The PNW Relay being my first experience with a coil shock, I've been learning a little bit. Figured I'd share my thoughts and what I've learned. .
First I'll share my experience in regards to Transition's spring rate decision for the PNW builds. Essentially, I think they are on the light side. I ordered size medium which comes with a 400# spring. (requires 400 pounds to compress the spring 1 inch) I ride a bit aggressive and I my ride weight is about 200 pounds so before ever riding the bike, I had them swap out the 400 for a 450 which comes on their size large. When I rode in Bellingham that felt just fine but when I got home and started hitting more drops and jumps, I was feeling bottom out quite regularly. So, having just sold a road bike and a mountain bike which covered the cost of my Relay and then some, I bought the Push Eleven-Six. The 11/6 came with a 450 spring, but I rarely ever feel a bottom out. The only time I feel a bottom out on the 11/6 is when I make a substantial mistake, basically a huge case. Where as with the DHX, I felt bottom out when landing smooth and where I was supposed to.
My GF's Relay came with a 350 on it and I swapped it for the 400 mine came with and she's feeling bottom out regally as well. But, I'll admit she tends to over send jumps and lands pretty deep.
So, in looking for maybe a 425 spring for her, I learned what the numbers on the spring mean. 400x2.8 = 400 pound spring rate for a spring which can compress 2.8" (71.1mm) before being fully compressed. This got me wondering about something because my Push 11/6 came with a 450x2.9 (73.6mm) spring. The stroke of the DHX on the PNW is 65mm (2.559 inches) that means the spring that comes in the DHX is 6mm (.241 inches) longer than the stroke of the shock. BUT... when you set the sag on a coil, the more preload you add, the more travel you remove from the spring. So if you add in more than .241" or 6mm of preload, you are effectively reducing the travel of your rear suspension.
Say you dial in 10mm of preload to the spring that came with your PNW. At that point, your spring will reach max compression at 61mm of stroke rather than 65mm. Doesn't seem like a big deal, but that brings up the question, is the sensation of a bottom out worse when the spring binds fully? My gut says yes. My gut says that when bottom out is reached by the spring being fully bound, metal on metal, it feels worse when the shock hits bottom out on the rubber stopper. I'm not an engineer and I don't have loads of experience setting up and optimizing a coil shock, but this seems like something that can drastically change the feel of a bike.
With my DHX, I would feel bottom out regularly and it felt very harsh. Not like an air shock bottom out and now that I have the Push shock, the DHX also felt way more harsh than my Push bottom out. The Push bottom out happens far less frequently and almost always is accompanied with a fork bottom out as well.
I suppose this is why it's important to get the right spring rate for you rather than just dialing more preload to get the desired sag measurement.
Would love to hear from an engineer or someone experienced with optimizing coil shock set ups.
**Bonus postulation... there are several jumps in my home trails which I never liked. I never felt comfortable on them at all. One specific jump named the "Gwazi jump". Once I got the PNW Relay, ALL the jumps at my home trails felt great. In fact, Gwazi felt perfect, I could go fast, slow, boost, scrub, didn't matter, it felt fine every time. So much so that the second day riding my home trails, I learned one handers, tire grabs and seat grabs on that jump. This shocked me as well as many of my friends because I always said I'd never take my hands off the bars.
So what changed? E-bike, yes. Very slack bike, yes. Longer travel bike, yes. Heavier more stable bike, yes. All of which likely contribute, but I now have come to believe the biggest contributor to me feeling so sold on all the jumps, is the coil shock. Here is my logic behind that statement. A coil shock is quite linear vs an air shock which is quite progressive. The more you compress an air spring the more pressure builds in the air spring and thus, the harder it rebounds. The rebound of a linear spring changes MUCH less with a bit more compression. Riding a full suspension bike into a jump will compress all the suspension. Unless you are pro level consistent we all are going to preload a bit differently on jump faces, even the same jump.
If preload were numbered 1 - 10 with 1 being almost no preload and 10 being max preload. Preloading the rear suspension on an air sprung bike to 8 will result in a harsher rebound than a preload of 4. Yes, both air and coil shocks have rebound dampening to control the speed of the rebound, but I'm guessing with rebound being equal, an air spring compressed to 500psi will rebound somewhat faster than the same air spring compressed to 300psi. I know that I've felt an air shock at 100psi barely seem to rebound and without changing the rebound settings, adding another 100psi to the air spring causes the shock to rebound much more sharply.
Basically, with a coil shock, I'm feeling like my differences in preload on the jump face doesn't result in bucking as much as it did with an air sprung shock. With an air sprung shock, I lacked all kinds of consistency. With a coil shock, consistency has shown up and stuck around.
