How to Build a Motorcycle Sidecar Frame (Amazing Info from an Expert)

This is a guest post from my pal Lee Bruns (twitter @RealLeeBruns) on the setup/configuration and driving of a motorcycle sidecarsidecar.  This guy is an expert on motorcycle sidecars, and I asked him to share his wealth of knowledge on motorcycle sidecars here at HappyWrench.  Big thanks to Lee!

Have you ever wanted to ruin a perfectly good motorcycle, but wanted to do it in the most fun way possible?  Add a motorcycle sidecar! 

The resulting rig will no longer be a motorcycle, but will be a lot of fun and have the added bonus of being a potential death-trap.  Sound Inviting?

Drive-Ability & Steering: How a Motorcycle with a Sidecar Handles

First thing to know is that a motorcycle sidecar rig is a multi-track vehicle and does not operate the same way as a single-track motorcycle. 

For starters, there is no longer a need to lean to go around corners. 

Additionally, instead of counter-steering, you turn the bars hard into the turn. 

Then, on acceleration, the sidecar will pull to the right since there is dead weight hung on that side of the bike that needs to be brought up to speed. 

Once up to speed, everything is fine until it is time to turn or stop.

Since the power and steering unit (the motorcycle) is not centered in the machine, it turns to the left differently than it turns to the right. 

If the rig is properly set up and aligned, you should be able to take left corners about as fast as your nerves and traction will allow – although hanging off the bike to the left can help keep the extra forces from collapsing the sidecar suspension.

Right corners, however, can be a bit more intense. 

To quote Newton’s first law “Mass in motion will remain in motion in a straight line unless acted upon by an external force.” 

This means that when you are going straight down the road, on the sidecar rig and you turn to the right, the sidecar itself will want to lift off of the ground as you force the rig to turn. 

Once the sidecar wheel leaves the ground, the rig abruptly turns into a very bizarre single track vehicle. 

To counter this, do all of your deceleration before you get to the corner, then accelerate through the corner to help keep the sidecar wheel on the ground. 

Hanging off of the bike to keep as much weight on the sidecar wheel helps. 

Balance and weight bias also play into corner behaviors, obviously.

Stopping behavior differs if you have a brake on the sidecar or not. 

For a light sidecar, a brake is not always your friend since they have a tendency to just lock-up the wheel when applied. 

On a heavier sidecar, the brake is usually hooked to the foot brake pedal. 

Just remember, that mass hung off to the side will try to keep moving as the bike decelerates, pushing the rig to the left. 

If you do not run a brake on the sidecar, be ready to apply force back to the right, to keep the rig tracking straight.

Weight Distribution & Ballast

Ideally the weight of the whole motorcycle sidecar rig should be spread two-thirds onto the bike and one third onto the sidecar. 

Meaning that, for example, if the bike weighs 900 lbs. with rider, then a 300 lbs. sidecar would be appropriate. 

If the bike with rider weighs 1200 lbs., then the sidecar should weigh 400 lbs. 

If the sidecar is over weight, it will pull to the right more on acceleration and push to the left more on deceleration. 

If the sidecar is too light, it will be very prone to lifting the sidecar (also known as ‘flying the chair’). 

This can be very dangerous if it happens when you are not expecting it.

Adding ballast can restore balance. 

I prefer jugs of water as ballast since it is easy to dump if a passenger climbs into the motorcycle sidecar or if I want to haul groceries. 

When you are new to sidecar driving, do yourself a favor and haul extra ballast. 

As your skill and confidence level increases, you can reduce ballast to whatever feels comfortable.

Initial Setup & Configuration

All of the operating knowledge and experience can be nullified by bad mounting and alignment. 

Even the best motorcycle sidecar pilot will have a hard time with a poorly installed or aligned rig. 

Unless you are riding a Ural, your motorcycle was never meant to have a sidecar on it.  

The loads that the motorcycle frame are exposed to as a multi track vehicle are wildly higher than it was designed for as a single track vehicle. 

So to keep frames from breaking and mounts from moving it is imperative to chose mounts and mount points wisely when attaching the motorcycle sidecar. 

In some applications, mounting hardware can be purchased from companies like Dauntless or Motorvation Engineering, depending on the bike and sidecar that you want to use. 

Other sidecars like Velorex and Trans-moto come with ‘Universal’ mounting hardware. 

‘Universal’ is code for ‘Doesn’t fit anything exactly right, but can usually be made to function.’

Often I find that making my own mounts is a safer way to go.  

Motorcycle Sidecar Frame Mounting

Whether you chose to make your own mounts, purchase a mounting kit, or use the universal mounts, there are a few things to keep in mind. 

A common mounting mistake is to install the two lower sidecar mounts too close to each other. 

