M900 suspension question

[ducpainter]

...and your ass will never feel the nuances of linear springs becoming 'somewhat progressive'.

[Speeddog]

<whispering>

Should I tell them that the rear suspension linkage is progressive?

</whispering>

[stopintime]

How about this:

'Linear' or 'straight rate' spring

For example, it's a 50 lb/inch spring.
It takes 50 lb to compress it the first inch.
It takes 50 lb *more* to compress it the second inch.
So, a total of 100 lb to compress it 2 inches.
150 lb to compress it 3 inches.
And so on...

'Progressive' spring

50 lb to compress it the first inch.
60 lbs *more* to compress it the second inch.
So, a total of 110 lb to compress it 2 inches.
70 lbs *more* to compress it the third inch.
So, 180 lb to compress it 3 inches.

Where were you when I needed you? 

In my mind (say what you will about it...) this is clear and obvious. The term "linear" is weak IMO - the resistance's growth might be linear (?), but the resistance itself is growing and could just as well be called.... progressive? 

<whispering>

Should I tell them that the rear suspension linkage is progressive?

</whispering>

I know, and I just might get back to you on that. Don't like it an will refuse to accept 

...and your ass will never feel the nuances of linear springs becoming 'somewhat progressive'.

Just so we're clear - you don't know what my ass is capable of. 

[junior varsity]

Where were you when I needed you? 

In my mind (say what you will about it...) this is clear and obvious. The term "linear" is weak IMO - the resistance's growth might be linear (?), but the resistance itself is growing and could just as well be called.... progressive? 

Linear is a perfect word for its behavior - draw a graph: x-axis is compression; y-axis is force required - the line plotted would be linear - old school y=mx+b function.

Progressive would be behave differently - it would curve.

Speeddog's breakdown is way more concise than mine. However, I thought only some of the suspensions had a progressive linkage?

[scott_araujo]

In my mind (say what you will about it...) this is clear and obvious. The term "linear" is weak IMO - the resistance's growth might be linear (?), but the resistance itself is growing and could just as well be called.... progressive? 

It's a math thing.  Throwing aside the slight progressive nature of all springs, if you plot compression vs. force for a linear spring on a graph you get a straight line.  For example with a 1# per inch spring, 1" compression = 1# of force, 2" = 2# of force, 3" = 3#, etc.

Now with a progressive spring you might get something like 1" = 1#, 2" = 3#, 3" = 5.5#, etc.  Plot that and you get a curve with a steeper slope as you apply more pressure.

Scott

[ajw85]

This thread is awesome, thanks guys.
Too bad I bought a sachs 748 shock and not a showa 748 shock.

[junior varsity]

meh. look into racetech valving or something and be done with it.

Sure the fancier oem shocks have benefits, but a person can change the internals of the shocks, leaving the exterior as a mere housing and have something quite nice.

[Speeddog]

~SNIP~

However, I thought only some of the suspensions had a progressive linkage?

SBK and ST-framed Monsters ('01 S4, all '02 and later with linkages) have progressive linkages.

851/hoop framed Monsters may have *some* progression.
I haven't done actual measurements on one, but the rocker is quite long, so I suspect not much progressivity.

[Armor]

Spring force will also change if the shock is mounted on an angle.  As the swingarm goes up, the angle of the shock decreases which changes the force on the wheel.

[stopintime]

Spring force will also change if the shock is mounted on an angle.  As the swingarm goes up, the angle of the shock decreases which changes the force on the wheel.

Maybe that's what the linkage is for - to counter that effect?

[koko64]

Time to threadjack the threadjack!

SBK and ST-framed Monsters ('01 S4, all '02 and later with linkages) have progressive linkages.

851/hoop framed Monsters may have *some* progression.
I haven't done actual measurements on one, but the rocker is quite long, so I suspect not much progressivity.

How much difference in progression is there between the ST/SBK linkage and the 851/888 hoop type linkage? I have heard/read two quite different stories about this from different suspension people.

One guy said that the ST linkage was fitted to make it "more supple" compared to the hoop linkage while another guy said that the hoop linkage was regressive at the last part of the shock stroke! The last comment was from a suspension guy who worked on 888 Corsas.

Did the factory change the linkage much from 888 to 900M?



Can anyone clarify/verify?

[ducpainter]

Time to threadjack the threadjack!

How much difference in progression is there between the ST/SBK linkage and the 851/888 hoop type linkage? I have heard/read two quite different stories about this from different suspension people.

One guy said that the ST linkage was fitted to make it "more supple" compared to the hoop linkage while another guy said that the hoop linkage was regressive at the last part of the shock stroke! The last comment was from a suspension guy who worked on 888 Corsas.

Did the factory change the linkage much from 888 to 900M?



Can anyone clarify/verify?

I'm fairly certain the linkage and rocker are the same between the 851/888 and M models with the hoop.

I know the parts will fit either bike, but I'm not certain all the rocker lengths are identical.

[battlecry]

Nate, that's probably true on the bikes imported into the States, but the Strada and the S.P.O. or S.P.5. versions had different rockers.  The S.P.O/5 frames had an adjustable eccentric in the rocker to change the linkage geometry through the Ohlins rear shock attachment point.  The Strada just straighbolted the Showa shock to the rocker.  Don't know how many of those made it here.

This fellow wrote a nice description of the S4R rear, and included some measurements:

http://www.ducatisti.co.uk/forum/technical-help/42566-s4r-rear-suspension.html

</threadjack>

[ducpainter]

Nate, that's probably true on the bikes imported into the States, but the Strada and the S.P.O. or S.P.5. versions had different rockers.  The S.P.O/5 frames had an adjustable eccentric in the rocker to change the linkage geometry through the Ohlins rear shock attachment point.  The Strada just straighbolted the Showa shock to the rocker.  Don't know how many of those made it here.

This fellow wrote a nice description of the S4R rear, and included some measurements:

http://www.ducatisti.co.uk/forum/technical-help/42566-s4r-rear-suspension.html

</threadjack>

I realize that.    I've seen the adjustable rocker, one on a Monster even, and should have mentioned it.

I guess I was just speaking to the Strada, and the fact the parts will bolt to all the bikes.

[battlecry]

nah, we're just getting ancient