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Open mouth, insert foot..
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I have an older, '83 Kawasaki KZ1100 LTD - low 27K mileage, runs great, has aftermarket Dyna coils, valves adjusted perfectly - new matched Dunlop tires at 32 PSI, new OEM air filter - everything would seem to indicate I should be getting maximum MPG from the bike - whatever "maximum" IS for this bike...

Only significant mods to the bike are larger main jets - 135's instead of the OEM 120's, to better work with the Kerker 4/1 exhaust setup - and then, there's a pretty large added windshield - pics below.

Now to the issue - out for a ride yesterday - first decent longer ride since I bought the bike last fall and winter weather set in. Been going thoroughly thru the bike since then, both routine stuff, as well as a few upgrades mentioned above.

I rode 70 miles, average speed about 60 MPH, temp at 65 degrees, altitude 3500 feet - level road. I topped off the tank before and after the ride, and it took 2 gallons for the 70 miles - 35 MPG.

That seems low for this bike - it starts easily, idles great - and runs great thru all gear ranges and RPM, and has good power - so shouldn't MPG be better? I wouldn't think the Kerker header and accompanying larger main jet would make a serious drain - but what about the relatively larger full windshield - will one of those drop MPG significantly? Has anyone here added a windshield similar to mine, and seen MPG in the same range as I'm getting?

Here's pics of the bike - taken before I switched back to the new OEM intake setup:


 

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Alien Test Subject
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That big windshield is almost definitely affecting you. It's not very aerodynamic, and is like putting a big sail on the bike. While it may keep the wind off of you, it's also pushing a big wall of air in front of, and around, the bike. So the engine has to work much harder to maintain the same speed than it would without.

Stick your hand out your car window at 60 mph, palm to the wind, and feel how much arm strength it takes to hold it there. The rotate your hand "knife-edged" to the wind, and it takes less effort to hold it steady. Same concept.

I don't know what MPG on that bike should be (and 35 isn't too awful bad) but I would almost guarantee that the shield knocks it down a few tics.
 

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Even more nuggets of wisdom....

But motorcycles are pretty much only good for gas as their lightweight and aerodynamics. They are milked for everything they can offer, thats why you see very very little aftermarket performance. With that much performance, gas mileage is terrible..

With all that performance, the aerodynamics and weight are vastly influencial in the gas department. I saw a few MPG loss with my windshield on my Vstar and but without it, I got a few better. Maybe 5 at the very best. And over the life of 3.5 gallons, thats 17.5 extra miles...But yes, I do believe you are losing some economy with the windshield.

To shield or not to shield?
>1 hour ride No
<1 hour ride Yes
Rain? Yes
High wind? Yes

This only works if you have the time to take it on and off like I do without the quick detach. 4 10mm bolts :) And if your cruising over an hour, it means you have 5 minutes to put it on ;)
 

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Open mouth, insert foot..
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Discussion Starter #4
WELL, as a followup to this thread question, and my own hope that dropping main jet size would deliver a bit better MPG, without seriously affecting power. I dropped the main jets from 135's, to 127.5's, and went for another 84 mile ride today - went that 84 miles on a bit less than 2 gallons of gas, so somewhere between 42-45 MPG - and LOTS better than the previous 35 MPG! Bike still starts and runs great at all loads/RPM, and plugs look great!

Be interesting to see what removing the windshield would do - it comes off easily - might try it sometime! ;)
 

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I have a 97 Vulcan Classic 1500 and my mpg is a little over 29 going to work and back, and about 33 on the hwy. Does anyone know if a windshield will help any on the mpg ?
 

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I had a 82 kz550 with the same windshield on it. I would get in the high 40's to low 50's with it. This was back in 1983 to 1994. I put over 80,000 miles on that bike. I would expect your bigger more performance bike to get less. The windshield is not helping the mpg but I liked mine. The only time it bothered me was climbing out of the CA central valley on my way to the bay area into a 30 mph head wind on that little 550 I could only maintain 45 mph with the gas wide open.
 

