Laverda 1000 3C Box section swingarm question

Why is so much emphasis placed on swingarms while the totally weedy and overwhelmed front forks (most especially the Cerianis as in these pics) and steering head set up are disregarded?

I don't get it, unless it's for bonus points outside the ice cream saloon...

piet
 
sfcpiet said:
Why is so much emphasis placed on swingarms while the totally weedy and overwhelmed front forks (most especially the Cerianis as in these pics) and steering head set up are disregarded?

I don't get it, unless it's for bonus points outside the ice cream saloon...

piet
Click to expand...
Well, the bike ended up with a Zane front end and 17 inch wheels.
Which just left the flexy frame.
Paul
 
sfcpiet said:
Why is so much emphasis placed on swingarms while the totally weedy and overwhelmed front forks (most especially the Cerianis as in these pics) and steering head set up are disregarded?

I don't get it, unless it's for bonus points outside the ice cream saloon...

piet
Click to expand...
Tend to agree Piet. The only reason I fitted a different (longer) swingarm to the 'Q' was to retain my wheelbase (lost when re-angling the head tube). I also didn't go down the double swingarm axle plate. I beefed up the rear engine mounts (that have cracked in the past), which also served to make the whole engine-swingarm pivot assembly very rigid, but I have every confidence in the std SF swingarm AND the mounting plates in terms of strength and rigidity.

I doubt the factory actually tested and proved that the SFC (750) was losing stability due to flex in this area - more than likely just a 'we should probably ...' situation. Fortunately with an SF I didn't need to concern myself with a bendy frame - the frames are rock solid (and the forks about 10cm shorter than a triple). Fit more supple shocks and you also reduce the stress on the swingarm from the standard Ceri or Marzo 'hard tails' when angled right over.
 
piranha-bro2 said:
I doubt the factory actually tested and proved that the SFC (750) was losing stability due to flex in this area - more than likely just a 'we should probably ...' situation.
Click to expand...
I rather believe that the doubling of the swingarm plate was the fruit of rider feedback.
I have a 750 race bike with some ex works bits on it, magnesium points cover, magnesium selector cover, SFC head with Amals, and special frame. History unknown.
What you call the swingarm plate is half doubled on this frame, only the top part, whereas the SFC is doubled from top to bottom as you know.
Laverda progressively beefed up the rear end of the 750s starting with the cross bar on the swingarm itself and then beefing up it's mounting on the frame.
No "we should probably" there.
Paul
 
Just imagine the twisting force extended along the swingarm to its pivot point when accelerating hard on sticky race rubber leaned over to the max in a long bend. And then add in a bump. That's got to create flex and get close to braking bits.
 
Not unknown to have a swingarm spindle shear on a 750, especially on badly maintained bikes where loose spindles have caused wear, in both frame and spindle, creating stress points. I've yet to find a fractured spindle on a triple, maybe the frame is more forgiving in this area.

I wouldn't dare suggest bikes from the factory racing stable were badly maintained, but I reckon they experienced fractures early on as well while racing their modified "S" models, hence the beefing up of the spindle itself and subsequential strengthening of the mounts on the SFCs.

The cross bar on the 750 swinger was only added when the swingarm was lengthened. No room for a strategically positioned cross bar before that.

Racing is an evolutional process, the final product is usually far superior to what was started out with.

piet
 
Similarly, many would do well to consider what happens when the front wheel hits a bump at high lean angles.
The fork will not be compressed but deflected sideways.
Super stiff front ends are not an advantage, here, especially on the road. A little give, in the forks, allows the tyre to maintain better contact.
 
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The Sock said:
Similarly, many would do well to consider what happens when the front wheel hits a bump at high lean angles.
The fork will not be compressed but deflected sideways.
Super stiff front ends are not an advantage, here, especially on the road. A little give, in the forks, allows the tyre to maintain contact better.
Click to expand...
Have you ever observed what the front axle does under heavy braking on Ceriani-equipped bikes? Marzocchi not much better, especially the longer RGS variant. Further increased by up-graded brakes. Scary...

