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Yeah so here are the spring rates..........huge thanks to @Cornerman
He gathered all the info and numbers, and did all the work

18-20' N400 - 96 N/mm - 548 lb/in
18' 600 - 101 N/mm - 577 lb/in
17' 750 - 91 N/mm - 520 lb/in
11-16' 1000 - 105 N/mm - 600 lb/in

So if you end up with a 750 shock, having 5 coils instead of the 4 your spring rate will be softer than the 400 spring.
I also heard a couple others taking a ZX6R spring and running it on the GSX-R "shock"....... I think it was @51Ninja400 and/or @JFMNINJA400 as well........they can chime in on exactly what spring they used and years, cause you might be able to grab one of those cheap, pull the spring off it and put it on the GSX-R shock to get even softer, but from what I have experienced and heard others, even with a stiffer shock and if you are small enough, almost no threads showing above the top collar on the shock and all the adjustability........the GSX-R shock is night and day compared to how the OEM N400 shock deals with bumps, road conditions and cornering......
 

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My bro suggested that since the GSXR 750 rear shock that I am getting is heavier than ninja 400, i might want to get a spring that is one level softer than the one suggested for my weight. What do you guys think?
From what I've found, the '11-'14 GSXR750 has a stiffer spring than the 600, while the '15-'19 model is softer than stock. What you should do depends on which version you're getting and how much you weigh.

Use Norton's spring rate chart, RT's calculator, etc. to find the ideal spring rate for your weight on your bike. Then just find or buy a spring that matches that rate.
 

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For my weight (140lb with gear on) 80N/mm rear spring was bang on for sports/street riding giving me 35mm of sag with me sitting on the bike. This corresponds with Nortons chart too.
 

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Discussion Starter #24
Dawn it! Just got my GSXR shock and it is too long. My ninja 400 shock is 31 cm and the GSXR is 35.5 cm. I asked the guy on ebay that selling his '18 ninja 400 shock to measure the length and he measured it at 35 cm. Help!
 

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Dawn it! Just got my GSXR shock and it is too long. My ninja 400 shock is 31 cm and the GSXR is 35.5 cm. I asked the guy on ebay that selling his '18 ninja 400 shock to measure the length and he measured it at 35 cm. Help!
My '18 Ninja 400 shock is 32cm but regardless the one you have is too long. You may have to try and on-sell it.
 

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Yeah so here are the spring rates..........huge thanks to @Cornerman
He gathered all the info and numbers, and did all the work

18-20' N400 - 96 N/mm - 548 lb/in
18' 600 - 101 N/mm - 577 lb/in
17' 750 - 91 N/mm - 520 lb/in
11-16' 1000 - 105 N/mm - 600 lb/in

So if you end up with a 750 shock, having 5 coils instead of the 4 your spring rate will be softer than the 400 spring.
I also heard a couple others taking a ZX6R spring and running it on the GSX-R spring....... I think it was @51Ninja400 and/or @JFMNINJA400 as well........they can chime in on exactly what spring they used and years, cause you might be able to grab one of those cheap, pull the spring off it and put it on the GSX-R shock to get even softer, but from what I have experienced and heard others, even with a stiffer shock and if you are small enough, almost no threads showing above the top collar on the shock and all the adjustability........the GSX-R shock is night and day compared to how the OEM N400 shock deals with bumps, road conditions and cornering......
I did use a 2012 ZX6r spring. The boy and I both weigh in close to 170#. Way cheaper to buy another shock than a spring from RT, Ohlins etc......
 

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Discussion Starter #27
My bad, i didn't know that you suppose to measure from the center of the screws. Richard at Race Tech measured for me this morning and both the GSXR and 2020 ninja 400 have similar length shocks. That GSXR shock is fully adjustable! Can't wait to put the softer spring on the GSXR shock and swap it out. Will keep you guys posted.
 
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