What we (me anyway) are curious about is whether the welded bar wraps around the front of the cross tube?
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Sidecar and swingarm
- Thread starter hans
- Start date
Correct, that in itself wouldn't help the twisting. I wasn't very clear, what I wanted to see is if there's anything else done to the cross tube. There's the gusset that ties the 3 tubes together in the front, and that works well enough I suppose, just curious what else was done, if anything.
As I said earlier, just beefing up the swing arm tubes without addressing swing arm cross tube twisting I don't think is a great idea. Stiffening up the swing arm tubes most likely makes the cross tube twisting worse. The gusseting is reasonably substantial, but it's still an off-design condition really as soon as you hook up a chair. I'd venture that stiffening up the tubes as shown without doing anything else is a bit of waste of time to be frank. Obviously, others will have different opinions, I'm really not a side car enthusiast at all.
Edited to add - the best way to stiffen the swing arm up without adding tons of unsprung weight is to do exactly what Yamaha did starting with race bikes. Triangulate the swing arm as in monoshock. Instant stiffness, little added unsprung weight. Snag is finding a place for the rear shock!
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Agree. If you want the swingarm stiffer in twisting, something like this would be a much better option.
Yep. Aircraft need to be rigid, yet light weight. That's why early (and present) aircraft like the Piper Cub are still with us almost 100 years after they first flew... triangulation.
We're definitely on the same page. In the world of two wheels, designs by Tonti (for Guzzi) , Colin Seeley and many others produced light, stiff exceptional bike frames from straight tubes and triangles. Many of the designs really are case studies in how simple but effective design can produce things of great function as well as beauty.
the third picture I have uploaded you can see that the square iron doesn't wrap around, but you can't see where it ends. In my opinion, the best solution is the swing arm in the picture which Jim uploded in case that reinforcing the swingarm is necessary at all. But to decide this it's necessary to recalculate the existing swingarm and therefor I must know the dimensions of the pipes.
Yes, it would be nice to see one out of the bike, then we could get a good look at it.
Yes, I'm familiar with the traditional tube bracing for a swingarm, but that's pretty hard for me to do. I can weld a couple strips of steel along the top and bottom of the arm though, lol.
Yes, I'm familiar with the traditional tube bracing for a swingarm, but that's pretty hard for me to do. I can weld a couple strips of steel along the top and bottom of the arm though, lol.
I asked an acquaintance and he send one more picture of a swing arm. He explained as follows:
“The company Stern https://www.gespannservice.de/ also had to face this painful challenge during the first conversions to 15" wheels and 125mm tires. The unreinforced swingarm legs cracked just behind the gusset plate, either at the top or bottom. This stopped happening after the square iron were welded to the swing arms. I even use a 4" wide rim and 135mm tires on the rear of my summer motorcycle wit a sidecar and the swingarm doesn’t bend. There are certainly better technical solutions, but they would also be more complex.”
“The company Stern https://www.gespannservice.de/ also had to face this painful challenge during the first conversions to 15" wheels and 125mm tires. The unreinforced swingarm legs cracked just behind the gusset plate, either at the top or bottom. This stopped happening after the square iron were welded to the swing arms. I even use a 4" wide rim and 135mm tires on the rear of my summer motorcycle wit a sidecar and the swingarm doesn’t bend. There are certainly better technical solutions, but they would also be more complex.”
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I have posted some pics of reinforced swingarms on XS650 motorcycles with an attached sidecar. As I already wrote, I still wonder, if the reinforcement is necessary. Has anybody seen such a reinforcement in the USA, or has anybody ever have problems without?
