Frame Asymmetry - why?

[peterg]

Can anyone explain why the seat posts are not the same? I'm referring to the sections that run from the shock mounts to the horizontal cross members below the seat. The left post curves inwards lower than the right side post. I have a 1980 Special and I cannot see any reason for them not to be the same. Probably some carry over from an earlier model?

 

[Paul Sutton]

The power delivery is asymmetric so I guess this will be reflected in the frame design??

 

[650Skull]

post some pics to show us what your observation query is................

 

[peterg]

Here are photos of my bike's frame.

 

[Jim]

He's talking about this. This is the left side.....

And this is the right side....

Near as I can tell, it's to accommodate the chain and chain guard.

 

[gggGary]

From memory; you hit it. The early models got in trouble with chain/shock clearance and a year or two in they jogged the frame and swing arm out to (mostly) fix it. These were designed a bit before the CAD era and some things just didn't get caught until the bike was in production. It's still a tight fit, we can't just grab a fat shock and bolt it on.

 

[peterg]

As far as I can tell the difference is only at the top not at the bottom where the chain is.

 

[gggGary]

An early frame.

a 74 standard

a 79 SPII

and a 79 Special.

 

[jabcb]

From memory; you hit it. The early models got in trouble with chain/shock clearance and a year or two in they jogged the frame and swing arm out to (mostly) fix it. These were designed a bit before the CAD era and some things just didn't get caught until the bike was in production. It's still a tight fit, we can't just grab a fat shock and bolt it on.

In 1972, the cat’s meow of calculators was the HP-35. The XS650 engineers likely would have been thrilled to be using one.

https://en.wikipedia.org/wiki/HP-35

 

[aldo5468]

Still have and use an SR-50A - just found a source for a replacement battery holder that takes 3 of any AA batteries you want to use; if NiCd, you can use the original charger.