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Miscl. Sidecar Tech

Copyright, 2014, R. Fleischer


(1) Tires: rims, handling, tread, un-sprung weight, car and m/c tires, etc...LOTS of "etc":

On a solo motorcycle, that is, one without a sidecar, better handling is with the lowest un-sprung weight.  That means that the moving part of the suspensions....wheel, tire, brake, etc......need to be light to enable the best handling on smaller or sudden road irregularities. Just adding the weight of a second front disc brake will noticeably reduce handling.

This is also true for sidecar rigs. But, sidecar rigs have other considerations.   A sidecarist wants lots of front brake, and wants the lightest possible steering forces, yet does not want any (or minimal) oscillations or other serious instabilities in the front end.   Many sidecars need a steering damper, even after tightening up the steering head bearings adjustment & paying attention to wheel bearings, etc.   What is NOT commonly known is that a larger diameter front wheel/tire will DAMPEN oscillations; but this is often NOT major, and certainly has only a very small effect at speeds under perhaps 25 mph.  The SAME damping, and yet still not major damping, will happen with a heavier assembly.  Sometimes, the effect is 'just enough' to make a real difference.  BUT....A flat tread, that is, a tread design that puts more square inches of rubber in contact with the road, will add a considerable amount of stability and increased damping ....without a too-noticeable increase in steering forces, on sidecar rigs ...that is, until the tread approaches small car tire in contact width.

The increased damping is particularly nice since damping by such as friction or a hydraulic damper can then usually be reduced, lowering steering effort, and improving the natural ability of the front end to re-center; which, with a strong damper, is reduced, unpleasantly, which means increased physical input from you.   Thus, use of such as the Avon Triple Duty and Metzeler K block tires can allow a reduction of steering damper forces.  Braking may or may not be improved with the additional contact area.  NOTE that a squared-off REAR tire on a TWO wheeler can cause serious high speed wobbles and instabilities.  On a sidecar rig, a squared-off or more flat tread has some advantages, but not always.  One of the problems with flat treads is that they follow irregularities in the road, very noticeably, including rain grooves.

DO NOT TAKE WHAT I HAVE SAID HERE TO MEAN THAT RELATIVELY SQUARE AND WIDE CAR TYPE TIRES ARE THE WAY TO GO ...THEY HAVE OTHER CONSIDERATIONS, AND A WIDE CAR TIRE (or wide sidecar type tire) CAN INCREASE STEERING EFFORT BY A VERY LARGE AMOUNT.  THE MAJOR reason, usually, to use a car tire, is the much longer tread life, compared to motorcycle tires or sidecar type tires.

Compared to the use of motorcycle type tires with round or sort-of-round profiles; use of a square tread front tire, such as an automotive tire, or a sidecar type tire such as a Metzeler Block K, or an Avon Triple-Duty, may give some good benefits in oscillatory stability.  It also may be a detriment. Those tires don't last all that long either.

A car tire will typically give VERY many more miles than any motorcycle or sidecar-type tire.    However...a square tread tire or car tire may also make the front end more susceptible to following road grooves, and, in fact, most any road irregularity, as I have mentioned, and I also mentioned the heavier steering.    There are other tradeoffs.  Weight of rims/assembly, and other things.  Some trade-offs may be advantageous ...such as using a modified car rim, which may be easily balanced on automotive equipment, the tires may be much cheaper, tires last longer as mentioned, wide range of tires available (both tube type and tubeless), etc.

ONE of the things to remember is that a sidecar rig is always a compromise of many things.  There is no such thing as a sidecar rig that does not have compromises!

can be an involved subject.  Tire wear, road contact, braking, stability...and several other things are involved.   My use of "Sidecar Tires" includes use of the tires on the tug too.

Here is a link to a rather nerdy article.   The article has extensive vector & other diagrams, & some conclusions about contact forces that may well astonish you.  When you read it, keep in mind what REALLY happens when you are cornering.  THINK ....about the effects of you changing a tire size ....from, example here, a 90/90 to a 100/90.  What REALLY happens when you go to a larger size tires (larger width).  You may be interested.

