The stock Zero DSR comes fitted with a belt final drive. This is quieter, and probably a bit more efficient than a chain drive, but is not a good choice for any significant off-pavement riding. Belts are more likely to snap and break with rocks and shock loading, and are more difficult to replace on the side of the road (on the DSR, you have to remove the swingarm). If the Zero was being used mostly as a street bike, and not trying to be used as a proper adventure bike, keeping the belt drive would be the obvious choice.
For 2021, I opted for the factory chain conversion kit. Over the course of a year, we’ve decided that the factory Zero chain conversion kit is poorly thought out, and seems like an afterthought from Zero. It is not durable, and wore out quickly. We cannot recommend buying it. (See below for what to buy instead). I am no longer using any of the parts supplied by Zero for the chain drive on the DSR.
Very quickly, it became clear that the sprocket ratios were significantly different than the stock belt drive. The stock belt drive has 20T front pulley, 90T rear, for a ratio of 4.5. The OEM chain conversion kit has 12T front sprocket, 65T rear, for a ratio of 5.42. This does provide more torque, but at 60 MPH the speedo reads 72 MPH. The speedo was excessively inaccurate, as was the odometer, which made accurately estimating range difficult. It is possible to take the bike to a dealer and have them re-program the speedometer for the new sprocket ratio. However, experience tells us that a 12 tooth front sprocket is getting pretty small, and tends to cause excessive chain wear. Also, the dealer is a 1.5 hr drive away.
Instead, I opted to change to a 15T front sprocket for a ratio of 4.33 for the 2021 TAT trip. Close enough to the stock ratio not to bother with a trip to the dealer, but now 3.8% taller. This worked ok, but the larger front sprocket caused the chain to rub on a motor mount at full suspension jounce.
During the trip, we also discovered the drawback of the aluminum 65 tooth rear sprocket provided by Zero. It wore out in less than 5000 mi, which was inconvenient on a 7600 mi trip.
Aluminum sprockets are short lived
In contrast, steel sprockets often last well over 10,000 miles (my 150 hp Multistrada once went nearly 25,000 miles on one set of chain and sprockets). Zero does not even have a part number for just the rear sprocket, only for the entire chain conversion kit. The dealer was able to order just the sprocket, but Zero won’t drop ship it to your location, only to the dealer. We had to pay to ship it to the dealer, and then pay to ship it to our location. It was expensive, time consuming, and difficult. Finding a large enough steel sprocket to fit turned out to be a bigger challenge than anticipated. After much searching over winter of 2021/2022, it wasn’t until our suspension guy suggested Supersprox that I got any traction. More on that in a bit.
More problems with the factory chain conversion kit became clear when was time to change the front sprocket again. The 12 tooth front sprocket supplied by Zero, and the 15 tooth that I replaced it with, have a much narrower engagement on the splined motor shaft than the original belt pulley. The hub on belt pulley (the part that engages with the splines on the shaft) is roughly 22mm thick. The hub on the 13 tooth sprocket supplied by Zero and the 15 tooth that I originally used are only about 5.7mm thick, and thus engage much less of the shaft. Zero supplies a spacer for this reason, to help locate the front sprocket on the shaft. Take a look at how much of the shaft is left after using the spacer: the sprocket is engaging on just 5.7mm at the end the end of the shaft. This seems like a poor design, and we’re a bit surprised it survived the entire Trans America Trail like that.
Front sprocket was just cantilevered out there on the end 5mm of shaft.
There are several more problems with what Zero supplied for the front sprocket: 1) the sprocket retaining washer supplied by Zero is aluminum, not steel. 2) the spacer provided to locate the sprocket on the shaft is aluminum, not steel, and 3) Due to the soft aluminum parts and the narrow shaft engagement, over time, the sprocket was becoming increasingly loose on the spline shaft. When I pulled the front sprocket to replace it, I discovered how loose it had become on the shaft, and that there was visible wear on the splines. The forces from the chain were gradually causing the sprocket to work its way looser and looser, and causing increasing wear on that spot on the shaft. It’s simply bad mechanical design.
