Author Topic: Spring pre load  (Read 12518 times)

Offline Huzo

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Spring pre load
« on: January 14, 2017, 06:17:21 AM »
For years I've sort of thought that winding up the pre load on a rear shock will make the ride stiffer, but recently I've wondered if that's just conventional wisdom, here's my question. If you take a shocker that has a given preload on it of say 20 kg then apply a load of 150 kg the unit will compress a bit, to a point where the spring will "feel" 150 kg of load  and will have compressed let's say 20mm. Now here's the thing, start again and wind on some more pre load, to say, 40 kg. Now apply the same 150 kg of load, the unit will depress until the spring stops compressing and that will be at a point where it is "feeling" that 150 kg except that it's compressed less to reach that state, let's say 10 mm. Now when you hit a bump in each situation, the spring will react the same because it's compressed to 150 kg but the ride height will be 10 mm different, am I in error here, because I've heard and seen some fairly well credentialed people say otherwise. Now anyone who's interested can of course comment, but please, no half baked analogies that don't apply. What I'm suggesting, is that altering the pre old only affects the ride height and not the "stiffness", as long as the load applied is enough to initially depress the shock from it's un loaded state. I've been accused of "over thinking" this sort of stuff, but what's the truth behind it ?
« Last Edit: January 14, 2017, 06:34:18 AM by Huzo »

Offline RANDM

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Re: Spring pre load
« Reply #1 on: January 14, 2017, 06:34:54 AM »
I'm pretty basic but for me the pre load sets the suspension
for the weight of the bike plus what your individual weight
and load is so that the suspension is at the optimal starting
point in it's stroke to have a full stroke, damping controls the stiffness.

Maurie.

Offline Huzo

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Re: Spring pre load
« Reply #2 on: January 14, 2017, 06:40:06 AM »
I'm pretty basic but for me the pre load sets the suspension
for the weight of the bike plus what your individual weight
and load is so that the suspension is at the optimal starting
point in it's stroke to have a full stroke, damping controls the stiffness.

Maurie.
Yeah good start Maurice I agree, but following your explanation, wouldn't an alteration of the pre load, just put the damper at a different part of it's stroke ? ie alter the ride height and bugger all else ?

Offline Wayne Orwig

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Re: Spring pre load
« Reply #3 on: January 14, 2017, 09:05:05 AM »
It also depends on the spring type.
With a normal spring I believe preload adjust only sets the height. Add load, adjust the preload to get the right height, and the spring is still going to react the same (though the added weight will dampen the ride)
With a progressive wound spring, if you add weight and adjust the preload, the ride will be harsher, because you are starting to bind coils. But, you are less likely to bottom out the shock. So it is a win/lose thing.
I think.
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Re: Spring pre load
« Reply #3 on: January 14, 2017, 09:05:05 AM »

Offline Dilliw

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Re: Spring pre load
« Reply #4 on: January 14, 2017, 09:49:41 AM »
Preload delays when the spring rate begins but doesn't change the spring rate.  More preload = more initial force to move the spring.  Once the spring starts moving the rate is the rate (if a Single Rate spring).   As Wayne says preload can impact the design of a shock system that has a dual rate or progressive rate spring. 

And I think that's the real consideration; you can't look at preload in isolation.  It impacts the geometry of the entire motorcycle so in some situations more preload/less rate is better and in some more rate/less preload is better.  That's why taking you and your bike to a pro is always the best idea...

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Offline Huzo

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Re: Spring pre load
« Reply #5 on: January 14, 2017, 02:57:07 PM »
Preload delays when the spring rate begins but doesn't change the spring rate.  More preload = more initial force to move the spring.  Once the spring starts moving the rate is the rate (if a Single Rate spring).   As Wayne says preload can impact the design of a shock system that has a dual rate or progressive rate spring. 

And I think that's the real consideration; you can't look at preload in isolation.  It impacts the geometry of the entire motorcycle so in some situations more preload/less rate is better and in some more rate/less preload is better.  That's why taking you and your bike to a pro is always the best idea...
Yeah it delays when the spring begins to compress I must grant you, but whether it's compressed  40 mm or 20 mm when loaded, the spring still only has the same load and is in the identical state, so I'm suggesting that the ONLY thing different in the two systems is the distance the bike had to sink when you jumped aboard to take up the weight, the rider will suggest "oh my suspension's firmer, it hardly sank when I sat on it", but I'm thinking that it's the same "stiffness" just at a higher position. Take an opposite example, what if you backed off the collar in your ohlins shock or whatever, so that there was no preload at all, now when you lept aboard, the bike would sink a long way but again once the spring "took up", it'd be in the same condition, but just a lot further down the stroke. No ? Hence ride height is now much lower, but everything else is unchanged. (I think!)
« Last Edit: January 14, 2017, 03:05:52 PM by Huzo »

Offline geoff in almonte

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Re: Spring pre load
« Reply #6 on: January 14, 2017, 04:36:27 PM »
What Mairie said.

