emilio700

iTrader: (3)

Is this question in regards to preloading the shim stack inside the damper as mentioned a few posts earlier or preload on the main coil spring?

greeenteeee

^Id be interested in either, but moreso on the preload on the main coil spring (since I probably will not have a hand on building a shock anyway). For years I've used 0 pre-load and understood that on bikes, they preload the shock based on spring rate and weight on that spring (to maintain full stroke at static height).

Also, I agree that once compression is set to spring rate, you should only have to worry about rebound... which is also why I prefer my shocks that adjust rebound only vs my shocks that adjust bump and rebound-- adjusting both usually ends up with too much bump for the compression levels (but in the end, my shocks are low-end shocks)

wannafbody

iTrader: (1)

Bernie, Emilio, I was referring to the coilover spring preload and whether adjusting it has any affect on ride quality or how you'd spec shock valving.

Bernie S.

The only adjustment the spring preload will do is ride height. The ride height does effect weight transfer, so you have to take this into consideration on the shock valving.

emilio700

iTrader: (3)

Coming from a car, bicycle and motorcycle background, spring preload does have an effect on suspension action and valving. For downhill mountain bike and motorcycle suspension that is more frequently fully extended, "topped out", we would always try to choose a spring stack (multi spring), progressive rate or overall spring length/rate that would allow us to use the least amount of preload.

Lets take an example of a 10" stroke damper with a 10" free length , 100 in/lb spring with zero preload.

At full droop, there is zero force pushing against the spring seats. At say, 1" compressed, you would have 100lbs of force trying to extend the shock. With 1" of preload, you would have 200lbs of force trying to extend the shock at 1" compression. In practice on a typical road car set up, the extra preload raises the vehicle so the assembly works in a different range of its stoke and ends up exerting the same force in extension for a given road bump. In other words, the car just gets raised up and the stored energy in the springs remains the same for a given bump force.

Where that example changes is when the shock is frequently topped out in either an offroad suspension or a short stroke car damper. In these cases, preload plays a key role in contact patch loading. That extra preload can quickly over power rebound damping and lead to harsh topping. This is one of the reasons you see position sensitive damping (PSD)(bypass shocks) and double or even triple rate springs in off road racing set ups. I have yet to see PSD in road race car dampers but that doesn't mean they aren't out there. So to answer your question on valving, no preload variances don't really affect valving spec in the context of Miata road suspensions.

What the rider/driver with too much preload would feel is a bit of additional harshness when the suspension was lightly loaded if it was near topped out. That is the remaining energy stored in the springs and and those wheels are no longer supporting much of the vehicle weight, overcomes the rebound damping otherwise designed to work against the sprung mass (weight of the car without moving suspension bits). In off road suspensions, the exotic stuff uses adjustable hydraulic bump stops for both topping and bottoming. The shocks on your typical million dollar Trophy Truck or WRC car are something to behold and absolutely cutting edge stuff.

This high preload causing harsh topping effect is usually not experienced in road car suspensions as they spend the bulk of their life in the other half of their travel range, near bottomed. The exception to this is the common "tuner" coilovers with adjustable length bodies for many cars, not just the Miata. There are several non-length adjustable shocks that are also inexplicably short stroke, Koni Race come to mind. See three locking collars and you are looking at a length adjustable damper. The adjustable length designs sacrifice stroke to gain the length adjustment. With so little available stroke, it becomes more critical to adjust them with sufficient droop as to avoid too frequent topping. Adjusted too short in length with a huge amount of preload is a recipe for an unpleasant ride and poor grip on bad surfaces. Conversely, no preload and shocks extended too long gives you lots of droop to avoid harsh topping but no bump travel. Trial and error adjustments will let each driver find what works best for them on that particular car. In general, I adjust shock length to give max possible bump travel given the tire/wheel being used, then set ride height as low as possible without causing excessive bottoming. The plus side of length adjustable dampers is their versatility by being able to quickly change ride height without changing bump/droop ratio.

With both the long stroke, non-length adjustable Xida's and the Bilstein HD's you have plenty of stroke to work with so the you aren't faced with any of the above mentioned sacrifices in terms of droop travel. The Bilstein will show it's street roots is in the longer body that doesn't quite have enough room for coaxial perches and dual springs without limiting stroke or custom made hyper extended upper mounts

Bernie S.

