Sofrider spring rates

We were approached by a customer wanting to make the rear suspension of his sofrider more compliant. Here is my reply:

Maria contacted me concerning the ride quality of your Sofrider. I thought I would share the research and information I’ve compiled over the last week on your questions.
Because, as manufacturers, we need to assure our bikes work safely at the rider weight limit plus the sprung weight of the bike and accessories (effectively 300 lbs), our Sofrider/Freeriders come equipped with an 850 lbs/inch spring on the shock, to keep the shock sag at about 25% of travel and prevent bottoming-out under extreme riding conditions. The overwhelming majority of our customers are satisfied with the resulting ride quality.

You’re basically saying our Sofrider doesn't ride the way you were expecting. I think I can provide you with information to tune it more to your liking, since you’re the owner and don’t have to consider the rider weight limit (Unless you contemplate super-loaded touring!)

I have calculated based on weight information you provided, taking into consideration total riding weight, rear weight bias, rear wheel travel & shock stroke, shock sag, preload adjustment and end-coil effect that the ride you want should be achievable with an appropriate safety factor using a 550 lbs/inch spring.

After doing these calculations manually, I found an online calculator that will do this for you.

http://www.bearandwife.com/bear/cycling/springcalc.html

The specific information you need to know for the Sofrider to get this to work is:
Rear wheel travel = 3.25"
Shock travel = 1.25"
Leverage ratio should calculate out to 2.6 by the online calculator
Set the rear weight bias to 100 percent and use the 88lb value you provided.
Add a safety factor to the resulting spring rate, or add weight to the 88lb. Figure to account for accessories or hard use.

After a lot of looking, I know the following:
1.    No one in the US has a replacement spring to fit our shock absorber.
2.    Sourcing parts in Taiwan from our OEM’s involves ordering in quantities of 100.
3.    I have located a direct replacement (equivalent to OEM) shock absorber unit with a 550 lbs/inch spring for $29.95 here:
at ebay .. New-Bike-MTB-Rear-Suspension-Shock-550LBS-IN-Black

(I am giving thought to ordering one for my V2K for testing.)

John Zabriskie has been very helpful to us with his exploration and customer-oriented development of our suspension systems, and I’ve discussed what you are trying to achieve with him.

We don’t plan to generally offer alternate suspension calibrations or an air shock on the Sofrider. But as the bike owner, you can do what you like to your own bike, taking responsibility (and credit!) for the results. But I warn you, this may turn you into a tinkerer like me!