RaceTech Gold Valve Emulators and Springs...

[DirtFlier]

Here's where I respectively disagree with a few of you.

Yes, the spring rate remains the same regardless of preload setting but it can and does effect the feel of harshness - and not just raising the bike at that end. Adding preload effects the first 20-25 mm of travel because it take more force to overcome the additional tension. At least to me, this is the nicest part of spring's travel and adding too much preload can ruin that feeling.

Lowering the oil level in forks to make them softer is only noticeable after about 1/2 stroke when the air inside starts to compress. During the first 20-25 mm of fork travel, dropping the oil level is not noticeable. I've always felt oil level adjustments worked best when trying to minimize or eliminate harsh bottoming.

 

[670cc]

Here's where I respectively disagree with a few of you.

Yes, the spring rate remains the same regardless of preload setting but it can and does effect the feel of harshness - and not just raising the bike at that end. Adding preload effects the first 20-25 mm of travel because it take more force to overcome the additional tension. At least to me, this is the nicest part of spring's travel and adding too much preload can ruin that feeling.

Lowering the oil level in forks to make them softer is only noticeable after about 1/2 stroke when the air inside starts to compress. During the first 20-25 mm of fork travel, dropping the oil level is not noticeable. I've always felt oil level adjustments worked best when trying to minimize or eliminate harsh bottoming.

Ah, but that's the issue. There is no additional tension. The weight of the bike presses down on the spring with the same force as the spring pushes up on the bike. Until you reach the end of fork travel, adding preload does not compress or add tension to the spring.

Put a coil spring on the floor and put a weight on top. Measure the spring length. Add "preload" by putting a block between the spring and the weight. With the same weight on top, measure the spring length. The spring length is the same and the spring rate is the same, but the weight is higher off the floor by the thickness of the block. Likewise if you add a spacer on top of a fork spring for preload, as long as the fork hasn't reached a physical limit, the spring rate, "tension", and spring length are the same but the bike sits higher.

Preload sets the sag or ride height so the suspension can operate effectively within it's limits of travel. If you can feel a difference in that first 20-25 mm of travel with added preload, can you explain the physics of why that is?

I think we've had this discussion before, but coming to an agreement was futile.

 

[DirtFlier]

Yes, we can agree to disagree...again.

 

[dduelin]

Here's where I respectively disagree with a few of you.

Yes, the spring rate remains the same regardless of preload setting but it can and does effect the feel of harshness - and not just raising the bike at that end. Adding preload effects the first 20-25 mm of travel because it take more force to overcome the additional tension. At least to me, this is the nicest part of spring's travel and adding too much preload can ruin that feeling.

A common misconception. It's simply not true. Respectfully of course.

Lowering the oil level in forks to make them softer is only noticeable after about 1/2 stroke when the air inside starts to compress. During the first 20-25 mm of fork travel, dropping the oil level is not noticeable. I've always felt oil level adjustments worked best when trying to minimize or eliminate harsh bottoming.

I do agree with you on oil level affecting the last 1/2 to 1/3 travel. The OP was (is) using non traditional terms to describe what he's trying to accomplish. I threw oil level out there because it does affect harshness in the last part of fork travel. Who knows what "tight" means?

 

[DirtFlier]

OK, it's first thing in the morning for me so I'll give it a stab.

670 said: "Add "preload" by putting a block between the spring and the weight. With the same weight on top, measure the spring length. The spring length is the same and the spring rate is the same.."

No - the spring did get shorter because of adding preload. The length could only remain the same if the opposite end of the spring was free but it's not free and is firmly retained by the shock or internally within the fork tube.

Yes - the spring rate remains the same because you haven't changed the diameter of the wire (coil spring) or the total length of the wire.

Let's stay you had a spring with 250 mm of free length when sitting on your workbench.

- When you compress it while it sits at "free length," it's fairly easy to compress.

- If you preload that spring by 20 mm, it will take more force to make the spring compress INITIALLY. Yes or No?

Spring rates are quoted as lbs-per-inch or kg-per-mm. And for each increment it increases by a set amount, for example: 1-inch = 100 lbs, 2-inch = 200 lbs, etc., and these are purely hypothetical numbers.

If you preload the spring so it takes 150 lbs to overcome that first inch, then it feels stiffer to the rider but once you get past that first inch, everything is the same as before: 200, 300, etc. You have not made the spring stronger via your preload adjustments and all you have effected is the initial movement.

Preload adjustments can only be expected to help on the small stuff - minor imperfections on the roadway or small bumps - and not for monster potholes or "g-out" dips. Manufacturers don't add preload adjusters to the shock and sometimes to forks to help the rider with seat height - it's all about making the bike comfy for the rider.

