rear wheel

Steve,
The rear wheel takes the stress from acceleration, power applied after each shift, engine braking, down shifting and actual braking effort along with side loading if used on a sidecar equipped bike.
The front wheel is a slave wheel as it were, having few of these stresses.
Braking and side loading (if in sidecar use) are about it.

Lonnie

Hello Steve,
Yes, your rear wheel DEFINITELY experiences more stress when a sidecar is mounted. The additional stresses are present in both in an axial and lateral direction.

{WARNING!!! Geek Engineering content follows...} 😉

Normally a motorcycle wheel has very little lateral stress on it, the bike leans into the turns, so almost all forces are placed directly down through the vertical axis of the wheel (perpendicular to the axle), even when cornering.

With a sidecar you no longer lean, so you suddenly place a great deal of side loading on the wheels, which places LOTS of extra load on the spokes. In addition, the rear wheel of the bike carries some of the weight of the sidecar itself, so the vertical loading on the wheel is increased as well.

Most of the time spokes fail from fatigue, like when you bend a wire back and forth several times before it breaks.

Fatigue failure depends on several inter-related factors. Some of the most important of them include: cyclitic stress, number of cycles, mean stress, mechanical properties of the material subjected to load, surface conditon of the part, environmental factors, and others that are less important.

To greaty simplify things:
As the wheel rotates the spokes see a fluctuating load, more tension when at the top of the wheel (the hub actually "hangs" from the top of the wheel) and less tension at the bottom. A graph of the stress in a spoke as a wheel rotates looks like a sine wave.
When you increase the maximum tension in the spoke by increasing the load on the wheel, the total magnitude of the cyclitic forces increases, which reduces the number of cycles that the spoke can withstand before breaking.

It is like bending the wire 130-degrees back and forth rather than just 90-degrees. It takes fewer bends (cycles) of the metal before it fails.

I will bet that your spoke failed by snaping where the spoke bends to go through the hub flange...
When the spoke sees the cyclitic stresses it actually opens and closes up that bend a tiny amount every time... just like bending that wire... Since you are only bending it a fraction of a degree every time the number of times it can withstand it are very high. But with extra stress introduced, they WILL fail faster...

The actual forces and fluctuations are much more complex and are influenced by the initial spoke tension, the cross pattern of the spokes, hub width and any offset of the rim over the hub, the fit of the spokes into the wheel hub, scratches/nicks/corrosion on the spokes, acceleration and braking forces, and others... This was just meant to give you the most basic understanding...

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The other thing that will be seeing additional stresses are your wheel bearings. You need to be aware of this and keep an eye on them.

If you look at automotive wheels/hubs what you will find is facing tapered roller bearings. preloaded tapered roller bearings have slightly higher rotational resistance, but resist loads in multiple directions, both the load carried down through the hub to the road, and the side forces introduced when cornering.

Most motorcycles use simple radial ball bearings in the wheels. For a two-wheeled vehicle they work great, inexpensive, reliable for the application, and very low rotational resistance. Unfortunately, axial ball bearings are NOT designed to resist side forces. They do withstand "some" side loads due to the shallow grooves in the bearing races that the balls ride in.
However, since there is a MUCH smaller area of material in contact under side load the pressures in the bearing material go WAY up and can lead to faster wear, spalling, or even catastrophic failure if not caught during the early stages.

There are some motorcycles that come with tapered roller bearings as standard equipment, and with a little work they can even be retrofit into many applications.

The BMW Boxer motorcycles up through the 1984 model year all came standard with tapered roller bearings which makes them excellent canidates for sidecar tugs.

Here's a real world actual experience;

100,000 plus miles on my Honda GL1100 - EML rig; when this rig was converted to a sidecar outfit, all three wheels were new EML welded tubular spoke wheels. Fast forward to my tenure with the rig, and eventually the rear drive wheel welds broke. There was metal fatigue showing on the rim. I could see where every rear wheel tubular spoke was located when I had the tire off and looked at the rim from the tire side. The steer wheel and hack wheel show no fatigue.

Since, I have replaced the rear wheel, and still run the other two original rims.