I have been dealing with this on my Vintage.  PO installed a set of 'too stiff' springs in te forks- like waaaay too much spring.

This, for starters, makes for a relly harsh ride.  More importatnly, if you have too much preload the suspension never gets into the range where the hydraulics (compression & rebound) work.  The spring, once compressed on a bump in a corner, doesnt have an opportunity to rebound and any subsequent force generated by another bump or cornering causes the bike to ocilate (wallow).

At least that is how I understood the suspension guy's explanation.

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Offline johnr

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Re: Spring pre load
« Reply #7 on: January 14, 2017, 05:38:05 PM »
Preload delays when the spring rate begins but doesn't change the spring rate.  More preload = more initial force to move the spring.  Once the spring starts moving the rate is the rate (if a Single Rate spring).   

This is my understanding too. (and that of Girling)

I once inserted 1/4" spacers above the fork springs of my BSA R3 with a view to improving cornering clearance by increasing the fork preload.  Not a good idea and they didn't stay in long. (the next step would have been to use the 1 1/2" longer Lightning forks. Expensive though and I would then have needed a fork brace so it didn't happen.)
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Offline Bazil

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Re: Spring pre load
« Reply #8 on: January 14, 2017, 05:43:14 PM »
Glad you raised this Huzo.
 I have been struggling to understand whether I need heavier or lighter springs on my Mark IV, using the original Koni / Ikon rear shocks with progressive springs.  Currently I use the full travel on the rear shocks with pre-load set to the highest setting, and I reckon the suspension is a bit harsh, especially on the crappy secondary roads around here. I'm a lightweight ( but not as light as I used to be !) at around 65 kg ( 140 lbs to those Stateside).
I'm thinking I might be better off with stiffer progressive springs with minimum pre-load rather than what I have at the maximum pre-load, to give a more compliant ride, with the added bonus of being less likely to bottom out. I figure softer springs will make the ride compliant too, but will be even more likely to bottom out. Do you reckon I kidding myself?
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Offline neverquit

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Re: Spring pre load
« Reply #9 on: January 14, 2017, 08:52:06 PM »
Quote
to a point where the spring will "feel" 150 kg of load

In the first instance the spring will "feel" 170 kg of force, not 150 and in the second instance it will "feel" 190 kg.  So in these two cases the spring is not in an identical state, it is compressed more in the second case and will not react the same.

Offline Huzo

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Re: Spring pre load
« Reply #10 on: January 14, 2017, 09:34:46 PM »
Glad you raised this Huzo.
 I have been struggling to understand whether I need heavier or lighter springs on my Mark IV, using the original Koni / Ikon rear shocks with progressive springs.  Currently I use the full travel on the rear shocks with pre-load set to the highest setting, and I reckon the suspension is a bit harsh, especially on the crappy secondary roads around here. I'm a lightweight ( but not as light as I used to be !) at around 65 kg ( 140 lbs to those Stateside).
I'm thinking I might be better off with stiffer progressive springs with minimum pre-load rather than what I have at the maximum pre-load, to give a more compliant ride, with the added bonus of being less likely to bottom out. I figure softer springs will make the ride compliant too, but will be even more likely to bottom out. Do you reckon I kidding myself?
Firstly (and more importantly) where the bloody hell in central Victoria do you live, I'm in Creswick. Now if I'm right, and I'm probably not, the smaller wire in your springs will give a more compliant and "softer" ride, but alteration of the preload won't affect the harshness or otherwise, it'll just mean the bike won't "sag" as far when you get on, thus higher ride height. Still not sure though, but increasing pre load will reduce the tendency to bottom out 'cos you're higher up the travel range. I think!!

oldbike54

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Re: Spring pre load
« Reply #11 on: January 14, 2017, 09:38:50 PM »
 Changing preload does NOT change the effective spring rate . Didn't we settle this like 2 months back ?

