flame if you want, i'm going with a pneumatic suspension for the track

[95lstegman]

BEFORE YOU FLAME, HEAR ME OUT. DON'T BE A PAIN IN MY REAR JUST BECAUSE YOU CAN'T THINK OUTSIDE THE BOX

i haven't posted hardly at all in quite a while. my name is jason and i've been an engineering student at USF since fall '03. my take on my car is to create the best solution for my needs, and this is the result of a lot of research (as are all of my more interesting modifications), a very healthy expenditure of free time, lots of physics/math (aka engineering), and some free thinking.

first, to catch your mind and not your BS and worthless jargon, let me tell you WHY this is the coolest suspension setup ever.

so, you're building a track car, or even a performance street car, or really any kind of performance setup. what do you want? well, you want high spring rates, plenty of dampening, preferably with adjustability, and you'll surely want to be able to change the height of the car, both to lower center of gravity and perhaps (if you're so equipped to set it up) corner-weight the car or adjust the balance of weight transferred by each end (change front and rear spring rates and dampening rates separately).in order to change the heights, you need to get out of the car, lift up each corner individually, and adjust as desired. but then you let the car down and see how that affected it. rinse and repeat until desired height is reached (although this may take only once for you with experience).best case scenario, you have EDFC or the like and you can adjust dampening from inside the car.and for spring rate changes, you have some capability to preload the springs of your coilovers, but mainly you'll have to pull the suspension to change springs.

so here's why this is cool:air suspension pros:1) adjustable height from inside the cockpit, relatively quickly (although for this system i'm designing, the car must be not moving and on relatively flat ground, and will take approx. 1-2 minutes)2) SURPRISE: adjustable spring rates from inside the cockpit, very very quickly. this can be done in less than 5 seconds, or pretty much as fast as you can move your hand from the wheel down to the control panel, flip 4 switches all next to each other, and come back to the wheel.3) SURPRISE: adjustable dampening. when this system comes into being, i will experiment with having to adjust on the bottom of the suspension versus in the cockpit. in-cockpit dampening may react too slowly for the track, so i may stick with getting out to adjust dampening, or have a switch to change between 1 hard track setting and cockpit-adjustable softer settings.4) TEIN FLEX coilovers have adjustable height, dampening, and sort of (not really) a system for changing spring rates, though nothing like this. they cost about $1400. my setup will cost between $1200-$1500 for all top notch parts.5) even with 6 different spring rates to choose from between 148lb/in and 467lb/in, i can change the 6 existing ones with a trip to ACE hardware and about $10. or for about $50-$100 i could add in another set of 3 spring rates.

air suspension cons:1) never been done before. not really on this car; although there are a few kits, none of them would be any good for performance. so i have to be the pioneer. all kits out there (except Praxis for BMW 3 and WRX) are for ride quality and have terrible spring rates.2) this setup will add approximately 20-30lbs to the car. but for us turbo guys, 30lbs isn't even noticeable. for all the advantages of this setup, 30lbs is a great price.3) everybody laughing the second after i post this, although they will stop if they ever get to ride in the car.

the basic specs of my system, said in a way you can understand:basically, i will have 2 sets of spring rates, one i will call Track Mode, and the other Sport Mode. each Mode will have 3 different settings, Soft, Medium, and Hard. Soft will be the highest ride height and lowest spring rate. i will probably set this initial height at near stock height, perhaps 0.5" lower than stock. Medium will be a 1" drop from Soft, and Hard will be a further 1" drop from Medium, so 2" overall from wherever i set Soft to (near stock). for the Sport Mode, the 3 settings will result in spring rates of 148lb/in to 215lb/in. suspension geometry will be unchanged, so these are relatively conservative rates. i may increase them slightly. in Track Mode, spring rates will go from 236lb/in to 467lb/in. i'm relatively happy with the Track Mode rates, even though 467lb/in is a bit harsh. but it is designed for the track, so a 2.5" drop (2" drop plus the 0.5" lower the setup will sit below stock) and 467lb/in should be right at home on the track.

