I thought I remember either a rear coil or fork spring that was all one spring but progressive. i.e the coil spacing changed from more seperate at the beginning to more tightly spaced at the end. I think this was before all the fancy damping shocks we have today. I also seem to remember some kind of suspension having a "helper" spring for small bump compliance.
I had one of those. It was way too progressive.
stratos had a progressive coil...in addition to an air spring in their coil over shocks. that must have had some impressive progression to it.
The coil spring is what I'm after though. I like the curnutt style spring system, that would probably accomplish the same thing. I'm thinking a 400lb spring and then a shorter 450, to basically give the bike some additional bottom out/ramp up assistance. The challenge is doing it on a modern, non-custom shock.
All coil-over shocks have air springs inside- the air on the other side of the IFP from the oil is a spring, bottom out adjusters usually change the volume of that spring.
I was under the impression the IFP or bladder serves as a compensator for oil expansion due to heat build-up. IE, oil gets hot, it expands, then to avoid hydrolock you need a little space for it to move to, thus the pressurized IFP. Correct me if I'm wrong...
True, but it's not much of an effect in conventional layouts. On some shocks, the air chamber acts against an oil valve that provides more resistance as it's compressed, this is where "progressive damping" comes from. This is the DHX and 5th element type shocks. On other more conventional shocks the ramp-up by the reservior is not significant. The air spring on the Stratos Helix Expert and Pro was a lot larger, so it was fairly significant to the overall progression. Those shocks were good for severe falling rate designs (Trek Y-bikes), but on my ride I found it exceptionally harsh, due to simply ramping up too fast.
The main reason for the pressurized air chamber is to allow oil displacement caused by the damper shaft entering the damper. Ie, as you compress a shock, the shaft that goes inside, uh huh huh, takes up space. Without the air spring, it would be hydro locked.
The first couple of years the Fox 40 was very linear in damping. It bottomed very easy and rode harsh when you installed stiffer springs that all but the lightest of riders needed. We did a dual rate Ti spring system for the 40 and it made a lot of improvement. Since that time Fox has really figured out the damper in the 40 and it now has very good progression while still being good in the chop. We no longer offer the dual rate springs, but do have Ti springs in the "Green" rate (one step stiffer than stock) that Fox does not offer.
I might be interested in those. Last time I checked Fox was offering Green Ti springs for around $200. My Large 2008 Glory came with one and I would assume most Fox sponsored riders are on a green Ti spring. Hmm.
The air can is a spring, the kind that exerts a static force. Mathematically, it is the reservoir pressure times the effective cross sectional area of the damper shaft.
Oh okay so it's a spring for the amount of air/oil displaced by the shaft. Trivial in the scheme of things. Like calling seals dampening as they slow the shaft speed. The piggy backs air springs purpose is to increase oil pressure/damping not to suspend the bike staticly, but to suspend the bike dynamically.
i put those springs in my first gen 40 when i had it and i thought it was a complete waste of money. i didnt notice a difference what so ever.
