Front end 'liveliness'

[Guest]

I know front end suspension facts are all over the place, but for some reason it never seems to resonate well with me - maybe because I haven't had the first hand experience until now. I recently installed 1.0 kg/mm sonic springs with 15lb fork oil (volume per Suzuki manual) and cut the shim for 1/2" of preload, per Sonic instructions.

The front end absorbs everything well but I'd like it to feel a little more lively. I still haven't wrapped my head around how the oil weight, preload, spring rate, etc all play together so I'm not sure what to change. I don't want it to feel too firm, but faster would be good, and a touch less dive during braking is always nice.

Thoughts/suggestions?

[RichDesmond]

I know front end suspension facts are all over the place, but for some reason it never seems to resonate well with me - maybe because I haven't had the first hand experience until now. I recently installed 100lb sonic springs with 15lb fork oil and cut the shim for 1/2" of preload, per Sonic instructions.

The front end absorbs everything well but I'd like it to feel a little more lively. I think the spring rate is right since I don't seem to over compress the forks when I sit on the bike (honestly I haven't measured the 'sag' or whatever it's called), and in my limited experience I can't say I've heard about people using anything but 10wt or 15wt oil.

I haven't thought much about the spring preload concept - I figure the front end will sit based on my weight and forces during braking, so preload shouldn't affect travel, but maybe it causes the front end to spring back a little faster? That kind of sounds like what I'm looking for - I don't really want it 'firmer' but would like it 'quicker'. Does that make sense?

Oil volume is another story - I know next to nothing about it and just used the volume suggested in the maintenance manual. I think the fork is a viscous damper, so damping rate should be based on the physical properties of the fluid, but not the volume as long as there's enough? So I figure leave the volume alone.

Oil level matters, there was a section in the instructions covering it. Using the volume in the manual isn't the right way. The volume doesn't affect damping much, but it does affect how much the trapped air volume affects your overall spring rate.
From what you're saying, it sounds like you would prefer less rebound damping. I'd switch to 10w fork oil, and set the level to 120mm, following the procedure in the instructions.
Changing preload won't give you what your after.

[Joe Garfield]

Thanks Rich. I didn't realize the air was sealed inside enough to affect the feel. It's been a rough year and I wanted to get the bike back together so I guess I cheated and went with the volume in the manual since it was easier I will change it.

Would lighter oil give more travel (dive during braking)?

I wasn't sure if you'd be on so I sent you an email - feel free to ignore that one...

[RichDesmond]

Yep, unless the seals are leaking the fork tube is airtight. Lighter oil will allow the bike to move a little more on the suspension, which I think will give you the feeling you're looking for. Brake dive is mostly controlled by the springs, but it will dive a touch faster with the 10w. Should still feel very controlled compared to the stock setup though.

[Joe Garfield]

Ok, thanks again.

[Steve]

Spring rate will control how MUCH the forks dive, oil viscosity will control how FAST they dive.

You want "quicker feel"? Let's just say that you started with the second-heaviest (naked) GS there is.

But it DOES do quite well for all its bulk.

.

[Joe Garfield]

Ha! Yeah this bike kicks some a$$, no doubt. This is my first time setting up forks so I'm just curious what levers there are to pull. There doesn't seem to be much feedback from the front end (probably because of the weight) and I was wondering if/how to get more feel w/o making it too firm. But that being said, the bike seems to plow through anything w/o a hiccup, so I'd be OK if I left it alone too

[Dogma]

What does "lively" mean to you in this context? To me, that sounds like a bad thing, like it's completely underdamped and bouncing a lot.

Suspension started making sense to me when I started thinking about it in terms that describe the physical phenomena involved. Spring rate, preload, damping, etc.

Rich deals in suspension and probably knows all the terminology people use. Like how a doctor can interpret the various ways patients describe symptoms. He's probably on target. 15w fork oil is a little stiff for the stock fork.

[Dogma]

Ha! Yeah this bike kicks some a$$, no doubt. This is my first time setting up forks so I'm just curious what levers there are to pull. There doesn't seem to be much feedback from the front end (probably because of the weight) and I was wondering if/how to get more feel w/o making it too firm. But that being said, the bike seems to plow through anything w/o a hiccup, so I'd be OK if I left it alone too

The variables available to you are spring rate, preload, oil viscosity or weight, oil volume, tire profile, and tire pressure. The stock fork has no independent adjustability for the damping categories of compression, rebound, high and low speed, but they can be added with cartridge emulators. High and low speed damping are not really settings for emulators, as much as a description of different circumstances you would tune for.

Edit: I left out moving the forks up and down in the triple clamps to tweak rake and trail.

[mmattockx]

There doesn't seem to be much feedback from the front end (probably because of the weight) and I was wondering if/how to get more feel w/o making it too firm.

You need more low speed compression damping to get more feel (speed in this case refers to how fast the suspension is moving, not how fast the bike is going). With a basic damper rod fork you have no way to control the low speed compression damping beyond using heavier oil, but that beats you to death on sharp bumps. The final answer is to install cartridge emulators, which let you tune low/high speed compression and rebound damping separately to get what you need.

I'm not sure about your 'lively' desire, that usually means suspension that is out of control.


Mark

[Buffalo Bill]

I'm sure RichDesmond understood what he's asking, and gave him the right answer.
Me, same bike 1100G, but chose the .95 springs for all the bumpy country roads I ride, 10w oil, and level same as the manual.
All very good, I don't sense any braking dive. Turn in is great for a 19" wheel.

[Joe Garfield]

I definitely don't have the terminology down for suspension tuning as most of you have surmised.

Bill - thanks. I'm happy to hear your setup - I'm guessing you prefer a sporty feel from the little bit I've read in another thread - so that (along with Rich's original recommendation) assures me I don't have to think about a stiffer spring.

