Joe Perez

iTrader: (8)

I'm sure that somebody around here will loan you a set of stock springs for long enough to get your 'Sports rebuilt.
Or you could just buy a new set of Koni Race shocks that won't leak and the shorter bodies will buy you a trifle more travel- you could even go back to a proper NB setup at that point.

AbeFM

iTrader: (3)

I like the idea. Except the part about buying it. Man those things are pricey....

Zabac

iTrader: (39)

a re-valve cost almost as much unless you make it down to Topeka and get them valved there at the nationals...they'll do it pretty cheap

AbeFM

iTrader: (3)

Herm... I'll have to check - I think I remember getting them done for like $70 each...

Savington

iTrader: (31)

700/450, RB tubular FSB, MSM RSB. Koni Race shocks. The ride is pretty smooth, as tolerant over rough roads as can be expected with full-blown racing spring rates, and it's a dream on tracks/autocross courses. I love it and I will never run anything softer.

Zabac

iTrader: (39)

Sav, we agree on that. Even though I'm at a measly 650/450 combo lol, believe it or not, but I found myself saying that i need more spring up front, but I am affraid my poor Yellows can't take much more abuse if i go higher spring rate. I plan on having my front ones re-valved to Race spec and to upgrade to a 750-800 spring.
Abe, $70??? Maybe that's why they keep blowing, lol. But seriously, the prices i remember reading were more like the in the $200's per shock. If you have a connection to get them done for $70 ea. please do share, i may end up re-valving mine sooner than expected.

AbeFM

iTrader: (3)

Guess I'll have to check my numbers, I got them done at koni.

650/450 sounds low in front for sure.

That's a lot of sway bar! I'm sure it keeps it flatter/faster, but I bet it would stick better with a little lighter bar, esp in the rear. Have you played with that at all?

Anyway, glad to hear the konis hold up for you with those springs. I think a pair of 850s are in my future.

I have the FM front bar, and the smallest of the OEM rear braces in, with two bigger sizes plus the FM on the side in case I want to change.

Zabac

iTrader: (39)

I have the stock rear bar, may take it out completely though...
may even consider 850's when i do the re-valve
the front sticks real well, only downside is that i really feel the need for more spring, i am super pleased with the rear though, i would like a bit more travel though, i hit the bumps a few times and wasn't thrilled

AbeFM

iTrader: (3)

Have you tried the FCM bumps? They are super nice - it's more sudden, initially, when you touch down there's more resistance than a light brush on the stockers. But they stay constant throughout. The stockers get suddenly stiffer (by design) as you progress through them.

Anyway, in the fronts I love the set up. In the rear it always felt way more harsh. My guess is the stops aren't long enough in the rear, and I'm feeling the shock bottoming.

Zabac

iTrader: (39)

I have the stock BS trimmed down to about 45mm IIRC.
In the back, I run my shocks at full soft, don't really bottom that often, i have an auto-x this sunday, i'll try to make it, if I do, I'll mark my rods in the back to see how close i get to bottoming out.
I don't think your rears are too harsh, I think you are bottoming, when you do your re-valve, sell those bumps over at Mnet and get the short fatcat ones and get different tophats, either NB, or the DIY ones like MXV has, or sell a kidney and get the FM ones...I still feel that the rear is more important than the front as far as top hats go, so do at least those, and get the stiffer springs up front...

man, this thread makes me want to redo my suspension, but I IS BROKE!

AbeFM

iTrader: (3)

Yeah, I'd love to see that!

Oh, I'm sure I'm bottoming. There are some bumps on which you will ALWAYS bottom. The idea is to bottom onto a bump stop, if they weren't there for that, why not take them out entirely?

Some things to concider:
1) I drive an NB
2) I'm nearly at stock ride height
3) At 300 lbs/in, they aren't exactly soft springs
4) I don't have the shortest bumps FCM makes, but they are shorter than stock
5) I have the little split ring in there to let trapped air out

So I'm not riding on the stops. And I don't want to argue, but I've yet to understand what it is about hitting the bump stop that will damage the shock. It seems to me a TALLER stop would prevent me from pounding the shock, metal-on-metal, with the full force of the car on a hard bump.