 Dusty

Offline Huzo

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Re: Spring pre load
« Reply #12 on: January 14, 2017, 09:45:16 PM »
In the first instance the spring will "feel" 170 kg of force, not 150 and in the second instance it will "feel" 190 kg.  So in these two cases the spring is not in an identical state, it is compressed more in the second case and will not react the same.
Yeah mate I can do that level of math ok too, but I don't honestly think that's correct but I'm buggered if I can explain why, maybe 'cos I'm wrong. But surely the load "felt" by a spring isn't the preload PLUS the added weight. It's just that when you begin to load a spring, if it has 50 kg of preload then when you put say 70 kg of burden on it, the first 50 kg does not compress the spring  and only the last 20 is there to depress it resulting in a total load of... 70kg. So once the spring has left the top stop, the amount it was preloaded ceases to be a factor and only the burden (if you will), on the spring is experienced by the coils. Come on please someone, tell me you understand my point even if I'm in error.

Offline Huzo

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Re: Spring pre load
« Reply #13 on: January 14, 2017, 09:50:02 PM »

With a normal spring I believe preload adjust only sets the height. Add load, adjust the preload to get the right height, and the spring is still going to react the same (though the added weight will dampen the ride)

Yeah Wayne I've snipped your post just to keep on the track of the thrust of my post. If I'm reading you correctly we are on somewhat the same page, jeez I hope so...

Offline Huzo

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Re: Spring pre load
« Reply #14 on: January 14, 2017, 09:53:16 PM »
Changing preload does NOT change the effective spring rate . Didn't we settle this like 2 months back ?

 Dusty
Oh dear, if we did I've either forgotten or I didn't follow the thread. What was the title Dusty, do you remember? I'll search it if I can.

oldbike54

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Re: Spring pre load
« Reply #15 on: January 14, 2017, 09:57:29 PM »
Oh dear, if we did I've either forgotten or I didn't follow the thread. What was the title Dusty, do you remember? I'll search it if I can.

 Sorry , didn't mean to sound snarky , but memory says it was a thread started by you  :evil:

 Dusty

oldbike54

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Re: Spring pre load
« Reply #16 on: January 14, 2017, 10:07:08 PM »
 Actually Huzo , I was going to pull my post , you quoted me first so ... Anyway , apologies .

 Dusty

Offline Huzo

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Re: Spring pre load
« Reply #17 on: January 14, 2017, 10:16:55 PM »
Actually Huzo , I was going to pull my post , you quoted me first so ... Anyway , apologies .

 Dusty
No Dusty you don't "sound" like anything, I take you on your word always, so no problem. I've had this argument a dozen times, I just didn't recall it being on this forum. I'll bail out until someone brings something new to the table.

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Re: Spring pre load
« Reply #18 on: January 14, 2017, 10:37:38 PM »
Ok guys my question will sound either simple or dumb after reading all this. Let's us me and my 07 Calvin as the example. I weigh 160 and ride with no passenger. If I want the bike to squat a little lower when I mount her would I shorten the spring or back it off?

oldbike54

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Re: Spring pre load
« Reply #19 on: January 14, 2017, 10:44:04 PM »
 Back it off Dan .

 Dusty

Offline Wayne Orwig

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Re: Spring pre load
« Reply #20 on: January 14, 2017, 10:56:16 PM »
Ok guys my question will sound either simple or dumb after reading all this. Let's us me and my 07 Calvin as the example. I weigh 160 and ride with no passenger. If I want the bike to squat a little lower when I mount her would I shorten the spring or back it off?

Does the CalVin have rear preload adjustment, or just damping adjustment?
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Offline redhawk47

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Re: Spring pre load
« Reply #21 on: January 15, 2017, 01:54:56 AM »
Huzo's OP and #12 are correct. Some of the other are correct, others are not.

Preload affects ride height, steering geometry and handling.
Too little preload can result in the suspension bottoming.
Too much preload and the suspension might top out during the rebound from a bump, causing the wheel to leave the ground (and traction).

Ride height examples - if you have a spring with a rate of 100 lbs per inch, and the shock is vertical (usually the shock is at an angle but that require trig - so we won't go there_.
With no preload, if you put a load of 150 lbs on the bike, directly above the shock, the shock will compress/shorten 1.5".
If you put a preload of 50 lbs on the shock by moving the adjuster 1/2 inch, when you put the 150 lb load on, the shock will shorten 1".
If you put a preload of 100 lbs on the shock by moving the adjuster an additional 1/2 inch, when you put the 150 lb load on, the shock will shorten 1/2 inch.
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Offline flip

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Re: Spring pre load
« Reply #22 on: January 15, 2017, 02:22:05 PM »
Ok guys my question will sound either simple or dumb after reading all this. Let's us me and my 07 Calvin as the example. I weigh 160 and ride with no passenger. If I want the bike to squat a little lower when I mount her would I shorten the spring or back it off?

