HarryB

You are absolutely right! 🙂 But, for a given (desired) ride height, spring does not affect available travel. Ride height affects travel (bumpstop length, shock body length and top hat depth being all the other parameters that affect it as well), and spring rates (and threaded adjuster position and spring length) affect ride height.

2slow

ok, got it. Still trying to udnerstand why I don't have any travel at 12.75" and 31mm bump.

deezums

iTrader: (3)

Stiff springs limit available droop travel unless you have softer tender/helper springs. Heavy springs will only compress so much under our light cars, whatever amount they compress at normal ride height is your total available droop travel. This won't change for different length shocks.

Jack the car up and see where the spring finally closes up the gap between perch and tophat, that's your shock travel at max droop. You want that as close to the full extension on the shock as possible. Chances are you can kick the wheel/suspension down further. Whatever you see there is wasted shock droop travel, you can use motion ratios or measure the shock with zip ties to get actual shock travel measurements.

Since so many of us have no need for droop travel, what with not running helper/soft springs, you can trade it for more bump travel with extended top hats. I'd recommend getting hats as long as the wasted droop travel measured earlier, maybe slightly shorter. Check with no spring installed for tire clearance, and fill the gap with progressive bumpstops instead of cut down ones. They will be much more forgiving than the 1/2" thick things you usually end up with.

It's not possible to ride low on NB shocks with NB hats on a NA, not without being all over the amazingly cut down bumpstops.

2slow

Ok, sure but this is all pure NB setup - 2001 Miata, NB front hats, NB HD shocks.

HarryB

Sure, but you can have so much bump travel before something else makes contact (fender liners, arms with frame etc). Plus touching the bumpstop is different that squshing the bumpstop. These behave as additional non linear springs, not as solid pucks.

2slow

I understand that part, it's just when reading about Bilstein based coilover on Miatas - many people have reported being able to put bigger bump (36mm FCM) and be lower on similar setup. I'm chatting with one chap from M.net who has almost identical setup and claims his front is 12.25" with 36mm bump and he still has some shock travel before hitting bump. My issue is riding on the bump 100% of the time and not being able to lower a bit more to get better alignment numbers and lower center of gravity.

HarryB

20mm difference in center of gravity height will go unnoticed. Behavior will be more affected by changed angles in a arms that will result in a different roll center position than originally designed, but even this is not much. What would be interesting and useful is having travel data for front and rear suspension. Starting at full droop and with the damper mounted but no spring, start moving the hub upwards at .5" increments and measure the distance from top of the shock to the top hat (or bumpstop given that you make sure it always contacts the top hat). Then you can calculate everything. I already have some data regarding this, will see if I can find them and post them here.

2slow

Any other comments all? Really need to figure this out ASAP as MRLS (Laguna Seca track days) coming up and i don't feel this suspension is ready for it in the current state. If i can't get it solved - i need to either cancel event or put my old stuff back in and run on stock wheels/tires since I can't put my 15x9 without 2.5 ID spring coil-overs due to rubbing with wider springs.

https://www.miataturbo.net/suspensio...4/#post1123918
12.5 front and has bump travel?


https://www.miataturbo.net/suspensio...8/#post1141990
12.5 front with 36mm bumps fitting and i assume some shock travel left


Bahurd in this post
Is this because of TSM hots up front?

https://www.miataturbo.net/suspensio...9/#post1202840
11.5 (!!!) front with NB miata, NB shocks, NB hats and 30mm bumps resting on the shock. A full 1" difference with me.

HarryB

Stupid comment form my side, but from memory the miata motion ratio is something like 0.65. That means that an inch of travel at the damper translates to 1.40sth at the wheel. For now, I would just run it a tad higher and see how it goes.

Bronson M

iTrader: (1)

I would run it as is as well, trim your bump stops like what's been talked about and then experiment with ride heights. Start high and lower until you can tell you're tagging the bump stops in the turns. Some of the variance can be chalked up to how close you're getting your tires to hard parts, I removed the inner liners or drastically cut them up. Also the top and bottom shock bushings will change the needed bump stop length. Because mine are old and collapsed I can run a little longer bump stop.

2slow

Ok, i went back to the car and checked - i'm sitting on bump stop even at rest with 12.75" at rest. So Any corners or bumps are compressing them further. I think at this point without extended front hats and maybe further cutting of bumps from 31mm i'm not going to find any more travel.

vteckiller2000

iTrader: (4)

Please post pics. Lots of them. I have about 7/8" travel with 36mm stops on on an nb with 12.0" fender to hub in the front.

sixshooter

iTrader: (12)

Please start using ground to pinch weld height so those of us with rolled/pulled/flared fenders can understand the heights discussed and contribute.

crispyBYM

If you have any pictures post them as well. I'm on an NB with NB HD shocks and stock NB Hats with about 1/4" travel at 12.25" fender to hub. Can shock bushings really be taking up this much travel?

2slow

Just went to buy new tape measure as i was using a flexible ruler before and then took a few pictures and measurements.

