Help me understand Pre-load

[Huzo]

The inherent stiffness (the resistance per mm/inch of travel) remains identical throughout the stroke,

I’d probably need another look at this bit with regards to a progressive spring, but I’ll settle for now.
Thanks for staying engaged.

[SIR REAL ED]

Why would it be stiffer?  Adding preload does not make the suspension stiffer, except in the fully topped-out position.  Read the rest of this thread - most people commenting know what they are talking about.

 

I should not have used the word stiffer.  What I meant to say was the force needed to get the suspension to initially move might be higher if a large amount of additional preload resulted in a small gain in leverage advantage.

As noted previously, the original post question was answered accurately and succinctly in the first reply over six years ago.  Everything since that post makes this an extremely entertaining thread!!   

[SIR REAL ED]

Progressive springs become stiffer with more preload, as one example.

You are correct in that by adding preload, the softer part of the progressive rate spring will be compressed first.

A progressive spring, say 50-100 pounds per inch, will be gradually transformed into a 60-100 spring, then a 70-100 spring, then a 80-100 spring, etc. as preload is added (or as the shock is compressed during riding) and the spring becomes shorter.

If this was not true, there would be no point in designing a progressive rate spring.

This was really obvious in the days when some shock absorbers had two springs with different wire diameters.

Springs in series function like electrical resistors in parallel.  Springs in parallel function like resistors in series.

[SIR REAL ED]

Whether you do or not, my head will not wrap around it 

Erik,

Don't sell yourself short.  Check out the picture in the link I posted in reply # 122.  It is a very simple concept.  We humans often make things seem complicated by over thinking and throwing in unnecessary verbiage.

[YellowDuck]

Progressive Spacing: Because the spring is progressive, the coils are spaced unevenly. Compressing it with preload shifts the shock into a different part of its travel, meaning it may sit slightly deeper into a stiffer or softer section of the overall progressive curve depending on the design.

No, this part is wrong.  It is AI confusing progressive springs with linkage ratios.

Like Huzo, I am running out of words to explain it.  The spring will be compressed as much as it needs to be compressed to support the weight of bike and rider.  All preload does is determine where the shock is in its stroke at that point.  It changes where the spring perch is located on the shock body.  That's it.  Or, in the case of forks, how far the top of the spring is from the fork cap.  If the spring is resting directly against the bottom of the fork cap, adding 1 mm preload is exactly the same as adding a 1 mm washer between the spring and the fork cap.  All it does is extend the forks by 1 mm, and therefore lift the bike by 1 mm.  That is true right up to the point where the forks are topped out.  After that, adding another 1 mm washer requires compressing the spring by 1 mm.   When people say that adding preload increases spring compression and therefore stiffness, what they are saying is only true in that last situation - topped out suspension.  How much of your riding occurs with the suspension fully extended?  Almost none, unless you are really into wheelies, or lifting the rear wheel under braking.

Progressive springs need a lower amount of force to compress them for each mm of travel at first, and as they get more compressed the more narrowly spaced coils eventually get coil bound, and so the spring now needs more force per unit compression.  This is true.  But adding preload doesn't change how much the spring needs to compress to support the vehicle weight, so it is acting in the same part of its compression range as it would be if you hadn't added the preload.   

Preload it just about getting the shock extended enough, but not too much, so that bottoming it out and topping it out are both unlikely.  Changing preload is about shifting the likelihood that one or the other of those two things happens.   

[kingoffleece]

I provided the link to Tony's book.
It's all there.

[SIR REAL ED]

I provided the link to Tony's book.
It's all there.

Yeah, but that would require reading, which is almost as hard as thinking......

Now, if we could find someone to read the book out loud.... and bring milk, cookies, and our favorite blankie.....

"Gather round posters, it's time for the Moto Guzzi story book hour!"

 

[jacksonracingcomau]

Never hurts to listen to the doctor
John Wittner talking about pre load in cycle world Jan 88
Point 14 in this

[faffi]

Never hurts to listen to the doctor
John Wittner talking about pre load in cycle world Jan 88

Thanks! Going to dig out the issue and make it an easier read for meself.