Yes, the rear wheel takes more pounding and stress. But I also agree, you can feel the pressure on the front fork when taking spirited turns.

A little more experience speaking here.
i own a '73 BMW R75/5 I bought new , with alloy rims and spoked wheels.
I now have 132,000 on the bike, with the last 20,000 with a SC attached. I still have the original spokes in the wheels and never had any problems in 33 years. never tightened them or replaced any spokes.
4 weeks ago I replaced the rear wheel with a Lester cast wheel, not because of the spokes..I spun an outer bearing in my original wheel and found the Lester wheel all set up ready to go.

Thanks for all the great comments. I think the Indian spokes were for show
and are really thin plus they were chromed. I think the new steel spoke
Harley rim is going to work fine.....well see
Thanks again you guys are awesome
Steve

Originally written by Bob in Wis on 11/7/2006 7:07 PM

A little more experience speaking here.
i own a '73 BMW R75/5 I bought new , with alloy rims and spoked wheels.
I now have 132,000 on the bike, with the last 20,000 with a SC attached. I still have the original spokes in the wheels and never had any problems in 33 years. never tightened them or replaced any spokes.
4 weeks ago I replaced the rear wheel with a Lester cast wheel, not because of the spokes..I spun an outer bearing in my original wheel and found the Lester wheel all set up ready to go.

That's great. When I worked at the motorcycle shop one of my regular duties was to true and balance the spoked wheels. There were only two of us who knew how to do it. In all the time that I did it, I don't think I found ten rims that didn't have loose spokes when they came in the door.

No, we didn't balance the rims by manipulating the spokes, we just used it to get them close, then balanced with wire rope.

Racing sidecars in Germany in the 50's:BMW's broke spokes,Zundapps did not.The Zundapp spokes were heavier.
Gary

In years past many would replace stock spokes with heavier ones for sidecar use. Has anyone hear had this done?
Spokes do need to be checked either way from time to time. It is doubtfull how many folks actually do this though. When one spoke is loose it may not be the one to fail but another one which gets overstressed. When one fails then it does put more stress on other ones. This can cause another one to fail etc etc.
Had a friend with a Honda 750a / E Z Rider sidecar. The sidecar had been modified to so the job but the bike suspension was quite mushy. Well he decided to make it into a hardtail and see how that worked. Rear shocks got replaced with solid struts. The rig actually handled very well after that. Then he went on a longer trip and spokes began to break....forst one was noticed at a gas stop. Then another , and another . Soon he was concerned if he would even make it home but he did. He ended up[ replacing all of the spokes and taking off the solid struts and never had any more issues with spokes.

I've owned many bikes with standard spoked wheels. It's certainly true that sidecars put more strain on them. By far the best spokes to prevent breakage are stainless steel ones with matching stainless steel nipples. I've laced several wheels with these and they don't seem to get loose or break.

It's also true that chrome-plated spokes are more susceptible to breakage than regular cadmium-plated ones due to the hardening process caused during plating. The makers of such spokes seldom take the time to heat-treat them and remove the excess hydrogen atoms that cause embrittlement.

So, IMHO, either re-lace with stainless or try to find a nice cast wheel with heavy spokes for your rig.

Larger diameter spokes are really the best way to go if possible. Some bikes do already have large spokes and , of course, so do not. Buchannon Wheel (google this) has been the icon in the spoked wheel world for many years and are worht talking to. Of course there are others around as well.
The deal on the chrome spokes being a concern that Gnm109 mentioned is a real one. Hydrogen Embrittlemt can be a concern with any chrome part that is put under stress. Normalizing is a requirment to alleviate this situation. Is it a real issue? Yes and no depending on the part, where and how it is used and how much overkill was designed into it. I have not had problems with chrome spokes but that is not to say , in theory, that they coudl or coudl not be a bad thing.
In the late sixties and early seventies when sprint cars first went to running roll cages many woudl chrome the cage which back then was typically a bolt on assembly. Thye looked good but soon it was found that some did not hold up in a crash. The reason? Hydrogen Embrittlement which was due to the chroming process.