Digressive vs Linear vs Progressive Piston & Valving Article (and video)

[*TRD*]

There are a lot of choices when it comes to what type of damping you want in your shocks so we put together an article which explains the pros and cons of each, and explains the technical details behind each.

Article: The Pro's and Con's of Digressive, Linear, & Progressive valving, and how each one works.

When it comes to OEM fitment shocks Fox and King have linear pistons with fairly progressive damping curves while Icon and Bilstein use digressive pistons and digressive damping curves.

This article is fairly generic and I'm happy to answer any specific questions you may have.

 

[fordracing19]

Makes me wonder what I am missing with the Icon 2.5 w/cdcv vs something different on my 4runner.

 

[Ryanmb21]

Nice artical!


Sent from my iPhone using Tapatalk

 

[toyick]

as some one who takes shocks apart often! that was a great read!


blahhhhhh

 

[comptiger5000]

I'll throw my 2 cents in and say that I hate digressive shocks with a burning passion in pretty much any vehicle. If they're valved well to not ride like crap, they're fine until you hit a big enough bump, then you just blow through all the travel and slam the bumpstops, which requires very progressive stops to not feel harsh. And if you hit a dip at speed, you'll sometimes get a bounce if the suspension rebounds too fast and the shocks start to soften up.

I have linear piston Bilstein 7100s in the Jeep and they're great. I kinda wish the rears were progressive to go along with the progressive rear springs, as it's tough to strike a good balance that's not over-damped in the early part of travel or under-damped at the end of travel where the springs have stiffened up a lot.

But even with the current setup, it rides quite well, despite my very stiff springs (280 lb/in up front compared to 190 stock, rear is about 350 lb/in at ride height, 600 at full compression compared to 160 stock). The biggest problem with the suspension is the temptation to drive over dips, bumps, etc. at unreasonable speeds... A big dip across a set of train tracks feels kinda rough and annoying at low speeds, but at 50 it's just a quick "thump, thump" that you barely feel.

 

[paranoid56]

another great article. loving my accutune shocks on my taco

 

[Hopeless Diamond]

When ever shocks are discussed it always seem that it's centered around some fast desert track with an urge to be a poster boy for some desert race team. Don't get me wrong, I've been known to get some decent air time (not always on purpose), but now trying to figure out how to set up for a different situation.

What's the best approach for a moderately heavy vehicle. Specifically a 1 ton with a truck camper. Doing the typical FS roads with ruts and pot holes, it can buck and launch the rear pretty good if you happen to miss it coming. The springs handle the weight pretty good, but I need to dial in the shocks I think to dampen down that rebound. Interestingly enough, I haven't had much trouble with washboard sections, seems to handle them better going up hill than down. The front with it's massive 2-3" of travel doesn't seem to be too bad, but the rear can get a little active. I'm typically watching out, but it can be real easy to let your speed creep up and wham, that pothole jumps out in front of you. The camper doesn't seem to like that, throws the tie downs off, crap gets bounced around, momma ain't happy - you know the drill. Unloaded, it is what is, I have no delusions of a nice comfy ride in a 1 ton, but don't want to make it any worse either. Is it worth it to go bigger in this situation, 2.5 vs 2.0 series. Is there more refined tunability with the larger adjustable shocks that justify the price. Would a 2.0 shock with compression adjustment (i.e. Fox 2.0 with CD) be adequate, or would it be better with with a bigger 2.5 with dual speed adjustability (i.e Fox 2.5 with DSC).

Figure some here will have some wisdom and probably many will have opinions...

 

[comptiger5000]

Does it slam over the holes as if the suspension isn't compressing? Or does it compress, but when you compress it far enough, it snaps back and gets a bit of bounce? If it's the first, you need more compression damping. If it's the second, you need more rebound. The challenge is to figure out whether you need medium or high speed rebound. I'd be inclined to say high speed, considering leaf packs on a 1 ton are typically somewhat progressive, so you're likely short on rebound when you get into the stiffer portion of the leaf pack and it snaps back.

I've got a similar issue in the rear of my Jeep with progressive springs. Rides great until you compress the rear far enough, then it feels a bit underdamped on rebound. I've got a set of stiffer valved shocks to swap in the rear and see if that fixes it. If it's still not right, it's going to be time to tear into a set and re-valve them.

 

[OCD Overland]

Looks like a nice article. I've only had a chance to skim it but I'll give it a good read later today when I have time.

It would be interesting to read a discussion of how the different dampers work with different springs; i.e., a digressive damper with a progressive spring should behave much differently than with a linear spring, right?

 

[Hopeless Diamond]

It doesn't slam down, the springs seem to be well matched to the load (~3k-3500lbs). The rebound is where I need the help I guess. I don't find much info on adjusting balance between compression and rebound.

 

[*TRD*]

When ever shocks are discussed it always seem that it's centered around some fast desert track with an urge to be a poster boy for some desert race team. Don't get me wrong, I've been known to get some decent air time (not always on purpose), but now trying to figure out how to set up for a different situation.

