Racetech Shock Spring

[chemicalsmile]

I'm trying to get rid of the mushiness of the rear by stiffening it up a bit. I feel like it's really taking a beating with the stiffened front and I find the rear really tucks in midcorner which makes holding a line hard because I lose ground clearance and/or lean angle. It's not a big deal on the tight stuff but in high speed sweepers (90% of local roads) it's really prominent.

Also, I'm doing the swingarm maintenance so I figured I might as well try this while I'm tearing the rear down.

I saw that thread.....I agree, although can of worms wouldn't be my word for it

According to RT and a few other places, the stocker can be rebuilt/revalved so failing this, I'll probably go that route.

 

[FinalImpact]

I think there is a misunderstanding of what you need and what you're doing.

Spring load capacity sets the bikes carrying ability. Measuring the SAG will help determine how your current spring is performing in regards to the load placed upon it. i.e. how far does it settle.

Setting the ride height on our bike with the STOCK OEM shock is done by changing the preload. Reducing the space between the two spring perches reduces the amount the bike drops when a load is applied.

In the ideal world, we could change the length of the shock assembly effectively making the distance between the eyelets longer. Picture adding a turnbuckle to the end of the shock so we can change the total length of the shock without changing the space where the spring is installed (installed spring height). This would change the ride height while keeping the springs preload the same.

Specifically to address your problem:
The spring is just a spring. THe question is can it carry the load at the desired ride height? If yes, now we need to know if it matches the other end of the bike. If both are OK, we need to address how much damping control we have. If it compresses to quickly the bike will feel squirelly as the nose will seem light when the back settles too fast. If after being compressed the seat shoots upward hitting you in the rear, you need more rebound control. To much rebound control and the bike packs down over repeated bumps.

IMO the the bike in stock trim had horrid spring rate matching front to rear. Adding to that, the nose compresses at too fast of rate compared to the rear. This leads to rocking horse effect when you hit a bump or sink hole in a corner. Because the spring rates differ. Meaning, with me as part of the bikes mass, the nose compresses twice as far as the rear given the same load applied. Add to this, it collapses at nearly twice the rate (Exaggerating here). These compromises the riders control during cornering and braking.

How much do you weigh?

 

[FinalImpact]

I'm trying to get rid of the mushiness of the rear by stiffening it up a bit. I feel like it's really taking a beating with the stiffened front and I find the rear really tucks in midcorner which makes holding a line hard because I lose ground clearance and/or lean angle.

This sounds like damping control issues vs spring rate issues.

It's not a big deal on the tight stuff but in high speed sweepers (90% of local roads) it's really prominent.

I saw that thread.....I agree, although can of worms wouldn't be my word for it

I have time to experiment and for me, handling and skills to ride smoothly (no matter what the conditions are) is more important than power so this is where I'll play and learn what I can.

According to RT and a few other places, the stocker can be rebuilt/revalved so failing this, I'll probably go that route.

It can and there are links to it. The R1 option is cheap, it installs without chopping up the bike, but our bikes have direct action applied to the shock and needs the valving corrected to reflect the setup.

Can you refresh me on what was done to the front of your bike?

 

[chemicalsmile]

I weigh around 300 geared up - I have Racetech springs out front, dialed in to 30mm sag. Currently with the preload maxed on the stock shock I'm getting 45mm out back. I would go with the Hyperpro rear spring but I don't want a progressive spring and IMO it's very overpriced so I'm hoping to get similar results with the predictability of a linear spring for less $.

To answer your questions - no, the spring isn't carrying the load at the desired height and is certainly not matching the front. While it doesn't feel like a rocking horse, the back is totally contradictory to the front - the front is all sportscar while the rear is mid-80's caddy lol.

 

[FinalImpact]

Hmm - - Something doesn't add up. 1400 lbs/in?

What rate is up front? FWIW: I'm roughly 215 w/gear and here is how it works out.



