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So you basically want stock spring rates and stock ride height. No need for adjustment collars and 2.5" springs. Just grab a stock set from those below (for cheap). Shoot, just buy a complete NB setup with the hats and all, the bumpstops you want, and spring spacers if any of these run too low for you.
NB base springs: 162 front, 118 rear
NB HARD S: 168 front, 130 rear
NB MSM: 215 front, 158 rear
Thanks for the response JoeTheZoe. So, you're almost right, and stock isn't way far away from what I'm looking for, but it's not the same thing either. For example, 200/150 springs are roughly 20% stiffer than stock. Not a great deal, but not insignificant either. MSM springs are pretty much right up there, but too short.
Now let's talk about spacers. Spacers raise the ride height, but maintain the original bump:droop travel ratio. That ratio is biased far towards droop, and can be on the order of 20:80. What I'm looking for is closer to 60:40, and that only happens by changing the shock parameters. So you see, spacers won't do it, though I might need some minor spacer height increase to accommodate larger diameter tires, but that's a separate issue.
Lastly, a stock setup is non-adjustable. In my case, I want a fair amount of adjustment and therefore adjustable spring perches are the only reasonable option.
I have been looking for a fairly soft, compliant setup that can handle potholes and broken pavement well myself. 350/250 work well for that type of duty to my experience.
Hello HarryB...
My '95 with 336/224 Swift springs and FCM re-valved Bilsteins is probably very similar to your setup, and I put that setup together for the same reason you did. Namely, to handle the sometimes very rough and broken goat paths that pass for roads here in the byways of northern California. For my roads, and most likely yours, that setup works really well. A setup with those spring rates would probably also work ok on the unpaved backroads of Death Valley, but they would be far from optimum. A far softer setup is preferable for the washboard, gravel, and rilled surfaces on the way to my favorite camping destinations, and softer rear springs without sway bars also significantly increase rear drive articulation, which is a big plus on uneven ground. Anyway, thanks for the suggestions.
GL with your pursuit of knowledge. You will have an iterative process to follow just like you were told in CR.
Hey vteckiller2000.
Well, not quite full circle as I'm making good progress. Thanks for the well wishes, but I'm confident that my first year engineering statics is more than enough to give me a fighting chance against having to take an iterative approach. The math is dead simple; the issue is having accurate measurements; the solution is to have the parts in hand to measure. It's really not rocket surgery, and it's not like I'm building a "big boy" suspension or anything.
Anyway, y'all need to look at this in a fresh light. I'm putting this together for a particular kind of road. That means lots of dirt, gravel, rocks, and sand. I need energy absorption and ground clearance, not track/autocross suspension geometry or stance. No offence to anyone at all, and I fully appreciate all of those setups that are well thought out, tailored, and effective for their respective purposes, but my intended environment is outside of the environment we are more generally familiar with, and it requires a completely different approach. Off pavement travel is actually quite interesting, and putting together a suitable vehicle offers at least as much engineering challenge, and arguably far more, than dealing with smooth pavement. For a real treat check out some of the historical Group B rally racing footage on YouTube; those drivers were the best in the world and no kind of motor-sports legal today comes close. Anyway, I hope you'll take my word for it that 800 lb springs and 11.5" ride heights aren't going to work for me in this particular case. And before anyone says it, a Paco lift kit is not the solution.
PS - you want knuckeheads, hang out at Grass Roots Motorsports. Great bunch of drivers!
Anyway, thanks to everyone who's responded, I appreciate your help.
Last edited by Thucydides; 02-13-2018 at 06:22 PM.
I rummaged through a big pile of shock absorbers and found some Bilsteins which Dick donated. Straight away I took them to Bilstein experts the "Baker Brothers" who adjusted the bump and rebound characteristics for off road/rally use. I decided to go with King springs and adjustable collars at the start with 300lb in the front and 250lb in the rear.
