OptionXIII

The shock dyno I used for FSAE was of the crank/sinusoidal type. It worked like this:

1. Cycle shock repeatedly to warm up until the shock body was at teh set temperature, I think it was 90*
2. Move the shock to two or three different positions slowly. This was to measure the gas pressure. If you know the shock rod diameter and the force required to hold the shock in position, you can find the shock pressure. Pretty sure it used this to get a better estimate on hysteresis.
3. Cycle the shock for 5 seconds or so.

Then out popped the football graph and the F/V charts. I turned ***** until I got the set starting curve, then we tuned from there.

My target starting point was 65% of critical in rebound, about half of that value in compression, and to have my available coilover travel 60% in compression, 40% for rebound. Outside of those recommendations, I have yet to find anyone be able to give better guidance than saying "go out and play with the settings". That's what the shock guys say at my current job, that's what they said at Joe Gibbs racing when we visited to get feedback on our FSAE car, and that's what they agreed with when we visited a 7 post shaker rig at VIR. Just test the thing. The problem is no one wants to remove and tear down Miata shocks that often.

deezums

iTrader: (3)

I think I've changed my mind and am going to build one more like what mekilljoydammit just posted. Last night I went on the chinabay and found the injection molding LVDT's for around $20. You can also find a 32mm bore 150mm stroke cylinder for another $20.

How do you hook a LDVT to arduino? That's as far as I got last night. Something about generating 3vac at 15khz, then sampling for a disturbance in the frequency? I don't do AC at all. Need to do much more readings.

Or, there's ultrasonic range finding, lidar too expensive for my blood. I think I could make ultrasonic work, just really low accuracy off those sensors.

Alright, I guess I ought to start a new thread

Bronson M

iTrader: (1)

Nice to see a fellow corner-carver on here, I've been watching your progress over there as well.

On the topic of calculating critical dampening I have a spreadsheet from a fellow corner-carver that I've expanded a bit and entered all the miata specific info into that I'll post later. You can enter your shock dyno results and see what the critical damping % is for a given spring rate, motio ratio, and unsprung weight, or enter the % damping and see what you need for a dyno curve. Pretty handy and one of the reasons I chose the spring rates I chose to run on my hard S bilsteins. I've found a few references on the net to aiming for 60% damping in the 0-3 in/s range and then blowing off to something in the 30-40% range at higher velocities to deal with bumps. Unsprung weight will dictate what you need here and is where I think a lot of "try it" recommendations come from. Adjustable shocks tend to make little adjustment at low speeds so it's critical to get the valving right to properly control turn in.

Case in point, at our last auto-x we had a sweeper across a rough section that would bounce the car pretty good at max g-load. I'm running 800/450 spring rates while 3 other guys are running spec rates of 700/400 I was able to carry more speed through these sections and the car visibly looked more composed. It was still bouncy but it was better than the lighter sprung cars. Once you see the spreadsheet I have you'll see that 800/450 rates look pretty good paired with the hard-s curves......not perfect but far from bad.

mekilljoydammit

deezums: I'd go for a potentiometer personally; LVDTs have cheaper sensors but you need more electronics to make it work. The right shopping around and linear travel pots aren't that bad.

Bronson: I've done my own plots like that, albeit mostly focusing on aftermarket coilover setups to try to figure out the why of things, and it seems like low speed damping of around 150% is used a lot, again rolling off. https://i.imgur.com/17uy06Y.jpg is a pair of setups with something like 800/500 springs, working from publicly available shock dynos.

I think a lot of the Miata specific stuff is hampered by the rear shock geometry though - I want to use a top hat that goes into a rod end and extend it into the trunk to get more shock body length.

Bronson M

iTrader: (1)

Usually the crazy damping is from with trying to control the shock on the bump stop, which is what I think the goal was on the miata. Or it could be a crutch for way too soft spring rates which is about 90% of applications out there trying to make street based rates work on track.

mekilljoydammit

Well, in the case of stuff like the Spec Miata package, yes, and I certainly agree with you on street based stuff. The graphs I posted are generated based on shock dynos for stuff that is not street based however; they are from well regarded coilovers using what seems to be reasonable clicker values (obviously this goes up and down but I was going by what people said they had their clickers at) that are intended for 800/500ish springs, and graphed with such.

Interesting, no?

Junkwhale

When I was putting together my bilstein setup, I worked out these out for my NB on MSM shocks based on the dynos that have been shared around for a few years (edit: these are rebound btw):




I'm running this setup now (although with 350lb rears which ended up being the right choice I think) and it's not bad for what it is.

Junkwhale

Interestingly though, the middle line on gen 1 xida w/ 700lb spring and same weight etc (from this dyno: http://949racing.com/images/Xida_S_Front.jpg) was much closer to 65% critical:


I was going to re-valve my own MSM bilsteins to something closer to this, but I just don't think it's worth it in terms of hassle now. Gen 2 Xidas are too much of an easy button & offer too much flexibility and optimization over what's possible with the bilsteins - they allow you to start in the right place (e.g. 65%) and tune from there easily.

crispyBYM

For anyone like me wondering how you can dampen a specific spring rate, I found a good few posts on the FT86 forums that go over the math and how it works. Pretty easy stuff to understand but the devil is in how to make it work. Anyone can valve to 65% of critical damping, not everyone knows how to translate damping ratios to make a well balanced setup. Interesting stuff!

Leafy

iTrader: (1)

if you want to be more advanced than to copy the damping curve from xidas then pickup a copy of racecar vehicle dynamics by milliken and milliken and read it cover to cover.

