw, great idea. How would this gearing be on the FXS? I had thought of buying a splined one and machining the center for a bushing or something to fit the keyed shaft. I would buy one.

[grmarks]

So thats why Zero went with a 20 tooth front. I guess the back would just be too large to keep the same ratio as 2016.

[Kocho]

There are fewer teeth, but I don't think the diameter is that different, because the teeth are bigger and spaced farther apart than on '16... I'm just eyeballing them though and not side by side, so there might indeed be some differences in diameter...

So thats why Zero went with a 20 tooth front. I guess the back would just be too large to keep the same ratio as 2016.

[mrwilsn]

All of the new 2017 Zero bikes that use the new fatter belt have a 20 tooth front sprocket and a 90 tooth rear giving a 4.5:1 ratio.  An 18t front and 90t rear will give a 5:1 ratio.  The same ratio could be reached keeping the 20t front but using a 100t rear (a belt with a larger diameter may also be required).  However, if you are trying to upgrade an older Zero to the new fatter belt you need to replace the front and rear sprocket but the sprocket on the motor shaft isn't plug and play due to the change from a keyed shaft to spline shaft (to handle the higher torque from the gen 4.5 size 6 controllers).  Only the SR/DSR really need the spline shaft but all of the 2017 bikes that use the fatter belt use the spline shaft so that they can all use the same 20t sprocket.

So, if you want to upgrade an older bike to the fatter belt AND you want 5:1 ratio you need new front and rear sprockets.  If you want to use 20t front and 100t rear then you need to design both sprockets.  The front needs to be designed for the keyed shaft and the rear needs to be designed because Zero only has 90t rear (for now).  Designing an 18t front for the keyed shaft is smart because you can use the stock 90t rear from Zero and achieve the 5:1 ratio.

Here are some gear ratios used by different Zero bikes.

2016 Zero S/DS/DSR 130t rear / 28t front for 4.6:1 ratio
2016 Zero SR 130t rear / 30t front for 4.3:1 ratio
2016 Zero FX/FXS 132t rear / 25t front for 5.2:1 ratio

2017 All bikes with 17mm belt 90t rear / 20t front for 4.5:1 ratio

If you use Farfle's sprocket on an older model S/SR/DS/DSR you will be increasing torque at the rear wheel and gaining the benefits of the fatter belt.  However, if you use the sprocket on an older model FX/FXS you will decreasing torque at the rear wheel but gaining the benefits of the fatter belt.

I expect that Zero will eventually develop different sprocket sizes and belt diameters to get back to the higher gear ratios of previous years on bikes like the FX/FXS.  Putting Farfle's sprocket on an older model Zero will set you up to potentially use 17mm sprockets and belts developed by Zero.

For reference here are the belt dimensions from a 2014 Zero S and a 2017 Zero SR.

2014 Zero S 14mm width 8mm pitch
2017 Zero SR 17mm width 11mm pitch

Also, notice the difference in belt construction that you can see from the side view.

2014 Zero S Belt Width


2014 Zero S Belt Pitch


2017 Zero SR Belt Width


2017 Zero SR Belt Pitch

[Kocho]

I'm confused... Is there a typo?

All of the new 2017 Zero bikes that use the new fatter belt have a 20 tooth front sprocket and a 90 tooth rear giving a 4.5:1 ratio.  An 18t front and 90t rear will give a 5:1 ratio.  .....

Designing an 18t front for the keyed shaft is smart because you can use the stock 90t rear from Zero and achieve the 5:1 ratio.

[mrwilsn]

I'm confused... Is there a typo?

All of the new 2017 Zero bikes that use the new fatter belt have a 20 tooth front sprocket and a 90 tooth rear giving a 4.5:1 ratio.  An 18t front and 90t rear will give a 5:1 ratio.  .....

Designing an 18t front for the keyed shaft is smart because you can use the stock 90t rear from Zero and achieve the 5:1 ratio.

I don't think so but I could have made an error....not sure what you are confused about.

2017 has a 20t front and 90t rear for a 4.5:1 ratio.  If you buy an 18t front with Farfle and then buy a 90t rear and a 17mm belt from Zero and put it on a 2016 Zero SR, for example, you will have a bike with a 5:1 ratio.

Did I make a mistake somewhere?

[Kocho]

Nope, I must have been half-asleep still. All clear now