OVER SPRUNG REAR SHOCK; what to expect?

[justplainbill]

are you throwing darts at a board? In one post you claim 650lb/in is "right" for your weight, and then observing that the ride from the OE 560 is jarring, you thought going with a 450 would improve matters? 
harsh ride isn't about spring really, it's about valving. A weaker spring leads to more travel per the same bump so stresses the damping more. on the other extreme a too stiff spring behaves 'rigid' even though the damping is no longer the problem as such.
 
The spring supports the weight/load. Damping controls movement rates. If movement is the problem chasing springs is the wrong answer. Now I realize I'm simplifying a bit since they both work in tandem. 

 
Actually Matt, I said a 650 lb/in spring was "recommended" for my weight.  Since I will be changing to a shock having a spring with a much higher than recommended spring rate, the fact that a harder (than recommended) spring would make a harsh ride convinced me to purchase the recommended spring. And, as you point out, with two damping adjustments with the new shock, I hope to get the ride smoothed out using damping, once I have the spring rate optimized for my weight.
 
My remark about the 450 lb/in spring was in response to your comment that you thought a 733 lb/in spring would give a harsher ride was a given. As they say, never underestimate the ignorance of your audience.  It wasn't a given to me - that's why I originally asked what to expect from an over-sprung shock.  But if it had been a given for me, the logical thing to do when my shock with a 560 lb/in. gave a harsh ride, would be to lower the spring rate to get a softer ride.  Note that I did not accept that logic - I followed the recommendation to use a 650 lb/in spring, understanding that I don't know enough about this stuff to trust what seem logical to me - a suspension novice.
 
Thanks for you input Matt, I appreciate and learn from it.
 

[norwest]

I measured a Eibach 8" 2.25" ID spring and the ID is actually 2.3". Did you measure the stock spring with a tape measure or a caliper? IMO .050+ is not acceptable in side to side play. I thought I had a busa shock laying around here so I could measure the oem spring but it is playing hide and seek with me and it is winning.

[xlxr]

First step in setting up suspension is getting the correct spring and static rider sag to match your weight. Then the second step is getting the correct dampening curves to match the spring. Dampening curves can be considered fine tuning of the spring rate. If your spring is bit too stiff, lighten up compression dampening and increase rebound dampening. If your spring is a bit too light, increase compression dampening and reduce rebound dampening. If the spring rate is way too far off, no amount of dampening can compensate. The ability to do this correctly is what makes a good suspension tuner well worth what ever they charge.
 
Sounds like you are well on the way to learning basic facts of suspension - trail and error takes a lot of effort to get it right.
 
I weigh 270 lbs in gear, I have a 650 lb shock spring.  With hydraulic adjuster installed on the shock and all preload set to absolute minimum, I get about 1 1/4" rider sag, which is also about minimum rider sag needed.  However, I am working with a different brand shock and spring.
 
So, if changing to a lighter spring, start with setting preload to get proper rider sag.  (If you cannot get rider sag correct, 1/3 to 1/4 total travel, get the correct spring.)  Then start with max compression dampening settings, minimum rebound dampening settings.  And move them to the middle as needed after test riding.  If you cannot find a happy medium, then send the shock off to get revalved to match that spring.
 
Going to a lighter spring does not ensure a less harsh ride if the high speed compression dampening is way too stiff, but you are going in the opposite direction.
 

[norwest]

I thought the damper controlled spring oscillation.
 

[norwest]

justplainbill,
 
What do you weigh w/o gear?

[xlxr]

I thought the damper controlled spring oscillation.

Very true, I was just explaining things in a slightly different manner to help the OP understand ........ 
he might as well send his shock to you first.
 

[norwest]

Something I had awhile back that shows a lighter rate spring with more preload vs a heavier rate spring with less preload.
 
Notice in this example that the heavier rate with less preload is actually more compliant at low suspension velocities.
 

 

[xlxr]

This illustrates that going to a lighter spring does not mean a softer rider over smaller road bumps if high speed compression dampening is way too stiff and/or you have to add too much preload to get the proper rider sag.

[norwest]

I setup that graph to show a member on another forum that going to a stiffer spring does not mean a stiffer ride at lo speed velocities. Also to point out that just because you can achieve rider sag with a spring with a rate of x does not mean it will be correct. Yes you are correct as the lighter rate spring will actually be stiffer at lo speed velocities then the higher rate spring. Damping is not shown in that graph as it is only spring force.

[justplainbill]

justplainbill, 
What do you weigh w/o gear?

 
I'm 197 wet...add 20 lbs for gear -- and 15 lbs for optional Yamaha saddlebag and rear trunk mounting hardware (including the trunk) , which should be counted as they are always on the bike. 
 
 
 

[norwest]

justplainbill, 
What do you weigh w/o gear?

I'm 197 wet...add 20 lbs for gear -- and 15 lbs for optional Yamaha saddlebag and rear trunk mounting hardware (including the trunk) , which should be counted as they are always on the bike.  
 

