How Do Rear Lowering Springs Work??

[skooter65]

I was hoping someone had some experience in the installation of a HyperPro or equivalent shock lowering spring.

Now I understand that a 30mm shorter spring is going to effectively reduce the seat height by ~30mm. However, how does the kit account for preload of the spring, and the lost travel range of the shock damper? Think of it this way: the stock spring pushes against the captive ends of the shock damper. The only reason that the cylinder and rod side do not separate is due to internal stops in the shock damper. These stops limit the total length, eye-to-eye, of the cylinder/rod assembly. Now, If you remove 30mm from the spring, wouldn't the shock damper still be able to travel to the original eye-to-eye length; essentially leaving a 30mm gap from the top of the spring???

Does this make sense? From what i can tell, there are no modifications to the shock housing itself with the lowering spring install.

???

Update: I added a spectacular Paint-o-shop photo which might help explain what I am asking.

 

[FinalImpact]

I am not the expert on this but I will point out a couple of things:
1) yes, you are bound to the original shock body dimensions relating to rear suspension travel. That is the collapsed and fully extended shock body are the same as before. If the spring were to completely collapse during compression, the bike can not go any lower than the limit of the rubber bumper on the shocks shaft (same as before).

2) The 30mm difference in installed height likely will not correlate to a 30mm drop on seat height as there are mechanical pivots involved. Meaning your bike will not settle 30mm due to pivot points, arm length and load added.

Its very likely the new coil has a higher spring rate (increased coil diameter) making it harder to compress when the same load is applied. Meaning, the original spring will compress easier and potentially settle a greater distance from the same load. Because the installed height of the new spring is physically shorter, the bike will likely have a lower stance and squat less under the same load. But this all depends on the spring rate which is largely governed by coil diameter and tempering of the spring.

Does that make sense?

Are you planing to address the front also or did you already?

EDIT: looking at the picture: you can see you lost one full coil from the stack. If the rate is unchanged (minimal to no coil diameter increase), the ride will be lower and softer. And yes, when you center stand the bike, the coil will likely be free as it is in the picture. This isn't a big deal unless you ride in a manner that completely unloads the rear like jumping it. Then the rebound dampening of the shock could allow the spring to rattle around until the suspension returns to its normal ride height.

 

[skooter65]

After doing some more research, looking at my shock assembly, and talking with another spring manufacturer; I am about ready to throw the B.S. flag on the functionality of HyperPro's "lowering" spring.

I know a few here have them installed; I would be curious to know if:

1): Actual seat height has been checked with the spring installed
2): What happens to the shock when the bike is placed on the centerstand.

I will wait to give my thoughts until I get some feedback...maybe i am out in left field (which happens often)

 

[Motogiro]

I would think the shock body would be shorter as well as the spring. If you think about the compression travel as you have it Photoshopped it would bottom out prematurely. So I'm imagining a lowering shock also having a different dimension, spring and total travel.

 

[skooter65]

I am not the expert on this but I will point out a couple of things:
1) yes, you are bound to the original shock body dimensions relating to rear suspension travel. That is the collapsed and fully extended shock body are the same as before. If the spring were to completely collapse during compression, the bike can not go any lower than the limit of the rubber bumper on the shocks shaft (same as before).

2) The 30mm difference in installed height likely will not correlate to a 30mm drop on seat height as there are mechanical pivots involved. Meaning your bike will not settle 30mm due to pivot points, arm length and load added.

Its very likely the new coil has a higher spring rate (increased coil diameter) making it harder to compress when the same load is applied. Meaning, the original spring will compress easier and potentially settle a greater distance from the same load. Because the installed height of the new spring is physically shorter, the bike will likely have a lower stance and squat less under the same load. But this all depends on the spring rate which is largely governed by coil diameter and tempering of the spring.

Does that make sense?

Are you planing to address the front also or did you already?

I think we are somewhat on the same page; but maybe my original point did not come across clearly.

