[gahdzila]

So I was coming home on the freeway today, using my throttle lock, and realized this...tried it over and over and got the same results. My bike is an S, btw, with the stock windscreen.

Sitting bolt upright in the saddle, with my arms fully extended to the handlebars, I reached a steady speed of 85 mph (indicated), and locked the throttle lock. I kept it that way for a few minutes to make sure that my speed was steady. I then crouched down into a full tuck, without making any change in the position of the throttle (since I have a throttle lock, there's no doubt that the throttle remained in the same position and didnt move). I tucked way down behind the windscreen, so that the wind off the top of the windscreen was going over my helmet. My speed started gradually climbing, up to 91, before traffic dictated that I had to slow down. I tried it several times, and every time I reached 91, and had to slow down because of traffic. By the time I reached 91, though, acceleration had slowed, so I dont think it would actually get a whole lot faster than that.

So...a few rough calculations show (err...if my assumptions and my math are correct) that tucking down behind the windscreen yields an increase in fuel economy of roughly 3 miles per gallon (assuming a speed of 90 mph, and a baseline fuel economy of 45 mpg).

very interesting stuff! I knew wind resistance would play a role in speed and fuel economy, but here's proof!

 

[Spirit of Bunny]

i said the same exact thing, but people told me I was on crack.

 

[DrummerDaveB]

Sounds perfectly reasonable to me.
When we're sitting upright on a bike, we're basically a parachute.
You tuck, the bike goes faster. . . or rather, has less wind resistance to overcome.

 

[DougZ]

Caveat: Head wind is not always a constant. ;D

 

[eisenfaust]

And cops dont like it when you're tucked in.

 

[{PMS}fishy]

And cops dont like it when you're tucked in.

And why is that?

If you are doing the speed limit, I don't see a problem with it.

 

[donniej]

i said the same exact thing, but people told me I was on crack.

you shouldn't listen to people... besides, maybe you are on crack? (j/K) ;D

The faster you go, the more important aerodynamics are. My 84 BMW box-on-wheels was as aerodynamic as a brick, I used to play with putting it in nuetral at 80+mph and fee how fast it would slow down to 50mph but would then gradually slow down.

On the track I would get up to ~130mph on the front straights, then while braking for turn 1 I'd pop out of the bubble... I was probably doing ~100mph at that point and sometimes I thought I was gonna get yanked right off the back of the bike!

 

[gahdzila]

i said the same exact thing, but people told me I was on crack.

nope, I'm not on crack...like I said, I tried it several times over the 30 mile or so trip home.  Reproduceable results!

Caveat: Head wind is not always a constant. ;D

bah!  I knew someone would try to rain on my parade!  

It would seem pretty unlikely that the wind would change from a headwind when I'm upright to a tailwind when I'm tucked, and only change exactly when I shifted position, and do it the same way several times on a road with turns (not a curvy road, but a few slow sweeping turns which would cause the wind to change direction slightly relative to my position).

So I stand by my results until you prove me wrong with a wind tunnel!!!!!   ;D

 

[JaredMcDonley]

Don't racers use this to help them stop?

I thought it was common knowledge that it would greatly increase drag coefficients....

No to say I am lessening your finds... still cool to see theory come full circle...

I like to tuck until my back says I suck at it.  

 

[DougZ]

I knew someone would try to rain on my parade!

Sorry, its just the scientist in me. One variable at a time. LOL

 

[avc8130]

Aerodynamics are the whole reason we have fairings. They werent for looks, they were for speed! Another thing I have read is that getting your knee out and ready for a turn helps aerodynamically to turn you also. Aerodynamics are cool. They allow flight.

 

[True Blue]

4 years of engineering and some grad work in fluid dynamics defininitely says you're right.

In a personal experiment of mine my car was only capable of doing about 105mph with it's ski rack on, rack off- 120+
(this was all done on a closed course with paramedics standing by, of course)

And I get worse gas mileage all winter long while I have the rack on

Tucking = better gas mileage & higher top speed(for the crazier people among us)

 

[DougZ]

This does bring up a funny point about people getting their bikes dynoed. They see a top speed, and think that their bike will actually do that top speed. What they fail to realize is that top speed is with out any wind/air resistance, so it doesn't mean anything. Makes me laugh every time. ;D

 

[gahdzila]

Aerodynamics are the whole reason we have fairings.  They werent for looks, they were for speed! 

This brings up a good point, and an interesting query:  I've never seen the Suzuki OEM lowers up close and personal, so it's possible they're just flat painted plastic, I guess, but they COULD lower wind resistance even more if they are designed properly.  

Anyone with experience with the factory lowers want to comment?  Are they pretty flat, or do they taper out to bulge in front of your legs?

 

[donmusic]

In a personal experiment of mine my car was only capable of doing about 105mph with it's ski rack on, rack off- 120+
(this was all done on a closed course with paramedics standing by, of course)
And I get worse gas mileage all winter long while I have the rack on

this reminds me of a road trip i took back in college. my buddy had this old beat-up honda accord station wagon and everytime we approached big hills or mountains we'd roll up the windows, close the elevated sun roof, lower the antenna, and turn off the air conditioning. then'd we put the hammer down and try to ramp up our speed before we started the climb. invariably we'd run out of steam, but we'd usually get pretty far up the hill -- we called it "pursuit mode" in honor of kitt from knight rider.

 

[Northwind]

This brings up a good point, and an interesting query:  I've never seen the Suzuki OEM lowers up close and personal, so it's possible they're just flat painted plastic, I guess, but they COULD lower wind resistance even more if they are designed properly.  

Anyone with experience with the factory lowers want to comment?  Are they pretty flat, or do they taper out to bulge in front of your legs?

Like the top fairing, they're designed for looks not aerodynamics. They may have some effect but it won't be huge.

 

[ridesideways]

tucking down behind the windscreen yields an increase in fuel economy of roughly 3 miles per gallon (assuming a speed of 90 mph, and a baseline fuel economy of 45 mpg).

this calculation assumes that the *all* of the energy 'gained' from the decreased wind-resistance (during the tucked position) translates directly to fuel savings. obviously this isn't 100% true. part of the energy gained from the decreased wind-resistance is actually lost to internal motor friction because the motor revs faster to reach the higher speed of 91 mph.

of course a good portion of the 'gained' energy *is* converted to fuel savings, but it's definitely not 100%.

 

[acedeluxe]

-- we called it "pursuit mode" in honor of kitt from knight rider.

he said pursuit mode ;D ;D