Coil Shock Shootout

Is there any consensus on how Sprindex performs vs. an equivalent rate standard steel spring?  I remember reading an article from like BikeRadar or somewhere when it was launched, saying that the spring rate was lower than reported, and also that it behaved in a digressive fashion rather than progressive as it was marketed.  I've also noticed none of the pro DH guys run them (but that could just be because they get a pile of dyno tested springs from their suspension sponsor).  On the other hand, Vorsprung specs them with their Tellum, and they're not dummies.

I've used them off and on myself, and appreciate the convenience of being able to click up / down the spring rate to tune by feel, but I also swear that they don't feel the same as a standard spring.

They are about as accurate as most other springs out there - the main thing to note is that they are slightly progressive and the adjuster is closing off the progressive section, so in its stiffest setting it is mostly linear. Vorsprung made a post on instagram about them and referenced the bikeradar article, so I'll paste the text here instead of linking it-

Put your nerd hats on, because here we go... thanks to Per Nyberg for bringing this up.

A Bikeradar review a good while back (Dec 2020) measured the spring rate variation of a particular Sprindex spring. Their findings were that the adjustment mechanism changed the spring rate by about 10% in the early stroke, but only about 2% in the last bit of the stroke. This was interpreted as "the rate adjuster is not as effective as claimed" - in practice, this is not quite the case. Spring RATE needs to be understood separately from spring FORCE. The RATE is the amount of difference in force, over a given distance.

The way the Sprindex adjustment works is to block part of the coil, to "deactivate" it, which stiffens the spring by reducing the length of active coils. This changes the RATE directly, not the force. However, what you can see from the curves on the second slide is that the softer setting is more progressive than the firmer setting on the same spring, because spring progression is introduced by partly (you guessed it) blocking some of the coils of the spring (basically, some coils contact each other and stop moving). The reason this progression is not observed in the stiffer setting is that those coils are already blocked by the adjuster. This is why the final RATE is similar with both the softest setting and the firmest one.

However, the spring FORCE is still offset considerably due to the difference in RATE over the first 2/3 or so of the travel. At around 2/3 travel, the same force at the wheel yields about 5mm difference in spring compression at the shock, which translates to about 13mm (half an inch) at the wheel. That is a reasonably significant change in ride height at that load (think: your head angle is half a degree steeper and your BB is about 9mm higher). The bottoming forces differ by about 7%, which is less than the approximately 10% nominal difference in spring rates, but not tremendously so.Reading further into that article, they mention that the spring tested softer than rated. The one tested here was surprisingly accurate, but it's actually irrelevant - because you can adjust it.

As for pro DH guys - a lot of privateers use them, and the factory guys are probably encouraged to use the proper branded springs. Also Sprindex doesn't fit every frame because of the adjuster tab - not common but it can be a hassle in some bikes.

Also at the end of the day there aren't many companies that test things as thoroughly as Vorsprung so if they are happy with them its a good enough endorsement IMO

Thanks, I'm not on Insta (fuck Zuck) so never saw that post by Steve/Vorsprung.  After my post I finally made the connection between what Sprindex does and what you answered earlier with regard to spring rates - by turning the indexer you're shortening the spring/bar length thus making it stiffer.