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Baseline suspension setup

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Baseline suspension setup

     “Anyone have a good baseline setup for a Marzocchi fork? Just need the baseline and I can fine tune it from there.
      - Thanks.”

Ya know – Suspension tuning would be a whole lot easier if you could always start from a “good spot”. The problem is setups for the “good spot” just aren’t around. 
But, there are some basic suspension tuning “rules of thumb” and those rules define the ballpark of where the “good spot” is:

  • Rebound damping needs to give suspension response zeta values of 0.7 to 0.75
  • Rebound/compression damping ratios need to be in the range of:
    • Shock: 2 to 2.5:1
    • Fork: 3 to 3.5:1
  • At ultra-low bump speeds (3 to 6 in/sec) the ratio of rebound/compression damping needs to be around 0.8:1

Those “rules of thumb” have solid reasons of the why for each value. Understanding “the why” is an important part of using those rules as well as fine tuning the setup around those baseline values.

1-rules-of-thumb.png

Suspension response

Suspension response is measured in fractions of a second like this shock clock data from vince46 shows. Fast response and random motions over unequally spaced bumps makes figuring out suspension response confusing and gives no clear path to what “optimum” looks like.

2-shock-clock.png

Suspension response is a whole lot easier to understand using the simplifications of spring-mass-damper theory. By that theory two parameters control suspension response: tau and zeta.

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Hi ,here's just an idea ,what about we pay for a setting you design ? And we can then tweak that to our personal preference? I just feel you have all the skills and the tools ,most of us are not good enough on the PC or at maths to get the answers we want ?

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Suspension resonance frequency, tau

Hit a mass on a spring and it bounces up and down. No mystery there. Tau (equation in figure below) defines how long the suspension takes to complete one oscillation cycle (aka suspension resonance frequency). Put wheel weight in the tau equation and you get wheel response. Put chassis weight in and you get chassis response. Simple. 

The link ratio terms in tau convert motions at the shock to response at the wheel. Evaluating suspension response at the wheel makes tau universal. It doesn’t matter if you are tuning a yz125 or a ktm950. Wheel motions are either damped or there not.

Smaller values of tau give faster response and that returns the suspension to race sag quicker. That requires stiffer springs or less mass - a basic statement of Duh. Tau quantifies that effect. Dirt bikes set race sag is set at four inches. That sets a specific relationship between mass/spring rate which in turn sets a specific value of tau and the suspension resonance frequency. That common resonance frequency is why braking bumps end up with the spacing they have.

3-spring-mass-damper.png

The bottom line for tau is spring rates are set by race sag concerns to get the chassis steering geometry right. For shock tuning the value of tau simply is what it is.

Damped response, zeta

Bump a mass on a spring and it bounces up and down. Put a damper on the spring and the oscillations damp out. No surprise there. 

The big question for suspension tuning is how much damping does it take to optimize response? Spring-mass-damper theory answers that question. 

The most hideous situation for any suspension is hitting the next bump at the point where the wheel is just returning from the previous bump. When that happens residual energy from the previous bump gets augmented by the current bump. That timing drives the suspension into resonance.

Spring-mass-damper theory specs the damping required to suppress suspension resonance. That damping is a zeta value of 1/sqrt(2)= 0.707 or higher. Stiffer damping with higher zeta values takes longer to suck the shock back to race sag. That slow response causes the suspension to pack and packing rebound is never a good thing.

4-optimum-zeta.png

 

Zeta values below 0.7 allow the suspension to baby-buggy after a bump. Sloppy response at low zeta values give poor chassis “feel”. Zeta values of 0.7 are spec’d by spring-mass-damper theory to give the fastest possible rebound response to prevent packing with damping that is still stiff enough to suppress suspension resonance. That fact sets the “rule of thumb” for rebound damping.

  • Rebound damping needs to produce zeta values of 0.7 to 0.75

Suspension response zeta values are a function of stroke depth. To get consistent response you want the zeta curve to be flat over the suspension stroke range. The example below goes under-damped on deep strokes. To fix that the shock needs more high speed rebound damping.

5-stroke-zeta.png

 

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Compression damping

The “rule of thumb” for compression damping is the ratio of rebound/compression needs to be around 2:1 for a shock. That ratio makes it sound like rebound damping is stiffer than compression. It is not.