Front:
hub to fender is 12 3/4"
pinch weld 5 3/4"

Shock with sleeve


31mm FM bump sitting on shock


On driver's side i have about 1/8" of space between bump and shock. On passenger side there is no space - bump is slightly squished, but pinch weld height is same. I think maybe one bump was cut slightly larger than the other. I can take the wheel off and take more pictures - just tell me what you want to see.

2slow

Yes, THAT! I don't understand how we can have such wildly different results with same hardware.

I don't know, but have to wonder the same.

I have both NEW OEM bushings on the shock (upper and lower) and a thick washer under lower bushings and above bump stop.

JoeTheZoe

iTrader: (1)

1. Are the bushings correctly compressed? As in, did you sufficiently torque the top nut? Additional squeeze of the bushings will buy you some bump travel.

2. How thick is this "thick washer" you are using below your bushing/above the bumpstop? Perhaps going to fatcatmotorsports bushings or a similar DIY MCU setup could result in shorter-than-stock bushing heights. This still does not explain the large variance in bump travel from the above setups, given the same top hats, shock bodies, and cars (NBs).

2slow

I believe so. The nut was pretty tight and I could see them squish.
Top bushings by itself is 1.587" and installed and compressed is 1.821"







It is 0.135" or 3.43mm



I have some bump stop cut offs that I could try using FatCat style instead of rubber bushings, or even just cut the lower bushing in half. It's 0.93" in free state and compresses quite a bit but probably 1/3-1/2 of it's thickness.


Right now I'm seriously considering going with extended tophats, but not sure how tall. My measurements show that NB hats are about 0.6" deep in the area where bushing goes in. By the time I add lower bushing and washer, the stack is sticking out from under the hat by about .51" before being compressed and probably about ~.3" after being compressed (it's hard to measure this thing compressed off the shock) . So if i get 1" deep hats, the lower bushing and washer will go into it (static height is about an inch) and after being compressed is probably about ~.8". So this would give me a difference of .5" in real terms. Not much...but something.

JoeTheZoe

iTrader: (1)

Even in the first post of this thread a cut "scrap" bumpstop was used in place of the top bushing. Give it a try off the car and compare the compressed height of the lower bushing in MCU versus the stock rubber. Some folks end up cutting the stock bushings just to fit NB hats on their NA shock, so it has been done. As far as I know, that may just increase NVH slightly. However, that may still be a bit extreme when you are estimating that it compresses to only 1/3-1/2 of the original height. Cutting it, and assuming equal strain in preload, you would only reduce the total height to 1/3-1/2 of the "new" thickness, just as it did before; it becomes a losing battle for minimal gain in travel. Again, this still does not address why your height vs. travel is differing so greatly from the others.

EDIT: 2Slow - Oopse, I see you were part of the discussion about these depths on the previous pages. You can likely disregard what I wrote below, as you are fully aware.
Keep in mind - as was discussed a page or 2 ago - that the advertised heights/depths of the extended tophats are not necessarily the actual depth, but may be the length "extended" from a reference, likely versus the NB depth (0.6" as you mentioned, though I am pretty sure it is closer to 0.75" but I can measure again tonight). So if they say, 1.5" extended tophats, it may mean 1.5" absolute depth or 1.5" deeper than stock (~2.00-2.25" total). Make sure to ask about this before buying, and check the previous posts that already verified this for 1 or 2 of the brands. If you end up with too much travel, resulting in tire contact or coil bind, you can increase the bumpstop length and/or shim above the bumpstop (perhaps with more of those thick washers you have). Also be aware of the inside diameter of the extended tophats, as you could also run into issues of your threaded sleeve making hard contact with the tophat, rather than your bumpstop doing its job. Others have cut their sleeves down or otherwise lowered them or the snap ring to avoid this.

HarryB

Your case really puzzles me, as I cannot pick up how it ended up differently right to left. Are you sure that the top washer sits atop the shoulder on the damper shaft, and that the washer itself had not bent?

I will also throw some data here from my notes. Front motion ratio in a NB(2) is 0.63 and rear is 0.75, therefore wheel travel would be 1.58 (F) and 1.33 (R) times the shock travel respectively. Below is what I have measured in an OEM suspension, fender to hub. Bump limit NOT imposed by bumpstops or shock travel, rather by parts making contact (wheels with wheel wells on the front, upper arm with frame on the rear); this was because I wanted to measure everything and be able to calculate top hat depths and bumpstop lengths with the best possible compromise between bump and droop travel and without hitting wheels or arms. Bump limits were taken off various resources/forums and not confirmed by me yet.

Max droop: 16.7F/17.5R
Ride height: 13.6F/14.2R
Bump limit: 11F/9.5R
Max travel bump: 2.6F/4.6R
Max travel droop: 3.1F/3.3R

Targeting at 12.6F/13R ride height, this means we will now have
Max travel bump: 1.6F/3.5R
Max travel droop: 4.1F/4.5R

For the given motion ratio (and no change in top mounts) the front shock travel should be 1", after fully squashing the bumpstop..