It did not work - too stiff - so back to basics with standard spring platforms with 1 inch spacers underneath for ground clearance and slightly stiffer than standard springs, 230lb front and 140lb rears.
valving that was based on the European Ford Escort, the closest small rear-wheel drive rally car they could think of. Springs were long - 10" in the front and 12" in the rear with fairly soft rates of 225 lb/in and 130 lb/in.
Just to be clear, I'm not building a rally Miata, and so David's and Dan's spring rates aren't directly applicable, but they do serve to illustrate that light spring rates are preferable on unpaved roads. Keith Tanner's successful rally Miata was raced on pavement, and therefore has higher spring rates than David's and Dan's.
Went to Home Creepot and they didn't have the fender washers you all got. Went to Lowe's instead, and found these, which are the same diameter, but twice the thickness. I ripped the bags open before I thought about taking a picture, but you get the point.
Last edited by Caverly; 02-17-2018 at 09:42 PM.
Reason: Formatting is hard
You will have an iterative process to follow just like you were told in CR.
Before I wander off to GRM to discuss spring rates, I wanted to leave you, and everyone else here, with very simple, effective, and accurate way with which you can calculate the spring length you need for any conventional suspension.
So, imagine you have your upper and lower spring perches assembled on your shocks with spring isolators along with everything else you need, minus the springs. You're minus the springs because you don't yet know how long a spring you need.
Step 1: Measure the distance between the spring seats with the shock shaft fully extended. Let's call that Lmax. Imagine a shock with Lmax = 9"
Step 2: Measure the distance between the spring seats with the shock shaft fully compressed. Let's call that Lmin. Imagine a shock with Lmin = 5"
Step 3: Subtract the Step 1 distance from the Step 2 distance; this is your maximum shock stroke. Let's call this Smax. So Smax = Lmax - Lmin, or in this case, Smax = 9" - 5" = 4" So far so good.
Step 4. Within the maximum shock stroke available, Smax, determine how much bump travel you want with the shocks installed under the dead weight of the car. For example, if you want you car to settle at the midpoint between bump and droop travel, you'd pick as a desired bump travel 50% of the maximum available shock stroke; let's call this Seff, for effective shock stroke. So if Smax is 4", 50% of Smax = Seff = 2".
Step 5 Add the desired bump travel to the minimum distance between the spring seats you measured in Step 2, Lmin, to the desired bump travel you calculated in Step 4, Seff. This is the desired confined static spring length. I'm going to call this Ld. So Ld = Lmin + Seff. In the case of our example, Ld = 5" + 2" = 7"
Let's pause for a moment to clarify what this Ld means to us as drivers. Ld is the length the spring needs to be when it's installed on the shock, and the shock is installed on the car. We need to choose, purchase, and install a spring that will get us that 7" without having to make guesses (another, more honest word, for iteration), and without having to swap springs when we guess wrong. That spring will be longer than 7", and next we'll determine just how much longer.
Step 6: Here's where you need to have some information about the weight of your car corner, the motion ratio of your suspension system, and the angle between the shock/spring system and the lower control arm. Those parameters will give you the effective spring load, and I'm going to cheat a bit here and say that with a corner weight of 575 lbs and a motion ratio of 1.52 in the front, and with a rear corner weight of 540 lbs and a motion ratio of 1.3 in the back, the effective spring load will be roughly about 874 lbs in the front, and 702 lbs in the rear. Let's call the effective spring load Ws.
Step 7: Whatever spring you choose, it will compress under the effective spring load a distance calculated by dividing the effective spring load by the spring rate. We'll call this C. If we choose a stock spring rate of 154 lbs/inch for the front of our miata with a front spring load of 874 lbs, we get C = 874 / 154 = 5.7"
Step 8: And here's the payoff. Simply add the desired confined static spring length (Ld) to C, and that is the spring length you'll need. I'm calling this L$. In this case, 7" + 5.7" = 12.7". Since 12.7" springs are hard to come by you'll probably choose 12" or 13"
That's a lot of steps so I'm going to summarize in the simple language of math:
So everything is super simple, if you have the parts to measure. I've taken some liberties, or more accurately many liberties, for the sake of simplicity, but this method should put you well within the ball park. Just be aware that we didn't consider the internal shock spring rate caused by the high pressure nitrogen within the shock, the angle of the shock to the lower control arm (other than to mention it briefly before ignoring it), the spring rate induced by the confined suspension bushings, and a bunch of other things I'm not going to think of now. I've made a simple spreadsheet to do this for me, because I'm lazy, and I can evaluate dozens of scenarios in half an hour, and so can you.
