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Question Spring rate change - 675lbs/inch to what?

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I installed a Sachs shock from a '16 Tuono with a Hypercoil 6" 675lbs/inch spring. Much better ride than stock but my preload is maxxed (about 17mm compressed from the 150mm total free length). I ran it like this with full camping gear and other kit with a measured static sag of 65mm, 35mm free sag. With my normal commuting gear the Static is 42, Free is 15mm. I weigh about 140.

I'd like to bring my preload adjustment range into the 5-10mm range, what spring rate should I go to? 750lb/inch, 800lb/inch?

I've been running 1 1/4 out compression damping, 16 out (down) rebound. I also installed 25mm jack up links to raise the rear back up. This does not correct the drop from the Sachs completely, but with the jacking links the difference from stock is only 7mm shorter (measured uncompressed on centerstand)
 
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If you weigh 140lb (63kg) then you are a light weight The OE shock stock spring stiffness should be fine for you solo.
The OE spring is 140 N/mm.
The Tuono Sachs OE is 95 N/mm, really weedy. I have this too with a 184 N/mm spring fitted. I weigh 100 kg in gear.
675 lb/inch is 118 N/mm
Sounds like you need a stiffer spring. I wouldn’t be too concerned about 750 or 800 lb/in.
Fit what you can find.
For info YSS make a lot of relatively inexpensive shock springs.
 
If you weigh 140lb (63kg) then you are a light weight The OE shock stock spring stiffness should be fine for you solo.
The OE spring is 140 N/mm.
The Tuono Sachs OE is 95 N/mm, really weedy. I have this too with a 184 N/mm spring fitted. I weigh 100 kg in gear.
675 lb/inch is 118 N/mm
Sounds like you need a stiffer spring. I wouldn’t be too concerned about 750 or 800 lb/in.
Fit what you can find.
For info YSS make a lot of relatively inexpensive shock springs.
What are your Static and free sag measurements? Have you changed the links from stock?

I've been using Ohlins spring charts to help me with the many confusing unit conversions.
  • 95N/mm is about 540 lb/inches
  • My 675 lb/in spring is about 118 N/mm.
  • 184 N/mm is about 1030 lb/in.
Lets say I am 65kg or 65% of your weight, 65% of 1030 is 670. In theory, if you are in a good adjustment range, I should be there as well with mine.

I settled on lb/inches because my source for springs (Hypercoil from Propartusa) sells those units. But yeah, as long as the spring sprungs like they say it does it doesn't matter much who makes it.

Next I need to guesstimate what spring I would need to bring me to a proper preload amount.
And OE 140N/mm just so happens to be bang on 800lb/inches.
 
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I run with about 10mm of preload on the rear. This is just
to keep the rear up. Being tall (1.93m or 6ft 3in) I have lowered the foot pegs so they were grinding out a lot.
I have not modified the linkages at all.
I have static sag and a bit of rider sag. I have measured it in the past but I am continually messing with it so the exact number I am not sure. It would be a lot less than your numbers. My spring is very stiff so my numbers are small but it rides OK.
I would suggest you see if you are bottoming out the shock by examining the tide mark on the damper rod.

When I got my bike it had the OE shock. It had too much rider sag with me on it but when I increased the preload to raise the ride height and reduce the rider sag, the static sag disappeared. Hence the Tuono shock with stiffer spring.

I scored a new cheap YSS shock off Ebay recently but this has a 150 N/mm spring so I will be swapping springs again.
 
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