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Friday, October 3, 2014

A Shifty Approach to Riding the Brammo Empulse

The Brammo Empulse has a 6-speed transmission. Adding a transmission was an unexpected move because electric motors have a very different torque profile than internal combustion engines and transmissions are generally not needed in EVs. The general wisdom said they add more moving parts and add little or no value. So why did Brammo do this? Was it folly to appease the gearheads or a genius move that improves the riding experience, acceleration, top speed, and range? 

Exploded-view of Empulse's 6-speed Integrated Electric Transmission (IET)

Since the Empulse's 2013 introduction, I have been curious how this story will turn out. Riders have now had time with the machine and to truly understand the way this impacts their experience. Below is one of the best write-ups I've seen that explains the nuances and advantages.

The following is from Shinysideup on the Brammo forum site:

I realized the other day that the Empulse has fundamentally changed the way I relate to using a transmission on a motorcycle. 

With my ICE bikes, I always started off in first gear and ran up through the gears in sequence to whatever gear was appropriate for the highest speed of the leg of the trip I was on. I also was in the habit of downshifting back through the sequence until I came to a stop. Of course my shift points were determined by the degree of acceleration I wanted vs. the economy of letting the engine operate at a slower speed without lugging. 

On the Empulse, I started off using the gearing in much the same way. However, gear selection was determined by aiming to keep the motor at the sweet spot for power and efficiency, around 5000 rpm. I didn't need to wind out the engine to get any torque. I didn't need to worry about lugging the engine. 

I've evolved, however, to a very different approach. While occasionally I still may run through the gears sequentially for more spirited riding (in the twisties or when I’m in my “streetfighter” mood), I usually anticipate how my speed is going to be for a given leg, select a gear that’s best suited for that speed, and just stay in that gear from the initial start to the next stop. The exception is for higher speed freeway travel, where I don’t start in 4th, 5th or 6th gear, but use them as I achieve higher speeds. (An after market 42T rear sprocket means I like 6th gear for anything above 70 mph or so).

Some examples (all are in Sport mode):

1)   I’m in stop-and-go rush hour traffic in San Francisco with lots of hills to climb and descend and not much opportunity for lane sharing. First gear fills the bill, allowing the motor to turn faster for more efficiency when climbing hills as well as aggressively helping out in braking, both down the steep hills and when cars suddenly stop in front of me. I’d guess I run in this mode maybe 5% of the time.

2)   Most of my dense city driving is below 30 mph with stop signs at just about every block. Second gear works beautifully to smooth out the starts and yet provide effective regenerative braking assistance at each stop, easier to modulate than first gear’s sharp deceleration. If traffic is light, as it is in many parts of San Francisco during the early afternoon, I find I can easily slowly roll through the stop signs (California stop), in second gear, without using any brakes. I usually choose second gear for lane sharing on the freeway, which I do up unto 40 mph. I run in this mode maybe 55% of the time.

3)   I also often travel in more suburban environments with more open boulevards, longer stretches between lights, and upper speeds from about 30 mph to 50 mph. Third gear is perfect.  Naturally, in third gear, start-ups are not “hole shots”, a fact that seems to make my range even better than usual, despite the lower rpm at cruising speeds with supposed less efficiency.* If I need to scoot suddenly out of the way, third gear (in Sport mode) still offers plenty of torque/acceleration. Compared with second and first gears, I find I need to lengthen the point at which I begin my regenerative braking when approaching lights, remembering to flash my brake lights to warn following vehicles. I run in this mode about 40% of the time.

These different modes also correlate to the mood I’m in. If I’m feeling mellow and just want to “cruise”, third gear covers just about all the speeds I’d encounter within city limits. I’m free from thinking about gear selection, using the clutch, proper gear change technique… sort of a really torquey scooter with great throttle response. Often I’m in this mood, but find that when that Ducati pulls up in the next lane at a light, I’ll have to get into first gear, just to educate the young whippersnapper about electric motorcycles!

I’ve come to appreciate and enjoy this set-and-forget way to use the tranny. I like the freedom as well as the versatility. AND I like being able to run through all the gears when I’m in my (rare) hooligan mood.

* I did a series of steady hill climbs at 15 mph up a steep, two-block-long hill where I live. I watched the power meter as carefully as I could, even though it bounces around a fair amount. I did about four runs in first gear, and then several more in third gear. I concluded that there wasn't any difference in power consumed that I could discern by just watching the dash readout. Probably if I did, say 20 runs each, examined the readout on the memory stick, and plotted the numbers in Excel, I would see a difference. But for real-world riding, my little test assured me I didn't have to worry about my range suffering very much by just leaving it in third gear. This corresponds with my experience of seeing (I think) a slightly increased range with using just third gear, rather than starting off in first and working up through the gears.

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