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Miscl. Sidecar Tech
https://bmwmotorcycletech.info/misclsidecartech.htm
SC7
© Copyright 2020, R. Fleischer
(1) Tires, rims, handling, tread, un-sprung weight, car and m/c tires, 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 qualities.
This is also true for sidecar rigs. But, sidecar rigs have other considerations. A sidecarist wants lots of effective braking when called-upon; and, wants the lightest possible steering forces, yet does not want any (or minimal) oscillations or other serious instabilities in the front end. Many sidecar rigs 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 has only a 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, 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 the this to mean that square and wide car type tires are the only way to go. There are numerous considerations, and a wide tread car tire, even a small car size, can increase steering effort by a very large amount, which is very tiring to the shoulders, etc. The usual major reason to use a car tire, is the much longer tread life, compared to motorcycle tires or sidecar type tires. Primarily, this is a concern for the rear tire, as it wears, even on the best rigs, rather quickly, although with proper alignment (particularly rig TOE-IN), it can be quite reasonable.
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 (available in 18"), or an Avon Triple-Duty (available in 19"), may give some reasonably good benefits in oscillatory stability. It also may be a detriment. Those tires don't last all that long either. There are some better wearing motorcycle tires, which work well as a front tire...and these are NOT the two types just mentioned.
A car tire will typically give considerably more miles than any motorcycle or sidecar-type tire, and, can be much cheaper too! However...a square tread tire or car tire may also make the front end more susceptible to road grooves, and, in fact, most any road irregularity, as I have mentioned, and I also mentioned the heavier steering. A motorcycle tire for the front will usually give more snappy handling. 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 small car type tires are usually much cheaper, tires last much longer as mentioned, and a wide range of tires is available (both tube type and tubeless), etc. Usually, but not always, a car type tire must be fitted to a rim designed for it.
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!
For the sidecarist, it should now be obvious that the subject of tires (and rims, etc.) at all three positions can be an involved subject. Tire wear, road contact, braking, stability, steering effot ...and several other things are involved.
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. https://www.goldwingfacts.com/threads/design-differences-between-car-and-motorcycle-rim-tire.400426/. That article is quite nerdy in places, but has some real jewels of information here and there. It really is worth the read. Keep in mind that a two-wheeled motorcycle is VERY different from a 3 wheel sidecar rig in a large number of ways, including the forces put on the tires.
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 these recommended tires: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 being used on motorcycle rims, 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 low tire pressures, 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.
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 necessarily stops us sidecarists! Just be aware, and if you are curious enough, measure the tire and the rim ...and be careful!
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 sizes 125-15 & 135-15, while I suggest an Internet search engine be used, you can also try this company:
www.2CVsource.com. See the next paragraph for an EXCELLENT source.
My present recommendation for hard-to-find tire sizes is https://www.cokertire.com/. For MANY years, they have been purchasing older tire moulds and equipment, refurbishing, etc., and are re-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 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 www.universaltire.com; 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 large stock of very obsolete tires, and they may not have been stored well, and any over 4 years old 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 ....it is not really true, and other things may happen to that tire if you use it.
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 of appropriate model and size should be strongly considered.
The two major so-called "Sidecar Tires" were really designed for the sidecar itself, ...and, later, for lower-power motorcycles, both front and rear. The load and speed rating of these is not all that high, and speed and use in turns on higher power heavier rigs tends to reduce their mileage life by quite a bit! Braking on these tires can also be questionable.
Metzeler brand flat tread sidecar tire, the most known, and oldest, is called the "Block K". It is available only in 4.00-18 size. It is a tube type tire, and new ones have 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). Older versions of this tire were rated at even lower speed. 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's "Sidecar Triple Duty" tire is also not designed for high power and/or heavy sidecar 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 https://durotire.com/. Specifically look at their HF308 models. The tread flatness and depth may well be to your liking. DO check https://www.Cokertire.com too. As noted earlier, Coker Tire Company has purchased moulds & builds its own classic tires on them ...fresh stock ...and the tires are usually of amazingly good quality.
