Speed sensitive or position sensitive or both

[couchrider]

I have been reading some of the past threads and might say I am a little confused on the issue of speed sensitive and position sensitive dampaning. After reading these threads just about everyone states that in the dirtbike world the forks and shocks are speed sensitive. Were I get confused on this issue is statements like " riding in the stiffer part of the stroke " or "riding lower part of the travel creating a harsh feeling " To me with statements as such I would tend to think that this is some what of position sensitive situation. If it was just a speed situation would the shock or fork not care were in the travel it might be. I would like to here some comments on this if possible.

 

[JTT]

Remember that with shocks they use a progressive linkage arrangement (with exception of KTM). This does become "position sensitive" as the ratio of wheel travel to shock travel changes slightly during the stroke.

 

[couchrider]

Ok I can see the issue with the shock but what about the forks!

 

[marcusgunby]

The forks have a rising rate spring in the use of the airgap in the fork-when the fork is compressed the airgap becomes smaller and the stiffness increases dramatically.The damping is speed sensitive but the spring is position sensitive.

JTT not to catch you out;) but the KTM does have a progression-just not as steep as a jap bike-i will send you a word doc to show the difference, i tried to post it here but it wont work:((

 

[couchrider]

So if you were to build the valving stack, you would have to consider for the rear the rising rate of the linkage. Would this also be a consideration in the forks also based on the oil levels of the fork. If so where can you find such info of these rising rates

 

[JTT]

Oops...I was not meaning to infer that KTM wasn't rising rate, just that they didn't have a linkage. I just didn't want to try to explain how PDS works :eek: ...particularly when I don't understand it myself :laugh:

...and yes, the linkage is taken into account when valving, as is the air gap to a degree. The oil level adds a "quick fix" to some bottoming issues.

 

[marcusgunby]

:)

 

[marcusgunby]

we can talk of the pds system design if you want:) especially now it has reverted to its 98 original design-makes me laugh.

 

[russ17]

From my understanding the ktm uses the secondary piston for bottoming Kind of a fixs for the no link

Russ