The Hyperpro spring is advertised as "lowering" the bike for people of shorter stature by reducing the overall length of the spring. Makes sense, shorter spring allows the shock body to "collapse" further before the spring begins to compress. As you said, it is not exactly 1mm decreased spring length for 1mm seat drop (although pretty close with the FZ as there are no linkages and the shock is mounted nearly vertical).

Also agreed that the Hyperpro will likely compress harder due to higher spring rates. However, this is a bit off the topic that I was hoping to address.

My point was, if the spring is shorter, and the shock body can still extend to the OEM eye-to-eye length; then what is holding the spring in a "compressed" state at full damper extension? It seems to me that if you were to put the bike on the centerstand, the rear wheel would drop until the internal damper stops bottomed out, and the spring would be free to move around.

And yes, my front has been slightly lowered due to a fork swap and now I am trying to balance the front & rear geometry. My eyes are set on an adjustable length aftermarket shock; however, my wallet can't take the hit at the moment.

Thank you for the feedback!

 

[skooter65]

I would think the shock body would be shorter as well as the spring. If you think about the compression travel as you have it Photoshopped it would bottom out prematurely. So I'm imagining a lowering shock also having a different dimension, spring and total travel.

That is what i would expect as well but, the Hyperpro kit comes only with a spring. From what I can tell by reading the installation notes of a few forum members, they only removed the old spring and installed the new without any modification to the shock body.

On the other point, I think the "bottoming out" is accounted for by higher spring rates. But, there has to be a loss in overall travel.

 

[FinalImpact]

Yes, you have lost a usable amount of travel as you are starting with lower ride height. One fix for this is to use the stock spring and shock and move the mounting point on the bike to lower it (cutting, welding, serious modifications). Example: Like sliding the front fork tubes up the clamp. It lowers the bike and uses the same hardware and spring/dampening rates.

Yes, if you suspend the in the air so the rear tire is "unsprung", the spring will be unloaded and free as your picture.
"....what is holding the spring in a "compressed" state at full extension?"
Answer = nothing is holding it. In the race world where anything can happen they would use a limiting strap to ensure it doesn't happen as you never want a coil over spring to be completely unloaded as some can come apart in these conditions. This would not be good!

As I mention above; if you jump the bike this could happen depending on the time in the air and the rebound dampening rate. Example: Lets say the shock controls rebound by allowing the shock to extend at a rate of 1" for every 1second. If you tire leaves the ground for 2 seconds the spring could be free to float around. This may or may not have serious implications. Overall, I don't like the sound of it and it should have a limiting device installed to prevent extension beyond a point where the spring is free to float.

Granted it is unlikely most of us will jump our bikes, its not like scene in a 007 movie with air time so most riders will be OK with this setup.

Does that help?

If you want to investigate further try this: Remove the spring from the shock. Install the shock into the bike. Move the rear swing arm through its entire range of motion bottoming and topping out the shock. That is the effective travel as Yamaha designed it. Measure from the rear axle bolt to the frame the two stopping points. Remove the shock. Now move the swing arm through the entire range of motion again noting where the tire hits the fender, where it binds, chain angles and other unexpected collisions. . . blah blah blah.
Can you get more usable travel than the Yamaha engineers gave it? Probably not too much I suspect. So even if you replace the coil over shock assembly, there are still other limitations to consider. Lowering the lower shock mount or raising the upper shock mount will lower the bike using the stock shock assembly. But there will be trade-offs in travel.
Here is something else to consider; lower profile tires will get you down also. but once again, more trade offs! :/

 

[skooter65]

Yes, you have lost a usable amount of travel as you are starting with lower ride height. One fix for this is to use the stock spring and shock and move the mounting point on the bike to lower it (cutting, welding, serious modifications). Example: Like sliding the front fork tubes up the clamp. It lowers the bike and uses the same hardware and spring/dampening rates.

Yes, if you suspend the in the air so the rear tire is "unsprung", the spring will be unloaded and free as your picture.
"....what is holding the spring in a "compressed" state at full extension?"
Answer = nothing is holding it. In the race world where anything can happen they would use a limiting strap to ensure it doesn't happen as you never want a coil over spring to be completely unloaded as some can come apart in these conditions. This would not be good!