That article is quite nerdy in places, but has some real jewels of information here and there. It really is worth the read.

For 16" rims, such as Harley Davidson rims, I recommend a relatively inexpensive tire that lasts a fairly long time, & there are both front and rear versions of this recommended one, & it has a decent load rating: 
Shinko Classic 240, in size MT90-16. 
You can also try the Austone 175-16, but it might rub the belt guard on some belt-driven Harley's....and is pretty close fitting.   Minor work should allow its use. For the chair that uses 16", you can try the Shinko Classic.  There is a 130-16 size.

For 15" rims be VERY careful about using car tires on them, as 15" motorcycle rims and 15" car rims are NOT exactly the same size, and you can explode car tires on the bike wheels, although many have gotten away with the smallest sizes of 15" car tires on motorcycle wheels.   This is ONLY a problem with 15".

Do not try to install a tire that is too wide for the rim width.  Rim width is not measured easily, just where on the inside of the rim the measuring is done is not going to be at all clear to you.   Too wide a tire will tend to ROLL on the rim during cornering.  Sidecarists tend to use rather low tire pressures sometimes, so the rolling due to too wide a tire for the rim may be more important than you think.  Usually we do not have to consider tire load-carrying ratings, although we do have to consider that the loads we have on the tires are typically much lower than on a car, so we use lower tire pressures.  NOT always.

NOTE! Some few of you may be using car rims with motorcycle tires, or motorcycle rims with small car tires.   This is done by some sidecarists, and sometimes with 16" wheels on Harley Davidsons, and I know of other instances.   There is a difference between all these things that is not commonly known.  Motorcycle tires have a THINNER bead area, where the tire fits between the edge of the side (where it meets the horizontal, before the safety ridge, IF THERE IS ONE).  If you think about this you will understand that if you use a car tire on a motorcycle rim, any safety ridge is fairly INeffective, as the tire bead will ride over it.  If the motorcycle tire is used on the tire rim, the motorcycle tire's bead can move back and forth a bit.  None of these things stops us sidecarists!  Just be aware, and if you are curious enough, measure the tire and the rim.

Small 15" car size tires are available, but one must sometimes hunt for them.   These small tires were used on such as Smart Cars and 2CV Citroens, etc.   For 125-15 & 135-15, while I suggest an Internet search engine be used, you can also try this company:    See the next paragraph for an EXCELLENT source.

My present recommendation for hard-to-find tire sizes is  For MANY years, they have been purchasing old tire moulds and equipment, refurbishing, etc., and are making many original-type classic tires.  Almost all the time the date of build is also very recent!!!  Shipping is by Fed-Ex.

Prices for what are essentially 'specialty-tires' vary all over the place, with some sources charging twice or more as much as others.   I suggest you inquire about availability from your local tire stores first; then try the Internet, and then Coker.    Another source, prices seem better than many, is; which has both 125 and 135 size Firestone F560, a good tire.   You may end up buying from Coker!

Do not purchase tires that are too old.  Some specialty tire stores have a lot of very obsolete stock, and it may not have been stored well, and ANY age that is over 4 years is suspect (some would say 2 years, depending on storage conditions).  Sidecarists can often use tires up to 6 or even 8 years old.  DO NOT pay much attention to those saying that old tires are better on a tug's rear, as they have 'hardened', and so will give longer mileage.

Tires "grow" from weight of the motorcycle, from temperature, and especially from speed. The minimum SIDEWAYS clearance between the room temperature tire and any fender, swing-arm, drive-belt, etc., is 1/4".  The minimum clearance between the top of the tire and the moving fender is 1/4" for a steel-belted tire; and 1/2" for all other tires.

There are specific flat tread tires for sidecarists.  There are good arguments for and against these tires.  IMHO, the use of standard motorcycle tires should be strongly considered. 

Metzeler brand flat tread sidecar tire is actually called the Block K.  It is available only in 4.00-18 size.   It is a tube type tire, and has a load/speed index rating of 64P.   64P means that its load rating is 617#, and its MAXIMUM rated speed at full maximum inflation is 93 mph (at 30-33 psi in old literature).  The tire has a mounted (on 2.50" rim width) maximum width of 103mm, diameter of 673mm, and is rated as OK on rims from 1.85 to 3.0".   Tread depth is 8 mm.   Many have run them without tubes without excessive air loss.