What's the best approach for a moderately heavy vehicle. Specifically a 1 ton with a truck camper. Doing the typical FS roads with ruts and pot holes, it can buck and launch the rear pretty good if you happen to miss it coming. The springs handle the weight pretty good, but I need to dial in the shocks I think to dampen down that rebound. Interestingly enough, I haven't had much trouble with washboard sections, seems to handle them better going up hill than down. The front with it's massive 2-3" of travel doesn't seem to be too bad, but the rear can get a little active. I'm typically watching out, but it can be real easy to let your speed creep up and wham, that pothole jumps out in front of you. The camper doesn't seem to like that, throws the tie downs off, crap gets bounced around, momma ain't happy - you know the drill. Unloaded, it is what is, I have no delusions of a nice comfy ride in a 1 ton, but don't want to make it any worse either. Is it worth it to go bigger in this situation, 2.5 vs 2.0 series. Is there more refined tunability with the larger adjustable shocks that justify the price. Would a 2.0 shock with compression adjustment (i.e. Fox 2.0 with CD) be adequate, or would it be better with with a bigger 2.5 with dual speed adjustability (i.e Fox 2.5 with DSC).

Figure some here will have some wisdom and probably many will have opinions...

People focus on the desert stuff because the suspension moves a lot and looks cool. Hard to make a cool video of most vehicles because it's really all about the feeling. We do a lot of both, but show more desert stuff because it's easier to articulate, and a lot of what's going on carries over.

For anyone that is subject to large weight changes we recommend adjustable shocks so momma can always be happy.

On full size trucks we can make a 2.0 work, but it's on the upper end of their normal tuning zone, and that can cause them to be harsh. If you're doing a lot of fire road the heat generated from a full size truck can kill them pretty quickly too. You'll be a lot happier in the long run with a 2.5" shock.

 

[*TRD*]

Does it slam over the holes as if the suspension isn't compressing? Or does it compress, but when you compress it far enough, it snaps back and gets a bit of bounce? If it's the first, you need more compression damping. If it's the second, you need more rebound. The challenge is to figure out whether you need medium or high speed rebound. I'd be inclined to say high speed, considering leaf packs on a 1 ton are typically somewhat progressive, so you're likely short on rebound when you get into the stiffer portion of the leaf pack and it snaps back.

I've got a similar issue in the rear of my Jeep with progressive springs. Rides great until you compress the rear far enough, then it feels a bit underdamped on rebound. I've got a set of stiffer valved shocks to swap in the rear and see if that fixes it. If it's still not right, it's going to be time to tear into a set and re-valve them.

I haven't met a rear JK spring that I like. They are too stiff to begin with, then they all transition very quickly into an even higher rate. The result is they ride like dump trucks.


We've been putting 125 lb/in straight rate springs in the back of JK's and it's been MUCH MUCH better.

 

[comptiger5000]

I haven't met a rear JK spring that I like. They are too stiff to begin with, then they all transition very quickly into an even higher rate. The result is they ride like dump trucks.


We've been putting 125 lb/in straight rate springs in the back of JK's and it's been MUCH MUCH better.

Funny, considering I've done the opposite in my ZJ. When I ditched the rear sway bar, I went from 260 lb/in linear springs (already 100 lb/in stiffer than stock) to progressive springs. If I'm not bad at math, they're somewhere around 320 - 350 lb/in at ride height and about 600 lb/in at full squish. That's paired with 280 lb/in linear front springs.

Other than being short on rear rebound in big bumps with the current setup, I like how the suspension behaves with the progressive springs. Works well with the Jeep empty and doesn't get mushy with the Jeep loaded up like the linear rears used to. It's also stiff enough at full squish that it doesn't start running out of travel easily when carrying some weight. I'm thinking the 400/100 shocks will help with the ride in the rear, as they've got more rebound and they'll slow the suspension a bit more on compression on big hits. IIRC, they have noticeably more low speed rebound than the 360/80 setup, so that should help the bounce from over-shooting when coming out of a hit that gets it into the stiff part of the spring.

 

[*TRD*]

That's a really complicated question, because it depends on so many factors.

It's better to start simple (linear piston, linear spring) and start adding more complicated tuneable elements when you need them to fix a specific problem.
On overland vehicles I'd start simple and add better bottoming control if that was an issue (likely due to low up travel on some vehicles).

 

[*TRD*]

Funny, considering I've done the opposite in my ZJ. When I ditched the rear sway bar, I went from 260 lb/in linear springs (already 100 lb/in stiffer than stock) to progressive springs. If I'm not bad at math, they're somewhere around 320 - 350 lb/in at ride height and about 600 lb/in at full squish. That's paired with 280 lb/in linear front springs.

Other than being short on rear rebound in big bumps with the current setup, I like how the suspension behaves with the progressive springs. Works well with the Jeep empty and doesn't get mushy with the Jeep loaded up like the linear rears used to. It's also stiff enough at full squish that it doesn't start running out of travel easily when carrying some weight. I'm thinking the 400/100 shocks will help with the ride in the rear, as they've got more rebound and they'll slow the suspension a bit more on compression on big hits. IIRC, they have noticeably more low speed rebound than the 360/80 setup, so that should help the bounce from over-shooting when coming out of a hit that gets it into the stiff part of the spring.

That's the cool thing about all this stuff is you can tune it for your preferences and what works for you.