Sidecar and swingarm

[hans]

I'm thinking about a sidecar for my XS650. A couple of weeks ago I bought a Dnepr MT11 for very little money because the motorcycle itself is far from roadworthy. A lot of parts such as both exhaust pipes, the driveshaft ... are missing but the side is o.k.

All XS650 motorcycles in Germany have a reinforced swingarm as shown in the picture. I wonder if this is really necessary. To do some calculation I need to know the inner diameter of the pipes or the thicknes of the wall. Does anybody know? I don't want to destroy a swingarm just to find out.

 

[magoo66]

I'm thinking about a sidecar for my XS650. A couple of weeks ago I bought a Dnepr MT11 for very little money because the motorcycle itself is far from roadworthy. A lot of parts such as both exhaust pipes, the driveshaft ... are missing but the side is o.k.

All XS650 motorcycles in Germany have a reinforced swingarm as shown in the picture. I wonder if this is really necessary. To do some calculation I need to know the inner diameter of the pipes or the thicknes of the wall. Does anybody know? I don't want to destroy a swingarm just to find out.

I have a 75b with a Hitch hiker Sidecar outfit.I’m no expert but will follow your thread and try to help if I can.I don’t have a modified or reinforced swing arm and have absolutely no issues.

 

[Miker Vee]

All XS650 motorcycles in Germany have a reinforced swingarm as shown in the picture. I wonder if this is really necessary. To do some calculation I need to know the inner diameter of the pipes or the thicknes of the wall. Does anybody know? I don't want to destroy a swingarm just to find out.

This picture seems to be from an original thread by HJ Pahl on the German site.
Somewhere, he argues this reinforcement works only in the vertical direction.
While for sidecar use, you want to reinforce in the horizontal direction instead, as the sidecar introduces extra horizontal forces.
I think he has a good point.

 

[5twins]

If you want a stronger swingarm, the one from the TX750 twin pretty much drops right in, and it has about 1/4" bigger diameter tubes so is much stiffer .....

 

[Miker Vee]

If you want a stronger swingarm, the one from the TX750 twin pretty much drops right in, and it has about 1/4" bigger diameter tubes so is much stiffer .....

I've been looking for one of those for quite some time now, but they seem close to unobtanium in our neck of the woods.

 

[5twins]

Yes, I guess I should have kept to myself the fact that they swap onto the 650 so easily, at least until I scored a few more cheap, lol.

 

[hans]

By the way I am HJ Pahl and I have asked this question already on the German site, but I didn't get any answer so far. When you ad a side car to a motorcycle or change something, it has to be approved by one of several organisations such as the TÜV, Dekra and some others.It would be much easier to get this approval when you have calculated that the existing frame or perhaps an auxiliary frame and of course the swingarm an the fork are strong enough for the additional forces.

In my opinion the swingarm doesn't get stronger when you weld an additional square to it, because the material gets brittle by the welding and the two squares don't ad much stiffness in the lateral to the pipes. But to calculate this you must know the exact dimensions of the pipe.

 

[Jim]

This picture seems to be from an original thread by HJ Pahl on the German site.
Somewhere, he argues this reinforcement works only in the vertical direction.
While for sidecar use, you want to reinforce in the horizontal direction instead, as the sidecar introduces extra horizontal forces.
I think he has a good point.

The force with a sidecar rig is gonna be a twisting moment. Bike stays upright, in turns the tires resist sliding sideways. Than imparts a twisting moment to the swingarm. So those reinforcement do indeed help.
Let's look at a right turn... The bike wants to slide left and is held by the tire. That means the right swingarm tube wants to bend up and the left wants to bend down. Those reinforcement are for up and down bending moments... so yeah, they'll work.

 

[5twins]

You also need/want to stiffen up the suspension. BMW actually made "sidecar" springs for the /2's. The rears in particular were much stiffer, too stiff for solo use. On my /5, I put 140lb. straight wound springs on the rear shocks, again, too stiff for solo use.

 

[Its been a long time]

The force with a sidecar rig is gonna be a twisting moment. Bike stays upright, in turns the tires resist sliding sideways. Than imparts a twisting moment to the swingarm. So those reinforcement do indeed help.
Let's look at a right turn... The bike wants to slide left and is held by the tire. That means the right swingarm tube wants to bend up and the left wants to bend down. Those reinforcement are for up and down bending moments... so yeah, they'll work.

Except that the top and bottom bracing along the swing arm tubes doesn't do anything to improve the twisting of the swing arm pivot tube. In fact making the arm tubes stiffer probably means the twisting at the pivot tube is worse.

 

[Jim]

It would be much easier to get this approval when you have calculated that the existing frame or

You could grab up every pic you can of an XS650 with a sidecar. There's lots of 'em out there. That should be proof enough.

In my opinion the swingarm doesn't get stronger when you weld an additional square to it, because the material gets brittle by the welding

No, it's made from mild steel. Welding and letting the weld air cool normalizes the tube. In other word, exactly like it was before you welded it.

 

[Jim]

Except that the top and bottom bracing along the swing arm tubes doesn't do anything to improve the twisting of the swing arm pivot tube. In fact making the arm tubes stiffer probably means the twisting at the pivot tube is worse.

Yep, but that cross tube is pretty short and pretty robust. I'd say it'll hold up just fine with minimal twisting.

 

[Its been a long time]

Yep, but that cross tube is pretty short and pretty robust. I'd say it'll hold up just fine with minimal twisting.

But not especially large in diameter, not so resistant to twisting. Given the relatively large number of 650's hauling chairs over the last half century, I'd say it's more an academic argument than a real concern. Never had a chair myself, seems to me more mileage in looking at the front end of the rig rather than the back.

 

[5twins]

Yes, that area isn't made any "beefier" on the TX750 arm, only the arm tubes are larger.

 

[Miker Vee]

By the way I am HJ Pahl

I should've guessed

 

[Jim]

I'd say it's more an academic argument than a real concern.

Yeah, that's my guess. Unless you plan on racing it, I'd say it's more than strong enough.

 

[Miker Vee]

But not especially large in diameter, not so resistant to twisting.

How about replacing the cross tube by a solid Suzuki swingarm bolt as has been promoted by fredintoon many times before?
Suzuki PN 61211-49301 or 61211-49000 or 61211-31001 or 61211-3100v if my information is correct; PN 08319-21168 for the accompanying self locking nut.

 

[5twins]

Not a bad "upgrade", but I doubt it would make things any stiffer.

I never knew that all German 650 swingarms were braced like that. Interesting. Got any more pics? I'd like to see the other end, up by the pivot, just to see how far the bracing goes. I'm no ace welder but I think I could do this, lol.

 

[magoo66]

Unquestionably,regardless of whether you use your stock swing arm or experiment with a modified one that you choose,correctly update the swingarm bushings.

 

[hans]

I will try to find better pictures