As I mention above, if you jump the bike this could happen depending on the time in the air and the rebound dampening rate. Example: Lets say the shock controls rebound by allowing the shock to extend at a rate of 1" for every 1second. If you tire leaves the ground for 2 seconds the spring could be free to float around. This may or may not have serious implications. Overall, I don't like the sound of it and it should have a limiting device installed to prevent extension beyond a point where the spring is free to float.

Granted it is unlikely most of us will jump our bikes, its not like scene in a 007 movie with air time so most riders will be OK with this setup.

Does that help?

I am not sure if this helps or not.

It seems that your and my understanding are similar; I am just surprised that a company would provide a kit which could yield and unrestrained spring. Honestly, I am still a little skeptical that they do.

I know you say that load will only be removed by "jumping" the bike; but that is not 100% true. There are multiple occasions including, heavy braking, emergency braking, corner exit, whoops/sharp declines in the road, which often completely unload the rear shock. I'm not sure if you have had the spring off the damper on the FZ before, but the compression/rebound rates leave alot to be desired.

I appreciate the feedback and I still hope that someone with this set-up will chime in. Maybe they are including a new lower shock support of decreased length...?? Doubtful, as lowering links usually cost more than the advertised price for the spring.

 

[FinalImpact]

I am not sure if this helps or not.

It seems that your and my understanding are similar; I am just surprised that a company would provide a kit which could yield and unrestrained spring. Honestly, I am still a little skeptical that they do.

I know you say that load will only be removed by "jumping" the bike; but that is not 100% true. There are multiple occasions including, heavy braking, emergency braking, corner exit, whoops/sharp declines in the road, which often completely unload the rear shock. I'm not sure if you have had the spring off the damper on the FZ before, but the compression/rebound rates leave alot to be desired.

I appreciate the feedback and I still hope that someone with this set-up will chime in. Maybe they are including a new lower shock support of decreased length...?? Doubtful, as lowering links usually cost more than the advertised price for the spring.

Agreed, you are 100% correct -there are many ways to unload it!
My question is, will it always go back together the same way. If the answer is no, I would send it back. The shocks spring retainer can come off or change adjustment when the spring is unloaded, send it back. Can you adjust the collar down to remove the free space?

 

[dean owens]

few things. maybe i don't fully understand how the rear shock works but i see it as two opposing forces. the shock body has a stem coming out of it. that is trying to pull the eyes as close as they can to each other. the other part is the spring. it is trying to push the eyes as far apart from each other. i'm pretty sure if you took the spring off your "shock" would be a lot shorter. it has a pretty good pull on it. i think there is enough pull to make up the difference in a shorter shock.

but if i'm wrong, there's another option for shortening the rear end... actually there are two.
Lowering Kits / Suspension Links for Motorcycles. Wild Hair Accessories. Motorcycle Accessories & Aftermarket European Parts.
this one is buying a piece of aluminum to replace the "eye" on the "post". it's expensive for what it is and the original eye is a pain in the rump to remove.
see
http://www.600riders.com/forum/fz6-mods/1295-lowering-kit-2007-fz6.html
http://www.600riders.com/forum/fz6-mods/6037-metisse-lowering-kit.html

your other option is to get a whole new shock. you can get a wilber shock as low as 1.5 inches lower. but i'm sure it'll be pretty pricy.
see
High performance motorcycle suspension price quote form from EPM Performance Imports

 

[skooter65]

few things. maybe i don't fully understand how the rear shock works but i see it as two opposing forces. the shock body has a stem coming out of it. that is trying to pull the eyes as close as they can to each other. the other part is the spring. it is trying to push the eyes as far apart from each other. i'm pretty sure if you took the spring off your "shock" would be a lot shorter. it has a pretty good pull on it. i think there is enough pull to make up the difference in a shorter shock.

