Author Topic: This might come as a shock.  (Read 3062 times)

Offline tris

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Re: This might come as a shock.
« Reply #30 on: September 23, 2021, 03:20:36 AM »
Again the PRIMARY function of the damper is to dissipate the residual energy in the system by compelling the spring to do WORK in the pumping of the fluid through the restrictions in the shock body.

Key phrase pop out in discussions like this and this is it for me. A far better way of phrasing it than my sorry attempt  :wink:

I think I'm about there now
https://www.youtube.com/watch?v=HmkvHTNQNxE

Thanks H and every one else for your input  :thumb: :thumb: :thumb:

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Offline SIR REAL ED

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Re: This might come as a shock.
« Reply #31 on: September 23, 2021, 06:01:42 AM »
Well...?
The thread hasn’t been nuked and a fight hasn’t broken out yet. That’s a bit of a shock isn’t it ?

Now that you mention it, it is a bit shocking that no one has gotten upset that the word "compression" is dangerously close to the work "oppression".... and that we should not be oppressing inanimate objects..... yet!

Springs have feelings too!!!!

We live in a very sensitive zeitgeist!
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Offline LowRyter

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Re: This might come as a shock.
« Reply #32 on: September 23, 2021, 12:56:44 PM »
Can you re word that LR ?
I don’t know Rich is.

Rich was the guy that was checking the sag on my Ducati last weekend.  Just as I described earlier, he held and measured the bike when I sat on it and picked it up.  Ultimately made no adjustments (which was close enough for me).   He was impressed how little stiction in the suspension but thought that heavier springs might improve the ride and that the shock had too much high speed compression (jolt -not adjustable). 

His statements were square with yours but I still don't quite grasp it all.  Rich was a club racer for many years and owned a company that sold motorcycle springs. 
John L 
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Online Huzo

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Re: This might come as a shock.
« Reply #33 on: September 23, 2021, 03:56:28 PM »
Rich was the guy that was checking the sag on my Ducati last weekend.  Just as I described earlier, he held and measured the bike when I sat on it and picked it up.  Ultimately made no adjustments (which was close enough for me).   He was impressed how little stiction in the suspension but thought that heavier springs might improve the ride and that the shock had too much high speed compression (jolt -not adjustable). 

His statements were square with yours but I still don't quite grasp it all.  Rich was a club racer for many years and owned a company that sold motorcycle springs.
Oh, ok mate.

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Re: This might come as a shock.
« Reply #33 on: September 23, 2021, 03:56:28 PM »

Online Huzo

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Re: This might come as a shock.
« Reply #34 on: September 26, 2021, 05:52:32 PM »
Kiwi Dave made a remark regarding progressive springs.
Even in the case of a progressive spring, the ride quality will not change  if you alter pre load and nothing else. Again you must remain between the top and bottom limits of your travel.
We all accept that the “softer” part of the spring is the first to be compressed as you commence loading and the spring rate increases as you continue to load.

But again let’s have our 200 mm coil spring out on the bench, but this time it’s progressive.
If you apply enough load to compress that coil 50 mm, the initial compressing action will have been relatively easy, but rapidly became more difficult.
But the total amount of compression remains to be 50 mm to give a compressed length of 150 mm.

Now if you assemble your unit with NO pre load, the damper will compress 50 mm under the same load.
Unload the unit.

If you wind on 25 mm of pre load the SPRING length will be 175 mm, now apply the same load again.
The shock will not start to compress until (say half) of the load is added, then as you let the full weight onto the shock, it will again compress to stabilise to the same 150 mm SPRING length as before.

Progressive or linear, ride quality is not affected by pre load.

Online Caffeineo

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Re: This might come as a shock.
« Reply #35 on: September 26, 2021, 06:19:00 PM »
<snip> ride quality is not affected by pre load.

This, for some reason is the hardest concept for me to fully grasp. I have always thought that adding preload will make the ride stiffer......becaus e you are "pre loading" the spring. I know the spring rate is still the same and it still takes the same weight/force to compress the spring a specific amount with/without preload. Maybe just hard to let go of after years of hearing about adding preload to stiffen up the spring...... Kind of reminds me of trying to understand trigonometry many,, many years ago. I just need to keep thinking about it until something clicks. Thanks for posting all this.  :thumb:
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Online lucian

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Re: This might come as a shock.
« Reply #36 on: September 26, 2021, 06:54:28 PM »
The term preload says it all . you are pre loading the spring to compensate for a given load yet to be applied to keep the desired ride height and  suspension geometry within the ideal operating range. A loaded rear spring relative to it's preload setting will have measurable effects on handling especially if compensation to the front suspension is not considered. My guess is if the op cranks up the rear pre load a bit as well as the rear rebound damping he will cure the wobble issue. Also, I would be banding the front forks to monitor  rider sag while actually riding to determine if front preload and damping adjustments are necessary. Anyone who has  ever overloaded a pickup truck and had their front end pointing towards the moon will remember the front end all over the road. Even though the rear springs were not bottomed out to the axle, Vehicle  load relative  to  pre load ,wheelbase/ chassis geometry may not affect spring rate but will  defiantly affect   handling . Speed only magnifies anomalies. 

