So I've had my rig for a month now. It's a 1987 BMW K75C with Dauntless sidecar undercarriage and a no-name Chinese car. I've got the Yellow book. I've adjusted toe-in and lean-out. I've done some parking lot exercises. I've done some riding with and without a passenger, backroad and highway. I figure I'm not wildly dangerous at this point, but I'm still a long way from competent.
So far, it all works pretty good. The 750cc Flying Brick has gobs of torque. I find myself pulling up from 'just barely rolling' in 4th and 5th gears, no problem. Above 5,000 RPM it really hits the power curve. I'm happy with the tug.
The Dauntless undercarriage is very nice. My passengers really like the ride. The whole rig is predictable. So far it hasn't jumped up and bit me.
The Chinese sidecar, I am told, was an experiment. Jay at Dauntless told me they bought a few of them some years ago, but didn't find the quality consistent enough. My only complaint right now is some rust that'll need attention. Cosmetic, I hope.
Now to the steering. An hour or so of riding gets really hard on my right hand. I'll be installing a throttle drag screw, like I have on my non-sidecar bikes, which I think will help a lot. And I am also planning to install a Steerite conversion this winter.
However, being the sort of guy who won't leave anything stock, I've been wondering about an aerodynamic steering modification. Let me explain...
At highway speeds most of your power goes into cutting the air. Having the sidecar out in the breeze creates an unbalanced aerodynamic drag on the tug, making it want to pull right. The traditional fix, giving the tug a one- or two-degree lean to the left helps counter that, but the correction isn't speed dependent. Enough correction to balance things at 70 is going to be too much at slower speeds.
Aerodynamic drag is a function of the square of the speed. You double your speed, the air drag goes up four times.
So I'm thinking about introducing aerodynamic correction. My K75C has a comes-with windshield mounted on the forks. I'm thinking about mounting something that'll look a little like an old 'no draft' window-let on the left side of that windshield. Point it edge-on into the wind, very little drag and very little torque on the steering. Turn it exactly 90-degrees to the wind, maximum drag and maximum torque on the steering. Adjust the angle somewhere in between, and you can adjust the torque accordingly.
The advantage here, if my thinking is correct, is the torque this gizmo would put on the steering would increase in step with the aerodynamic torque the sidecar places on the whole rig as the speed increases. With a bit of tweaking and twiddling it may be possible to get the steering balanced right for ALL speeds.
Now I'm not new to the Gyro Gearloose school of engineering. I've been tweaking and modifying stuff since I was a young'n, back before dirt was invented. So I know without asking that SOMEBODY has thought of this before, and tried it.
All I'd like to know is, does anybody know who that (brilliant!) person is/was? Can I get in contact with him/her? Or can you tell me where to find that unfortunate's grave so I can lay flowers?
Best,
Ed Bianchi
Delaware USA
'87 K75C/Dauntless "Lady Carol"
Your Chang Jiang sidecar will create a lot more wind (and rolling) resistance at speed than a small wind vane could offset.
Add road crown, road surface smoothness and wind direction to the equation and you have too many variables present for even a large area resistance "gismo" to be of any practical use.
I'd suggest staying with lean-out, trail reduction and your steering damper for a neutral steering outfit.
Lonnie
(I'm no engineer either, but I've been on a lot of freight trains.)
The idea is to use the wing-thingie to apply torque to the steering, not the whole rig. The idea is to cancel out the constant steering effort required to make the rig go straight at speed. I believe a small wing is all that would be needed.
Hanging a barn door off the left side of the bike also occurred to me, but I think putting a smaller gimcrack on the steering would be much more practical.
Ed Bianchi
Ed Bianchi - 9/9/2010 2:47 PM
The idea is to use the wing-thingie to apply torque to the steering, not the whole rig. The idea is to cancel out the constant steering effort required to make the rig go straight at speed. I believe a small wing is all that would be needed.
Hanging a barn door off the left side of the bike also occurred to me, but I think putting a smaller gimcrack on the steering would be much more practical.
Ed Bianchi
Possibly install a linear actuator to allow you to tilt the whole rig left or right as needed. This is very common with most all sidecar companies in the states today under various names. It raises or lowers the sidecar suspension which acts about the same as leaning the bike in or out from the sidecar.
Another thing that helps is an anti-swaybar. I know this is not an areodynamic device but it does compensate for suspension compression caused by wind drag on one side or the other.
If you have stock steering geometry try reducing the trail. Yes, this is a coverup but less steering effort will do wonders as a bandaid for areo drag in most cases.
If you have a windshield on the sidecar try changing to something that is not like a barn door or taking it off if that is acceptable.
Face it Sidecar outfits for the most part have a Coefficient of Drag worse than a shoebox.
Actually you should not be having all that much of a problem with the outfit you have if the lean out is set propely for your situation, there is no toe out happening and if the sidecar mounting systme is not flexing at speed.
Oh, on the k bikes you can reduce trail a little by swapping the left fork to the right and visa versa. You can also run the forks up though the trees a little and go to wider bars for more leverage.
Of course the old school standby of hooking a bungee cord the the left handle bar when at speed has it's own time proven benefits that are hard to argue with.
Dunno if a huge rudder could be adapted to the steering or not to steer by wind force but it could be interesting when a tractor trailer passes you or a sudden wind gust comes out of no where. If you go that route please have a friend with a video camera at hand as it could surely generate a great photo op situation.
Hmmm ... Stanley,
And I allways was sure that a rig would have the aerodynamics of a parachute....
That was the reason why on both rigs the first thing that went over board were the s/c wind screens, beside it disturbed me to monkey..
Ed, may I suggest you to invest a few dimes and take the rig to somebody knowledgable for to check the set up. Myself on the first rig I never got things right allthough I measureed and tweeked many times dozends of hours.
Now that I became old and supposed to become wise, I invest once upon the time a few buck in taking the rig to the importer who has an excellent hand on this.
The hours on tinkering I prefer to spend on the road.
And for sure an Earles fork would do a hell of a job.
How you recognize a happy biker:
"When the flies in between the teeth are smiling!"
Sven
I agree 100% with Claude. I have a Kawasaki Vulcan 1700 with an Astro GT sidecar, which is a big rig. The rig as installed by Hannigan came with an electric servo mounted on the sidecar that allows me to raise and lower the sidecar to compensate for passenger loading, road crown, etc. Quite frankly I cannot imagine riding without it. The servo is controlled with a toggle switch that is mounted near the clutch on top of my turn signal control. I adjust frequently while riding to compensate for road and driving conditions. It allows you to neutralize the steering and drag under virtually all types of conditions. PS - I am an engineer:))