Good luck all, and thank's to everyone who pitched in to give me a hand! I appreciated every response.
Oh, yeah. If your L$ is less than your Lmax, you're going to need helper springs. Let's have a look at that scenario.
To keep things simple, let's keep everything the same as the last example, but this time we're going to install some Big Boy brand 800 lbs/inch springs:
So what's the point of having a spring with significantly more travel than the shock? A 7" spring with no preload has more travel than NB Bilsteins, and that's all you really have to worry about.
So what's the point of having a spring with significantly more travel than the shock? A 7" spring with no preload has more travel than NB Bilsteins, and that's all you really have to worry about.
Great question! The short answer is to hold your car up.
To use Mazda's stock spring rate for the back of the Miata as an example, any length spring is going to compress about 7.25" under the vehicle weight alone. So yes, with the bottom perch in the right location your spring hasn't bound, and the spring works perfectly well within the range of your Bilstein shock stroke, but you're resting on the bump stop. because the 5" stroke of the shock isn't enough to allow the spring to compress sufficiently to hold up the car. In fact, your spring isn't long enough to compress enough to hold up the weight of the car under any circumstances, unless you use coil bind to do the job. Come to think of it, plenty of Miatas are running around exactly like that, so I guess you can say it works after a fashion.
Give a shock's stroke, vehicle weight, and spring rate, there will be a fairly narrow range of spring length that works optimally. I was looking at your 7" spring, and ran some numbers. You can check me if you'd like with the formulas I gave you, but if your spring perches are 7" apart (Lmax) and you have a 4" shock stroke (Smax), and you want 50% bump (because suspension matters and snap over-steer is bad), the length of spring you'll need under the front corner with the car sitting on it is 5". With a 450 lb/in spring rate the spring compression under the vehicle weight will be about 1.94", so the total spring length you'll need is 6.94", so you're good. But, given that 7" spring, if you go up on your spring rate your spring won't be long enough to not need a helper, and if you go down on spring rate, it will be too short to hold the car up at that 50% bump location.
You can always compromise somewhere else so you can use a 7" spring, but why? If you need a 6" spring, buy a 6" spring. If you need an 8" spring, get one of those. But the first thing you need to do is calculate how long a spring you'll need to optimize your suspension for the parameters you want. You can pick your own spring rate and bump %, or you can copy someone elses and hope they're right. If you're buying your setup from Emilio, you can bank on a correct design and execution. If you copy's Bubba's setup, who knows? He probably used the iterative process and may or may not have arrived at the optimum solution.
Last edited by Thucydides; 02-15-2018 at 09:18 PM.
Sounds like spreadsheet work is complete and it's time for A/B/A testing. Get out there and see what setups you've theorized actually work best on your non-rally rally miata.
Great question! The short answer is to hold your car up.
To use Mazda's stock spring rate for the back of the Miata as an example, any length spring is going to compress about 7.25" under the vehicle weight alone. So yes, with the bottom perch in the right location your spring hasn't bound, and the spring works perfectly well within the range of your Bilstein shock stroke, but you're resting on the bump stop. because the 5" stroke of the shock isn't enough to allow the spring to compress sufficiently to hold up the car. In fact, your spring isn't long enough to compress enough to hold up the weight of the car under any circumstances, unless you use coil bind to do the job. Come to think of it, plenty of Miatas are running around exactly like that, so I guess you can say it works after a fashion.
