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Also - i'm rolling NB HD on NB2 - i should be able to snug up the spring against the tophat with reasonable height around 12.5-13" right?
I wasn't able to on my car. Putting the ever slightest amount of preload on the spring caused my ride heights to be around 14". I was also using Spec Miata sleeves so mileage may vary a bit.
So I've just got everything for the rears and here is what they look like:
I've removed the spring, put the shock on the car, put the wheel and jacked it up to desired height. At 13" center of hub to fender, in order to get 1" shock travel before hitting a bump stop in an extended hat my bump stops would need to be cut down to 31mm.
If i tried to get even lower height, then there is very little if any shock travel before getting on a cut down bump. I really don't quite understand how people with NBs run on stock hats or 12" height. Just seems like one would have no travel or would need to run 1.5-2" hats in order not to just abuse bumps or blow shocks.
Also - with 7" springs and no helpers there is no way that they won't be unseated under full droop. Will probably get unseated while going over major bumps.
That's what I've found as well. I'm guessing your average drive probably won't unseat the springs but I've found evidence that shows my springs are definitely coming loose during driving. Maybe I drive crazy?
I put an order for 1.5" Rear top hats off ISC. I'm hoping for a bit more confidence hitting bumps in a turn.
So you found the worst kept secret to modifying Miatas, if you lower the car too much it'll ride like crap. This is why stiffer springs are a must if you're going to run this low. I'm not talking about 400/300 street rates either. I'm at 800/450 and need more rate to run lower than 12.75" in the rear to keep off the bump stops on mid corner bumps. It's allready loose so I'll stay where I'm at for now.
I personally don't think that rattling springs are a problem, you literally have to get air with your car for them to unseat, bumps aren't going to do this. The only way to really have this happen is to hang a front inside tire with very soft springs and really sticky tires, it just doesn't happen.
From reading this and other threads my impression was that most people who run miata's at track and auto-x are below 13" and some are as low as 12" front 12 1/4" in the rear, with majority at 12 1/4 - 12 3/4" F/R range. I'm just trying to understand if everyone really has no shock travel or if I'm missing something. Is an inch of shock travel before bumps enough for Miatas?
You have to look at spring rates when you look at ride height. Throw a 1000 lb/in spring in the front and you can get away with 1/2" of travel most likely, but at 150 lb/in stock rates you'll need to rely on the bump stops and 2 to 3" of travel to keep it from being painfull.
The reality is a huge amount of folks are riding around and racing on the bump stops and just haven't figured it out yet. When they get a hold of a well engineered shock, spring, and bump stop setup like a fat cat, exida, ect. It's earth shattering to them because it was so wrong with their last setup.
It's possible to get 75% of the way there with OEM bilsteins and eBay sleeves. The key is getting your spring rates matched to your ride height and getting your bump stops trimmed to match your top hats and wheel to fender clearance. The final piece of the puzzle is the shock valving, the stock bilsteins are only half right, a revalve can get them the rest of the way there. Even with so so valving for the stiffer rates they are miles ahead of all but the best shocks out there at a price point of 1/3rd of the good stuff.
^Sway bars can help to keep cars off the bump stops in corners because they essentially borrow spring capacity from one side of the car to help the other side. Very large sways can compensate for undersized spring rates to some degree without ruining highway ride comfort. Cars required to run stock sways in racing classes must run very high spring rates to compensate for tiny sways.
So I've done some more measuring - in front with NB shocks/hats and bumps cut to 29-30mm - i get zero space between shock and bump at 12 3/4 height. I really don't understand how everyone else runs 36mm bumps and has any shock travel or runs any bumps below 12 3/4" front height. I feel like I'm either doing something seriously wrong or people don't actually check their shock travel and bump engagement when building these.
Well, here is the shot of my front assembly before bump was cut and went onto the car. It's all standard stuff and there isn't really any way to make a mistake from what I can see.
AWR/Spec Miata 4" sleeve and perch with set screw, torrington bearing, 7" Eibach spring, AWR/Spec Miata spring locator (glued to tophat), NB tophat
Not in the picture, but installed on the shocks are 2 nuts at the very top, OE top bushing washer, OE upper bushing, OE lower bushing, thick steel washer under lower bushings
Here is the mock-up before i removed the tab and added OE bushings and washers.
2001 SE NB2, pretty much stock except for minor mods : intake, muffler, seats, roll-bar. Suspension: Bilsteins (duh), FM sways front and rear, 949 SuperMiata end-links, stock 16" wheels with OE size Bridgestone RE760's.
I took the car out for 2 mile ride after Billies install, so it should have shacken-out/settled if anything wasn't in place. I've adjusted and tightened end-links and sways with car sitting on wheels on the ground. Checked all nuts and bolts before putting wheels on. I really don't see anything at all that could be wrong from assembly or fitment standpoint, but my numbers are so out of line with what others are reporting. I can get 1/4" front shock movement before bump with car at almost 13", but that's it. Rear has a decent amount of travel, so seems to be OK.
Springs should not play ANY role to travel left; it is purely a function of shock body length, ride height, bumpstop length and top hat depth, nothing more.
Well, the spring does compress to some static height after the car's weight it placed on it so the softer springs should compress some more than stiffer when the car is lowered onto wheels from the jacks. Each corner is carrying at least 600lbs of the 2400lb (rough estimate) so the 450 and 325 springs will compress at least an inch so they do play role in reduction of compression travel at rest. Unless I'm grossly misunderstanding how suspension and springs work.
Well, the spring does compress to some static height after the car's weight it placed on it so the softer springs should compress some more than stiffer when the car is lowered onto wheels from the jacks. Each corner is carrying at least 600lbs of the 2400lb (rough estimate) so the 450 and 325 springs will compress at least an inch so they do play role in reduction of compression travel at rest. Unless I'm grossly misunderstanding how suspension and springs work.
You are absolutely right. However this will only affect your ride height (and how much the suspension compresses under load), not how much travel you have from your ride height till the bumpstop.
But those two functions are directly linked - change in ride height changes available rod travel since both are directly connected at the tophat. If we push the spring on the sleeve upwards - this will push the hat up increasing ride height, but at the same time pulling the shock rod upwards with it and increasing compression travel. Same is true for the opposite - spring compresses on the perch under weight of the car - the more it compresses, the more rod goes into the shock reducing available travel. So if the bump length is left unchanged, ride height direct directly affects available compression travel.
Sorry, not trying to argue here for the sake of arguing - just really trying to make sure that my understanding of suspension is correct.
I don't think my spring rates or length would be a problem since many reported running similar setups. I've just re-read a similar thread on CR and some are saying they run as low as high 11" to mid 12's. I don't see how that's physically possible on NB shocks/hats with anything smaller than 12-15mm bumps and extended hats in front.
08-16-2016, 03:16 PM
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