Author Topic: This might come as a shock.  (Read 1326 times)

Online Huzo

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #30 on: September 22, 2021, 03:01:37 PM »
I'll have a stab for sh*ts and giggles

Compression damping
Controls the rate at which the spring compresses when an upward force is applied to the wheel - say a bump in the road

Rebound damping
Controls the rate at which the spring expands when the wheel comes across (say) - a hole in the road


I'm happy to delete this reply in it's entirety if I have that wrong!  :grin: :grin:
The damper will have a position where it is sitting during travel along a smooth surface, shall we say mid stroke.
When you hit a bump for example (it could have been a depression), the damper will be forced to compress somewhat until the bump is cleared, then the spring will force the wheel back down to the road surface. Note that the spring will slam the wheel back down faster than it would have fallen under itís own weight.
But without damping, the suspension will theoretically try to oscillate to and fro, past that idealised mid point that we have in our example, due to the inertia in the mass of the suspension components.

If we leave the bike for a moment so as to not be distracted by all the stuff going on in the reality of riding.

Again if we have our 200 mm spring out on the bench disassembled from the damper.
If you were to compress that spring say 50 mm then release it suddenly, high speed photography would show you that it recoils out PAST the 200 mm point to say 210 mm then back to 180 then out to 205 ....etc
That is an idealised set of numbers and possibly they would be a lot less, but the point is, the spring would oscillate around that mid point until enough WORK had been done for it to come to rest.
It wonít take long because the spring has low mass and therefore low kinetic energy.
In the reality of our heavy suspension components, they will try to oscillate for a longer time up and down each side of our mid point until the energy is dissipated, this is why we have our damping.
It forces the spring to act against a hydraulic resistance after the bump has been cleared and you are back on smooth road, so that oscillation is quickly reduced to zero.
Imagine you had a bike cranked up clear of the floor with the damper removed from the rear shock(s).
Compress the suspension to itís physical limit by some apparatus, the release it suddenly.
Youíd see the spring fire the swingarm back out to the normal position but the energy stored would take it past until the spring was actually STRETCHING, then that oscillation around the mid point would commence.
The work required in moving fluid through the ports of a damping unit is what dissipates that kinetic energy.

To directly address your suggestion.
If you run over a six inch high speed hump for example..
The primary task of the damper is not to control the RATE that the suspension compresses, because unless the suspension can compress to ALL of that six inches in the instant that you hit the bump the shortfall will be transferred into the frame and YOU will go up by the residual amount.
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.
« Last Edit: September 22, 2021, 03:14:06 PM by Huzo »

Online LowRyter

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • *
  • *
  • Posts: 15593
  • Location: Edmond OK
Re: This might come as a shock.
« Reply #31 on: September 22, 2021, 03:24:09 PM »
As soon as your butt hits the seat as you climb aboard, you get a signal as to the perceived ďfirmnessĒ of the suspension.

As an exercise.
Wind all the preload off your shock and jump on the bike, feet up with someone holding you level.
Have an assistant measure the length of the SPRING.
Now climb off and wind on a realistic amount of preload (say, 10mm).
Hop back on the bike with your feet up and with your scantily clad assistant holding you level, have your other assistant measure the SPRING length again.
It will be the same...(it will therefore perform the same).
Now put the tape measure away and stop looking at your scantily clad assistant..(donít be tempted to try measuring anything else...) :wink:

I hope the preceeding may serve useful to anyone who made no sense of my earlier offering.

That was discussion.  Although I didn't want to see Rich scantily clad.  BTW- I took his word on it that you're both right.
John L 
When life gets you down remember it's one down and the rest are up.  (1-N-23456)

Online Huzo

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #32 on: September 22, 2021, 05:19:21 PM »
That was discussion.  Although I didn't want to see Rich scantily clad.  BTW- I took his word on it that you're both right.
Can you re word that LR ?
I donít know Rich is.

Offline tris

  • Guzzi Hero
  • *****
  • *
  • *
  • Posts: 2377
  • Location: United Kingdom
Re: This might come as a shock.
« Reply #33 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:

2017 V9 Roamer
2005 Breva 1100 (non ABS) "Bruno" - now sold
1995 Cali 1100 - carby   "Dino" -now SOLD

Wildgoose Chase Moto Guzzi

Re: This might come as a shock.
« Reply #33 on: September 23, 2021, 03:20:36 AM »

Online SIR REAL ED

  • Guzzi Hero
  • *****
  • *
  • *
  • Posts: 1249
  • uh.... it's personal....
  • Location: Forest, VA
Re: This might come as a shock.
« Reply #34 on: September 23, 2021, 06:01:42 AM »
Well...?
The thread hasnít been nuked and a fight hasnít broken out yet. Thatís a bit of a shock isnít 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!
"There's two kinds of people in the world; those for whom no explanation is necessary, and those for whom no explanation is possible."

2016 KTM Duke 690
2019 Beta EVO 250
1982 Yamaha Seca 650
1999 Suzuki DR 650 w/790cc kit
1986 Honda XL600R

Online LowRyter

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • *
  • *
  • Posts: 15593
  • Location: Edmond OK
Re: This might come as a shock.
« Reply #35 on: September 23, 2021, 12:56:44 PM »
Can you re word that LR ?
I donít 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 
When life gets you down remember it's one down and the rest are up.  (1-N-23456)

Online Huzo

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #36 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.

Online Huzo

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #37 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 ďsofterĒ 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 letís have our 200 mm coil spring out on the bench, but this time itís 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

  • Guzzi B00b
  • Guzzi Mentor
  • ****
  • *
  • *
  • *
  • *
  • *
  • Posts: 828
  • Location: Nampa, Idaho
Re: This might come as a shock.
« Reply #38 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:
2019 Moto Guzzi Bobber Sport
2013 Beta Evo 300
2014 Husaberg FE501

Online lucian

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • *
  • Posts: 2823
  • Location: Maine, Ayuh
Re: This might come as a shock.
« Reply #39 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

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #40 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 whoís 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

  • Guzzi Hero
  • *****
  • *
  • *
  • *
  • Posts: 10110
  • Location: Creswick Australia
Re: This might come as a shock.
« Reply #41 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 itís top stop, it becomes irrelevant what force it took to preload it.
Itís just that the first bit of weight you applied when you STARTED to climb aboard, is not enough to start compression.
(Thatís where the seed is sown that itís ďstifferĒ).
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 itís 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 wonít 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 »

Online Caffeineo

  • Guzzi B00b
  • Guzzi Mentor
  • ****
  • *
  • *
  • *
  • *
  • *
  • Posts: 828
  • Location: Nampa, Idaho
Re: This might come as a shock.
« Reply #42 on: September 27, 2021, 12:39:17 PM »
At the instant that the damper comes off itís top stop, it becomes irrelevant what force it took to preload it.
Itís just that the first bit of weight you applied when you STARTED to climb aboard, is not enough to start compression.
(Thatís where the seed is sown that itís ďstifferĒ).
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 itís 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 wonít 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...... ;)
2019 Moto Guzzi Bobber Sport
2013 Beta Evo 300
2014 Husaberg FE501

Offline Guzzished

  • New Goose
  • *
  • Posts: 5
  • Location: UK
Re: This might come as a shock.
« Reply #43 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 ?

 

20 Ounce Stainless Steel Double Insulated Tumbler with donation credit
Buy a quality tumbler and support the forum at the same time!
Better than a YETI! BPA and Lead free.
Advertise Here