Give a shock's stroke, vehicle weight, and spring rate, there will be a fairly narrow range of spring length that works optimally. I was looking at your 7" spring, and ran some numbers. You can check me if you'd like with the formulas I gave you, but if your spring perches are 7" apart (Lmax) and you have a 4" shock stroke (Smax), and you want 50% bump (because suspension matters and snap over-steer is bad), the length of spring you'll need under the front corner with the car sitting on it is 5". With a 450 lb/in spring rate the spring compression under the vehicle weight will be about 1.94", so the total spring length you'll need is 6.94", so you're good. But, given that 7" spring, if you go up on your spring rate your spring won't be long enough to not need a helper, and if you go down on spring rate, it will be too short to hold the car up at that 50% bump location.
You can always compromise somewhere else so you can use a 7" spring, but why? If you need a 6" spring, buy a 6" spring. If you need an 8" spring, get one of those. But the first thing you need to do is calculate how long a spring you'll need to optimize your suspension for the parameters you want. You can pick your own spring rate and bump %, or you can copy someone elses and hope they're right. If you're buying your setup from Emilio, you can bank on a correct design and execution. If you copy's Bubba's setup, who knows? He probably used the iterative process and may or may not have arrived at the optimum solution.
Math is math, but in the real world i somewhat doubt that WELL over half an oem spring's free length, let alone actual available travel-to-bind, is taken up just with holding the car up.
What do you plan on doing with the additional 6"+ of spring that you're talking about, using this picture as reference?
Math is math, but in the real world i somewhat doubt that WELL over half an oem spring's free length, let alone actual available travel-to-bind, is taken up just with holding the car up.
What do you plan on doing with the additional 6"+ of spring that you're talking about, using this picture as reference?
I guess my first question is whether or not you believe in the concept of spring rate, or is that not a real world phenomena? For the sake of argument, let's say you do.
If the weight of the corner of your car supported by your spring is 702 lbs, and your OEM rear spring rate is 97 lbs/in (1994-1995), your spring is going to compress 702 / 97 = 7.2" Your formally 11.7" OEM spring is now 4.5" long. Not sure how to make this any simpler.
On the other hand, if you are a spring rate denier, then you'll have to come up with a means of determining suspension design in a manner consistent with your beliefs. There are folks out there who adamantly believe the world is flat, and have what appears to them perfectly plausible explanations and proofs to support their beliefs. What can I say. There's always the iterative approach.
Sorry, couldn't see your photo so can't comment on that...
Sounds like spreadsheet work is complete and it's time for A/B/A testing. Get out there and see what setups you've theorized actually work best on your non-rally rally miata.
Everything but the shocks have arrived. NB Bilsteins are backordered until sometime in March. Looking forward to A/B/A testing, whatever that is.
Well.... i guess in my real world, spring rates are not a reality, then.
I'd say you should find a way to view the picture i posted. Using lengths you speak of, you will either/or/and 1) be compressing your springs by a good 3-4" just to install them, which negates any potential benefit you think you'll reap by using springs that long in the first place, and if you do that 2) won't be able to adjust height anywhere except lower, by compressing them an additional 1-2" to hit the targets you were talking about.
Which of course... makes your spring length choice, wrong.
This is real world.
Unless you're doing custom sleeves/perches ground up, at which point you should consider re-working your "already purchased" list.
If you'd like some more real world:
Bilsteins with 6" springs on left. Xidas on right. Both have pretty close to oem droop travel (in fact, the Bilstein is oem droop travel, because well... it's the shocks that you purchased). Both require bump stops to avoid jamming the tire into the body of the cars. The Bilstein setup is EASILY capable of reaching your desired right heights. It is NOT capable of swallowing 12-14" springs without compressing them 2-4" for the sole purpose of being able to bolt on the top hats. The Bilsteins are NOT capable of travel required to match the theoretical travel of a 12-14" spring. The car is NOT capable of travel required to match the theoretical travel of a 12-14" spring.
Guess you are both right; I believe Thucydides says that you need to compress the spring to get the top hat on, because it is exactly that preload that will keep the car at his desired height.
02-13-2018, 05:44 PM
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