Does this look safe

[Gixer1460]

Probably - old Brit bikes used to have near vertical shocks on their short stubby arms, but shock & damping technology has moved on since then!

[Duckndive]

3 hours ago, DAZ said:

When Mr Yoshimura moved the mounting point did the class rules require the bike to retain stock length shocks ? But make no mention of mounting location in the rule book ? Just a thought as to why ....

Most likely i would say .. 

[bitzz]

On 1/30/2024 at 4:08 PM, Toecutter said:

What actual benefit does moving the shock mounts in this way actually achieve though? When you look at their position in relation to stock,  they are almost at 45 degrees to the swingarm. This surely doesn't allow the shocks to perform optimally.

If you get the shocks in at exactly 45 degrees, in the triangle of the lower mount, upper mount and the swing arm pivot, the forces put on the shocks will "graph" linear as it goes through travel. It's easier to tune the shocks.

[bitzz]

NEVER put a hole through a tube. That mount has to be built into a gusset, and the plates of the gusset have to welded to the tube like the original was.

Engineering 101.

[bitzz]

15 hours ago, DAZ said:

When Mr Yoshimura moved the mounting point did the class rules require the bike to retain stock length shocks ? But make no mention of mounting location in the rule book ? Just a thought as to why ....

I've seen pics of that first bike, the frame and suspension supplied by Suzuki, modeled off the XR69, with Kayuba shocks, mounted at 45 degrees, not even close to the GS750 setup. It lost the KYB shocks pretty quick.

[TonyGee]

4 hours ago, bitzz said:

NEVER put a hole through a tube.

I can't see a problem with it  if its welded good and a gusset is behind it for support it ain't gona go anywhere !!!!!  

[Tony Nitrous]

Note to self:  Don’t post up the welding on my cracked Hayabusa frame that’s had 17 years of abuse.    

[TonyGee]

9 minutes ago, Tony Nitrous said:

Note to self:  Don’t post up the welding on my cracked Hayabusa frame that’s had 17 years of abuse.    

go on Tony, you know you want to 

[DAZ]

1 hour ago, TonyGee said:

go on Tony, you know you want to 

Even more he knows we want him to ..... What a tease 

[BillyR]

I had a gsx softail with the shocks mounted similar, took me and the mrs to the south of france and back with no issues.

I think people overthink and worry too much. 

The first streetbike in this country to crack 200mph had the headstock cut, pulled out, and welded back up without the aid of a jig. No problems there either.

[Gixer1460]

1 hour ago, BillyR said:

I had a gsx softail with the shocks mounted similar, took me and the mrs to the south of france and back with no issues.

I think people overthink and worry too much. 

The first streetbike in this country to crack 200mph had the headstock cut, pulled out, and welded back up without the aid of a jig. No problems there either.

Just because something hasn't failed YET, doesn't mean it won't in the future. Better to 'over engineer' something now so that failure isn't an option later.

[TLRS]

10 hours ago, bitzz said:

If you get the shocks in at exactly 45 degrees, in the triangle of the lower mount, upper mount and the swing arm pivot, the forces put on the shocks will "graph" linear as it goes through travel. It's easier to tune the shocks.

I'm with @Gixer1460  on this one. If you want linear action the shock has to sit perpendicular to the swingarm. That way most movement is going 'into' the shock, instead of rotation the shock. With no spring or damping to limit that rotation.

5 hours ago, TonyGee said:

I can't see a problem with it  if its welded good and a gusset is behind it for support it ain't gona go anywhere !!!!!  

With a big hole it does seem like a lot of the tube is replaced by a weld. Plus a mount that is offset from the tube.. will try and twist it under load. As well as the usual load from what the subframe needs to take on top anyway.

A gusset that spreads that suspension load over a greater surface of tube.. seems like a good idea.

That said.. it's steel.. and there are two shocks. If it fails it probably won't do so on both sides without any warning or cracking what so ever.