Avon Sidecar Triple Duty tire is NOT designed for high power rigs.  It is available only in 3.50 x 19 size.  It is a tube type tire, and has a load/speed index rating of 57L.   57L means that its load rating is 507#; and its MAXIMUM rated speed is 75 mph.   The tire has a mounted width of 92mm; diameter of 679mm, and a tread depth of 9.4 mm.  The recommended rim diameter is 2.15", but is OK, per Avon, for 1.85 to 2.50 inches.   Many have run them without tubes without excessive air loss. 

Some original inch-size tires are rather difficult to find.   A source for suitable flatter-tread tires in inch (and some metric) sizes for sidecars, such as 3.25-18 and many others, is from   Specifically look at their HF308 models. The tread flatness and depth may well be to your liking.  DO check too. As noted earlier, Coker Tire Company has purchased moulds & builds its own classic tires on them ...fresh stock ...and the tires are of good quality.  I, and others, will be happy to discuss sidecarists' tires HERE:

I have a lot of information on tires for sidecar rigs that is not here. 

There is more information on tires usage for sidecar rigs here:

(2) Nitrogen:

There is BAD information, or just plain hype, on the use of nitrogen in any type of tire for road & off-road use.  The facts are, that while there ARE benefits, use of nitrogen to fill tires is NOT all that practical for anything but racing.   On the plus side, molecules of nitrogen are larger than average air molecules.  These larger molecules do NOT pass through the rubber used in tires and tubes as easily as common air molecules.  Thus, pressure loss over time is lower, this is particularly so with higher percentage natural rubber tubes, as opposed to the lower percentage natural rubber, often just called plastic tubes.  On a practical basis, the slower loss is NOT a BIG difference to most.    One factor not talked about much is that nitrogen is available in different percentages, and the very high percentage version is THE BEST.  BTW...CostCo, which does NOT sell motorcycle tires, DOES use the premium nitrogen.  A plus factor for nitrogen is that it is less prone to accumulate water vapor, and, is very DRY when installed into the tire, not so the 'outside air' from your average compressor setup, nor a gas station.   Water vapor in common compressed air can lead to rather wild fluctuations in pressure as the tire heats up & cools down.  Obviously, this is minimized by using clean, dry, air.   Nitrogen, due to its lack of extra affinity for water vapor, delivers a safer, more stable tire pressure, which can be somewhat important for very high speed driving (much more so at racing speeds).  The final good point about nitrogen is that it does not contain oxygen, which tends to degrade rubber compounds over long periods of time.   The PROBLEM with nitrogen is cost, not easily available (unless you rent or purchase a bottle at a welding supply store), and if you top off the tire with too much compressed air, especially if the air is not dead dry, some advantages of the nitrogen is LOST.  This is very much LESS SO, if the nitrogen that was used is a very high percentage type.    Nitrogen's good effects work with tubeless AND tubes.

There are instances wherein someone uses a tube-rated tire without a tube.   In some instances this is done with various motorcycle tires, but also done with two special sidecar type tires ....and, there are only TWO types of these square-profile sidecar tires available, as far as I know.   One in 18" and one in 19", and not from the same manufacturer! (19"=Avon Triple Duty; 18"=Metzeler Block K).  I have tried nitrogen in these tires as tubeless, and it appears that tire pressure loss IS SLOWER.

An allied use is tubeless used on tube-rated rims.  That brings up a whole story in itself, and has its own article on this website:   I have done some preliminary testing;  leakage does seem less with nitrogen.   The bottom line, of course, is  few of you are going to buy or lease nitrogen tanks for use at home ...but some bike dealerships may be using nitrogen.  You could always purchase a bottle of nitrogen for your home shop/garage, and ONLY fill the tires with nitrogen.   TRUE is that you can top up a fully nitrogen-filled tire now and then with regular compressed air, and you do NOT lose all the benefits of the nitrogen.

