The fourth part in a series on sidecar attachment.
by Sev Pearman
If you have been following along at home, you know that we are finally ready to install our new Velorex 565 sidecar to our Suzuki GSX-1100G mule. This time we’ll discuss the physics that affect sidecar dynamics as well as share what we learned during the installation. For our purposes, we refer to rigs with the car on the right.
When I ordered the Velorex from Side Strider Sidecars I arranged to have the car shipped directly to our installer, Lee Bruns, in Watertown, South Dakota. Choosing Lee to do the installation was easy. He has built many sidecar rigs including the beloved Metallic Waste outfit (see MMM #71.)
Sidecar rigs are unique animals. They change your motorcycle from a single-track vehicle into one with two tracks, but this doesn’t mean that they handle like cars. As we shall see, they have their own peculiar handling. Why?
In a nutshell, the addition of a sidecar affects the way you drive a rig. The unaccelerated mass lags behind when you accelerate, turning the rig to the right. Likewise, it continues on ahead when you brake, which yaws you to the left. The mass affects cornering as well. The technique for completing left turns differs from that of rights. The deep involved physics is beyond the scope of these articles. This data is available at www.sidecar.com. Or, simply ask a sidecar geek, but be prepared for an earful.
Sidecar Set-up Variables
How do you optimize the odd handling? You need to pay attention to four different aspects; wheel track, wheel lead, motorcycle lean-out and sidecar wheel toe-in. Get any one of them wrong, and the rig will be an evil-handling, tire-eating beast. Of course, tweak any one of these variables and you affect the other three. Alchemy indeed…
Wheel track is the width (track) of the sidecar wheel relative to the wheels of the bike. A wider track makes the rig more stable. The downside is that a wider rig turns slower and it is, well, wider. A narrow track trades stability for agility. A narrower rig is easier to pilot through traffic. Track is also a function of motorcycle wheelbase. Outfits built on motorcycles with longer wheelbases can handle more track. A rig built on a motorcycle with a shorter wheelbase should have less track. If you buy most cars, this dimension will be roughed in at the factory. The track on Beluga is 49 inches, measured between the centers of the bike rear and sidecar tire.
Wheel lead is the distance the axle of the sidecar wheel is ahead of (leads) the rear axle of the motorcycle. If the sidecar wheel is even with the rear wheel (zero lead) you’ll minimize lateral sidecar wheel skate, but decrease stability in left hand turns. Maximum rig stability would be found if the sidecar wheel is equidistant between the front and rear motorcycle wheels. Picture an isosceles triangle with each wheel of the rig at one of the corners. The triangle is most stable when a line drawn between the contact patches of the front and sidecar wheels is the same length as that of a line drawn between the contact patches of the sidecar and rear wheels. This is undesirable because the sidecar wheel no longer rotates along the arc of the corner. Instead, it drags or skates sideways at a tangent.
Grab a bicycle and try this experiment. Extend your right arm to your side and take hold of the steering stem with your right hand. Now walk forward while arcing gently to your left. Do not turn the handlebars of the bicycle. You’ll notice that in addition to rotating, the front tire is dragged to the left. Repeat this with the bicycle slightly in front and behind you. You should see that lateral skating is minimized when the front wheel of the bicycle is aligned with your hips.
Lateral wheel drag on your rig is a function of sidecar wheel lead. While overall rig stability increases with lead, the cost is increased lateral wheel skate and tire wear. The good news is that most sidecars have all of this in mind when they design their cars. Depending on where you mount the car relative to the bike, you can adjust this a little bit. Sidecar Yodas suggests 6 to 14 inches of wheel lead. As long as you are within these numbers, you should be OK.
Lean on Me
If you examine most sidecar tugs from the rear you’ll see that they lean away from the sidecar. This is called “lean-out.” Remember that the undriven mass of the sidecar lags behind the motorcycle. This lag plus wind resistance (drag) makes the rig turn to the right. This is corrected by adjusting the upper struts so that the motorcycle leans to the left.
You turn a solo motorcycle by leaning it (initiated by counter-steering). Since you can no longer lean the motorcycle relative to the sidecar (with few exceptions) you add or subtract lean-out until the rig tracks straight. The faster you drive your outfit, the greater the drag on the car. If your car is set up to track straight at 30 mph, it will likely turn to the right at higher speeds. We recommend dialing in your rig so it tracks straight at your typical cruising speed. With Beluga, we discovered it is better to have it track neutrally at freeway speeds (and pull slightly to the left at 30 mph) than it is to have it be neutral at city speeds and pull to the right on the highway.