Yeah sounds like you are on the money with spring selection, Give it 8mm preload and that should put you right in the correct sag range. You may have to back the rebound out a bit since you went to a lighter rate spring. 
Looking at my past work with a Hayabusa shock the stock compression is considerably stiffer then the stock FJ-09 shock compression damping. But if in ones mind they already have it that it is going to be better then it is going to better.
 

[justplainbill]

I measured a Eibach 8" 2.25" ID spring and the ID is actually 2.3". Did you measure the stock spring with a tape measure or a caliper? IMO .050+ is not acceptable in side to side play. I thought I had a busa shock laying around here so I could measure the oem spring but it is playing hide and seek with me and it is winning.

I had not heard of "side to side play" before Norwest and gather it has to do with the length of the spring, it's ID and (maybe) the chance that a long spring might flex side to side without a collar (sleeve?) extending into the spring to control the flex.  I also have no idea what kind of handling or other consequences might arise from excessive side to side play.      
Anyway, my Busa spring and shock were still together, so I removed the spring to get accurate measurements (telescope gauge & caliper). 
Spring length: 195 mm (7.68")
Spring ID: 57 mm (2.24")
Shock body diameter: 48 mm (1.9")  (un-threaded portion)
 
As to the difference between the OEM Busa spring and Eibach, it's 0.055". Will that require a collar and both ends? 
 
 
 
 
 
 
 
 
 
 
 

[justplainbill]

Actually Norwest, I'm not quite that suggestible. There's a dirt road a quarter mile from my front door that is pounded daily by trucks, quads, and dirt bikes into one of the best suspension test tracks you can imagine and I use it to test changes to my suspension as they are made.  With all those stutter bumps, rocks and various depth potholes I have plenty of opportunities to assess impacts at both ends of the bike.  And I have learned to stop and take notes on setting changes and effects.  
 
Because of my advanced age and natural caution (that's how I got to be this old), high speed handling isn't much of an issue and I focus on reducing pain more than going around corners.  If the Busa shock doesn't improve on the FJ shock it will find itself in a UPS box on the way to getting whatever help you or Matt can provide.
 
Thanks,

 

[justplainbill]

First step in setting up suspension is getting the correct spring and static rider sag to match your weight. Then the second step is getting the correct dampening curves to match the spring. Dampening curves can be considered fine tuning of the spring rate. If your spring is bit too stiff, lighten up compression dampening and reduce rebound dampening. If your spring is a bit too light, increase compression dampening and reduce rebound dampening. If the spring rate is way too far off, no amount of dampening can compensate. The ability to do this correctly is what makes a good suspension tuner well worth what ever they charge.  
Sounds like you are well on the way to learning basic facts of suspension - trail and error takes a lot of effort to get it right.
 
I weigh 270 lbs in gear, I have a 650 lb shock spring.  With hydraulic adjuster installed on the shock and all preload set to absolute minimum, I get about 1 1/4" rider sag, which is also about minimum rider sag needed.  However, I am working with a different brand shock and spring.
 
So, if changing to a lighter spring, start with setting preload to get proper rider sag.  (If you cannot get rider sag correct, 1/3 to 1/4 total travel, get the correct spring.)  Then start with max compression dampening settings, minimum rebound dampening settings.  And move them to the middle as needed after test riding.  If you cannot find a happy medium, then send the shock off to get revalved to match that spring.
 
Going to a lighter spring does not ensure a less harsh ride if the high speed compression dampening is way too stiff, but you are going in the opposite direction.

Getting the spring rate and sag right as the first step is pretty much what I'm trying to accomplish at this stage.  As you and Norwest have shown, there is a lot of counter-intuitive s**t going on with springs and spring rates. Better to learn it here than after hours of wasted effort.  What happens with valving and damping will come next.
 
Thanks, 
 
 

[norwest]

I measured a Eibach 8" 2.25" ID spring and the ID is actually 2.3". Did you measure the stock spring with a tape measure or a caliper? IMO .050+ is not acceptable in side to side play. I thought I had a busa shock laying around here so I could measure the oem spring but it is playing hide and seek with me and it is winning.

I had not heard of "side to side play" before Norwest and gather it has to do with the length of the spring, it's ID and (maybe) the chance that a long spring might flex side to side without a collar (sleeve?) extending into the spring to control the flex.  I also have no idea what kind of handling or other consequences might arise from excessive side to side play.      
Anyway, my Busa spring and shock were still together, so I removed the spring to get accurate measurements (telescope gauge & caliper). 
Spring length: 195 mm (7.68")
Spring ID: 57 mm (2.24")
Shock body diameter: 48 mm (1.9")  (un-threaded portion)
 
As to the difference between the OEM Busa spring and Eibach, it's 0.055". Will that require a collar and both ends? 
 
 
 
 
 
 
 
 
 
 
 

I would personally run a collar on both ends but I have seen others just skip it, Ex machinist so I am a bit anal when it comes to side clearances. Is it going to hurt anything to not run them? Probably not.