If you use your own compressor for your tires, you MIGHT think about installing an inexpensive DRYER.  Frankly, the tire pressure on a sidecar rig is not nearly as critical as on a 2-wheeler, and I don't have a dryer on my own compressor; because I don't do painting with the compressor.  I would not even consider a dryer unless ...and then only a 'maybe' ... if I lived in a very high humidity area and/or painted.   Even then, the effect is only somewhat better using a dryer, in MOST situations.  If you want to use a compressor air dryer, I have NO negatives to tell you about; but dry air is NOT nitrogen.

(3) Tubes?  Tubeless?  Tube tires without tubes?  More on these subjects.

****There are instances wherein someone uses a tube-rated tire without a tube.  This happens on sidecar rigs a fair amount.   Sidecarists do all sorts of unconventional things.  Sidecarists may use tube-type tires withOUT tubes on BMW snowflake and other wheels; this is usually done because of not wanting to use a tube and the associated more complicated tire repairs, or whatever other reasons. 

There are only TWO types (and sizes!) of real square-profile sidecar tires commonly available, one in 18" and one in 19", and not from the same manufacturer!   (19"=Avon Triple Duty; 18"=Metzeler Block K).   I have tried nitrogen in these tires in these situations, and it appears that tire pressure loss is SLOWER.  Not sure it is important, in MOST situations.   There are drawbacks to these tires too, mostly for the rear tire, as mileage on those if used as a rear tire is not as good as some 'high mileage' motorcycle tires.  Handling on square profile sidecar type tires is a bit different too.

Note that the use of nitrogen on car size of tires can also be helpful.

Another usage is a tubeless-rated tire used on tube-rated rims.  That brings up a whole story in itself, and has its own article on this website:   I have done some testing, and pressure loss does seem less with nitrogen.  In fact, with the "sidecar" flat tread tires, that are specifically not for tubeless use, but sidecarists sometimes DO use them that way, the pressure loss is noticeably lower if nitrogen is used.

The bottom line, of course, is that almost none of you are going to buy or lease nitrogen tanks for use at home!

FEW tubes-only rated rims are as totally safe with tires of any type, tubeless rated or tube rated.   But, there is a lot to know you may not have thought of.  Read that above article.  Make your own decision ....and, remember, sidecar rigs are SAFER than 2-wheelers to begin with!

(5) Brakes:

FRONT brakes:
For the sidecarist, having a second front disc brake assembly, perhaps brakes with a large multi-piston caliper, will often reap benefits in stability (mostly due to weight increase), besides the increase in braking. For the sidecarist, these advantages can come with FEWER poor effects from un-sprung weight than on a solo bike.

SIDECAR brakes:
What are the pros and cons of using any sort of sidecar brake?
Can electric brakes be used?
How about a discussion of sidecar brakes, in depth?

There are several types of electric brakes used on ‘trailers’. The old Kelsey’s and to a great extent the Dexter’s, etc: use a special drum, and there are more and different components. The primary different component is a flat electromagnet and friction-material plate, that contacts the INSIDE FACE of the drum. That part does NOT contact the inside RIM like a conventional drum brake. As electric current increases, the magnetic friction plate part has higher magnetic energy, and tries to hold onto the inside face of the drum, this gives higher friction.  The rotation of the drum tries to move that plate, which has linkage that connects to the relatively conventional drum brake shoes. Thus, there is a servo action. That makes for a bit of touchiness, and the current controlling is, or can be, rather touchy for use on something as light as a sidecar, for STOCK CONTROLLERS.

Both Oak (Okleshen) and I have done some serious experimentation with these types of brakes, for the small trailers used for motorcycle towing, from really light trailers to the more heavy and larger ones used for motorcycle camping. With proper series resistors to the typical simple rheostat controller, they can work well. I still have all my...and his... test data and modifications information. Oak's test mule was a Time-Out motorcyclists' camping trailer. Without modifying the circuitry, the brakes were very grabby & hard to modulate for smooth operation.   ONE OTHER thing to think about, if you decide to get into an electric brake for the sidecar wheel, is that you ideally want to link the sidecar brake to the tug's system, and have the sidecar wheel brake power change with your tug's brake power.  Super-ideally, you might want to be able to use the sidecar brake all by itself, WHEN you want to, which enables VERY sharp turns towards the sidecar.

