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[biolife]

Any reason why it wouldn't work?

http://www.zeromotorcycles.com/shop/index.php?main_page=product_info&cPath=15_6&products_id=182&zenid=ht5dhkopu5pttsu97nre47unl0

It shows that it's officially only compatible with the S and DS, not the SR. I notice that the SR has a 30 tooth sprocket, whereas the S uses a 28 tooth sprocket.

For someone who drives primarily (like 98%) in the city and lives in a place where most highways have a posted speed limit of 80-90km/h (50-55mph), I don't really see much need to ever maintain a speed any higher than 100km/h (60mph), though based on my calculations (which are entirely assuming the ratios in the SR would result in similar adjustments in speed/torque when reducing the size of the sprocket like in the S), I'd still have a max sustained speed of about 120km/h (72mph).

Any reason why the 25T sprocket won't fit the Zero SR, and are there any other things that I'm overlooking while pondering this potential future modification?

[protomech]

Some thoughts:

- you might exceed the torque limitations of the belt (or other drive train components)
- you might lose some highway range (but possibly gain city range)
- you might experience some unexpected weight transfer to the rear wheel, possibly as much as 100%

[krash7172]

Same question here. I am seriously considering an S or SR right now. I could see some safety issues but if you have experience on a sport bike, I'm sure you'll be ok. Besides, if you don't need to go 80+ mph, why wouldn't you buy this $30 part!?! You can obviously configure the bike for less power. The info I was given by the dealership is that it should fit. I am waiting for official word from their Zero contact.

First post BTW

[biolife]

I decided to go ahead and email Zero anyway, since I figured they would know best. Here's what Ryan from Zero says:

The hi-torque physically will fit the SR. We have used this set up on a few of our race bikes but don’t have not done any true evaluations to go from. Your launch speed would increase, mostly from 30 to 80 but you would probably top out at 80-85 mph.  The other issue I would be concerned with is belt tension.  The SR requires a tighter belt spec. than the S/DS.  I have seen teeth ripped from belts that were not correctly tensioned. I don’t know if the swing arm will allow the axle to slide back enough to tension the belt properly.   Sorry I don’t have any hard answers for you, it would be a true experiment on your part.

Doesn't sound like there are any real issues regarding the drive train components outside of the belt, so it's probably worth ordering the $30 sprocket and giving it a try. I should probably order another belt with it, just to be sure...

I'll probably try this some time in the next few weeks, since I'll be moving into a new place with a proper garage that should make tinkering easier. Will report back with how it goes!

[GNU]

Keep us in the loop!

I'm really curious about replacing mine too. More acceleration would be nice.

[krash7172]

If I pull the trigger on a Zero, I will definitely give it a go.  I personally don't plan to ride hard enough to cause any additional stress on a daily basis. Just can't see not spending $30 for " _____" (not sure how to fill in the blank until I ride it. was thinking "optional ridiculousness").

Oh, and don't expect Zero to recommend this mod. They aren't stupid.

[NoiseBoy]

@krash, if you don't plan on riding hard, why bother downgearing?

Why not order a 28 tooth sprocket as used on the S. It would give you an intermediate option.  I planned to do this on the SR if I ever justify buying one to myself.  I have downgeared every ICE bike i have owned because the speed limit here is 40mph. It makes alot of sense.

[krash7172]

I will ride hard from time to time but 90% of my riding will be commuting to work and around town with only short trips on the highway.

[krash7172]

Ordered my SR today! 

Also bought the front sprocket but will wait to install after I feel the bike out. When the dealer asked about the sprocket, Zero person asked "Why?"

[krash7172]

Ok, so my 25T front sprocket is still sitting on my workbench. Anyone done this yet on an SR? My main concern is range/efficiency. An ICE would definitely suffer from a change in gearing but a variable speed electric motor is different.

[Doug S]

An ICE would definitely suffer from a change in gearing but a variable speed electric motor is different.

As I understand it, that's exactly right. The motor will turn somewhat faster at any given road speed, which will result in SLIGHTLY more bearing friction, and maybe SLIGHTLY lower efficiency from the controller, but you probably won't even be able to detect those things.

That said, I can't for the life of me understand why you'd want to give up what little top speed the SR has for even more torque than this monster already puts out. I think Zero did an excellent job gearing this bike.

[krash7172]

To accelerate faster, Duh

[RickSteeb]

During the month I've had my SR, it has spent VERY little time any where near full-throttle.  I've seen triple digits on the speedometer [MPH] a few times, and am grateful for the ability to keep up with 75+ MPH traffic on my commute, with plenty of acceleration available even then.  I wouldn't trade the ability to exceed 85MPH without red-lining the motor for belt-snapping drag-racing performance... but that's just me!

 

[krash7172]

We're talking about going from 100 top end to 90 top end. It's $30 and even if you need to buy the stock sprocket to put it back to factory, its still $30!

Edit: the SR with 25T sprocket should max at 86mph without programming.

[Doug S]

To accelerate faster, Duh

Or just smoke the rear tire faster.

Hey, whatever floats your boat. Like I said, I just can't imagine giving up top end for bottom end, on a bike that can already leave a Tesla, a Ferrari or a Hayabusa for dead in the road. Just seems a little heavy on the overkill to me.

Speaking of bottom end, though, does it seem to anybody else like Zero's "softened" the bottom end a bit? A 407-lb bike with 106 ft-lbs of torque should be unable to accelerate from a dead stop at full throttle without going up in smoke or pulling the front wheel off the ground in a very powerful way. And in the Brammo vs Zero comparison that was just recently posted, it was said that the two bikes pretty much pull together until 20-30 mph, at which point the Zero pulls away. I'm pretty convinced that Zero has limited the torque available at very low speeds to keep people from getting themselves in trouble launching at full throttle. I'm not really concerned about it, as I keep saying the bike has PLENTY of torque for me, I'm just curious.