but if i'm wrong, there's another option for shortening the rear end... actually there are two.
Lowering Kits / Suspension Links for Motorcycles. Wild Hair Accessories. Motorcycle Accessories & Aftermarket European Parts.
this one is buying a piece of aluminum to replace the "eye" on the "post". it's expensive for what it is and the original eye is a pain in the rump to remove.
see
http://www.600riders.com/forum/fz6-mods/1295-lowering-kit-2007-fz6.html
http://www.600riders.com/forum/fz6-mods/6037-metisse-lowering-kit.html

your other option is to get a whole new shock. you can get a wilber shock as low as 1.5 inches lower. but i'm sure it'll be pretty pricy.
see
High performance motorcycle suspension price quote form from EPM Performance Imports

You are a little off on the workings of the rear shock.The rear shock and the front fork on our bikes are not all that much different from on another. They each have a spring and a damper. As you said, the spring is trying to force the eyes of the shock further apart from one another (Similarly to the front fork spring pushing the fork tube away from the axle). On the other hand, the damper portion is just that, a damper. There is a piston inside the cylinder which pushes fluid through a series of small valves. As the spring compresses and tries to "rebound", the fluid is forced through the small orifice in the valve providing resistance, thereby dampening the rate of return of the spring (This works on compression as well). However, if you remove the spring and pull/push on the damper assembly, it will stay is whatever place that you let go of the rod. Our bikes do not have a accumulator style gas chamber that provides positive force in either direction.

That said, I am hoping to use one of your other options (Aftermarket shock:sinister but need to save a few bucks beforehand. For the time being, I was thinking of getting a lowered spring so I can balance the height of the front and rear of the bike with my new forks installed.

What red flagged me, was when two spring vendors said that they have no such thing as a "lowering" spring and that the only way to properly lower the rear of the bike is to adjust the linkage/shock body.

And...here we are!

 

[Senior]

all the above is very interesting . . . .

however there is another way to lower the bike . . . . which is how mine came from it's previous owner.

looking at the picture, in the first post, at the right end of the shock (which will be fitted at the bottom on the swing arm) the eye connecting part that screws onto the shaft of the shock, it is possible to shorten this and re-drill and tap the hole and refit on to the shock shaft. You now have a lower rear end, so next push the fork legs up through the yoke and you have a lowered FZ6.

and nearly forgot the side stand will also need to be shortened if lowering with this method.

I've still got the original lower shock mounting link and side stand, as the mods were done to spares that were obtained, so it can all go back stock if needed :thumbup:

hopefully from the photos you can see its lower when on the side stand, but does look a bit "odd" on the centre stand because the rear wheel so high above the ground and the last photo show the forks through the yoke . . .

http://www.600riders.com/forum/atta...lowering-springs-work-rearshockcomparison.jpg

I'll do some measuring tomorrow if you want . . . .

 

[skooter65]

all the above is very interesting . . . .

however there is another way to lower the bike . . . . which is how mine came from it's previous owner.

looking at the picture, in the first post, at the right end of the shock (which will be fitted at the bottom on the swing arm) the eye connecting part that screws onto the shaft of the shock, it is possible to shorten this and re-drill and tap the hole and refit on to the shock shaft. You now have a lower rear end, so next push the fork legs up through the yoke and you have a lowered FZ6.

and nearly forgot the side stand will also need to be shortened if lowering with this method.

I've still got the original lower shock mounting link and side stand, as the mods were done to spares that were obtained, so it can all go back stock if needed :thumbup:

hopefully from the photos you can see its lower when on the side stand, but does look a bit "odd" on the centre stand because the rear wheel so high above the ground and the last photo show the forks through the yoke . . .

http://www.600riders.com/forum/atta...lowering-springs-work-rearshockcomparison.jpg

I'll do some measuring tomorrow if you want . . . .

I was actually wondering if anyone had actually done this before. there is alot of extra material on the lower connector. I may end up going this route. Thank you for the confidence inspiring inspiration

 

[Zzzz]

Keep in mind that if you are planning on cutting down the 'eye' as I plan to, that you can only remove about 6mm from this linkage - if you remove any more, the base of the damper will actually butt up against the swingarm assembly. Now I've just gotta find that little piece, for a reasonable price to australia.