Does anyone know the mechanism by which the shocks are damaged by hitting the bump stop?

Zabac

iTrader: (39)

Sorry, i should have specified more on my view on the bump stops.
Bumpstops are a must have!!! No if's or but's about it.
You need bumpstops, but at the same time, you don't want to ride on them and/or bounce of them, they are literally the very last resort to stop your shock from going further up.
http://www.fatcatmotorsports.com/suspension.htm
Look at pic in the link, when you lower the car your shock body moves closer to the bump stop. This means it has less travel then before and is now closer to the bumpstop. So you get a shorter bump stop or you get e top hat that gives you more room up top. Your shock body stays in same place, but you extended the rod length now and gave the shcok body more travel room/space and it has to compress more in order to hit the bumpstop. Sorry I suck at explaining things, but do you get what I'm saying?

Savington

iTrader: (31)

My car won't rotate for **** without the MSM rear bar in. I had the stock rear bar in before, and it was better, but still pretty bad. The MSM rear bar really made it nice, and with the sticky tires it's great. I may drop a degree of camber out of the rear and pull the sway, just for ***** and giggles.

Remember my shocks are factory Koni Races, not revalved/shortened Sports.

AbeFM

iTrader: (3)

You're explaining it fine.

What I don't get is where the damage comes from.

As I understand it, the problem is the inner parts of the shock hitting the bottom of the tube.

So a bump stop would prevent that, and therefor a longer bump stop would prevent damage. Maybe my stops are just upside down.

Savington

iTrader: (31)

Whose stops are you using? I am using the bumpstops that came with my shocks. They are pretty similar to the FCM, little short things.

Zabac

iTrader: (39)

Right, but your bumpstops compress, and everytime they compress they get weaker, and if you compress them too much, your rod still bottoms out inside the shock body, that's why a tophat with more room up top alows your shock to live longer, by keeping it from hitting the bump stop all the time...
it you can keep your shock from hitting the bumpstop as hard and as often you reduce the chance of bottoming it out, therefore prolonging shock life...

Joe Perez

iTrader: (8)

I've been lurking on this thread, and the same thing has been bothering me. Either I'm misunderstanding what Zabac et. al. are saying, or they're misunderstanding what you're describing.

Here's a hugely simplified view of the inside of a shock. Yeah, it's a monotube and I'm sure I got the oil/gas ratio wrong, but this is essentially what it looks like:




If distance A is greater than distance B, then there is a potential for the piston to bottom out in the chamber, which is what bends rods and destroys shocks. As the overall length of the shock body decreases (and Konis have shorter bodies than stock), then the ratio of A to B increases. This buys you more useful travel before the bumpstop, but also increases the potential for bottoming the shock.

Now, to be honest I have no idea whether the internal design of the Koni Sport is such that it can bottom when installed on a Miata. It depends on the length of the rod (which I don't know) relative to the amount of travel before other pieces of the suspension come into contact- either spring coil bind or just control arms hitting solid things.

However, if we assume that it is capable of bottoming, then I don't agree with Zabac when he says: "I don't get it man. Only thing I heared of blowing these is bottoming them out i.e. hitting the bump stops too much, that's why top mounts that give you more travel are such a good thing. Fatcat sells shorter bumpstops as well giving you a little more travel."

First, hitting the bumpstops repeatedly does not kill the shock. Hitting the bumpstops routinely is just a fact of life when driving a Miata, particularly a lowered one with otherwise stock-ish suspension geometry. What kills shocks is if the bumpstop is too soft, too short, or both, such that you are able to compress it so much that the shock does indeed bottom.