Bronson M

iTrader: (1)

As promised like a week ago.....

https://docs.google.com/spreadsheets...it?usp=sharing

See if that link works for you, should be able to view and download. I would appreciate someone smarter than myself looking that over. I started with a sheet given to me by David Borden (of GTM fame) and modified it to better display the data. I can't really follow the heavy math since it uses some constants that don't ring a bell but the output seems about right.

The data in the sheet is from what I've found on the forum, you'll need to adjust the sprung and unsprung weights to reflect your chassis. The shock data is based on the published data from Bilstein for hard S shocks. Since they only give you a few points not the whole graph I assumed a knee point and made the curve linear through the data points I had. A full dyno of the hard S would be better.

From playing around with this spreadsheet i can deduce that Mazda was trying to control the chassis while the bump stop was engaged.

Rickracer

I just made a set of extended top hats (two 1", and two 1.5"), from a set of NBs, and I found one thing I hadn't seen mentioned. Extending the top hat limits the amount of droop by the same amount as the extension. My sleeves are with my machinist getting circlip grooves cut like the factory Bilstein spring seats, only deeper.

HHammerly

iTrader: (3)

That is what i did on my last two suspension settups

Rickracer

I just opened up the hole a little so my hole saw pilot would go through, made the hole 2.5", put a 2"/1.5" high piece of 2.5" pipe in there, welded the pipe to the hat, then the top of the hat back to the pipe, leaving a 1/2 shoulder hanging down through the hat for the spring to center up on. Now I'm trying to decide whether to try out the 5.5" springs that came with the sleeves, (they look like the same exact springs and sleeves in the first post of this thread), , or just to go ahead and order some 7" 450/300 lb. Summit springs. I can leave the stock Bilstein spring pads in there to take up some room for the shorter springs, but I'm having my sleeves cut for the circlips anyway, so I don't have to do it later. If I like these springs, I'm done, if not, I can go ahead and order some and leave the shorties in till the new ones get here.
On a somewhat related topic, just out of curiousity, I wonder what shocks I have. I know they are NA for sure, and the numbers I find are: Front - 2411601W1 & N02334700A , Rear - 2411600W01 & N02328700A, it would be nice to know what I'm working with just for the sake of knowing....

BTW, I calculated the rate of the Ebay springs, and they are 615 front, and 384 rear.

Rickracer

I had the Summit coil-over page up this afternoon, and the only thing keeping me from ordering 450/300 lb or 500/350 lb 7" springs was the "cheapskate" in me. I was kinda hoping I'd see some encouragement in one direction or the other. I think I could live with the 615/384 lb ratings of the Ebay springs, but not so sure about the 5.5" length....

Rickracer

Well, I went and did it anyway. It has confirmed my suspicion that I was bouncing off the bump stops pretty often. Hit the railroad tracks by the shop, and the "oak root" bulge in the road around the corner from my house, (as I do every day going to and from work), to test my theory. I took the factory NA bump stops and cut off the bottom half and reused them, but I don't think they are coming into play at all yet. The car rides MUCH better. It may take me a few days to decide whether or not to order new springs.....

Bronson M

iTrader: (1)

Told ya so...... Keep in mind though you need to up the spring rates as you shorten the bump stop. Otherwise when you do get into them it'll be pretty harsh. Stiff springs and short bump stops ride better and perform better than soft springs and long bump stops.

sixshooter

iTrader: (12)

To test travel, tightly secure a zip tie to the shaft just above the shock body. Drive around and then inspect. It should move up and stay at the point of greatest compression if it was cinched tight enough. This will tell you if you were touching the bump stops or not.

Rickracer

Good idea! I may be hitting them once in a while now, but I think I was on em A LOT before. Judging by a comparison between the NA top hats and the NBs, it looks like the NBs give at least 1/2" more "bump clearance", then I added 1" Front. and 1.5" Rear respectively to them, plus cutting about 3/4" off the bump stops themselves. gives more clearance as well. These springs calculated out to 615 and 384, so they are plenty stiff, but since they are so short, they might coil bind under a lot of compression, just gotta wait and see about that....

Erick69

Hi Everyone,

Just picked up an NA and a full set of used MSM shocks (came with hats, springs, etc) for cheap. I just finished reading through this awesome 52 page thread, but just want to run the parts through y'all before ordering.

Basically going to be using mgeoffriau's setup (https://docs.google.com/spreadsheets...gid=1098453665)

Front:
MSM Front Shocks
NB Top Hats
Advanced sleeve/perches - https://www.advanced-autosports.com/...sleeve-and-nut
Integra shock bumpers cut to 36mm - https://www.summitracing.com/parts/i...9-50/overview/
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->Energy Suspension Coil Spring Isolators 9-6103R - https://www.summitracing.com/parts/ens-9-6103r
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->RideTech 70010828 delrin thrust washers - https://www.summitracing.com/parts/art-70010828
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->Summit Racing 550lbs 7" L 2.5" ID - https://www.summitracing.com/parts/sum-72-07-550

Rear:
MSM Rear Shocks
TSM top hats - TSM Shock Mounts
Advanced sleeve/perches - https://www.advanced-autosports.com/...sleeve-and-nut
Integra shock bumpers cut to 36mm - https://www.summitracing.com/parts/i...9-50/overview/
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->Energy Suspension Coil Spring Isolators 9-6103R - https://www.summitracing.com/parts/ens-9-6103r
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->RideTech 70010828 delrin thrust washers - https://www.summitracing.com/parts/art-70010828
<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->Summit Racing 350lbs 7" L 2.5" ID - https://www.summitracing.com/parts/SUM-72-07-350

Thanks in advance for the input!!