Another example of this would be with the big bar, soft spring setups that many of the oval track teams are running. You have to compress/preload a softer spring more for the same wheel load than you do a stiffer spring. This is why they ride around in the pits with the nose of the car much higher than on the track. The shock is almost at full extension when static.

This got to the extreme to where teams would "chain" the front suspension from extending using the extension of the shock as a limiter to be able to run the softer springs. Even though the spring was preloaded more, it still had the same rate and allowed for more grip and a lower ride height dynamically with the downforce. The front suspension topping did not affect the car do to the downforce keeping the suspension compressed, but in a normal application you would always feel the suspension trying to lift a wheel during weight transfer.

A couple of rule changes later, you were required to remove the shocks during technical inspection to prevent this.

greeenteeee

I've always set my pre-load to 0, keeping the spring seated at full droop. Haven't ran into bumpstop issues with my ride height and rubber compound as of yet. Might be changing out the suspension again and was wondering if I should set shock length to bottom out on the bumpstop before the tire does, prior to setting ride height? I am worried doing it this way the spring will not be loaded during droop and may cause problems in case the wheel gets unloaded during track time...

EDIT: Perhaps my grammar is horrible, for that I'm sorry. Just trying to get expert advice which is why I am in this thread-- here is my clarification:

I have set the spring to 0 preload (car on stands, sussy at full droop, spring is seated, no up and down movement) on both of my cars. I never hit bump stops at my ride height and tire compound.

BUT I maybe swapping out the suspension and since I have to set them all up again I am considering setting shock length so that the bumpstop bottoms out first rather than the tire against fender (pretty much what emilio was saying).

This is not something new to me as I've heard of this way of doing it before, but I did not like how with this way of the shocks being setup, the spring will inevitably have play at full droop (e.g. not seated). This can be bad once vehicle weight loads that corner again and the spring did not seat correctly. (or should I just add helper springs for this reason?)

As I said, I don't have issues of bottoming out w/ my ride height and tire compound as of now so I have no reason to change it, but if it would be better to set the shock to bottom out before the tire does, then I will.

y8s

iTrader: (8)

the top spring is like 10 lb/in just to hold your springs in place under droop.

greeenteeee

So I need helper springs... is one way better than the other? I don't bottom out my shock at all with my ride height, spring rate and tire compound-- would it benefit me to make the shock bottom out first?

Bernie S.

To be honest, I have no clue what you are saying/asking.

Bumpstop before the tire does? How are you adjusting your preload?

Please explain.

emilio700

iTrader: (3)

For a track or autocross specific set up and adjustable length shocks, I suggest setting shock length for maximum bump travel for the tire being used. If it's a street car mainly and ground clearance is an issue, then try a longer shock setting. No hard and fast rule or dimension here, it's trial and error.

The Xida length is optimized to be just a hair long with 225/45 race tires on our 15x9 +36. Tire touches when bump stop is about halfway into block height. With a narrower 205/50 on a 15x7 or 15x8 like an ITA, STS or PTE Miata would run the suspension will compress a tiny bit further before the tire hits the shock tower bulge/upper mount in front. In the rear, the shock will compress right up until the kinematic limit of the suspension, the bump stop going to block height just prior.

When choosing bump stops to maximize bump travel, you have to take a few things into account. With most billet aluminum upper mounts 225/45's on our 9's, the sidewall of the tire will just brush the upper front mount at full bump. Not an issue with smooth and compact alloy mounts. With an OEM NB mount, there is a sharp edge of the stamping that protrudes further into the tires path that could potentially damage the sidewall. So with the 225/45 & 9" and NB mount, you have to limit bump travel a bit unless you are running full OEM camber. Again, no hard and fast numbers here. Don't assume anything after reading this, go and check your car out to see what, if anything, contacts and if it will be a problem.

For competition set ups in general, I'll try to set shock length so that bump stop block height occurs part just after the tire starts hitting stuff and just before and metal to metal contact anywhere. The tire will flex a bit and that gives me a few more mm of bump travel. All our cars have a big polished area on the tub at the front shock tower bulge. Pretty common with our 8's and 9's from the pictures my customers send me.

greeenteeee

Thank you for the reply. Now, if I set shock length for maximum bump travel for tire being used, that is essentially letting the bumpstop bottom out before the tire really bottoms out (so tire may scrub a little), am I right? I would rather scrub tires and bottom out the shock as I'm sure it is detrimental to shock life if it is bottoming out. So since bump travel is adjusted via shock length, spring height (e.g. preload whether positive or negative) would be used to set ride height... and if say a helper spring is needed for the desired ride height--let's make it 1" for ease-- that 1" of shock travel is pretty much wasted?

