After spending a full morning with the 2015 Zero S and DS on the gorgeous, twisty roads of California, and tucking into a Kawasaki burger for lunch at Alice's, it was time to ride the jewel in Zero's crown: the 2015 Zero SR. While it stops short of all-out sportsbike performance, the SR still unleashes more torque than any petrol-powered superbike you can buy. Enough, as it turns out, to catch an experienced motorcycle tester by surprise. Enjoy the last of our 2015 Zero fleet reviews.

The SR is the Zero S on angry juice. Dimensionally it's the same as the S, albeit with Pirelli Diablo Rosso IIs replacing the Sport Demons, and overall battery capacity is the same, but the motor is beefed up significantly to the tune of 67 horsepower (50 kW) and a whopping 106 lb-ft (144 Nm) of torque. That's 5 lb-ft (7 Nm) more than the 1200cc EBR 1190RX, which is the torquiest petrol-powered superbike you can buy today.

For the most part, riding the SR is the same awesome experience as it was when we lost our minds over this bike back in 2014 – tempered slightly by familiarity and also by how surprisingly good the S and DS are. So we'll keep this review short, as just about everything we said last year still stands.

The new Showa suspension, Pirelli tires and J-Juan brakes are noticeably nicer than the 2014 model's no-name gear, but if I'm honest I didn't think the 2014 gear was all that bad anyway. And the Bosch ABS system? Well, you don't notice that until you need it, and apart from a quick check that it was functioning by slamming on the rear brake, I didn't notice it.

While the gap back to the S might not feel that far, the SR is certainly a machine to be reckoned with. On wet or loose surfaces, a handful of throttle in Sport mode is more than enough to break traction at the rear wheel. In fact, the German tester we were riding with got a hard lesson in respect when he gassed it on a corner exit, spun up the back tire and ended up on his butt. Neither rider nor bike were damaged – in fact it's fair to say the SR bounced pretty well from a low-speed crash – but the rest of us were suitably chastened by our German buddy's poor fortune.

The SR's penchant for hard acceleration bit me too, in its own way. The game of hang back-catch up I'd been playing all afternoon to give myself a bit of extra fun in the corners, as well as the good 30 or 40 kilograms I was carrying over the smaller European riders, got me into battery trouble by the time we hit the run back into town. Setting out for the final leg, the German rider had 37 percent battery left where I was down to 22 percent.

Time to engage Eco mode then – a softer power map with increased regenerative braking. Regen quietly works away in all power modes for all the Zero bikes and you can set how much you want via a smartphone app. When you hit the brake levers, you can watch the regen braking power spike on the power and torque meters on the redesigned Zero dash. It's pretty nifty.

Still, things started to get a touch hairy as I dipped under 10 percent on the extraordinary Felton Empire Road back towards Scotts Valley. Luckily, as it was mainly downhill, I was actually able to put a precious 1 percent of energy back into the battery on the way down.

The way back to Zero HQ was torturous. I accelerated at roughly the speed of treacle, I held up caravans and semi-trailers, and I Fred Flintstoned myself away from the lights as I tried desperately to hang on to the back of the group without burning a single watt-second I didn't need to. My efforts were rewarded when I coasted into the carpark with just 2 percent left on the dash.

There's nothing built in as a reserve on a Zero bike. The company has taken the view that its customers want to know exactly what they're dealing with, and I fully agree that's the way to do it. Having an accurate gauge let me squeeze every last mile out of the bike after getting myself into a range pickle.

The range anxiety I experienced, it must be noted, was purely my own fault. The other guys all got back with at least 15 percent up their sleeves. Likewise, this was an idealized test day that involved a pre-planned route and fully charged bikes dropped off to meet us at lunch time, so it was much more about ride impressions than the experience of living with a Zero longer term.

Still, the entire fleet test was yet another great experience from the top dog in the electric performance market. While 2015 may not have brought another leap in battery range, these bikes still go further than any other electric. And while the prices are still going to upset people, the new bikes are a classier ride thanks to a raft of new high-quality running gear that has only pushed prices up a few hundred bucks from 2014. A fully loaded SR with a power tank costs US$19,840, or it's US$17,345 if you're happy with the 12.5 kWh monolith alone.

In terms of production and refinement, Zero is miles out in front of the game and still pushing hard. Enjoy our full fleet test of the Xero FX, S, DS and SR below and check out our technical briefing and factory tour, as well as our reviews of the 2015 Zero S and DS

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