More stable without windshield


Information and questions on GL1200 Goldwings (1984-1987)
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aladdin
Posts: 36
Joined: Mon Aug 06, 2012 11:04 pm
Location: Auckland, Auckland, New Zealand
Motorcycle: 1987 Honda GL1200 Aspencade

More stable without windshield

Postby aladdin » Sat Sep 01, 2012 9:58 pm



Hi all, I have an 87 Aspy, in reasonably good condition, first bike I have owned since 1991. I noticed the tendency for the bike to go off course if you take your hands off the handlebars, especially at town speeds, but no shaking or shimmying. Nevertheless I had a mechanic check the front wheel bearings and steering head, he said it was all ok, and in his experience all GL1200s do this to some degree.
But whats REALLY getting to me is the tendency for the bike to want to constantly change lines even at highway speeds on a flat, level stretch of road. This requires constant steering correction, and then it immediately starts to wander off the other way, so I'm going down the road in a series of slight zig zags, the front end noticeably wandering from side to side about 2 inches each way.
Whats even stranger is that removing the windscreen altogether stops this whole thing (until below 34mph where it gets noticeable again). Should I look for a different windscreen - my bike has a Slipstreamer wraparound windshield. Are these screens known to affect the handling? There is no way I would want to ride any distance with this happening as it is impossible to just relax and enjoy the ride (its like having a pillion who keeps constantly changing their body position, forcing you to always be correcting the bikes line). Any suggestions would be appreciated very much.



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WingAdmin
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Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: More stable without windshield

Postby WingAdmin » Sun Sep 02, 2012 12:09 pm

Check your rear swingarm for lateral (side to side) free play, as well as the wheel bearings. If the swingarm pivot bearings are loose or worn, it can allow the swingarm to caster from side to side, producing what you're experiencing. As well, worn wheel bearings with too much free play can also cause similar problems.

aladdin
Posts: 36
Joined: Mon Aug 06, 2012 11:04 pm
Location: Auckland, Auckland, New Zealand
Motorcycle: 1987 Honda GL1200 Aspencade

Re: More stable without windshield

Postby aladdin » Mon Sep 03, 2012 5:04 am

I checked the rear swingarm but found no movement at all, also wheel bearings are A-OK, but I appreciate the advice. Since the problem was a lot better without the windscreen on, and I have discovered I really don't enjoy looking either through or just above the top of a screen, I tried some radical surgery. I cut about 4 1/2" off the top of the screen in a straight line across the top, a little like the Euro sports screens. I figured I had nothing to lose, as I was ready to either ride with no screen on at all, or buy an aftermarket Euro sports screen, or failing that cut the screen right down to around 10-12" high.

Having started by taking off 4 1/2", I was very keen to try it out, so I did my first night ride on the Wing last night (first night ride in over twenty years!). I was a bit apprehensive, but soon settled into the ride. I could detect no yawing at slow speed in town, so headed for the highway (or motorway as we call them over here). I thought maybe the problem will manifest itself worse at higher speeds. I was surprised to find absolutely no mistracking or yawing at any speed, and no tendency for the bike to want to change lines. I found I could take my hands off the handlebar (cautiously) and there was absolutely no wobble or turning away to one side. I tried this right down to 30mph or less, and the bike behaved flawlessly. Voila!! - problem completely gone :o

All I can surmise is that the rounded top of the screen acted like the tip of an aeroplane wing. A planes wing is subject to tip rotors or vortexes created by airflow over the tip of the wing from the high pressure to the low pressure side (i.e from underneath to top), in a twisting motion which causes dynamic drag (its the reason they have started putting vertical tips on the wing ends to reduce the spill-over and the drag it causes). The rounded top may have induced windflow in from the side and up over the end, whereas the square or straight top with sharper corners separates the airflow coming from the side into two distinct rotors which cancel each other out, rather than one larger rotor moving in the one direction or the other at random. I noticed my helmet fogged up a lot more, and there was much less airflow coming up around the visor. I was able to clearly hear the radio upto around 50mph, above which point it was just pure smooth windflow. Without even realising it I found I was cruising at nearly 80, which is the fastest I've ridden this bike, and it felt effortless. :D

I am totally stoked, and would be interested to hear from anyone with a similar experience.