If you guys still disagree then it's fine with me and please have a wonderful day.

 

[670cc]

OK, it's first thing in the morning for me so I'll give it a stab.

670 said: "Add "preload" by putting a block between the spring and the weight. With the same weight on top, measure the spring length. The spring length is the same and the spring rate is the same.."

No - the spring did get shorter because of adding preload. The length could only remain the same if the opposite end of the spring was free but it's not free and is firmly retained by the shock or internally within the fork tube.

Yes - the spring rate remains the same because you haven't changed the diameter of the wire (coil spring) or the total length of the wire.

Let's stay you had a spring with 250 mm of free length when sitting on your workbench.

- When you compress it while it sits at "free length," it's fairly easy to compress.

- If you preload that spring by 20 mm, it will take more force to make the spring compress INITIALLY. Yes or No?

Spring rates are quoted as lbs-per-inch or kg-per-mm. And for each increment it increases by a set amount, for example: 1-inch = 100 lbs, 2-inch = 200 lbs, etc., and these are purely hypothetical numbers.

If you preload the spring so it takes 150 lbs to overcome that first inch, then it feels stiffer to the rider but once you get past that first inch, everything is the same as before: 200, 300, etc. You have not made the spring stronger via your preload adjustments and all you have effected is the initial movement.

Preload adjustments can only be expected to help on the small stuff - minor imperfections on the roadway or small bumps - and not for monster potholes or "g-out" dips. Manufacturers don't add preload adjusters to the shock and sometimes to forks to help the rider with seat height - it's all about making the bike comfy for the rider.

If you guys still disagree then it's fine with me and please have a wonderful day.

I tried to simplify the physics by posing the scenario of the weighted, free standing spring on the floor. My attempt at illustrating the affects of a preload spacer failed to be understood. The part marked in red is where the common misconception comes from.

When the fork or shock is installed on the bike, and the fork or shock is not against either end of it’s travel, which it should not normally be. the spring is not, as you said “fully retained by the shock or internally within the fork tube”. Let us say the sag on a laden motorcycle is such that 70% fork compression travel is available and 30% fork rebound travel is available on a fork with 5 inches of total travel. If you were to add 0.5“ spacers between the fork springs and the fork caps, in an attempt to add so called “preload”, the forks will simply extend by 0.5“ and the front of the bike will sit approximately 0.5” higher (not exact because of the rake angle). The fork is not at either end of It’s travel, so the inner tube can freely move 0.5 inches out of the outer tube. There is nothing restraining the spring from maintaining it’s original length and the spacer simply extending the fork length by 0.5”.

Only when the fork of shock reaches it’s mechanical limits will the fork preload spacer, fork cap adjuster, or shock adjuster ring have an affect on the spring action. And if you are frequently hitting the upper or lower limits of suspension travel, either the sag setting or the spring rate is wrong for the bike.

I think we would all be better off if we stopped stop using the term “preload.” It makes total sense if you are mounting a spring on a shock body when it is off of the bike, because then you are preloading the spring against the mechanical limit of the shock, so that when the shock/spring assembly is installed and the bike weight compresses the spring, the sag will be correct. Other than that usage, “preload” just causes people to misunderstand the affects of turning the shock spring ring/fork cap adjuster or adding spacers to the fork spring.

 

[DirtFlier]

When you add the 0.5" spacer, the spring is now compressed by that amount and is not the same installed length as it was before.

Yes, the fork or shock may extend a bit more because of the additional spacer (sometimes called: preload) but the spring is still compressed by 0.5" because that doesn't change. The shock spring can't go back to its original length because it's fixed to the spring seat at one end and the adjuster at the other end.

You may be misreading the shock returning to its original length as the spring returning to its original length but they're two different animals.

 

[670cc]

When you add the 0.5" spacer, the spring is now compressed by that amount and is not the same installed length as it was before.

Yes, the fork or shock may extend a bit more because of the additional spacer (sometimes called: preload) but the spring is still compressed by 0.5" because that doesn't change. The shock spring can't go back to its original length because it's fixed to the spring seat at one end and the adjuster at the other end.

You may be misreading the shock returning to its original length as the spring returning to its original length but they're two different animals.

Your description clearly explains where/why people misunderstand the “preload” concept. I thought that the free standing spring/block/weight comparison would help, but people are still hung up on mistakenly thinking that the spring is always restrained when it is mounted to a shock or inside a fork tube. Let me take a different approach.