[cappisj1]

The sole purpose of adding preload to the rear shock is it puts more weight on the front tire contact patch. Have you ever loaded for a trip pulled out of the drive and the front was light feeling and funky to steer? Then you got off and added preload or spring tension to the shocks. That adjustment moved weight to the front tire. Preload will shorten/reduce your sag numbers and raise your ride high. Ride hight and sag and even measuring the spring are just ways to measure the same thing and so you can keep track of your changes. Most of us need new shocks or new springs at a minimum built for our personal weight to get preload and ride hight to work correctly. Rebound simply slows down or speeds up how fast the shocks return after a bump collapses them. Faster rebound or a harsher ride for spirted rides or slow soft rebound for luxuries rides.

[faffi]

I would claim that it is just as much done to prevent bottoming of the suspension with added load and/or to improve comfort, as it is to improve handling.

[Huzo]

I would claim that it is just as much done to prevent bottoming of the suspension with added load and/or to improve comfort, as it is to improve handling.

Yep.
Would move the c of m bugger all.
Try a set of bathroom scales under the front wheel with zero and then full preload.
That’ll tell you.
Remember faffi, it won’t alter the comfort level because it hasn’t changed the spring performance. As you say, it’s just kept the suspension somewhere near the middle of the available stroke.
ie…Away from the bump stops.

[cappisj1]

Comfort is a byproduct of a properly adjusted suspension. Correct suspension adjustment is to make the bike perform the way you want. When it performs the way you want it feels better to ride (giving you confidence). Comfort is just the result of the geometry for the bike and you being correctly adjusted.

[bad Chad]

This thread is a testament to why 80-90% of riders never touch their suspension.

[Huzo]

This thread is a testament to why 80-90% of riders never touch their suspension.

Well Chad, I don’t have any evidence to the contrary, but I have NEVER altered the preload on my front forks…Never.
Last time they were set was in Mandello del Lario in 2007.
Also I fitted a Nitron shock in London at 90,000 km and 9 years and have never altered it either. It’s still a better handling bike than I am a rider, so I leave the damn thing alone.
I will confess though, I am getting keen to get my hands on the new Ohlins.

[faffi]

I have modified the damper rods in several fork assemblies, altered preload, altered oil viscosity and level, changed springs and also cut down springs to better suit my needs. I have one rule of thumb; When I brake as hard as possible over a slightly rough surface, I want at least 1/4 inch of unused travel that can deal with bumps, because a bottomed out fork means the tire will lock with little provocation.

[Huzo]

I want at least 1/4 inch of unused travel that can deal with bumps, because a bottomed out fork means the tire will lock with little provocation.

So in that condition, doesn’t that mean that any bump greater than 1/4 inch, will bottom out the forks ?
Also, for a guy that freely admits he doesn’t understand preload, you sure have done a lot of “fine tuning…”
But I guess a bit of judicious hacksaw and hole drilling action, should fix up any mistakes and poor engineering that took place in Mandello del Lario.

[faffi]

So in that condition, doesn’t that mean that any bump greater than 1/4 inch, will bottom out the forks ?
Also, for a guy that freely admits he doesn’t understand preload, you sure have done a lot of “fine tuning…”
But I guess a bit of judicious hacksaw and hole drilling action, should fix up any mistakes and poor engineering that took place in Mandello del Lario.

Oil will slow down the action, so it will take more than a 1/4in bump. Also, the "rate" of the bump matter - if it is a sharp line going up 1/4in, the kick will be far more severe than if it goes up 1/4" over 2 inches in length.

I understand you are trying to take the pee out of me, and I probably derserve that, but I have learned enough through Race Tech's suspension bible (are we allowed to write bible?) and my Dave Moss membership for years to understand how damping and sprining affects the bike. Not well enough to set up a motoGP bike, but well enough to understand whether my actions led to improvements. Or not. Despite not understanding the calculus.

For instance, even if I do not automatically comprehend it, cutting a straight spring in two will double its spring rate. On a progressive spring, the spring will stiffen less if I cut off the widely spaced coils than the tightly wound ones. Also, when it comes to old style fork dampers, I know that I prefer my bikes to be supported mostly by the springs, and less by compression damping. Hence I will live with rapid dive under braking in order for my suspension to react over sharp bumps rather than going into hydro-lock. Quite often, Japanese motorcycles came with too much compression damping and too little rebound. So making the holes for the compression damping larger and finding the oil viscosity that give me the desired amount of rebound damping gives me a much more compliant ride that is still well controlled. And I want a spring rate that do not require more than an inch of preload in order to achieve the correct amount of sag. Also, there should be noticeable sag from the bike alone, if the bike sit nearly topped out without a rider in order to get the correct total sag, the springs are too soft. And so on. Not claiming it will work for everyone, but it works for me, and I have found it to be well worth the invested time.