Thus, stating that "that's why top mounts that give you more travel are such a good thing." makes no sense in this particular context. More travel is a good thing in terms of improving ride quality and predictability, but gaining more travel by either shortening the bumpstop or raising the upper mount, in theory, increases the likelihood of killing the shock.

Thus, Abe is dead on with "So I would think a taller bump stop (while more likely to give you a sudden jolt in a turn and be bad for handling) can only increase the life of the shock by preventing this internal mashing."

Incidentally, that's what those split washers that Shaikh gave you are for- they increase the effective length of the shock body.

Zabac

iTrader: (39)

Thanks for the pic Joe.
A taller tophat will make "A" longer and therefore reduce the chance of you bottoming out the rod inside the shock body.

when i said bottom out in previous posts, I implied the shock body hitting the bump stop and compressing it...this causes you to get closer to bottoming out the rid inside the shock

Joe Perez

iTrader: (8)

Assuming that the rod length and relative spring position remains constant, it simply lowers the car and increases the likelihood that some other mechanical interference will become the limiting factor. Assuming the same bumpstop, it does not alter the relationship between the piston and the bottom of the shock at full compression.

And this is wrong, at least insofar as a recommendation for shorter bumpstops is concerned. Assuming that the upper mount, length of rod, and length of shock body remain constant, increasing the length of the bumpstop will cause the top of the shock body to contact and compress the bumpstop more often and by a greater amount, however this does not in any way increase the likelihood of damage to the shock. Quite to the contrary- increasing the length and/or stiffness of the bumpstop will keep the piston further away from the bottom of the inside the shock.

Check out this illustration. A and B are the exact same setup. A is at rest, and B is at full compression. In B, the bumpstop has been compressed fully, and yet the piston has not quite bottomed out. This might be considered an "ideal" bumpstop choice for this particular combination.

C is the same setup, at full compression, but with a longer / stiffer bumpstop than B. The longer / stiffer bumpstop has not allowed the shock body to travel as far upward, and so the piston is further away from bottoming out. No damage, but you've sacrificed some potential suspension travel and roughened up your ride.

D is the same setup but with a shorter / softer bumpstop than B. The shock has fully compressed the bumpstop, and the piston has bottomed out. It's now rebuild time.

E is the same shock, spring, and bumpstop as A and B, however the tophat has been raised. The static ride height is lower. At full compression, the bumpstop has squished down to the same thickness, and thus the relationship between the piston and the bottom of the shock body is no greater or less than in B, using the same bumpstop but with a lower tophat. The only difference is an increased likelihood of coil bind or other interferenace.

Now, I'm not arguing against raised tophats. Quite the contrary- I use them myself, and for a given ride height they will provide more usable suspension travel relative to stock tophats. This is subject to the assumption made in F, that the spring perches have been raised up to achieve the same static ride height. Note that the bottom of the shock body in F is at the same place as in A, however the piston is further up inside the shock. That's the one penalty for this setup- decreased droop travel.

AbeFM

iTrader: (3)

I don't think so, as Joe said, if A gets really long, what stops the rod from hitting? Nothing.

In my case, I have 7" springs, so I would assume the springs would keep me from hitting, and the bump stops, but I can't say for sure.

The plastic ring, Joe, as I heard it is to give air a chance to escape. Since the bump stops are custom why would they be 8mm short just to put plastic in there? The 'ring' has a cut out of it, I forget where the air gets trapped, maybe it was just making the bump stops suck down and wear out on the shaft, but whatever the reason, the ring is there to allow air to flow out (perhaps the top of the shock).

Anyway, I'm glad you tend to agree with me. I'll just have to find out what all the travels are and see if that's what's going on. Much more likely I hit a giant bump going 100 mph with a full trunk, and blew the seals.

That sort of thing happens all the time to me. I should be an action adventure hero. Instead of a 1.6 liter zero. hahahaha. Oh, I'm funny.

I do wonder if soaking the bump stops in oil is bad for them. I haven't gotten any love from Shaikh, I wonder if he's out of town or something....