Lean-out is also affected by road camber and load. More crown will require additional leanout, as will heavier loads in the car. Again, ‘tune’ your rig so that it tracks straight for an average road crown, your regular load, and your typical cruising speed. Experiment with between 1 and 3 degrees of lean out. If you need more than 3 degrees for the rig to track straight, then something else is wrong. Beluga currently has 1 degree of lean-out, but we are still fine-tuning her.
Toe-in refers to the amount that the sidecar wheel aims left, or is toed-in. It is measured in inches. Lee Bruns simply bungees one 8-foot straight edge to the left side of the rear tire of the bike, and a second to the right side of the sidecar tire. Note that you do not attach the straight edge to the front tire. If tires aren’t exactly the same width or your wheels are not centered (as is true on many Harleys) your measurement will be off. The straight edge should just touch the front and rear edges of the rear tire. Now, measure between the straight edges at both ends. You are looking for a number in front that is between 1/2 to 3/4 of an inch less than the measurement at the rear. Too much toe-in and you accelerate tire wear. Too little, or heaven-forbid, Toe-out, and your rig will handle like crap.
Attach Sidecar “A” to Motorcycle “B”
Here are the basic steps. Remove the sidecar body from the frame. It detaches easy and greatly simplifies the installation. Block up the chassis so it is level both left-to-right and front-to-rear. Lee prefers a slight forward pitch on his cars, but I didn’t like the look. If you want to be smart, beg a furniture dolly and place it under the left side of the chassis. Trim the level with scrap lumber. Both of these steps are SO worth the effort.
Park the bike on its center or side stand. Remove the tank, seat and side panels for frame access. Bring the car adjacent. Align the two front-to-back, keeping in mind wheel lead. Adjust the front, lower strut parts so that it can clamp both the sidecar chassis and motorcycle frame as low, and forward, as possible. Lightly fit the clamp to the bike frame. Fit the lower front strut between the car and bike, but do not tighten.
Repeat this procedure for the lower rear strut. Try to have this strut as low and rear as possible. Lee wasn’t happy with the options on the GSX. He chose to fabricate a sub-frame that moved the lower rear mounting clamp to the rear. Lightly fit the clamp to the bike and loosely attach the strut. The centerlines of both the bike and sidecar should be parallel. Do not worry about toe-in at this point.
Detach the lower front (LF) strut from the bike. Secure the clamp to the motorcycle frame and reattach the strut. Leave the strut loose. Repeat with the LR strut, making sure that the motorcycle frame clamp is tight, but leave the strut loose. You can now remove the dolly.
Take the bike off its center stand, but leave the sidestand deployed. Have a helper hold the motorcycle upright. Find a spot on the motorcycle frame for the UR clamp and lightly clamp it to the frame. Loosely fit the UR strut between bike and car. The optimum spot may foul the passenger pegs. Some builders relocate the passenger peg, others compromise the spot and keep the peg in place. This wasn’t an issue with this Suzuki and the Velorex, but each rig presents its own challenges. You may have to cut your sidecover as we did. Adjust the UR strut until it meets the clamp. Lightly fit the UR strut. Do not worry about lean-out yet.
Fit the UF strut between the car and bike. Remember, you want to be as high and far forward as possible. Lightly mount the clamp to the frame and loosely fit the UF strut. Place the tank on the bike and make sure it clears the UF hardware. If these are no clearance problems, remove the tank.
Detach the UF and UR struts and place the bike on its sidestand. As you did with the lower mounts securely tighten both upper clamps to the motorcycle frame. Leave the upper struts detached.
Now you set toe-in. Reconnect the UR strut with the bike vertical. Set your straightedges and take your measurements. Remember, you want the front measurement to be 1/2 to 3/4 of an inch less than the rear. Adjust your lower mounts until you are happy. Tighten all hardware on both lower struts. Leave the UR strut loose. Make sure you fit cotter pins if they are used. Double-check your work.
With toe-in set you can set lean-out. Have your helper hold the bike vertical. You may wish to use a level against the rear tire. Lean the motorcycle to the left until you have half a bubble in the level. Hold this angle while you fit the strut to the clamp. Do not tighten. Lee set this quickly and accurately by eye.
Next, fit the UF strut between the car and bike. You want to adjust the strut length until it slips into the frame clamp. Tighten both upper struts. Work your way from one end of each strut, tightening everything as you go. Remember to use cotter pins. Double check your work. Better yet, have your helper check your work.
Reattach the sidecar to the chassis and you are done with the hard part! This is a good time to wire the sidecar lights. I made up a harness between the tail light on the bike and the bare ends on the car. You’ll need the right blinker, tail light and brake circuits as well as a ground wire. I added a connecter in case I have to take the car off. Remember to disable or remove both right blinkers on the bike. Check your hardware, add some ballast to the car and we are off!
NEXT MONTH—Fine Tuning, Additional Mods and Future Plans