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Thread: Why do so many people say to put a "fly screen" on a scooter to make it faster?

  1. #1
    apriliaforum Junkie
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    Why do so many people say to put a "fly screen" on a scooter to make it faster?

    I don't understand why so many scooter riders say a "fly screen" has increased their "top speed" or "performance" of their scooters. It reminds me of front wheel drive cars that put a huge spoiler on the trunk (or boot if yer not American)
    I can see removing mirrors to make that claim.

    What gives with this "un" sage advice??

  2. #2
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    For best performance you want just enough of a sport fairing to divert air so its not hitting the rider square in the chest without putting a large fairly flat barn door type windshield on the bike.

    A windshield on a bike should come up below eye level so you are not looking through it.

    On my Aprilia Sport City 250 the Puig Sport Fairing does this and can make it seem like you installed a larger bore cylinder on the bike when you are riding at speeds over 25 mph where aerodynamics really come into play. When I first installed one on my bike it was an "Oh My" moment the first time I pulled onto an entrance ramp to the Interstate, rolled on the throttle and blasted up past 75 mph before exiting the ramp onto the Interstate after coming into it from a dead stop at the traffic light. Headwinds end up having less of an impact on maintaining cruising speed too plus you can see an increase in fuel economy if you resist the urge to ride like your on a Sport Bike.

    The Sport City does not hit the rev limiter until past 100 mph with a 130/90-15 Metric Cruiser rear tire on it and the 250cc bike with the Puig set up correctly (as the angled back fairing it was intended to be and not a vertical windshield) will easily keep up with traffic on a 75 mph interstate with wiggle room to venture into the far left passing lane. I have found myself going at 99 mph per GPS keeping up with traffic on our insane Interstates with the fairing on the bike instead of a windshield however I quickly correct that when I am caught off guard watching traffic instead of my own speedometer or GPS. If they want to chance getting a $300/$400 speeding ticket or enough points to loose the privilege to drive/ride that's their own decision.

  3. #3
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    Quote Originally Posted by Rockynv View Post
    A windshield on a bike should come up below eye level so you are not looking through it.

    On my Aprilia Sport City 250 the Puig Sport Fairing does this and can make it seem like you installed a larger bore cylinder on the bike when you are riding at speeds over 25 mph where aerodynamics really come into play. When I first installed one on my bike it was an "Oh My" moment the first time I pulled onto an entrance ramp to the Interstate, rolled on the throttle and blasted up past 75 mph before exiting the ramp onto the Interstate after coming into it from a dead stop at the traffic light. Headwinds end up having less of an impact on maintaining cruising speed too plus you can see an increase in fuel economy if you resist the urge to ride like your on a Sport Bike.
    but your experience is purely subjective. Im no aerodynamics engineer but I do know some of the basics... and "frontal area" is one of those basic principles that Salt Flat and Land Speed racers use. Obviously those racers have different classes which include displacement, aero body modification, or simply unfaired. They arent simply bolting on a windshield or increasing frontal area in any of the classes.

    But my point was your scooter & mine come, without accessories... dont have much frontal area with the mirrors removed & no rider aboard. With the speeds you say you can attain... your sportcity must have significantly less frontal area (or more HP) than my GTS. I can only get ~85 (indicated) in a full tuck... at the 9000 rpm rev limit. (actually hitting the limiter)

  4. #4
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    You can have two cars with the same frontal area and based on the aerodynamics of their shape you can get a the same 0.26 drag coefficient from a vehicle such as the Nissan Leaf which has more frontal area than say a BMW i8 which has the same drag coefficient.

    A fairly vertical windshield is going to react the same as a vertical rider however the more bullet nosed sport fairing is going to do a much better job at cutting through the air than the flat barn door of a windshield more commonly used. Why do you think they put the bullet nosed fairings and diverters on top of large trucks? They at times technically have a larger frontal area than the box that they are in front of but do ease the flow of air around them lowering the drag coefficient. On the Leaf one of the things that helps lower its drag coefficient despite its height and width is the odd shape of the headlamp housings which divert air around the mirrors. The Puig Sport Fairing (not the taller flatter windshield) set up properly can provide similar in concept (not anywhere as good mind you) for a bike and the rider is not going to need to go into a full tuck to benefit from it. The Sport City does take some of its basic shape from the Aprilia RSV Sport Bikes however the concept of using a more aerodynamic sport fairing instead of a plain flat curved windshield are the same.

    The Sport City besides taking a 15 inch rear tire is geared different than the Vespa with its much smaller rear tire and being a long case engine its about the same as the BV250 with its 14 inch rear tire. Using Dr Pulley Sliders of the same weight as the OEM rollers while taking care to trim the oil sump gasket that sticks out in the CVT area (so the belt won't rub on the excess and pull it out) can also greatly change the dynamics of both our bikes adding top speed since they allow the belt to ride higher in the drive sheave.

    Why would I do a time consuming Empirical Study on the matter? First ride was all it took to see the difference while noting that on the same roads with the regular prevailing winds top speed being 10 to 15 mph higher were sufficient for my purposes. Remember too that drive ratio on a mechanical CVT is based on load and not just rpm.

    A clothed rider even at full tuck will slow you down more than say a rider wearing a bathing cap and speedo as Rollie Freed found out while riding his Vincent on the Salt Flats. Your choice of clothing and helmet on bike with a little less than 25 HP can have a dramatic effect on top speed. A half or three quarter helmet aside from being tiring also can slow you down compared to a full faced helmet while wearing more body fitting riding jacket zipped up and cinched nice and tight.
    Last edited by Rockynv; 01-09-2017 at 05:35 AM.

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