Other people solve this problem by using Loctite 680 bearing retaining compound to install the sprocket on the shaft. The Loctite helps take up any space between the sprocket hub and the shaft, preventing the sprocket from working its way loose over time. (It also makes it really tough to remove the sprocket for replacement). The Loctite may have been enough to prevent shaft damage had I known to use it the first time. (Zero did not provide any written instructions for installing the chain conversion kit). However, after many thousands of miles, the spline shaft on my bike is now worn too much to get full engagement, even with a new sprocket. It’s doubtful that the Loctite can completely compensate at this point. After looking into it, it does not appear possible to replace the spline shaft. Zero claims you have to buy a whole new motor, which would be very expensive. (I do think I caught the damage before actually damaging the motor).
To avoid buying a new motor, I did a little more research on front sprockets with a wider hub, that would have more engagement with the unworn parts of the spline shaft. That, in combination with the Loctite 680, may be enough to have proper mechanical engagement.
Thus, the plan for 2022 is: 1) an off-the-shelf 13T steel front sprocket (Supersprox CST-1307-13-2) that has a wider hub (13.55mm) and will fit the Zero’s drive shaft, 2) a custom 60T rear from Supersprox, and 3) a standard 520 D.I.D. VX3 O-ring chain.
The sprocket ratio is now 4.62. This is 2.5% shorter than stock – close enough to not bother with reprogramming. The front steel sprocket has a wide 13.55mm hub for more engagement on the shaft, is installed using Loctite 680, with a steel retaining washer. I had a custom steel spacer made (thanks, Mike!) with the correct dimensions to locate the new sprocket properly on the shaft. The steel spacer and new steel retaining washer should not yield like the aluminum parts Zero supplied, which contributed to the sprocket working its way loose. The rear sprocket from Supersprox is custom made to order with an aluminum center to match the Zero’s wheel bolt pattern, and a steel outer ring for durability. It’s pretty trick. We’re excited to see how it performs.
One caveat – the Supersprox front sprocket was a little loose on the motor shaft, around 0.035” play, and ended up not exactly centered on the shaft the first time he installed it. At certain speeds, this eccentricity caused some pulsation from the drivetrain. I took it all back apart (NOT easy!) and used this old trick to center the sprocket on the shaft: Strands from #10 Cu wire, each about 0.019? diameter, worked great. This centered the sprocket, then the Loctite 680 bonds it all together.
COUNTERSHAFT WEAR - FIX AND PREVENT
http://bloggis.se/Tramsvalp/85103TheHere is the parts list for the Zero DSR chain conversion that should work much better than the factory Zero chain conversion kit. I’ll try to remember to update this space after running this for a while to see if this system performs as expected.
BOM for the Zero DSR chain conversion:
• 60T custom aluminum and steel rear sprocket – Supersprox [see order form pic]
• 13T front steel sprocket – Supersprox stock part # CST-1307-13-2
• Spacer for front sprocket [see PDF for drawing] (I made 3 spacer rings of different lengths. The Middle one 0.340? long worked best.)
• Steel front sprocket retaining washer – McMaster-Carr 98424A111
• 520 D.I.D. VX3 O-ring chain – 108 links? Buy 120 links and cut it as needed.
• 10-pack bolts for rear sprocket (4 needed) McMaster-Carr 90236A168
• Loctite 680 – for sprocket on splines
• Loctite 242 – for the front and rear sprocket bolts
• The front sprocket bolt is from Zero’s belt drive; the only reused part.
I've tested it a good bit, and it seems solid. This summer we're riding the NEBDR and up to Newfoundland with it, so I'll report back afterwards. I hope this helps.
Thanks to lukec53 for finding many front sprocket options:
https://www.electricmotorcycleforum.com/boards/index.php?topic=11018.0Adapted from:
https://amytracker.wordpress.com/2022/06/26/2022-zero-dsr-mods-in-pursuit-of-more-electric-adventure-riding