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bwagner6
Posts: 88
Joined: Wed May 30, 2012 6:16 pm
Location: Norwalk, Ohio
Motorcycle: 1986 Gl1200A Aspencade

Re: More stable without windshield

Postby bwagner6 » Mon Sep 03, 2012 6:40 am

Hard to believe a windshield could cause such radical handeling issues... But glad you solved things :D

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WingAdmin
Site Admin
Posts: 17050
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: More stable without windshield

Postby WingAdmin » Mon Sep 03, 2012 9:30 pm

I believe it - at highway speeds, it can take a very small amount of area to create a large amount of lateral pressure. Glad to hear you nailed your problem!

aladdin
Posts: 36
Joined: Mon Aug 06, 2012 11:04 pm
Location: Auckland, Auckland, New Zealand
Motorcycle: 1987 Honda GL1200 Aspencade

Re: More stable without windshield

Postby aladdin » Mon Sep 03, 2012 9:56 pm

I was talking to an owner of a GL1500. He commented that his windshield is flat across the top too, and has no front end wandering either.

aladdin
Posts: 36
Joined: Mon Aug 06, 2012 11:04 pm
Location: Auckland, Auckland, New Zealand
Motorcycle: 1987 Honda GL1200 Aspencade

Re: More stable without windshield

Postby aladdin » Wed Sep 26, 2012 3:08 am

I did some more experimentation as my screen has a crack, so I decided to see what effect bending the top of the screen around further each side to match the approximate curve at the bottom of the screen would have - it was quite flat across the top.

Doing this by hand with a hot air gun it is not possible to get the curve exactly the same all the way across like a factory made screen, but reasonably close. This has the effect of lowering the top at each side, so it now looks like a standard screen again and visibility for cornering is improved.

However, the nett result was more turbulence around the helmet. I cut out a 10" by 3" hole in the centre just above the instrument pod and used the top of the screen which I had removed earlier to make an inside layer to redirect the airflow up the inside of the screen. This works really well but there is still more turbulence than I would prefer around the helmet.

Also less stable handling than previously, i.e. a slight tendency for the bike to want to change lines, even in a corner. Nowhere near as bad as previously, but noticeable. I put this down to the slight differences in curvature on each side of the screen creating a complex airflow which becomes slightly unbalanced every few seconds depending on speed.

I think this demonstrates how much the symmetry and curvature of the screen affects the handling of these bikes, and any deviation from a 'true' and perfectly balanced screen produces noticeable handling quirks.

Next step is to try an airflow stabiliser, possibly running vertically up the front of the screen each side.

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tom84std
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Motorcycle: '84 STD 1200
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Re: More stable without windshield

Postby tom84std » Wed Sep 26, 2012 10:48 am

I started with a '79 1000 that had a Vetter Windjammer fairing. On my first long highway trip I found that while passing a truck, the bike wanted to 'wander' really bad. While easily correctable, it was annoying at first because I was totally unaware of the behavior. Once I got used to it, no problem. At one point years later I removed the bags, trunk and fairing altogether and returned the bike to factory. With the wind once again in my face I found that by removing the big 'sail' it was like replacing the engine with a much hotter unit. Quickness and handling were greatly improved by the loss of the drag and the load.

aladdin
Posts: 36
Joined: Mon Aug 06, 2012 11:04 pm
Location: Auckland, Auckland, New Zealand
Motorcycle: 1987 Honda GL1200 Aspencade

Re: More stable without windshield

Postby aladdin » Wed Sep 26, 2012 4:36 pm

Hey Tom I had a '78 1000 back in 1984. My recollection of that bike is that it handled fantastically and went like stink. this was after having several 750s and a 900 Honda. I used to throw that that thing around like you would not believe, and the handling was just so stable and neutral. I have slowly came to the realisation that the full fairing and panniers/rear trunk really does detract quite a bit from the naked bike like you said. Hence I am trying to modify the screen on this bike to emulate the feeling and freedom of a naked bike, but with the advantage of no wind pressure. Lowering the screen height has really improved the riding experience and feeling 'connected' to the ride. I reckon I'm about halfway there now! If I can entrain the main airflow up the front of the shorter screen into a concentrated laminar flow directly up and over, I may be able to get it to go high enough to leave my helmet in quiet air. I'm thinking of putting two strips of perspex, each about an inch wide, up the front of the screen vertically each side of centre, about 10 inches apart. I've never seen anyone try this on a bike screen before, but it should stop the air from the front of the screen moving around the sides so much.
The factory-set angle of the goldwing screen is too steep for laminar flow over the screen (like a sports bike screen achieves), and I've found that laying the screen back further interferes with the handlebars at full lock. I've layed the screen back slightly with extra rubber under the front, but have had to scallop the sides slightly to allow for the handlebars at full turn. Its still a work in progress.




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