DO keep in mind that you do NOT usually need flat tread tires for a sidecar rig. Particularly, for the sidecar itself, almost any tire will do, since the tire hardly wears much, and the characteristics of the tire are vastly less important than for the tug.
There is one instance where the sidecar tire type is more important, and that is on a 2-wheel drive sidecar rig. You may want a more aggressive tread if venturing well off paved surfaces, especially into deeper softer ground areas.
I have a lot of information on tires for sidecar rigs that is not in this article you are reading.
There is more information on tires usage for sidecar rigs here: https://bmwmotorcycletech.info/sidecartech.htm
(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 tubes, 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 compressor. 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 easy availability (unless you rent or purchase a bottle), 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 where 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. https://bmwmotorcycletech.info/section6.htm. 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. If you want to use an air dryer with your compressor, 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.
As I have noted, 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 different. As I noted, the use of nitrogen can 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: https://bmwmotorcycletech.info/section6.htm. I have done some testing, and pressure loss does seem less with nitrogen.
The bottom line, of course, is that almost none of you are going to buy or lease nitrogen tanks for use at home!
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, and/or 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 FAR FEWER poor effects from un-sprung weight ....than on a solo motorcycle.
REAR brakes:
For most sidecar rigs, a modest rear brake is adequate. A somewhat more powerful rear brake is or can be useful. Many a sidecar rig has its rear brake (some the front brake) mechanically or hydraulically tied to the sidecar brake. Some folks use separate pedals for sidecar and rear brake. Some motorcycles, such as some Honda Gold Wing's, use integrated brakes. All these methods can work. Many a sidecar rig does not have sidecar brakes at all. The heavier rigs usually do.
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 for a light weight vehicle like a sidecar, and the current controlling is, or can be, rather touchy for STOCK CONTROLLERS.
Both Oak (Okleshen) and I have done serious experimentation with these types of brakes for the small trailers used for towing by motorcycles. The trailers varied from quite light utility trailers to more heavy & large 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, which I may eventually digitize and post on this site. 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. Another 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. 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 http://www.FreedomSidecars.com; and others.
***I have speculated that using JUST the MAIN electromagnetic plate (no linked shoes used) 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, there is no need, and can be dangerous, as the sidecar has enormous inertia.
Except for such as some old BMW Steib styles, a few others, and the URAL sidecar, the typical sidecar wheel setup is not easy to install electric brakes. I could be wrong, 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. Ask Claude Stanley.
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 nicely. Just the right amount of strength, typically NOT grabby, 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: https://bmwmotorcycletech.info/sidecartech.htm
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 small hydraulic disc brake on the hack and it 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 OK. 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, but does not necessarily have the same effect you may be thinking-of, as the pressure has not changed. 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 will NOT want a very powerful sidecar wheel brake.
I have thought about adapting a heavy-duty BICYCLE disc brake to a sidecar. Thinking is as far as it has gone.
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 thus inertia, and the weight is far to one side of the motorcycle, so the leverage is high. The forces are such that the sidecar wants to continue at its original speed. Thus, the sidecar 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. Thus, NOT having a sidecar brake leads to poorer over-all braking, possibility of unwanted swerving, and potentially loss of control. For many a mild-driving sidecarist, the lack of a sidecar brake is not a problem.
The faster you are going; and the heavier the weight of the chair and its contents ....and the further the distance is from the tug's wheels to the sidecar's wheel, the higher 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 extremely 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 rainy-wet road. 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 various considerations are why higher performance rigs and heavier rigs may have brakes on the chair, and carefully set-up over-all braking systems. 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 jaunt ...to 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 squared function.
Weight of the sidecar does make a difference, as noted above. 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 also much closer to the tug's centerline. NOT so easy to visualize are such as wheel lead changes, sidecar nose tilt, 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.
(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 Group.
(7) MISCL:
My Airhead-Ural rig (sold quite some time ago), and my present K1100LT-EML rig, have many modifications not shown on the linked page https://bmwmotorcycletech.info/sidecartech.htm
If you are interested in the modifications, ask me with specific questions, on the SCT Yahoo Groups list.
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.
© Copyright 2020, R. Fleischer
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Last check/edit: Thursday, August 17, 2023