Mine in STOCK TRIM:
Front sag = 43mm (compresses 1.7" from me sitting on it)
Rear sag = 29mm (compresses 1.1" from me sitting on it)

R6 forks installed:
Front sag = 31mm and adjustable +/-20mm
Rear sag 29mm

R6 forks are fixed rate at 0.83kg/mm up front and stock in back and it rides pretty nice for me.
====================

OK back to the rear and the spring you need. Here is the stock stuff:
2008 FZ6 Rear Shock:
Setting #1 light: 175.2mm (6.90")
Setting #7 firm: 165.8mm (6.53")
Installed length MANUAL: 172.0 mm (6.77 in), doesn't say what setting tho.

Range of preload: 9.4mm (0.37")
Coil OD: 77.6mm (3.055")
Coil Dia: 11.76mm (0.463")
Spring free length 185.0 mm (7.28")
Spring rate K1: 12.99 kgf/mm (727.45 lb/in), 127.40 N/mm

How did they go from 727 to 1400?? You said up there it scared you that they doubled it. I'm with ya on that. I get it now. Here is what I get

Lets say you had 0.95 up front, i'd guess you'd want about a 14.0kg/mm in the back to keep it balance. Perhaps that is where the numbers got crossed? To increase the rear an amount to match the 0.95kg/mm, I get 14kg/mm - roughly 784lbs/in. But thats just a guess.

 

[chemicalsmile]

I've got 1.0k springs out front. For the rear spring, the RT calculator recommended 14.5kg/mm (800 lb/in closest) and the Penske chart posted earlier in this thread recommends 850 for my weight. Also, looking around various forums for spring swaps it seems 800 is a pretty common rate to swap in. Since I came across the 850 on ebay I grabbed it to test.

Got the swingarm and shock off last night - apparently my bike was built on QA day because after 28k miles the shock bushing/bearing and swingarm bolt/race/bearings are still very well lubed and came out very easily. Still going to clean and re-lube with bel-ray but I was really surprised - I was prepping for warfare with that bottom shock bushing since it seems like everyone has problems with it. Should have the spring swapped tonight and will post differences by this weekend hopefully.

 

[chemicalsmile]

Ok, got the spring swapped out last night. I was able to get the stock one off with a rental tool from O'Reilly's but the coils were too large and/or close on the Eibach to work so I had to get the $14 one from Harbor Freight.

As stated before, the stock spring is a little more than 1/4" longer - doesn't seem to be an issue since I still had to compress the spring to install and there's no vertical movement HOWEVER....
The ID of the stock spring is actually closer to 2 1/8" so there's unfortunately a gap between the inner step on the perches and the inside of the spring. Even though there's no vertical movement I was able to shift the spring horizontally until I cranked up the preload. Not sure if this will be a big issue - there's no way I'm seeing that the spring could let go since the perch bases still cover 80% of the spring base but it's something I'll have to keep an eye on.

 

[chemicalsmile]

Got everything mounted up last night and checked sag and both the static and rider sag is more than the stock spring - static is 10mm more and rider is 20mm more...this is with preload maxed. I assume it's because of the shorter spring..might try to find some washers to make up the length difference

 

[chemicalsmile]

Alright so finding a suitable spacer was much harder than I thought...
I mocked up a spacer out of wood .5" thick with a 3" diameter and found the numbers much better. With preload maxed, I was getting 7mm of static and 36mm of full sag so clearly the issue was the shorter spring and lack of preload. After shopping around for quite a while, looking into having a custom piece turned down, choking at the cost, then searching some more I eventually found some 2" ID x 3" OD machine bushings which were 1/8" thick. With 3 of these and the stock spacer I ended up a little less than .5" thick. Threw it back together and took a ride and it's definitely an improvement. The 'droop' I felt before is gone and although I haven't ridden it too hard yet, it seems to hold a line much better in turns. I was a little apprehensive about the damping but I thoroughly tested it on our pothole-laden streets and a few speed bumps and it feels good - rebound is a bit more harsh but hardly noticeable. Only thing I'm worried about is the static sag - most info I've read say it's not a big deal as long as you're close to stock. I know this thread has a serious lack of pics so here you go:

Difference between stock spring and Eibach (bottom perch is on the Eibach..idk why I left it on there..):

Eibach spring mounting up with spacers (wrapped valve body in black vinyl):

Installed on bike: