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Lots of good info here. Perhaps I can clarify a thing or two in this (resurrected) thread. I am in the midst of a full suspension mod, so I now feel qualified to opine.

To begin, the spring in the left fork leg of the G310GS is a normal fork spring. It is only a "helper" spring in a pedantic/marketing sense, it being weaker than the aftermarket unit in the right leg.

All other things equal, the effective spring rate for springs in parallel (e.g., fork springs) is the simple sum of the spring rate of each individual spring. Nothing more and nothing less. Hyperpro and others serving the professional installer market therefore ship two springs. Why wouldn't they? A pro installer can surely get past red Loctite and the (presumed) need for a special tool. Right? <grin>

But Rally Raid's stated market includes the DIY/prosumer crowd. Getting into that left fork leg presents a major challenge to many home mechanics. So RR, knowing that there are no damping components in the left leg that need new (thicker) fluid, came up with a right-leg-only approach. They just bumped up the spring rate for the right-side spring to achieve the effective rate that they were shooting for. Both reasonable and canny IMO (clever even).

I'll offer without proof that the RR solution presents no measurable imbalances or other technical shortcomings to the two-spring approach. Just different paths.
 

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BTW, after I have installed my new components, I will take the three OEM springs to a local shop for measurement of spring rates.

Too much mystery on the subject....

Edit: The Cogent website lists the G310GS spring rates at 0.35 (fr) and 11.7 (r). I think that they mean "0.35 per leg" for an effective fork rate of 0.7. I would have guessed lower on both, but that's just conjecture at this point.
 

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Go full mod! Should be interesting to see practical, effective and economical vs DIY without financial restrictions! Are you going to allow for easier fork oil changes?, Thats a mod I wish but it won’t affect performance and does require drilling and tapping.
 

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Drilling holes isn’t your thing and really it’s just as easy to remove the fork to change the oil for you I’m sure.
How often do you advise changing fork oil oil?
 

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Drilling holes isn’t your thing and really it’s just as easy to remove the fork to change the oil for you I’m sure.
How often do you advise changing fork oil oil?
I like to get the factory fluid out sometime in the first 1K miles. I'm usually upgrading things by then, so it works out.

After that, I change fork fluid when I inspect the seals and bushings, typically at one year or 10K miles.
 

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I’d highly advise anyone considering progressive springs to peruse a reference guide before going this route. Took me about 20 minutes to get a very clear answer, and my reading skills are suspect. Has to do with intended use.
 
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