At bump impact suspension velocities are the highest. High velocities drive the compression damping force up. On rebound, damping fights against the spring force creating a rebound stroke stall speed. Lower velocities at that stall speed drive the rebound damping force down. It turns out that a damping ratio of 2.25:1 gives a peak compression damping force that is approximately equal to the peak rebound force. Equal force in both directions gives the suspension a consistent symmetric “feel”. That fact sets the “rule of thumb” damping ratios at 2.25:1.

6-rc-ratio.png

Forks run race sag around ¼ of travel, shocks run 1/3. Less race sag gives forks more bump travel and that longer travel gives forks higher bottoming compression speeds. To get symmetric damping force on a fork the rule of thumb is the ratio of rebound/compression damping needs to be around 3.25:1. 

  • Rebound/compression damping ratios
    • Shock: r/c= 2 to 2.5:1
    • Fork: r/c= 3 to 3.5:1

Measured on a dyno at the same shaft speed rebound damping is stiffer than compression. When installed in a suspension, higher bump speeds in compression require damping ratios in the 2 to 3:1 range to get forces in compression that match rebound. Symmetric damping forces in both directions gives the suspension a consistent “feel” and that sets the “rule of thumb” for damping ratios.

Plush versus fast setups

The “rule of thumb” damping ratios have a range and that range defines the difference between a “plush” and “fast” setup. 

7-plush-v-fast.png

Plush suspension setup

At bump impact suspension velocities are the highest. That makes compression damping start with a “bang” and ramp down as the suspension slows over the stroke. To get “plush” you have to back-off compression damping to get rid of the bump impact “bang”. That forces plush setups to run at the upper end of r/c damping ratio range (2.5:1 for a shock). 

On a plush setup compression forces start low and build through the stroke as the spring force kicks in deeper in the stroke. That progressive force increase defines the “feel” of a plush setup.

If backing off compression damping to the 2.5:1 limit (3.5:1 on a fork) is still to stiff you need to go to a softer spring. A softer spring gives more compliance and a better ride compared to reducing compression damping outside the “rule of thumb” range which creates an over-sprung and under-damped setup.

Fast suspension setup

Fast setups need more compression damping to prevent bottoming. Fast setups push rebound/compression damping ratios to the bottom end of the range (2:1 for a shock). That limit produces a peak compression damping force that is stiffer than the peak spring force. Stiff damping at the start of the stroke makes the compression stroke start with a bang (which is harsh) and ramp down to the peak spring force at bottoming. Stiff but then blows through.

If the suspension still bottoms at the 2:1 damping ratio limit (3:1 for a fork) you need to go to a stiffer spring and the stiffer damping needed for that spring. Options for a stiffer spring have a limit. Once the installed spring preload falls below 5mm there is no option for a stiffer spring and you have to go to stiffer compression damping to control bottoming.

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Low speed damping

When a suspension hits a series of bumps it will either pack or jack. Stiff rebound damping prevents the suspension from fully extending between bumps. That causes the suspension to pack down in the travel until the spring force becomes high enough to return the suspension to some partially extended position between bumps. High spring force at that partially extended position makes the suspension ride like a jack hammer over closely spaced bumps. Packing rebound is never a good thing.

Compression damping on-the-other-hand pops the chassis up slightly when hitting a bump. That forces the suspension to run “high in the stroke”. Lower spring force at that elevated position makes the suspension ride a little more compliant over small “trail trash” bumps.

To get good small bump compliance the suspension needs compression damping to be slightly stiffer than rebound on ultra-low speed suspension motions. The “rule of thumb” is the ratio of rebound/compression damping needs to be in the 0.8:1 range at bump speeds below 3 to 6 in/sec at the wheel. 

  • r/c= 0.8 on ultra-low speed suspension motions below 3 to 6 in/sec (wheel speed not shaft speed)
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Baseline setup "rules of thumb"

Those three “rules of thumb” spec the damping needed for a baseline setup:

  • Rebound: zeta 0.7 to 0.75
  • Compression damping:
    • Shock: r/c ratio of 2 to 2.5:1
    • Fork: r/c ratio of 3 to 3.5:1
  • Low speed compression
    • r/c= 0.8 below 3 to 6 in/sec

8-rules-of-thumb.png

Those basic tuning rules apply to both street and dirt setups. The difference is street setups damp the chassis for small motions around the normal ride height and switch over to wheel damping at high speed. Dirt setups are tuned with the single focus of damping the chassis over the entire stroke range.

