I read a study (cant find it now) but it went something like this.
a larger shield costs 2 -3 mpg while a smaller shield deflects just enough air to reduce the drag that the body would create anyway and increases mpg 1 - 2 mpg
either way its usually hardly noticeable but i will say this, we ride with a woman that has a Yamaha virago that tops out at 72 mph, after she installed the shield the top end was 78 mph, that tells me that small shield on that small engine reduced drag
I freaked out from my first tank after I put my windshield on my 900. 38 mph. Just went 102 miles without cranking the throttle to hear the exhaust and I'm back up to 51. Basically, it's all in how you twist the grip.
I think there is a difference. I added a switchblade 2 up about 2K miles ago, so not many shields bigger....
I used to fill up and do the math for 40mpg and see a little above. Now I do the same math and come up a few miles short. To guess, I'd say 40 or 41 vs. 39 or 38 for most tanks. The faster I go, the bigger the difference.
If I ride a naked bike stock, it generally gets worse mileage, than it does with a windshield installed.
My latest bike I noticed this on was an old Honda Nighthawk I have, stock is not as good as when I put on a large aftermarket windshield I bought for it.
I took the windshield off for a ride, and MPG dropped again, put it back on and up went my mileage.
Not saying all bikes are the same, but in this case it adds comfort, i eat less bugs, and get better MPG with it on the bike.
Dunno if my MPG has gone down... maybe a lil bit... but my top end speed has suffered a tad.. but I'm also on a 550... with a Memphis Shades Roadmaster shield.... lol, the stars 'n stripes on my sissybar waves towards me like im goin in reverse.. haha.
Windshield was a lil larger than I anticipated.. but eh.. still looks/performs excellent, do need to find someone to chop it a bit shorter (without it looking like it was done with a hack-saw), as I look through it, not over it.
Wife and I both have 800A with Plexistar II windshield on mine and a Plexistar I on hers. When we ride we fuel same time, always. Her bike usually takes a bout .05 more fuel than mine on a near empty fill. My windshield broke and was removed for a day ride. i used nearly.4 gallon less than her. That is .35 difference for roughly 110 miles. Roughly 5mpg difference. Average speed was 60mph with a 70mph blast on the freeway.
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