piet
 
sfcpiet said:
Not unknown to have a swingarm spindle shear on a 750, especially on badly maintained bikes where loose spindles have caused wear, in both frame and spindle, creating stress points. I've yet to find a fractured spindle on a triple, maybe the frame is more forgiving in this area.
Click to expand...
I saw an ex-Spanish Triple, for sale at a local (not Laverda) dealer some years ago.
To fit the fashion of the time, the TDTPO (Totally Dumb Twat Previous Owner) had ground both ends off the front axle. It was held (?), in place, only by the clamp bolts.
As if that wasn't bad enough, they'd drilled out the axle centre, to "lighten" it!!!!
I drew the attention of the dealer to the catastrophic danger it posed. He appeared about as interested as if I'd pointed out it had the wrong pattern on the seat cover.
Wonder whatever happened to that one
 
sfcpiet said:
Have you ever observed what the front axle does under heavy braking on Ceriani-equipped bikes? Marzocchi not much better, especially the longer RGS variant. Further increased by up-graded brakes. Scary...

piet
Click to expand...
I used to explain to passengers, upset by seeing the aeroplane's wings bending.
"Bending is good.
If they didn't bend, they would break.
That's much worse, from our point of view."
 
sfcpiet said:
Not unknown to have a swingarm spindle shear on a 750, especially on badly maintained bikes where loose spindles have caused wear, in both frame and spindle, creating stress points. I've yet to find a fractured spindle on a triple, maybe the frame is more forgiving in this area.

I wouldn't dare suggest bikes from the factory racing stable were badly maintained, but I reckon they experienced fractures early on as well while racing their modified "S" models, hence the beefing up of the spindle itself and subsequential strengthening of the mounts on the SFCs.

The cross bar on the 750 swinger was only added when the swingarm was lengthened. No room for a strategically positioned cross bar before that.

Racing is an evolutional process, the final product is usually far superior to what was started out with.

piet
Click to expand...
Yes, I'd forgotten about the thicker spindles.
Paul
 
The Sock said:
I saw an ex-Spanish Triple, for sale at a local (not Laverda) dealer some years ago.
To fit the fashion of the time, the TDTPO (Totally Dumb Twat Previous Owner) had ground both ends off the front axle. It was held (?), in place, only by the clamp bolts.
As if that wasn't bad enough, they'd drilled out the axle centre, to "lighten" it!!!!
I drew the attention of the dealer to the catastrophic danger it posed. He appeared about as interested as if I'd pointed out it had the wrong pattern on the seat cover.
Wonder whatever happened to that one
Click to expand...
I drilled my front axle not long after I started racing and did 16 more seasons on it. Also the rear, slightly larger Kawa axle, with not the slightest sign of problem, done at the advice of some top racing engineers. Maybe I was lucky that I never broke a swing-arm spindle either. The Cerianis obviously flexed though because the front tyre wore through the strengthening rib on the fibreglass front guard which sat quite a few mm away from the tyre. The bike handled fantastic on the track, cornering and braking were all I had to play with against all the more powerful bikes.
 
If I recall correctly, all the GSX-R axles have been hollow for decades. Of course they were designed that way from the beginning and are of a large diameter. Doesn’t a tube have less flex than a rod? Stiffer?
 
Alzero said:
If I recall correctly, all the GSX-R axles have been hollow for decades. Of course they were designed that way from the beginning and are of a large diameter. Doesn’t a tube have less flex than a rod? Stiffer?
Click to expand...
Not the early ones with a 15 or 17mm diametre front axle iIrc. While the forks themselves were quite sturdy, the axle connection was definitely the weakest link. This may well have contributed to their handling problems.

A tube will be far stiffer than a rod of the same cross-sectional area, because of the ensuing larger diametre and the resulting geometry of bending forces that are induced.

piet
 
The Sock said:
I used to explain to passengers, upset by seeing the aeroplane's wings bending.
"Bending is good.
If they didn't bend, they would break.
That's much worse, from our point of view."
Click to expand...
So more supple and compliant suspension possibly assumes the duties of the previously 'bending' and flexing frame/swingarm/fork?
 
The problem with supple and compliant suspension is that it dives under braking steepening rake and shortening trail and it squats under acceleration increasing rake and trail. This is why MotoGP bikes have flex built into the frames to allow some give when leaned over and use computer controlled suspension to minimize dive and squat induced geometry changes.
 
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