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Aerodynamic drag increases by the square of speed. To double speed requires four times the hp. Once up to cruising speed the bulk of power produced is consumed pushing air. The windshield is adding significant flat plate area to the motorcycle. Motorcycles in general when compared to cares and aircraft have very poor drag coefficient numbers. The only help they get is that though the coefficient numbers are poor they have relatively small flat plate numbers. Anything that increases flat plate area will lower mileage. If you look under most modern cars you will see how seriously auto manufactures are about decreasing drag. Everything is tucked up flush and much of the bottom of the car is covered with smooth plastic covers. Look closely at a Moto GP fairing and compare it to your windshield. Moto GP wind tunnel designed for low drag, your windshield is designed for comfort. Motorcycles are in general, with the exception of some of the small lightweight machines, a poor choice for economy. Not just gas mileage, look at how often a motorcycle needs tires compared to a family car. Cost of service and parts. One of my current bikes is a CBR250R,, ridiculously cheap to operate but most riders want bigger more powerful machines. If it runs well and you enjoy the ride don't worry about mileage, it is part of the price we pay for the experience.
 

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There are ways to minimize the impact of using a wind shield. Curved and tilted are 2 words that come to mind.
 

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Yes, you may be able to make a small improvement but the bottom line is that street bikes have very poor aerodynamics. We have first to deal with viscous drag. friction of air over the surface. This can be minimized by reducing surface area, google Lanceair and look at the aft fuselage. The biggest problem with road going machines is the inability to maintain laminar flow. As air is pushed aside by the motorcycle, rider, windshield it separates and becomes turbulent. This significantly increases drag. There is good reason that boat tail speedsters and Craig Vetters motorcycle streamlines had streamlining at the rear. Take your car down a dirt road, stop at the end and observe the amount of dust on the rear bumper compared to that on the front. The rear bumper will be covered with dirt because there was a large low pressure at the rear of the vehicle. This low pressure area is tugging at the vesicle reducing efficiency. The windshield will do the same, not only are you pushing are aside but you are creating a high drag low pressure area behind the windshield. An ideal form parts the air and then slowly tapers at the rear allowing the air stream to remain la miner with no separation turbulence. Obviously we are not even close to achieving this with current motorcycles but so what. Lets just enjoy what we have. You want high mileage buy a hybrid.
 

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All good info but does anyone else think Howard's bike that does not have a windshield, should get a bit better than 29 MPG? Perhaps it is time for a tuneup? New air filter? Tire pressure? 29 seems pretty low to me but I am not familiar with the Vulcan.
 

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Follow-up to my last post. I went to fuelly.com and according to them, the average fuel economy for a 1997 Vulcan 1500 is 29.1. So Howard, I guess that's all she wrote. But like GPZ said and I quote him, "If it runs well and you enjoy the ride don't worry about mileage, it is part of the price we pay for the experience."
 

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I don't really care. My ZN700 gets 40mpg around town and 50mpg on the highway with the shield. I like the protection from the shield especially when it rains.
 

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A windshield could help OR hurt mileage. Depends on whether you or the windshield is more aerodynamic. If you get lots of turbulence with the shield, that can cause drag and make the mileage worse. Higher speed usually makes the mileage worse. I replaced the factory shield on my Nomad with a +2" (wider and taller) Clearview and noticed about 2 mpg loss on my daily commute. There was a terrible head-shaking turbulence with both shields on that bike, and a vacuum behind the shield that wanted to suck your head forward to the point it became painful. Larger than stock on my Versys has dropped it a couple mpg. (As does cranking the throttle hard just a couple times. ) The Nomad would get around 43 mpg staying on the secondary roads and below 60. would drop to low 30's at higher speeds and a headwind.

Interesting note: Was riding my 1100 Shadow Tourer on a ride with a guy on a Vulcan 2000, We both filled up at the same station, Rode approx 125 miles and filled up again. The 2000 with fuel injection got 20% better fuel mileage than my 1100 with carbs. while riding exactly the same roads and speeds in Arkansas. That's irritating,,,
 
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