alignment will be the only real problem here. i'll probably set it up to be happy at the 1" drop, and i plan only to raise it up to Soft for bumps, parking lot bumps, etc. then the track mode the rear will gain some negative camber, and i'll add in adjustable front camber plates. this is really a problem that will only really be solved after i get the setup running.

reliability:pneumatics are very reliable when built properly. i will use all manual switches and hardware. i've created plenty of pneumatic systems before, and none so far have any real leaks. besides, an air ride system will not notice a small leak at all. it has a compressor to deal with air losses.

i will be using air cylinders for their inherent rigidity as opposed to bags, which flex like crazy. also, to the delight of my engineer inside me, since they are very rigid, they behave almost perfectly according to basic fluid principles, so what i calculate is very very close to real life.

okay, i guess you can flame if you like, but you'll only be proving that you don't know what you're talking about. the physics and engineering aren't even all that difficult. there are only a few numbers that make a big difference. the only thing is getting past the notion that air suspensions are for sissies.

[nissan_blood]

should post pictures of it when you are complete and do a walk threw how everything works. Im not a engineer......So it would be hard to convince me or alot of people to use an air suspension just from words of wisdom.Sounds like a pretty cool idea though good luck

[ricebike]

no flaming needed

it has been proven in other models on how much better air ride suspensions are... they're not just for lowriders anymore!

[nightkid86]

lamborghinis and citroens have had pneumatic suspension for a while, so it can't be that bad.

[SeVa-S13]

Yeah, I kinda came to that conclusion a while back after riding in some nice air suspended cars; I just lack the know-how in that area to do it.

Keep this thread updated occasionally with progress reports.

[180fan]

werd. lots of merc's have them too.

[DjTravisSW]

My recently sold 95 Ford Lincoln Continental had 'em too. Smoothest ride -ever-.

Now i'm in my lowered 240 with 17's and Tokicos. yeah...not soo smooth. lol

[95lstegman]

well, i seriously hate it when people post up something cool or interesting or whatnot, so i'll keep everybody posted. i just bought my fiancee a little motorcycle for her birthday, so money is extremely tight. i've gotten pretty much all the bugs/issues worked out, except that i know i will have to create some custom bracketry once i have the parts in my hands and i need a good way to make sure that i get the exact ride height correctly every time.spring rate depends GREATLY on height, so i need something that will give me accuracy preferrably down to about 1/20th of an inch or so. 1/10th would be okay but hey, i'm an engineer. perfection is what i strive for. in any case, i haven't found anything that can be used remotely that will give me even close to the minimum accuracy i will need, except possibly for creation and monitoring of small magnetic fields, one for each corner. i need to keep it in budget. fallback plan for this is to keep precision blocks of metal in the car for measurement, but that would mean getting out and spending several minutes setting heights, and while that doesn't kill all the other nice performance benefits, it sure makes it hard to lower it back down after going over bumps or whatnot. so i'm trying really hard to figure something out that will take care of this w/o being in the car. actually, spring rates will change some because heights are set while in the car, but it won't be much of an issue. ~50ish lb/in change may occur, but i consider this acceptable since most aftermarket and indeed stock springs are rising-rate anyways, and give similar effects when the driver adds weight to one side. the option will be corner-weighting the car for having just the driver. this system by design will be able to adjust more than 1" at each corner for this type of thing, aside from being able to raise and lower normally as desired.the brackets won't be hard, although myself not personally having a welder, it'll cost me a pretty penny. anybody on here that has the skills and supplies that would please help me can post or email me at [email protected]. i'm in central FL.as a sidenote, since this isn't going to be very hard to operate, and the performance makes so much sense, i may end up making a few more of these kits once mine is done and sell them. i would charge more than the $1200-$1400 or so it'll cost for parts, but since i'm not using fancy electronic automatic self-levelling hardware/software, it'll stay below $2000, or about half what it costs for the WRX (by Praxis, child i believe of Bridgestone). also, if i do sell a similar kit, the spring rates will be extremely easy to vary and will be at the discretion of each buyer. we'll see how mine goes, but i assure you all the parts will be top notch and very reliable. when i get pics, i'll post them up. sometime this week i should have a pretty much finalized table of spring rates, and i'll post that up for your enjoyment.