You can get further information on sidecar brakes, usage, etc., by contacting Claude Stanley at; and others.

***I have speculated that JUST the main electromagnetic plate might be enough for sidecar use.*** I have NOT YET tried to build such a simple brake.  I THINK it might do well.  Generally speaking, you do NOT want a 'powerful' sidecar brake.

Except for such as some old BMW Steib styles, a few others, and the URAL sidecar, the typical sidecar wheel setup is not very conducive to installing electric brakes; and, frankly, even those are real fun to do.  I could be WAY in error, and there might well be such, but I don’t know of them....and have NOT looked into it in many years.  Do a Google search on electric brakes or electric trailer brakes, to see. Some of these brakes are a bit complicated!  NOTE!  ADDING weight to the wheel of a sidecar can be ADVANTAGEOUS for handling, during turns towards the sidecar.

Mechanical brakes on sidecars work fine, and so do hydraulic types. The drum type mechanical brakes (stock on some Ural’s), is a bastardization of the old /2 BMW brakes, and works very nicely. Just the right amount of strength, typically NOT grabby, work well, and last for a huge amount of miles, and are easy to adjust. These types tend to be NON-leading shoe, so are not too powerful (not any big servo action), so are perfect for sidecars.  You do NOT want excessive brakes, nor touchy brakes, on a sidecar!

I like simplicity if it is truly functional, and on my R100RT tug with Ural chair, I used the Ural-provided mechanical brake on the chair, and coupled that in a simple way that was quite functional, quite controllable, and had NO bad effects.  I purposely added a pedal for the sidecar brake, and linked it mechanically to the motorcycle rear brake pedal, in a special way, for 100% versatility. Worked fine.   I have photos of this setup on this website.    It uses the stock BMW rear disc brake setup on the tug.  See the next paragraph for use with bike mechanical rear brakes. My use with the disc brake is inside this article:

I have done BMW-Ural rigs for other folks. Two had the mechanical braking system using my idea of dual pedals WITH DUAL FUNCTION!) somewhat similarly to my own old rig; but, a third rig was mechanically jumpered to the single BMW rear DRUM brake pedal, in a similar way as I did the disc rear coupling by mechanical means.  For all these, I did the mechanicals as an over-center cam arrangement, made by shaping the pedal with a hand file (!!), also making it impossible for the chair brake to be overpowered. In every one of these brake installations, I have been pleased with the performance.  One rig came to me for improving its brakes, and I, at owner's request, did not use my over-center type of installation.  It was not as nice as my invention.

My present K1100LT-EML rig has a hydraulic disc rear brake on the hack, works fine. I think hydraulics can be a bit trickier to get them 'perfect', such as proportionately correct in braking situations; as a proportional valve may or may not be needed, and sometimes master cylinder sizes become a factor depending on what is stock and what is available.  Hydraulic brakes, if done reasonably right, are FINE.   I also have done some hydraulic disc brakes (yes, there are mechanical disc brakes) where the proportional braking was accomplished by simply reducing the size of the friction area of the disc caliper pad.  This is extremely simple and easy to do, and quite effective.   I used a very hard thick hacksaw blade or a mill, to add grooves to the pads.   Keep in mind that there are pros and cons to even having a sidecar wheel brake.  Further, you usually will NOT want a very powerful sidecar wheel brake.

I have thought about adapting a heavy-duty BICYCLE disc brake to a sidecar.

There are those who argue against sidecar brakes. Yes, you can drive sidecar rigs without sidecar brakes, particularly with lighter sidecars.  But, read on:

Try to visualize this in your mind:
When you apply a tug’s brakes, assuming no brakes on the chair (or not being used), the motorcycle is slowing down, but the chair has weight and inertia, and it wants to continue at its original speed. Thus, the CHAIR INERTIA is going to try to TURN the entire rig. In essence, the chair wants to lead the tug; the tug will turn away from the chair. You compensate for that by moving the handlebars. When you do that, you have the front tire turned somewhat towards the chair, and are, in essence, having the chair’s weight and inertia pushing the tire on an angle, using up some of its available road friction that IT needs for braking ...and handling.  You are also going to expend more energy in changing inputs to steering, etc.

