Long vs short shock spring?

[BK_856er]

Great discussion, especially on the length topic from Nick.  My understanding is that shorter is fine as long as the stroke for a particular application doesn't start to cause binding.  Not sure how to know that in advance or figure it out without testing in a jig.

Ideally you want three measurements to help determine the right rate:  rider sag, free sag and preload.  Preload is the mm the spring is compressed when installed.

On my M695, which has the same parts as the S2R800, with ~160lb rider I had an Ohlins DU321 shock (aka, 46DR) with a 542lb spring p/n 1091-31/95.  I purchased it new from Jason at Dept. of Suspension (is he still around?) and he valved/sprung it based on my inputs and his Ducati experience.  Worked really well, but I eventually wanted full adjustability.

Later I changed to a Penske 8987 and had a chance to trial 500#, 575#, 600#, 625# springs (blue Hyperco).  It was their first M695 and the 500# was an error.  With the heaviest spring I was getting 15mm preload and 7mm free sag and 31mm rider sag.  The two heavier ones worked well for my application/preferences (and upgraded forks).

FWIW, I hear many suspension tuners measure and sort the springs since they can/do vary.  My blue ones were engraved with the measured value on the end of the coil - can only see it with the spring removed.

BK

[manwithgun]

On my M695 (same geometry as the S2R800) and ~160lb rider I had an Ohlins DU321 shock with a 542lb spring (part 1091-31/95).  I purchased it new from a knowledgeable distributor and went with their spring recommendation - can't recall, but likely Dan Kyle.

Later I changed to a Penske 8987 and had a chance to trial 500#, 575#, 600#, 625# springs (blue Hyperco).  It was their first M695.  With the heaviest spring I was getting 15mm preload and 7mm free sag and 31mm rider sag.  The two heavier ones worked well for my application/preferences (and upgraded forks).

FWIW, I hear many suspension tuners measure and sort the springs since they can/do vary.  My blue ones were engraved with the measured value on the end of the coil - can only see it when removed.

BK

At 165lbs, I was happy with a 600# spring (105nm) on the S2R800, which is also in line with the chart That is linked to from Ducati Up North.   

It's common for people to over-preload a spring that is too light and think that they are good, having achieved proper rider sag.   The lack of static/free sag unsettles the bike under heavy braking while still blowing through travel when loaded through a corner...   Not a real solution.  And I'm sure we've all heard it before but might as well toss it into this suspension thread!

Regarding spring length,  if you take a spring at a given rate and cut it shorter,  you have just made it stiffer by reducing the number of active coils. 

[BK_856er]

At 165lbs, I was happy with a 600# spring (105nm) on the S2R800, which is also in line with the chart That is linked to from Ducati Up North.   

It's common for people to over-preload a spring that is too light and think that they are good, having achieved proper rider sag.   The lack of static/free sag unsettles the bike under heavy braking while still blowing through travel when loaded through a corner...   Not a real solution.  And I'm sure we've all heard it before but might as well toss it into this suspension thread!

Regarding spring length,  if you take a spring at a given rate and cut it shorter,  you have just made it stiffer by reducing the number of active coils. 

Exactly, that's why it's best to refer to all three values:  rider sag, free sag and pre-load.  Those will tell most of the story.  The rest is preference/road surface/riding style.

That link brought back memories.  Section8 = Dept. of Suspension = Jason.  Lots of colorful characters in the suspension world.

BK

[Moronic]

I'm just 20% less than that.... 


IIRC the sag numbers were ok (~30 something mm), but I can't verify that the spring was 150N. It's just what I was told by the suspension guy. It wasn't very compliant - I remember that. Maybe I had little preload to get ~30mm rider sag and the rest was on the (too) firm side.

Okay now I understand. Glad if I have been of some help.

Yes, it seems to me that people suggesting the 120N/mm spring for you are about right. Again as other people have said the linkage on these bikes gives you a lot of leverage near the top of the stroke, so the small-bump compliance will be there.

I doubt very much you will need more than that. I had a custom dual seat and had made up a rack that supported a big tail bag, so that two of us could go on trips with the Monster. Even two-up with the 115 spring, and probably carrying another 10kg behind, it was very rare that we used all the travel. And that included some speedy riding on quite rough roads. (The Ohlins shock we used did have nice compression tuning, however.)

Solo of course you tend to go a bit harder than two-up. OTOH the balance of your weight is further forward.

So I believe you could order a 120 spring with confidence that it will not be too light. Then if over time you found you never used all the travel, you could go a bit softer. It has surprised me how much difference 5N/mm makes to the ride quality.