Street bike setup

The re-valved Yamaha super Tenere response curve below shows an example of a street setup. On strokes depths up to 5 inches (green curve) chassis rebound is damped at zeta values of 0.7 to 0.75. That keeps control of the chassis up to the bump rubber stroke depth and gives control pushing the bike into and out of corners. When the suspension is pushed deeper in the stroke zeta values fall off. That fall off is by design and tuned to damp the wheels (blue curve) at high speed.

Obviously keeping the wheels on the ground is an important part of control. To get the right wheel damping at high speed street setups have to run highly digressive rebound curves that generate stiff damping at low speed for chassis control and light damping at high speed for wheel control. The Tenere setup does that nicely.

Low speed compression damping generates rebound/compression damping ratios of 0.8:1 on ultra-low speed wheel motions in the 3 to 6 in/sec range. That keeps the suspension from packing. At high speed damping ratios run in the 2:1 to 2.5:1 range. The Tenere pushes compression damping to the bottom end of the “rule of thumb”  range to improve bottoming resistance.

9-tenere-response.png

Dirt bike setup

Dirt setups tune the suspension differently. Dirt bikes, even a play bike, sooner or later end up in a whoop field where every bump impact drives the suspension into the 10 inch stroke range. To give the rider a chance of making it, dirt setups have to control chassis motions over the entire suspension stroke range. That requires rebound damping at zeta values of 0.7 to 0.75 just like a street bike. 

Unfortunately, the stiff rebound damping needed for chassis control pushes the wheels into and over damped condition (blue curve). The fix, is run the tires at low pressure and rely on tire compliance to soak up high speed terrain motions. 

10-dirt-target.png

The above examples show the two extremes of suspension tuning. Street setups damp the chassis at low speed and the wheels at high speed. Dirt setups damp the chassis over the entire suspension stroke range.

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Enduro vs MX setups

MX setups run stiff springs to prevent bottoming. Enduro setups run soft springs to improve suspension compliance. Those setups tune compression damping differently to work with the bottoming versus compliance trade.

Enduro suspension setup

Enduro setups have to deal with square edge root and rock impacts. To give the suspension a consistent “feel” on the high speed wheel bottoming stroke enduro setups tune compression damping to produce a peak compression damping force that is equal to the peak spring force and rebound force. Equal forces over the stroke gives the suspension a consistent “feel” on high speed wheel bottoming hits. 

11-enduro.png

Chassis bottoming occurs at lower velocities and at those speeds the shock produces less compression damping. Lower force on the chassis bottoming stroke gives the suspension more compliance. 

MX suspension setup

MX setups focus on controlling chassis bottoming on jump landings. To get a consistent “feel” through the chassis bottoming stroke compression damping is tuned to equal the peak rebound force. Matched forces on chassis bottoming requires r/c damping ratios in the 1.6:1 range.

12-mx.png

On high speed wheel bottoming strokes stiff damping used in MX setups produces a peak compression damping force that is higher than the peak spring force. That creates a setup that is stiff at bump impact and gets softer as forces fall to the peak spring force at bottoming. Stiff, but then blows through. That is why MX setups don’t work very well as a trail setup. For groomed mx tracks root and rock impacts are not an issue.

MX and enduro setups both tune rebound to zeta values of 0.7 for chassis control. Low speed compression damping is tuned to a 0.8:1 ratio to prevent packing. MX setups tune high speed compression damping to control chassis bottoming. Enduro setups tune for wheel bottoming. If you want to jump your bike you need to move toward the chassis compression damping control of an MX setup. If you want to make it on hill climbs you need to move toward the compliance of an enduro setup. Either way, force over stroke data shows you where your suspension is setup and the compromise made between chassis and wheel bottoming control.

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Marzocchi fork tuning for a Husqvarna te610

To compute suspension response you need three things: The shock compression damping curve; the rebound curve; and measurements of wheel versus shock position to figure out the suspension link ratio. That info along with the bike weight and spring rate dictate suspension response.

13-stock-damping.png

The above damping curves are from a stock 45mm Marzocchi fork on a Husqvarna te610. That same Marzocchi fork shows up on Ducati street bikes and you can see the street bike bend to the fork valving producing chassis damping at low speed and wheel damping at high speed.