Back it off assuming the spring rate is good for you. I can't tell you by how much but if you shorten the spring it you will actually change the spring rate, making it heavier(stiffer).
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Offline RANDM

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Re: Spring pre load
« Reply #23 on: January 15, 2017, 04:12:16 PM »
Yeah good start Maurice I agree, but following your explanation, wouldn't an alteration of the pre load, just put the damper at a different part of it's stroke ? ie alter the ride height and bugger all else ?

Yes - that's exactly what it's for, and that's all it's for.

Let's get the picture right in our heads from the start -
A bike floats on it's springs, the right spring for a bike
is roughly one that will compress around 30-40mm with
the weight of the bike alone. When you hop on it will
compress more, the ideal being around another 25-30mm
And it's that bit that the Pre Load takes care of. If your
heavier than average you'll need more, if lighter less
Pre-load to set the suspension at that 25-30mm sag
when you hop on
which will then have the suspension
And Damping in the ideal part of its travel to work at it's best.

If you try to say sharpen your steering by raising the pre-load
on your rear suspension and the back now feels harsh it's
because you've changed the part of it's stroke the rear suspension
is working in - not "stiffened" anything.

A springs rate is it's rate it doesn't change. A Damper controls the
Springs movement at either end of it's useful travel. The Pre-Load
sets the suspension at the ideal height for Damping to be most
effective.

Maurie.

Offline Kiwi Dave

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Re: Spring pre load
« Reply #24 on: January 15, 2017, 05:34:56 PM »
A springs rate is it's rate it doesn't change. A Damper controls the
Springs movement at either end of it's useful travel. The Pre-Load
sets the suspension at the ideal height for Damping to be most
effective.

An excellent explanation.

What's also correct but perhaps a little hard to initially accept, if you shorten the spring by cutting it, the spring rate increases.  Conversely, place two identical springs in series and the overall spring rate is halved.

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Re: Spring pre load
« Reply #25 on: January 15, 2017, 06:49:35 PM »
Does the CalVin have rear preload adjustment, or just damping adjustment?
Wayne, the shock has the standard knoches at variable height settings on the bottom and on top of the shock a turn knob type of gadget. I've never seen one like this on any bike I've ever owned. I think that's the preload you were referring to. This is going to get complicated for someone with no experience with these shocks isn't it.

Offline Huzo

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Re: Spring pre load
« Reply #26 on: January 15, 2017, 07:45:31 PM »
An excellent explanation.

What's also correct but perhaps a little hard to initially accept, if you shorten the spring by cutting it, the spring rate increases.  Conversely, place two identical springs in series and the overall spring rate is halved.
Nah that's not too hard to accept, given that if you shorten a spring, there's less total distance in the length of the wire so each element of the spring has to flex further to achieve the same amount of compression ? The amount of force required to compress a spring is not proportional to the distance it's compressed, ie, it takes more than double the force to compress a coil 40 mm than it did to compress it 20 mm.

Offline LowRyter

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Re: Spring pre load
« Reply #27 on: January 15, 2017, 07:56:38 PM »
I must agree with Kiwi Dave.
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Re: Spring pre load
« Reply #28 on: January 15, 2017, 08:46:53 PM »
Can someone maybe give me a rule of thumb what would be the adjustment on the rear shocks on my 07 Calvin please. I am 160 lb and do not ride aggressively. I just want a soft as ride as possible without any bottoming out when sharper bumps are encountered. Please keep it simple as most of what I have read on this thread went right over my head. Maybe like the bottom adjustment should be on which notch ant the top adjuster at which position. This type of shock if Alien to me as my last bike had air shocks.

Offline RANDM

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Re: Spring pre load
« Reply #29 on: January 15, 2017, 11:35:36 PM »
Ncdan,
The normal layout of those type of shocks will have the stepped ring and a "pin" that fit s the step.
That's the preload - you'll have three to five steps at different heights and adjust it by rotating the ring
with a "C" spanner. I'd start by setting it to the middle as a base point and go from there.
 
The adjustment at the top is most likely for Rebound Damping - too much will slow the suspensions return
to it's original position too much resulting in the suspension packing down over say a series of bumps.

Too little rebound damping can create wallowing as the spring overcomes the damping and pushes the suspension
back after a bump past it's original starting point.

Think of the spring on it's own with no damping - you hit a bump, the wheel bounces up with the impact and will
bounce higher than the actual bump and then return and also push past the starting point and then cycle back and forth
until it settles back at the starting point, like early Cars with no Shocks. The Compression Damping controls the springs action so it doesn't just bounce
up wildly and follows the bumps contour more closely. The Rebound Damping controls the springs action as the suspension
comes back to it's starting point so it doesn't overextend.

Maurie.

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