Get the front lower mount as far forward as you can and the lower rear mount as far back as you can. 

The farther the distance is between the two mounts, the more rigid the rig will be. 

Do not ever install a mount on the swingarm of the motorcycle though. 

It is amazing that it needs to be said, but I have seen it done and it is scary.

I have often found it helpful to use the two lower mount points to attach a long steel plate to the bike. (30 inches long, 5/8 inch thick and 1 ½ inches tall). 

Then, put the two sidecar mounts on each end of this plate. 

If the only available mount points are in less-than-ideal locations, this is a good way to get the sidecar mounts where you want them. 

Each installation is different, so adapt as needed.

The Upright arms are usually not as difficult. 

The headstock area is usually a very stout area to grab onto as well as the down tubes. 

A plate mounted across both down tubes usually makes a fine front-upper mount point. 

The rear upper mount point can usually grab on the frame rail under the seat.  Try very hard to keep all link-arms perpendicular to the bike.

Stagger & Alignment

As you are eyeballing how to mount the sidecar to the bike, try to keep wheel stagger in mind. 

On motorcycle sidecar rigs, the rear wheel of the bike (called the tug) cannot be directly across from the sidecar (called the hack) wheel. 

The sidecar wheel needs to be between 10 and 12 inches ahead of the rear wheel of the bike. 

Too much wheel stagger (wheel too far forward) makes right turns more difficult since the wheel has to slide sideways during turns. 

Too little wheel stagger (sidecar wheel too far back) can result in the whole rig flipping over on hard left turns.

Once the mounting is out of the way with proper wheel stagger, you can work on alignment. 

Since the sidecar mounts on the right side of the bike, you’ll want the bike to lean away from the sidecar about three degrees from vertical. 

High-end sidecars use power adjustable lean-out systems like linear actuators to adapt to road crown or sidecar load as conditions change.  Simpler set-ups just use turn buckles and other threaded arms to adjust lean-out.

The last piece of the alignment puzzle is toe-in. 

It is the setting that is most intolerant of variation. 

Your goal is to set the toe-in at between ½ and ¾ inches over an 8 foot distance.  

The 8 foot distance is a standard, no matter how long or short the bike is. 

Toe-in of less than ½ inch can result in a very twitchy and hard-to-control rig when at speed. 

Toe-in if more than ¾ inches will result in dramatically shorter tire life. 

Even just ¼ inch of excess toe-in will take thousands of miles off of the life of the drive tire. 

Fork flex, bearing free-play, tire carcass flex and even tiny amounts of mount free-play will take up a bit of the ½ inch of toe in. 

If there is too little toe-in when sitting still, the rig could achieve a toe-out condition once underway. 

This will result in a nearly un-rideable rig that will try to kill you by either diving into the ditch or veering into oncoming traffic.

So to check your toe-in you’ll need two very straight things that are at least 8 feet long. 

I have often used 8 foot long florescent light bulbs, but as you can guess they are fragile. 

I now have a pair of aluminum extrusions that work well.  Do not use lumber. 

It has to be straighter than straight over the 8 foot distance. 

Even steel ‘angle iron’ is rarely straight enough. 

So assuming that you are going to use the 8 foot light bulbs, carefully strap one bulb to the side of the sidecar tire using tarp straps or bungee cords. 

Strap the other bulb to the side of the rear wheel of the bike. 

Be careful that the front wheel, exhaust, side-stand or anything else does not interfere with it. 

Measure the distance between the ends of the bulbs at the rear of the rig and the front of the rig.  Set the toe-in so that there is between ½ and ¾ inch LESS distance at the front than the back. 

For example, if at the back of the rig the distance is 60 inches between the tips, then at the front of the rig the distance needs to be 59 ¼ to 59 ½ inches. 

The number itself is not important, only that it be ½ to ¾ smaller at the front than the back.

Conclusion

That’s it for the initial set up for the rig. 

The next step is to go for a ride. 

Remember, on acceleration it is normal for the rig to pull slightly to the right as you accelerate up to speed. 

Once at speed it should track straight.  If it pulls to the right, then you need more lean-out. 

If it pushes to the left, then you need less lean-out. 

Do not adjust toe-in to compensate for pushing or pulling. 

There you go. 

Those are the basics of motorcycle sidecar function and operation. 

There is a lot more detail that you will learn over time as your experience and confidence level increases, but this should give you enough data to go ride.

Motorcycle sidecars are a fun way to experience a completely different facet of the motorcycle world.  Parents and children alike will stop you and ask about your motorcycle sidecar rig.  Trips to the grocery or hardware store become much more fun with a motorcycle sidecar rig.  Enjoy.  Tweet me @RealLeeBruns if you have any questions.