I think I understand Rich's comments about damping - I figured heavier oil would give more 'feel' and/or feel more sporty and firm, but I was missing the fact that there's both compression and rebound damping. Maybe heavy oil feels firmer initially, but also slows recovery and overall response? Suspension definitely seems like a system function where you can't effectively change one part without understanding how everything else will respond.

The cartridge emulator makes sense, too. I've got projects needing priority so I'll learn a little more about them while I play with oil volume and weight. I assume modern rear shock assemblies have something similar (even if preset/non-adjustable) where compression and rebound damping are tuned?

I need to replace my lower clamp and bearing soon (hopefully this weekend if parts get here) so the timing is good for a quick adjustment.

I still don't really get what preload does, other than affect ride height and total fork travel. Does it affect feel or front end dive? I didn't think it did with a constant rate spring, but I don't really know.

[mmattockx]

I think I understand Rich's comments about damping - I figured heavier oil would give more 'feel' and/or feel more sporty and firm, but I was missing the fact that there's both compression and rebound damping. Maybe heavy oil feels firmer initially, but also slows recovery and overall response? Suspension definitely seems like a system function where you can't effectively change one part without understanding how everything else will respond.

It certainly can. The problem with our old tech damper rod forks is that the rebound and compression damping circuits are intertwined and you cannot tweak one without affecting the other. Modern cartridge damping forks have the two circuits separated so you can tune one without messing up the other.

The cartridge emulator makes sense, too. I've got projects needing priority so I'll learn a little more about them while I play with oil volume and weight. I assume modern rear shock assemblies have something similar (even if preset/non-adjustable) where compression and rebound damping are tuned?

Modern shocks use cartridge damping the same as forks and keep the rebound and compression circuits separate. Have a look at this page on Race Tech's site for how damper rod forks work and what cartridge emulators do:

http://www.racetech.com/page/title/Emulators-How%20They%20Work

I still don't really get what preload does, other than affect ride height and total fork travel. Does it affect feel or front end dive? I didn't think it did with a constant rate spring, but I don't really know.

You are correct, it only affects sag. Total fork travel is determined by the internal fork components or when the spring coil binds (which you never want). Here is maybe more info than you want, but it describes how to set your suspension from the pro perspective:

1) You select your spring rate based on your desired suspension frequency. This is the frequency that the sprung weight will bounce up and down on the suspension if damping were not present (ie - the natural frequency). You don't actually have to worry about this if you don't want to because it is baked into the spring rate calculators that are provided on Rich's site and most other suspension sellers. When you answer the questions about riding type, style, rider weight, etc. what you are really doing is letting the calculator know what frequency will be most suitable for you and then it spits out the spring rate to match.

2) Once your spring rate is chosen, then you set the preload to get your desired laden sag. That is the sag with the rider on board in full gear. In general, you want this to be ~25% of total fork travel. In another thread Rich commented that 28% works well for these old, heavy, softly suspended bikes and that is a good starting point based on all of his experience with these bikes. The amount of laden sag is really somewhat arbitrary, but you must have some because you need some travel available to follow dips and hollows in the road. Without some sag you will lift wheels off the ground on these features and that is bad for traction and stability, along with providing a nasty ride for the passengers on top. Cars often run closer to 50% sag, but their suspension doesn't compress with braking and cornering loads like a bike does so they can get away with much more sag than we can.

3) Now that your spring rates are chosen and sag set you set your oil height in the forks. This is more of a racer thing than street riding, but it doesn't hurt to work at it on a street bike as well. The minimum amount of oil required is whatever it takes to keep the damper rod and internal components always covered so they are damping with oil and not air/oil foam. The max amount is where you start blowing seals. The air inside the forks acts as a supplementary spring when the forks compress, increasing the effective spring rate. This helps prevent bottoming over big bumps and especially under heavy braking. The racer method is to set the oil height to just avoid bottoming at the heaviest braking point on the track. You can do similar for a street bike, but running a bit more oil to avoid trouble in an emergency braking situation is OK as long as the ride isn't too harsh for you over bumps and normal road features. Rich gave you an oil level to start with earlier in this thread so I would start there and see what you think. If the front end feels too harsh/stiff when braking over bumps try lowering the oil level a bit (I would go no more than 10mm at a time). If you feel it is too soft under braking, has too much dive and/or bottoms easily over bumps while on the brakes then add oil. As long as you aren't blowing fork seals and have the internal components under oil all the time there is no correct amount beyond what you like for feel and performance.


Mark

[Joe Garfield]

Here is maybe more info than you want, but it describes how to set your suspension from the pro perspective:

1) You select your spring rate ...

Mark

Thanks - this is not more than I want, more like exactly what I was looking for

[Dogma]

...
You are correct, it only affects sag. Total fork travel is determined by the internal fork components or when the spring coil binds (which you never want). Here is maybe more info than you want, but it describes how to set your suspension from the pro perspective:
...

I think there's more to say about sag, since it affects rake and trail, and therefore cornering behavior. Once sag is set up and with correct tire pressure, preload may need to be adjusted for desired cornering behavior. Increased preload shortens the rake and trail, making the bike tip in easier. If preload (or tire pressure and profile) are wrong, you will need to maintain steering effort to keep the bike leaned over or keep it from falling farther in. There is some preference here, but I like it neutral, where is stays in the corner with minimal effort. Front end behavior will also change as the front tire wears, so you can't ever have it perfect.

After thinking about this thread more, I think you're going to have to consider emulators pretty seriously. You want a tightly controlled front end, but getting that with the stock fork is going to make it really harsh on bumps. Emulators can fix this. Read here to learn how.