The faster you are going; and to some extent the higher the weight of the chair and its contents, and further, to some extent about what the distance is from the tug’s wheels to the sidecar’s wheel, the more the turning moment force is. Thus, in some situations, particularly in a quick brisk stop, or panic stop, the chair’s turning force can be rather high. Yes, you can almost always compensate by turning the bars. BUT, you are also ‘using up’ traction on your front tire. You also have the problem of just how much rear brake to use. You might end up sliding, and NOT in the safe direction!  NOTE that it is chair inertia that is a prime component; as opposed to the chair’s tire friction.

Now that you have the above pictured in your mind; repeat, with a wet road from it being rainy. The chair’s weight and inertia has NOT changed...but the front end friction available...which is what you NEED to steer, is LESSENED.

These things are why higher performance rigs and heavier rigs usually have brakes on the chair. You need not have a true HP rig for ‘higher performance’.  To me, a higher performance rig is one that might have the power to do higher speeds, go from slow going winding country roads, out for a 30-50 mph a secondary or freeway....where higher speeds are common. While the same effects happen at ANY speed, the over-all effects are greatly magnified as speed increases. Actually by a square function.

Weight of the sidecar does make a difference, as above noted.  Some types of rigs are rather less affected by not having brakes. It is not difficult to imagine or visualize this for a light hack, perhaps it is closer to the tug’s centerline.  NOT so easy to visualize for wheel lead changes, etc.

LOTS of rigs do not have hack brakes and have huge numbers of safe miles. Still, there are REAL reasons to have a brake on a hack.  One of the reasons seldom mentioned is that it takes less effort on the bars, particularly in the twisties on mountain passes, where you use the brakes often. Another reason is more often mentioned, the ability on some braking setups to put on the hack brake separately, making for quicker turns towards the hack; this is especially so if you are a brisk rider, on slippery stuff. You can also use the hack brake to 'turn on a dime', basically turning on the hack tire’s footprint. Some have found that ability useful in tight parking areas, sharp turns into driveways, ETC.

For ME, until I find some sort of simple electric brake that is easily adaptable to hacks, I doubt I will ever attempt to install an electric brake.

(6) Fuel Tanks:   
Many are math-challenged, to put this politely.  I have been asked quite a few times how to make or install fuel tanks, capacity calculations, weight, etc. Here is some information on capacities and weights:
Gasoline weighs about 6.3 pounds per gallon.
Water weighs about 8.4 pounds per gallon.
One gallon is 231 cubic inches.
Multiply the tank height by the width by the depth, all in inches, to get cubic inches.
I will be happy to discuss mounting, inlets, outlets, pumps, etc., via E-mail to the SCT list.

(7)  MISCL:

My Airhead-Ural rig (sold some time ago), and my present K1100LT-EML rig, have many modifications not shown on the linked page

If you are interested in any of the modifications, ask me.

Here is a photo of one method of making your sidecar rig into a powerhouse street vehicle for snowy icy Winters; or for off-road use.  This is applicable to 2-wheeling or sidecar use.   There are MANY ways of gaining more traction on the tug's rear wheel. 

03/12/2010:  Add 4.
10/10/2012:  Add QR code, add language button, update Google Ad-Sense code
12/01/2012:  Greatly expand brakes section
03/11/2013:  Move tire information article to this article, and expand it.
04/15/2013:  Add 6.
10/07/2013:  Add Duro info
05/06/2014:  completely update
10/05/2014:  Fix SCT link, update article for clarity and cleanliness
10/25/2015:  Clean up article, edit for clarity.
03/07/2016:  Update metacodes, layout improved.
09/04/2016:  Update metacodes, scripts, H.L., html, layout, fonts.

Copyright, 2014, R. Fleischer

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Last check/edit: Friday, November 18, 2016