Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Different swingarm lengths - which is better?

[polarexpress]

It has come to my attention that Ducati makes more than one version of the magnesium swingarm.

I've heard they've gone from 25mm added length to 19mm (with an unknown number of variants in between).

I'm getting a sneaking suspicion I should find out why before bleeding my financials dry on the "wrong" mag swingarm.

Did they go from 25mm to a shorter version because the 25mm proved too long?

And how does the difference in length affect the handling of the bike considering you cannot adjust the rake any further (as far as I know) once you've placed it in the steep position?

Thanks to all of you for sharing your knowledge!

[skidlids]

My Mag arm, Dymag Carbon arm and extended Spondon arm are all 25mm longer. I didn't know they did any shorter versions as it seems pointless. On any of mine the eccentric adjuster can be rotated to reduce the wheelbase.
If I were you I would just get the 25mm longer version and then adjust your wheelbase to suit which will depend on sprockets and chain length.

The longer arm is used to improve rear traction, along with moving the weight bias forward and should be used in conjunction with race offset yokes.
From what I have read Foggy used his bike on the less steep rake angle but with different trail figures.

[Edited on 27-12-2004 by skidlids]

[Shazaam!]

Changing a motorcycle’s basic geometry by increasing the length of the swingarm increases stability at the sacrifice of quicker steering. The longer the swingarm the greater the effect.

There are two linked forms of motorcycle instability: Wobble, which occurs at low speed and causes the front wheel to rapidly flip back and forth like that of an unruly shopping trolley; and weave, the fish-tailing effect that happens at high speed.

At street speeds, the standard swingarm lengths give better handling, but at higher track speeds instability issues often limit maximum overall performance. At triple-digit speeds, more stability - at some sacrifice in handling - can give you faster lap times.

The longer the swingarm, the better the bike’s ability to combat high-speed weave but (by definition) the more difficult it becomes to turn the bike into corners. In recent years, the factory riders have chosen more stability over faster turning to achieve faster lap times. The first generation Corsa magnesium swingarms were 15mm longer than stock, the last generation were 30mm longer than stock. What length to use boils down to what’s best for each rider given their riding technique and preference.

There are other handling consequences too. These changes also put higher cornering loads on the front wheel that has a tendency to induce the front to slide sooner. Better traction out of corners is a another characteristic of longer swingarms.

Placing the steering head in the steep position reduces steering forces but increases the tendency for wobble, more commonly known as a tankslapper. If you’re unfamiliar with this phenomena, see one here:

http://www.randtclub.com/Video/cedwa...pper_tt99.mpeg

In order to reduce the tendency of wobble, the Corsa bikes combine triple clamps that have less offset (more trail) than stock with longer swingarms. More trail requires more of the rider's strength to turn the bike in corners but most riders gladly accept higher steering resistance to get more stability.



[Edited on 12-28-2004 by Shazaam!]

[polarexpress]

Thanks for helping me out, skidlids and Shazaam!

Originally posted by Shazaam!
In order to reduce the tendency of wobble, the Corsa bikes combine triple clamps that have less offset (more trail) than stock with longer swingarms.

Is there such thing as an ideal (predefined) offset in combination with any given swingarm length or is it a question of personal preference?

I guess what I'm askin is this: does one go for an adjustable triple clamp or a fixed one?

[skidlids]

Originally posted by polarexpress
Is there such thing as an ideal (predefined) offset in combination with any given swingarm length or is it a question of personal preference?

Not so much personal preference as what is required to get the rider around the track as fast as possible. As Shazaam said this is basically a race setup we are talking about here and different settings will suit different tracks as well as different riding styles. With adjustable triple clamps at £440 a set I can't see a set of Non standard fixed offset ones retailing for a lot less. I hate to think what my Mag Yokes cost new.

[Felix]

Adjustable offset magnesium yokes are about a grand. They're only really useful if you've got setup data for the tracks and you bike.