[Huzo]

On a progressive spring, the spring will stiffen more if I cut off the widely spaced coils than the tightly wound ones.

Would you like to try that the other way around, or are you happy with it ?
Remember on your progressive spring, the “softer” part of the spring is the tightly wound part, so cutting off the widely spaced part will leave a greater percentage of the spring comprised of the closely wound section.

[kingoffleece]

Well, for one thing no matter what one does to a damper rod setup it will never be good with the exception of a very narrow range.  The oil will either move too slow to matter or too fast and suffer from a hydraulic lock.  For you tech types this is VERY basic but purposely so as to be understood.  Get Gold Valves if you have damper rods.  Cheap enough and, amazingly, you'll get it right the first time.

As for 80-90% of folks never touching adjustments?  Let's say it again and keep it simple.  Set the sag and you'll be MUCH better off.+  That's how you'll know if your spring rate is in the building.  Without that forget it.  You're toasted until it's fixed.

For those "hey, it's stock and it's fine for me", yes, it is.  No worries.  For those asking the questions and you want better (like not being thrown out of the seat better-not MotoGP better) than the simple steps are sag and Gold valves for the front if you have damper rods.  Not real expensive.  Riders who have never experienced a properly set up and tuned suspension have no idea how much more enjoyable an everyday road motorcycle can be.  A V7 will be transformed.  A V85 will be very much improved. 

A proper rear spring won't make a crappy OEM shock good, but it will make it better than it was.

I should define "good".  Keeping the tires in contact in all situations and the geometry of the motorcycle consistent are the desired outcomes.  Just to be clear.

[faffi]

Would you like to try that the other way around, or are you happy with it ?
Remember on your progressive spring, the “softer” part of the spring is the tightly wound part, so cutting off the widely spaced part will leave a greater percentage of the spring comprised of the closely wound section.

That is what you get when typing while on the phone  Thanks, I will correct my post accordingly.

[faffi]

Well, for one thing no matter what one does to a damper rod setup it will never be good with the exception of a very narrow range.  The oil will either move too slow to matter or too fast and suffer from a hydraulic lock.  For you tech types this is VERY basic but purposely so as to be understood.  Get Gold Valves if you have damper rods.  Cheap enough and, amazingly, you'll get it right the first time.

Absolutely correct. YSS also sell valves similar to Race Tech gold valves at a much lower price, but they are not custom made/set up for each model, only to fit inside the fork leg in question.

DDC valves by Cogent are the simplest to put in, but they are made only for a limited range of models. Unlike gold valves/YSS valves, these just drop in, no drilling required, no adjustments. Downside? Just like with the stock setup, you will alter both compression and rebound when changing oil viscosity, and oil viscosity is the only way to adjust damping. Regardless, I found them to work very well on the MT-07.

[YellowDuck]

For those in the "I never touch it and it's fine" camp, be aware that for Moto Guzzis with adjustable suspension, there are suggested suspension settings printed in the manual, but there is no guarantee that your bike came delivered adjusted that way. 

I don't know if suspension adjustment is a factory thing, or something the dealer does when the uncrate it, but my front suspension came with preload set to one line out from full in, when the manual says one line in from full out. 

I am a total suspension weenie, and so always play with all of the settings right away on an new bike - trying both extreme ends of the damping setup, for example, to see what difference it makes.

I can report that on my V85 Strada, the settings printed in the manual ended up being as good as anything I could come up with, for the type of riding I do.  Now that the suspension is broken in, I can say that the stock stuff is better than the OEM suspension that has come on any new bike I have ever purchased.  I may eventually modify it just for something to do, but honestly it really doesn't need anything.  Normally I would be annoyed by the lack of compression damping adjustment, but on this bike it really is just fine.

Re: preload I agree with faffi.  Monitor travel with a zip tie and brake and corner as hard as you think you ever will, ride the bumpiest roads, etc.  Adjust preload so those conditions still leave you some positive travel, but not too much, otherwise you are sacrificing extension travel for no reason.  It doesn't need to be more complicated than that.
   

[Ncdan]

This thread is a testament to why 80-90% of riders never touch their suspension.