 

[imago]

49 minutes ago, TLRS said:

Plus a mount that is offset from the tube.. will try and twist it under load.

That and the tube wall thickness are the key issues. The shock mount becomes a lever and the tube the pivot. As I mentioned before, think of stilsons on the tube, or a spanner on a bolt and it's easy to see how much force is being applied. That force is in a direction that nothing involved is designed or spec'd for, and also bear in mind that the tube which was under spec when new is now over 40 years old. It's a shit idea, based on piss all in the way of engineering knowledge or even basic physics. However, as always people are free to do as they chose and ignore what they don't like.

It always makes me chuckle when you get the "I've done this that or the other for years and it was fine." comments. You get it on every subject from wiring, through engineering to structural design.  There's no point in arguing with it as if they didn't get it the first time round they won't any subsequent times either. The information is widely available, and these days you can even get engineering calcs done by simply inputting numbers. Still, the ubiquitous 'Bloke on the internet' will have his say and it's much quicker than actually finding the relevant information. 

Edited February 1 by imago

[TonyGee]

this is what the sanctuary guys do in Japan on the big zed's. 

 

[TLRS]

6 hours ago, imago said:

That and the tube wall thickness are the key issues. The shock mount becomes a lever and the tube the pivot. As I mentioned before, think of stilsons on the tube, or a spanner on a bolt and it's easy to see how much force is being applied. That force is in a direction that nothing involved is designed or spec'd for, and also bear in mind that the tube which was under spec when new is now over 40 years old. It's a shit idea, based on piss all in the way of engineering knowledge or even basic physics. However, as always people are free to do as they chose and ignore what they don't like.

It always makes me chuckle when you get the "I've done this that or the other for years and it was fine." comments. You get it on every subject from wiring, through engineering to structural design.  There's no point in arguing with it as if they didn't get it the first time round they won't any subsequent times either. The information is widely available, and these days you can even get engineering calcs done by simply inputting numbers. Still, the ubiquitous 'Bloke on the internet' will have his say and it's much quicker than actually finding the relevant information.

There's this train of thought.. and there's the overthink everything and get very little done (my area of expertise ). Learning = making mistakes.

[DAZ]

T

15 hours ago, TonyGee said:

this is what the sanctuary guys do in Japan on the big zed's. 

 

The image that @TonyGee provides is what I would likely do , I think triangulating (wether by tubes or gussets)  the area as much as is feasable /reasonable to transfer the loads into other tubes is the best/safest way, I read that a inch of weld can hold a tonne of that is true then the 25mm bar stock the shock mounts are turned from have 3 inches of weld so much stronger than a straight frame tube and as @imago points out without triangulation/gussets it's going to try to twist the tube 

Edit: most any article I've ever seen on chassis/frame design,has used triangulation to spread loads through the chassis and create strength

Edited February 2 by DAZ
Addition

[imago]

15 minutes ago, DAZ said:

Edit: most any article I've ever seen on chassis/frame design,has used triangulation to spread loads through the chassis and create strength

This is a key, and really important point for me. No one knows everything, no one has the theory on everything, but the information is available and all you have to do is take a few minutes to find it, read it, and then apply it to whatever you're doing. 

[Dezza]

18 hours ago, TonyGee said:

this is what the sanctuary guys do in Japan on the big zed's. 

 

Some of their bikes although they look like modified stock bikes have bespoke frames, a bit like some AMA bikes in the 80s when some teams were blatently cheating.

[bluedog59]

"Some teams were blatantly cheating" ?!

I think "They were all cheating but some didn't cheat enough to win" would be nearer the truth. 

[Reinhoud]

On 1/31/2024 at 4:27 AM, gsx said:

Going back to twin shocks on me gsx and bloke at Newark was kind enough to show me photos of how he did shock mounts , looks like the rubber bushing in the top mount has been sacrificed to get desired wall thickness. What's my best option ? This or original ish with nut on the end 

If that's welded properly it shouldn't be a problem