With the NC front suspension, the bottom of the spring sits on the damper tube which is bolted to the bottom of the lower fork tube which is connected to the axle which is supported by the wheel resting on the ground. The bottom of the fork spring is basically fixed by resting indirectly on the ground.

The weight of the front sprung half of the motorcycle is carried by the triple clamps, which are bolted to the upper fork tubes, and that weight rests upon the top of the springs by way of the fork caps.

In summary, the bottom of the springs is fixed by the ground, and the weight of the upper front half of the motorcycle rests on the top of the springs. As delivered from the factory, when the NC is loaded with a rider, the forks are midrange in travel, neither topped out or bottomed out.

The weight of the motorcycle is a force pushing down on the springs, and the springs push back up with the same force. The distance the springs are compressed is a result of how much weight is resting upon them.

Here is the secret people don’t get. If you add a spacer on the top of the spring and you have not reached the upper limit of fork travel, there is no force in play that compresses the spring further. The bottom of the spring is fixed, and the same weight of the motorcycle still rests upon the top, so the spring length and “tension“ remain the same. The fork is free to extend because it is not topped out, so the fork simply extends by the thickness of the spacer, and the front of the motorcycle is raised.

You can play out the same story on a rear shock/spring assembly with aduster ring, or old style step ring. Same deal. If the motorcycle is loaded for riding, and the shock has not reached an upper or lower physical limit, the rear of the motorcycle just raises or lowers as you turn the ring. The spring length and “tension” does not change.

If this was a class, I would now send all the students to the lab, where they could take measurements on the motorcycles, add spacers, turn adjusters, etc, and observe the effects. A simple tape measure is all one would need to realize what is going on.

 

[TacomaJD]

When you add the 0.5" spacer, the spring is now compressed by that amount and is not the same installed length as it was before.

Yes, the fork or shock may extend a bit more because of the additional spacer (sometimes called: preload) but the spring is still compressed by 0.5" because that doesn't change. The shock spring can't go back to its original length because it's fixed to the spring seat at one end and the adjuster at the other end.

You may be misreading the shock returning to its original length as the spring returning to its original length but they're two different animals.

So if you add the hypothetical 0.5" spacer, the bike's front ride height is raised by nearly 0.5" (accounting for rake angle), you think the spring is compressed? Nah....The only way adding preload is compressing the spring is if the suspension is already maxed, "spread apart", whatever you want to call it. If you can pick the front or the back of the bike up in the air and either tire not drop down one bit, then the suspension's downward travel is already maxed out, thus adding preload at this point would definitely be compressing, or preloading, the spring(s). That is the only scenario where adding preload actually preloads the spring....but most bikes aren't out there driving around with suspension down travel maxed out.

When I got my first NC and began to track it, the rear shock preload was backed off quite a bit, almost as low as it would go, because the previous owner had it lowered with links and was trying to make it more rideable for him by lowering the rear more via backing off the shock preload. I had not looked at the shock preload prior to going to the track, and man the rear end SUCKED at the track. Before the next track day, I ended up maxing out the rear shock preload, which removed most of the sag but not all. It was MUCH better on track. I guess you could say it felt "stiffer" but what really happened is that is has less down travel since I maxed the "preload". Less down travel brings the bike's chassis back to the ground faster in the event of hitting a bump, which creates the illusion of being "stiffer", but it's really not. The end result is the ride is more harsh and less bouncy, but the spring is not "preloaded" and nothing about the shock is stiffer at all, it just runs out of down travel and keeps the bike planted more firmly. Don't get me wrong, it still sucks as compared to where I want to be, but was a huge improvement over how it was previously. I am eventually going to replace it with an Ohlins TTX rear shock.


And for fun:
Example of the term "preload" being used in suspension tuning as it should be is in rock crawling. The typical setup when running long travel coilovers is running dual rate springs (a top and bottom spring). So if you have a 14" travel coilover shock, you want your bottom spring to be 2" longer than the shock travel, and the upper spring to be equal to shock travel. The bottom spring will have a heavier rate and the top spring will be a lighter weight, for example on my old crawler, the bottom spring was 200 and the top spring was a 150 spring. With the shock fully extended, the preload adjusters were spun down to preload the top spring a bit against the bottom spring (between two "fixed" points) to prevent any slack in the springs during full travel. This is the purpose of running a 2" longer bottom spring, to allow for extra preload adjustment and ends up giving a more plush ride over small bumps than running both springs equal to the shocks travel. The rig is able to ride on the softer top spring over small bumps, but the lower spring is there to provide stability when more uptravel is used.

I know that doesn't apply here, but that is a perfect example of preloading the shock actually adding preload to the spring.