I am considering a set of FLEXs then, and my old method of keeping 0 preload and shock length for ride height would work with the kit right out of the box... but now it seems I would need to purchase helper springs if I were to set it up to maximize bump travel.,

Oh and btw, with 4.1F 4.4R heights with 15x8 et36 6ULs on 205/50-15" RE-11 with 10k rates up front, I have no problem with lack of travel-- that's not to mention that I have 20mm spacers up front inevitably worsening the wheel rate ratio, yet still does not bottom out.

greeenteeee

I can't believe it... is my english this bad?

I said, "I've always set preload to 0"

If you need clarification on that, I also said, "keeping the spring seated at full droop"

METHOD #1... MY WAY
1) ZERO pre-load, spring (no helper) is seated at all times, even at full droop. Preload is set and forgotten. Set ride height via shock length. Done and done.

METHOD #2... Maximizing bump travel
1) Install shock, set shock length when wheel setup hits and bumpstop hits at the same time. (my fenders are shiny, from previous ride heights) Set and forget.
2) This means, ride height is set by the spring preload... negative preload to go lower or preloading the spring to go higher (depending on the setup). Helpers would be needed for this.

I was initially asking which method was better for performance as I've always done #1, and I've never had to use helper springs because that is why I thought I bought suspension with shock length adjustability-- so the spring remains seated.

Bernie S.

If you want clarification, try not stating that you are adjusting the amount of preload. That is the way I read it.

After talking to Emilio about the Teins, a product that has never been in my shop, I understand what you are trying to say. The preload that you are referring to is changing the exposed shaft at right height, allowing you more travel in one direction or another. It's not that you are topping out the shock and preloading the spring more with the same right height.

I apologize for misunderstanding you, but using a product this unique you may want to mention the brand first.

While your spring may remain seated at full extension, you are starting at a higher ride height and not allowing the car to travel as much on compression.

emilio700

iTrader: (3)

It's OK to let the damper bottom out, it's designed to do just that without issue. You decide how much of that you want the tire to share. For me, it's just 5mm or so.

greeenteeee

Sorry if I wasn't clear. Thank you for the reply. I set the spring to 0 preload, spring is not compressed at full droop. I don't see how I am starting at a higher ride height, not allowing the car to travel as much on compression. Are you suggesting I add helper springs and let it eat up some shock travel? I think only preloading the spring by 2" (on a 10kg/mm spring) would not allow the car to travel as much on compression because of that pre-load... it would need 1120 lbs on that corner to overcome the preload. With 0 preload at full droop, it is already compressing the moment I drop the car from stands...

With 10kg/mm (560lbs/in) rates up front, and with zero preload, the spring starts to compress immediately, and shock travel starts being used as soon as the vehicle's weight starts to act upon it. Assuming each corner is about 560 lbs, the spring and shock is already compressed 1"--spring compressed 1" and 1" of shock travel used up-- at static height.

If I've been setting up coil-overs wrong all this time, it makes me wonder why TEIN does not include helper springs for this. Their own manual says to set it the way I have set it (set spring preload to zero) and height via shock length.

Now I wish the TEINs come with helper springs. Adjusting for max bump travel and height via spring preload might lead to room btwn the spring and perches.

Bernie S.

If you need helper springs and spring dividers either of use would be more than happy to help you.

greeenteeee

Thanks, I came here looking for information, not where to buy helper springs. I don't even know where the ride height will end up yet as I am not sure if I am ready to throw off my height, alignment, and corner balance just yet. I would appreciate further technical responses, however.

Bernie S.

It's funny you say that about the helper springs. Neither Emilio or I sell these parts, but both of us would be willing to help you contact the right people.

Bernie S.

If you want to run helper springs, we can help you determine the correct ones and who has them. It's up to you on what set-up you choose for your car. We are just here to provide you with information so you can make a decision. Either way, our goal is to optimize your decision. At no point is anything going to be "sold" in this thread.