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[waynebhayes]

So, I did some interesting experiments last night on a mostly empty freeway.

The SR/S requires almost exactly 2v+7 Wh/mile at speed v for v from 30 to about 80 or 85 mph, in steps of 5 mph. Above 80 or 85 it goes up faster. At 90mph it was quite a bit above 2x+7, I don't recall exactly how much. This was all sitting normally (upright, comfortable) in the saddle.

Also, ducking behind the windscreen makes a huge difference. I was able to get back, or even below, to 2v+7 at 90mph by ducking behind it. (Was also much less buffeting on my head. :-)  Ducking behind the windscreen allowed me to get below even 2v (ie., 2v+0) for the larger values of v (makes no difference below about 45-50mph). So quite a difference having the torso + head up in the breeze vs. tucked in behind the windscreen.

These experiments got me back to the hilly area around my home with only 4% battery.... so of course I decided to see what happens when you reach 0%. My home is at the bottom of a moderately sized hill, so I just went up and down the hill a bunch of times. Going up this hill required just over 1% battery each time... so I went up+down about 4 times before it reached zero.... and then did another 4 times.  So even at 0% there seems to be a buffer of about another 3-4% remaining.... though torque + power are both greatly reduced. I was unable to get beyond about 25-30mph even with full throttle when it was 0% and "below".  (All the time I was wondering whether this would injure the battery, but I've run lithium-ion laptop batteries into the ground tons of times without ill-effect, so I'm guessing the same is true of the bike's battery.)

The battery "died" on the way down the hill on the last run. Message came up saying "Battery depleted" on the dash, though the lights + dash were still illuminated. Doing the same on my older SR, there was literally nothing left when the juice died--headlight went off, bike was totally dead. On the SR/S at least the lights stayed on. But in both cases, turning the bike off for about 10 minutes and turning it back on, there was power to the engine... though on the SR/S I didn't have the courage to take it back out again.  It was past midnight by that point, well past my normal bedtime.

Another thing: during the day yesterday there was quite a strong wind on the Pacific Coast Highway. It was about 15-20mph. I noticed that, yes, when I was going directly into the wind, then just adding about 15 to my indicated speed gave approximately 2v... that is, energy required was about 2(v+w), where w is the wind speed. Was hard to measure precisely since the road is not straight and there was traffic.

Interestingly, when the wind was oblique, say at 45 degrees, the energy requirement seemed to go up, not down.  It's possibly because the cross-section of the bike at 45 degrees is much bigger than head-on, so that counteracts the cosine(angle) decrease that you'd expect from an object with constant cross-section.

Not sure what I'm going to do with all this info... I was just curious.

I think it would be fairly easy to create a phone app that, without any map or navigation ability, simply predicted Wh/mile under simple conditions like the above. Beyond that would be much harder. Would there be any interest in such an app?

PS: I did the same measurements on an SR/F and the result was about 2v+10 Wh/mile. Though the SR/F is a bit better (add 7 rather than add 10), I would've expected the difference to be greater given the nice fairing + windscreen. Alas, it doesn't appear to be a huge difference.

--
Wayne B. Hayes
(previously owned an S, SR, and SR/F, now have an SR/S).

[Crissa]

2v+7?

-Crissa

[TheRan]

V for velocity I imagine, so 50mph would require 107 Wh per mile travelled.

[MVetter]

Are you getting this from the instantaneous consumption screen on the dash?

[Fred]

I'd expect that there would be a component of v² in there, as wind resistance increases with the square of velocity.

Personally though, I just concentrate on enjoying riding the bike. 

[waynebhayes]

In reply to all at once:

Yes, 2v+7 means v is velocity, so 50mph requires about 107 Wh/mile, on a flat highway with no wind.

Yes, I'm getting Wh/mile from the "instant" number on the dash, but only after it settles down since it's become obvious that it's not really "instant" but a running average over the past 10-20s or so. So I maintain the speed (using cruise control) until the number stops changing.

And as for the v² component, you are correct except that would be if we were measuring Watt-hours per unit time, which is usually how a physicist would do it.... but we're not. We're measuring Watt-hours per unit distance. So if you double your speed, the Wh/second would quadruple (square of 2), but you'd cover the same distance in half the time; and if you triple your speed, Wh/s would go up by a factor of 9 (square of 3) but you'd cover the distance in 1/3 the time, etc... so those factors cancel out and the whole equation comes back to being linear. So when measuring Wh/mile, we actually expect it to increase linearly with speed (at least approximately).

[peterwarm]

Nice one Wayne.

I'm trying something similar on my SR/F, but using a 13 mile test piece of dual carriageway. I'm doing it before fitting an old style fairing,  I'm doing it once per week as follows:

 * stop at start of dual carriageway (needs planning) reset trip A so Wk/mile is zero. note mileage, time, %SoC
 * do the trip one way, using the cruise (I've swapped this switch with the hazard switch for ease), stop at end, note all above plus new Wh/mile, Reset trip A again.
 * Do the reverse trip, stop at end and note Wh/mile etc.

go home, add internet wind speed and direction, plus temp, rain and traffic level. ( yes sadly have traffic)

In early stages yet, but will post results.

Your method seems a lot quicker!  Interesting to see the 45 degree wind issue. Keep posting!

[waynebhayes]

Peter,

Very cool. We should connect. Wanna send me an email? I'm whayes@uci.edu. Let's compare notes.

[gt13013]

I have collected some data from older measurements. See attached spreadsheet. You could be interested.

[peterwarm]

I hesitate to add my measurements as they are definitely not a smooth curve.
Ill enclose them anyway.

The first set I did showed no real correlation with speed (correlation r2<0.1!), so I added in the wind speed and direction using the local wing guru prediction.  This made a difference, there now seems to be a vague correlation to a square law. So hey surprise, wind direction makes a real difference.

I next looked at the average speed and found that my estimation of speed is very error prone, so the next step is to get more accurate speed info.

I am also aware that rain and slip-streaming make a difference too, so have added some columns for these. I like the idea of trying it without other traffic, but probably unrealistic round here in the UK. I just keep a distance from anything else.

Its worth mentioning that there was a discussion about doing this some time back, Ill try and find the reference. Some very helpful stuff.