Sonic or Progressive fork springs, abandon air shock?

[Chuck78]

I will be rebuilding my front shocks this coming year, and am considering Progressive, Sonic, or Hagon springs in my forks. I was undecided at progressive rate or straight rate springs. I really don't like having a lot of brake dive, so the Sonic sraight rate springs seem to be the ticket for me. The slight bit of extra comfort that a progressive rate spring would offer is enticing however.
Based on my bike weight body weight and riding style, sonic tells me to use their medium weight springs for our bikes.

I have a set of air/oil GS650 dual disc forks that I will install on my currently single disc front brake bike. I have read others saying just put the aftermarket springs in and don't use the air shock feature. I was wondering if it would benefit me to go with the progressive rate progressive/hagon brand springs or lighter rate sonic springs, & pump up the shocks with a little air pressure when I wanted it stiffer or just to fine tune the ride? Or just abandon the air shock feature and rely strictly on the springs for suspension stiffness?? Is the air shock idea in the stone age as far as suspension technology nowadays?

[tkent02]

Try a little air and see what you think.

[Chuck78]

The air/oil forks are not on my bike right now, & the springs I purchase will be dictated by whether or not using the air is a bad idea. I had been leaning towards just using the Sonic medium weight springs as I weigh 155 and and shedding weight on my bike, but then I wondered if I could get the best of both worlds if I utilize the air cushion a little bit with the progressive springs

[tkent02]

The only difference is the fork cap with the Schrader valve, my 650G has the valves, as does the 650 G forks going on the 550 project. I am surprised you 650 forks don't have them. You should be able to find the valves and try a little air.

Air is good, it works well, it's easy to adjust, the hard part is to keep the pressure even between the two fork tubes, and to prevent the air leaking out. Most of us don't use air forks anymore because of this.

Even non air forks use the compression of the air inside them as part of the spring rate, this is why it is important to get the oil levels the same, you are actually getting the amount of air in each tube the same. If you were to put an air pressure gauge on a non air fork, there would be a lot of pressure at full fork compression.

[Steve]

Believe it or not, ALL the GS forks are "air forks".

There are some that only use what is trapped inside when you install the caps on the fork tubes and there are some that allow you to add more air, but they ALL use the trapped air as a supplement to the metal spring.

Air, by nature, is already a progressive spring, so using Progressive (brand) springs will somewhat compound the "progressiveness". Using a straight-rate spring like Sonic will make the rate a bit more predictable.

Either way, you can select the rate of the metal spring that will best support your bike and you, meaning that you will not need to rely on additional air that will likely leak out, lowering your preferred spring rate.

.

[salty_monk]

In any fork you can adjust the "air" spring (i.e. the air trapped above the oil) by adjusting the oil height.

Also if it's mostly brake dive you are concerned with I suggest cartridge emulators. Using the spring rate / preload as a primary way to get rid of fork dive is not the best way as it will make the suspension less compliant when it's trying to do its real job of handling bumps in the road...

Ideal setup would be:

1. Straight weight springs giving you the correct static Sag with minimal preload.
2. Cartridge emulators adjusted as appropriate (controls compression damping)
3. adjust oil weight (adjusts rebound damping only with emulators fitted) & height as appropriate (adjusts the rate of "ramp up" & helps to resist bottoming the fork).

[JonnyC]

On my bike I just went with the Sonic springs and welded the air port hole shut on the forks. I think I have an issue with the caps leaking air though, and those damn things are such a pain to get in and out (wish they were just threaded on there).

[tkent02]

I like brake dive.

[gsgeezer]

Ideal setup would be:
1. Straight weight springs giving you the correct static Sag with minimal preload.
2. Cartridge emulators adjusted as appropriate (controls compression damping)
3. adjust oil weight (adjusts rebound damping only with emulators fitted) & height as appropriate (adjusts the rate of "ramp up" & helps to resist bottoming the fork).

What he said^^

[salty_monk]

I like brake dive.

So you've mentioned a few times now... you've yet to elaborate why though!

Some is necessary, it helps with weight transfer to the front wheel & as such increases grip as you apply the brakes. The GS as stock does not control it very well though. Controlled brake dive is ideally what you are after...

[Chuck78]

RaceTech Cartridge Emulators cost around $200, I was considering them, but then thought about skipping them as I added $400 to the cost of my build by getting wider aluminum rims to run wider lower profile tires... I was wondering how much of a difference cartridge emulators would make vs new seals/bushings/shock oil and some Sonic springs. Will it be a hugely noticeable difference? Will the difference be mostly on rough roads, or will even mild surface changes feel way better with them?

[salty_monk]

Everything should feel better if you have it set-up right....

Basically you now get independent control of compression and rebound damping which allows you to use the correct spring rate instead of trying to "prop" the fork up with extra spring/air/preload to get the correct brake dive characteristic you want. In general most people use more spring / preload than is ideal.

Progressive springs are sort of a compromise.

So basically using the emulators allows more adjustment & the use of a softer spring which helps small bump sensitivity, tracking etc etc.

There is a reason all forks (except for real budget ones) went away from the "push some oil through a hole in a tube" sort of damping our GS's use in the 90's...

[JonnyC]

RaceTech Cartridge Emulators cost around $200, I was considering them, but then thought about skipping them as I added $400 to the cost of my build by getting wider aluminum rims to run wider lower profile tires...

Heck for that kind of money, I would just swap my front end with a late model set of inverted forks...something I can't seem to get my mind off of even though my '83 forks are freshly rebuilt

[Chuck78]

Heck for that kind of money, I would just swap my front end with a late model set of inverted forks...something I can't seem to get my mind off of even though my '83 forks are freshly rebuilt

But then you end up with something that looks like a modern "naked street bike," classy vintage street bike with futuristic looking wheels! I am a sucker for wire wheels, tasteful mags are sometimes ok looking to me. I'll never be doing a modern wheel upgrade, just better hubs and wider rims to keep the look that made me want to own a vintage bike! To each his/her own

[Chuck78]

So with the Emulators, should I step down one size in spring compared to what Sonic recommended for a 490 pound and dropping bike 150 lb rider and aggressive street riding