Online Huzo

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Re: This might come as a shock.
« Reply #37 on: September 26, 2021, 07:45:23 PM »
Anyone who has  ever overloaded a pickup truck and had their front end pointing towards the moon will remember the front end all over the road.
Yes Lucian.
That is primarily because of the large rearwards displacement of the centre of mass.
The rear drives on a rigid tray truck, are a fair way forward of the back end. Indeed, ANY mass applied rearwards of the drives, will remove weight from the steer wheels...(no surprises there for anyone who’s ever been on a seesaw or teeter totter).
But in any and all cases in rigid trucks, addition of mass evenly over the cargo area, will move the C of M rearwards.

Online Huzo

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Re: This might come as a shock.
« Reply #38 on: September 26, 2021, 07:57:42 PM »
This, for some reason is the hardest concept for me to fully grasp. I have always thought that adding preload will make the ride stiffer......becaus e you are "pre loading" the spring. I know the spring rate is still the same and it still takes the same weight/force to compress the spring a specific amount with/without preload. Maybe just hard to let go of after years of hearing about adding preload to stiffen up the spring...... Kind of reminds me of trying to understand trigonometry many,, many years ago. I just need to keep thinking about it until something clicks. Thanks for posting all this.  :thumb:
At the instant that the damper comes off it’s top stop, it becomes irrelevant what force it took to preload it.
It’s just that the first bit of weight you applied when you STARTED to climb aboard, is not enough to start compression.
(That’s where the seed is sown that it’s “stiffer”).
If 25 mm of pre load (as in our example), has applied 40 kg, then any load less than 40 kg will not cause further compression.
But exceeding that 40 kg with the remaining load, will then take the spring to it’s stabilised length.

It may help to think of preload in terms of mass (kg), rather than distance (mm).

If your spring is bearing 200 kg it will compress to 150 mm.
If you pre load it 40 kg, the first 40 kg that YOU supply when getting on won’t move the shock, but the remaining 160 kg will.
In each case, the spring when loaded with 200 kg and stabilised, will be 150 mm length.
So the progressive PERFORMANCE of the spring will still be evident in use, but how much it was PRELOADED is irrelevant.
« Last Edit: September 27, 2021, 01:24:27 AM by Huzo »

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Re: This might come as a shock.
« Reply #39 on: September 27, 2021, 12:39:17 PM »
At the instant that the damper comes off it’s top stop, it becomes irrelevant what force it took to preload it.
It’s just that the first bit of weight you applied when you STARTED to climb aboard, is not enough to start compression.
(That’s where the seed is sown that it’s “stiffer”).
If 25 mm of pre load (as in our example), has applied 40 kg, then any load less than 40 kg will not cause further compression.
But exceeding that 40 kg with the remaining load, will then take the spring to it’s stabilised length.

It may help to think of preload in terms of mass (kg), rather than distance (mm).

If your spring is bearing 200 kg it will compress to 150 mm.
If you pre load it 40 kg, the first 40 kg that YOU supply when getting on won’t move the shock, but the remaining 160 kg will.
In each case, the spring when loaded with 200 kg and stabilised, will be 150 mm length.
So the progressive PERFORMANCE of the spring will still be evident in use, but how much it was PRELOADED is irrelevant.

Thanks for all the explanations and......just when I think I am getting "it" I add in the position of the dampner.... It helped me to think that if I only put say 50% of my weight on the bike the spring will "preload" then the rest of my weight will still cause the spring to compress the same amount as if I had just put all my weight on the bike. But......preload is to get the shock to ride higher in the stroke so it will be in the soft range and not ride in the higher resistance toward the end of the range of travel. I just need to let this roll around in my head but think I am making progress...... ;)
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Offline Guzzished

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Re: This might come as a shock.
« Reply #40 on: September 27, 2021, 04:02:15 PM »


Hagon have come back to tell me I need 18Kg (/mm?) springs as opposed the 17Kg on the bike now

Per cm I think you'll find.
I'll be VERY interested in your impressions/conclusions of the replacements.
Personally I find Hagons invariably supply intolerably hard shocks.
Do the 17Kg/cm shocks you have now feel too soft ?

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