14-te610-stock-rspn.png

Street style damping curves are not a bad setup for a dual sport, especially something with a supermoto bend. But I don’t want a dual-sport. I want an enduro setup for the te610 and fork valving that can take a whoop hit.

Switching the stock damping over to an enduro setup will take some work. Chassis rebound damping (green curve) needs to give zeta values of 0.7 to 0.75 across the stroke range. At stroke depths of 10 inches that requires doubling rebound damping. 

Low speed rebound/compression damping ratios need to be around 0.8:1 to prevent packing. That requires low speed compression damping to be increased by something around a factor of three. High speed r/c ratios need to be increased into the 3 to 3.5:1 range by “rule of thumb” tuning targets. Those compression damping targets are all ratios, so you have to get rebound damping setup first before compression damping can be tuned. 

Hitting those “rule of thumb” tuning targets will require some big changes to the setup. I’m going to step through the shim stack mods needed to hit those targets. But am stopping here to get some feedback on what is needed for a “good” baseline fork setup.

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Baseline suspension setup

No doubt, anything labeled a “baseline” is going to be heavily mocked as inadequate. I’m pushing out the setup anyway because I need a benchmark to compare suspension setups too in simple terms like softer or stiffer than the baseline.

The fast review is:

  • Spring calculators spec the spring rate
  • Rebound damping set for chassis control at zeta values of 0.7 to 0.75
  • Rebound/compression damping ratios:
    • 3.25:1 for a fork
    • 2.25:1 for a shock
  • Low speed compression
    • 0.8:1 below wheel speeds of 3 to 6 in/sec

Those “rules of thumb” set the peak damping force in compression and rebound to be approximately equal to the peak spring force. Thats enduro tuning and sets the forces yanking the wheel around to be approximately constant through the wheel bottoming stroke giving a consistent “feel” through the stroke. Chassis bottoming produces a progressive force increase through the compression stroke with rebound tuned for chassis control at zeta values of 0.7.

15-baseline-setup.png

Those “rules of thumb” aren’t new, just cobbled together suspension tuning webology junk. Each rule has a solid reason of “the why” and a tuning range that gives some clues when to switch to a softer or stiffer spring. For a baseline setup that is about all you can ask.

But is it good enough? There is no way to know without test riding it for yourself.

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Husky te610 fork rebound damping

The stock te610 fork needs more rebound damping to get zeta in the target range of 0.7. To get a damping target I plotted the increase in zeta needed on the rebound damping force curve. That gives some points to shoot for when hacking around on the rebound shim stack.

16-stock-rbnd.png

The clamp nut on a Marzocchi fork has a 9.4 mm shoulder clamping the stack. Since the stack needs to be stiffer I put some thick shims under the nut to get a larger, stiffer and more reliable clamp surface on the shim stack. Adding a 13.2, 15.2 and 18.15 shims to the top of the stack brings high speed rebound into the target range of a 2.5* increase.

17-stiffer-clamp.png

The stiffer clamp gets high speed rebound in the ballpark, but low speed is too stiff. To soften up load speed the rebound stack needs a crossover to soften low speed damping. 

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so if i understand all that correctly, i should go about 10 clicks out for the best baseline setting?

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Don't know if my deductions are good but this is what seems to work for me when experimenting on my forks/shock of both my bikes.

 

Set all the clickers halfway in their adjustment range, say you have 20 clicks available, set them at 10.  (if 22 @ 11, 24 @ 12 etc.)

If to get your perfect adjustments you need to open or close the clickers 5 clicks or more in either direction from the initial starting point,

you should remove/add a face shim from that dampening circuit and re-set your clickers at the middle point (10) and retry your testing.

 

When your perfect settings are achieved with the clickers within 1-2 clicks of the middle of the available range, 

it leaves you enough play in either direction to fine tune for daily conditions (hard/soft/muddy/rutted track etc.)

 

The detailed infos posted by Clicked are certainly very interesting but IMO way too elaborate for the average suspension tinkerer like myself.

The Race Tech Suspension Bible explains generalities on how each circuit functions

but what's really missing for us average guys is some sort of simpler guide which would suggest guidelines like:

 

-sand/soft track: preferred to stiffen these circuit (base valve, rebound) and/or run stiffer springs and, explanations for what reasons

-enduro/off-roading: soften the mid-valve and add float (starting points), soften the HS COMP, rocky/roots versus faster flowing terrain specs. etc.