This^^^^
and the other 10-20 percent makes it worse when WE do🤔

[Huzo]

Anywaaayyyy….
The main job is done here, no one will now say…
“I cranked up the preload to get the suspension a bit firmer…”
(Jeeez, they had better not..) 

[SIR REAL ED]

Anywaaayyyy….
The main job is done here, no one will now say…
“I cranked up the preload to get the suspension a bit firmer…”
(Jeeez, they had better not..) 

C'mon mate!  That is exactly the function of pre-load.  It says so right in the word "pre-load!"   

Ya just have to decide, what size bumps you want to hit to get the rear suspension moving.

"I didn't feel the 1/2" bumps at 30 mph, but the bike bottomed out on the 2" bumps at 60 mph!  So I jacked up the pre-load and now the bike does not bottom on the 2" bumps at 60 mph, but I can now feel the 1/2" bumps at 30 mph!  I should probably get on the internet to find a solution......"

 

[bad Chad]

I posted this thread, and dispite Huzo’s claim, I still don’t have a reasonable understanding of the process.

[Bulldog9]

Well this thread did NOT disappoint for entertainment.   Then again, sometimes Dan gets to the thread and sends the more interesting posts to the trashbin before many can see it 

One thing that helped me understand preload was when I had the Hagon Shocks built for the Mello Yello Stornello

They were a dual spring shock, with a small upper spring for 'initial softness' but the main spring was a constant tension, and they put in a spring that when set at the lowest preload was for a 200lb rider, the 3 preload settings went up from there with:

#1 for a rider with loaded bags, IIRC 250,
#2 was for a rider and passenger so 300,
#3 The highest preload setting was for the rider, passenger and full luggage 325-350.

Each setting/ramp of the spring increased preloaded therefore more tension on the spring, and as a result kept sag at appropriate levels depending on how much weight you were carrying. This not only helped protect against bottoming out the shock when loaded, it also kept the sag in line.  The hagons had little bumper slides on the shock rod, so I could see if I was bottoming the shock out. The ideal setting guaranteed that the bumpers were never pushed all the way to the bottom, or bottoming out (the hagons were USD). The preload setting did also make a difference in how the bike sat static (just bike weight) or with rider seated. On the lowest preload, the bike would drop about 1/2" and on the highest preload, it stayed almost topped out when taken off the center stand. The same was true depending on load. I set the preload 0n #2 so I wouldn't have to keep messing with it. I don't recall the lovely Mrs Bulldog ever riding pillion on the Stornello.

Not sure this will help Chad, but it helped me.

I'm not picky on suspension, heck, I rode an XS1100 on the stock rear shocks and front air fork for 30 years, and only changed my fork oil once..... (Yeah, I'm a savage). 

I guess I am in the 20% that does, and I've always been happy. My 'scientific' method for getting preload and suspension sorted is to adjust whatever there is to adjust, grab the front brake and bounce up and down on the seat until the bike 'settled' equally. I found this helped to remove porpoising (pitching back and forth) over bumps.  Each bike is different, some have front preload/compression only, some (most) rear only. Some like the Stornello only have rear preload.

On bikes like the Griso, 1200 Sport, or Norge, I will generally start with what the OM says is the base setting and adjust from there. I'd never claim that it is 'right' but that balanced front/rear response for sag and speed has worked for me. The rest "Is what it is" and I adjust to the bike.

I just came back from a long ride on the Norge (3500+ miles and 15 states) Given the weight of my load, I was scraping the pegs and my boots on the fast sweepers especially with camber, so I upped the preload for a higher/highest preload and loaded rear ride height. And I am NOT a peg scraper anymore, nor did I scrub the tire to the edges. It was all suspension height, and upping the preload to MAX gave me the rear ride height I needed.  And NO it was not any stiffer as a result. I like the handling of the bike so much better, I'm leaving it that way.

[MikeP996]

 I've purchased high-dollar cartridge forks/fully adjustable rears for two different machines and I have active suspension on another.  TBH, for street riding I've never been able to tell any useful difference between them and the basic OEM suspension regardless of adjustment. 

IOW, FOR ME...the shock/fork "upgrades" were a waste of money...

[faffi]

TBH, for street riding I've never been able to tell any useful difference between them and the basic OEM suspension regardless of adjustment. 

Perhaps you have just been lucky with the starting points, but for me the improvements have mostly been impressive.