-handling effects of soft springs & stiff valving versus stiff springs and soft valving (off-roaders are often tempted to use way soft springs)

-handling effects of changing the fork and shock spring preload

-what to tune first ?: face shims/clickers, high speed portion of the stack, mid-valve etc.

etc etc.

Real on track situations the average rider can relate to rather than charts and percentages.

Edited by mlatour
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Yep. All the gobbledygook many produce just puts the avg guy off. I think way too many are just stroking their egos. Wasted effort!

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A wasted effort is adding face shims to the stack thinking that is going to fix anything. That is a great way to fine tune a setup. The problem is the stock setup is way off – approaches for fine tuning just isn’t going to help.

1-stock.png

With the clickers at “10” zeta is pretty close to 0.7 for strokes around race sag. That makes the bike “feel” good on small strokes or bouncing the bike on the shown room floor. You aren’t going to know the suspension goes under damped on deep strokes until you start bouncing the bike off stuff on the trail.

To get stiffer rebound adding face shims makes sense, but there’s a limit. The shaft length on the rebound valve only allows adding four more shims. Still that is a 66% increase.

Adding those shims increases high speed damping to get zeta response values around 0.4, up from the stock values of 0.3. Still under damped at high speed. 

2-stiffer.png

The bigger problem is the stiffer stack generates a boat load of low speed damping and that is going to cause the suspension to pack on stroke depths around 5 inches. DRS already outlined the fix for that – open the clickers.

So - resetting the clickers from 10 to 26 clicks out fixes low speed and the open clickers don’t effect high speed much.

3-clickers.png

Adding face shims is an improvement, but to fix the setup zeta values at 10 inch stroke depths need to be in the 0.7 range and that requires high speed rebound damping to get a whole lot stiffer. We can’t add any more face shims because we are out of shaft length. But we can remove some of the 0.11mm thick stock shims and replace them with stiffer 0.2mm shims and keep the same shim stack height.

The stiffer stack is going to make low speed go over-damped and to keep that from happening I added four 1.2mm leak jets to the valve.

4-thicker.png

That combo gets high speed damping in the 0.7 zeta range – so we fixed that – but low speed damping at race sag is way down at zeta values around 0.2. That is way too under-damped and sloppy to consider riding imo. Close down the bleed to try and get some low speed damping and zeta values around 8 inch stroke depths is going to be over damped causing the suspension to pack. 

Adding face shims isn’t going to fix this setup.

The Fix

Going back to the stock setup zeta values were pretty nice around race sag. The problem is damping falls off at high speed. That setup is just screaming for a crossover. With a crossover you can keep the stock stack stiffness and damping at low speed and re-tune high speed to keep damping force from falling off.

That is the direction I am going.

1-stock.png

Edited by Clicked
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I would love to see this same sort of analysis for a Yamaha KYB rear shock, which is notorious for having a weak rebound setting.  Lots of ways out there of addressing it, and I'm pretty sure very few people have quantified the various methods like this to sort through which end up being BS.

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2 hours ago, GHILL28 said:

I would love to see this same sort of analysis for a Yamaha KYB rear shock, which is notorious for having a weak rebound setting.  Lots of ways out there of addressing it, and I'm pretty sure very few people have quantified the various methods like this to sort through which end up being BS.

They also have a very blunt needle and a narrow operating window I think. 

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On 05/06/2018 at 7:11 AM, Piney Woods said:

Yep. All the gobbledygook many produce just puts the avg guy off. I think way too many are just stroking their egos. Wasted effort!

Each to their own I personally enjoy clicked posts. The oid saying if you have nothing nice to say say nothing and move on. 

MM 

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Agreed MM. This stuff is gold, how to tune different parts of the damping range without affecting the other. It's a question often asked and often not answered.

The wisdom contained in this thread may well explain why some people struggle to get their shit sorted, you know, like 'it's great on the whoops but sucks on roots and stuff, I've tried changing springs and shims but still can't get it right' etc.

Carry on sharing Clicked, some of us appreciate it.

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Yes I mentioned it was complex for the average guy

but just understanding some of the generalities of it is always welcomed knowledge.

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Clicked - these threads are great and a wealth of information. Don't stop posting!

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