[95lstegman]

after looking through spec sheets and diagrams and waaaayy too much technical mounting stuff, i think what i'm going to do for the tops is fabricate a piece to attatch each cylinder to a standard-issue 240SX camber plate top mount. this will save me from having to figure out the mounting pattern (although it would be pretty easy), and - more importantly - allow quick and easy camber adjustments. for the rear i'll fab the exact same mounts and just use the standard-issue 240SX rear top mount w/ sperical bearing and i guess i'll have to pick up some adjustable rear upper control arms. i'll look through the NICO sponsors again sometime closer to crunch time, but i didn't see anything promising when i was there earlier today.for the front lower mounts i've got a great design that will *hopefully* allow very wide wheels up front. i'll have to see how they clear through their range of motion but the idea i have should allow use of fairly high offset wheels sticking further into the fender than possible with coilovers. for the rear i'll try to find spherical bearings big enough and strong enough to cope with these loads, but it may not happen. i may have to go to an off-the-shelf Energy Suspension round bearing, maybe something they sell normally for some large control arm bushing.as a note, my 240 (the car this is going on) has all ES bushings installed, so if anybody gets a ride at a track and it's hella stiff like a go-kart then understand you've got hours of pressing and pounding and burning bushings ahead of you to achieve such precise handling.

attatched is the current spring rate graph. it may get a big tweak this week to get a better looking stroke from the suspension, but if/when it does i'll be shooting for similar rates to these (and i'll post a new one if/when that happens). you have to understand it starts at 1" of suspension compression. the first 1" of compression is VERY soft, and the weight of the car itself will take up most if not all of it, so you won't really notice it. so the spring rates you see at x=1" is the static spring rate, like what you would see listed for any aftermarket spring. further compression from there will yield the spring rates shown. in the hardest mode, the spring rate climbs astronomically, so unless you get a bus landing on top of your car, you won't be seeing much compression at all. at 1.5" (so 0.5" of compression past the first 1"), the spring rate is a whopping 934lb/in. if you do manage to get it to compress fully in this mode the spring rate gets up to 1535lb/in before hitting the stop.
Modified by 95lstegman at 4:05 AM 9/18/2006

[onosqv]

Actually, it has been done already...

Grenade:

http://www.grenade.jp/air.asp

Tanabe:Although I can't find the picture anymore, they did dabble w/ it in 94, and I believe they have an air suspension kit coming out/already out for higher end performance/luxury cars.

[quote=""http://www.modacar.com/tanabe.html""] 1993: Tanabe increased total capital investment to 15,000,000 yen.

Tanabe released stainless steel exhaust manifold and air suspension tuning kit.[/quote]Good luck w/ the kit, will definately be different.

Also, if you feel nice, please space out and format your paragraphs better. It may just be that I'm reading this @ 1:39am my time, but it's pretty hard to read when you make such large paragraphs and don't separate the sentences properly.

less text, more pics of beta/prototypes would be awesome.

[ricebike]

ah, i knew it was out thurr somewheres... my search skillz suxorz... thanks QV for the link.

now, he can reverse-engineer it

[95lstegman]

i hit carriage return after each paragraph, but true, i could make it neater. i do put 2 spaces between each sentence, although i don't bother with capitalization online. i think NICO narrows it down to 1 space, though. i was just trying to explain where my head was, which is usually very difficult to do. i have moments of genius followed by hours of thinking inside the box, then i smack one out of the park again and then i'm stumped again . . . ah, well.

in any case, i won't be making anything near that simplistic. that can't possibly be performance-oriented. 1 gauge, no valving? and besides, that's pretty lame for $4,900 in US currency. i'm going to GREAT lengths to create definite spring rates at definite heights/suspension strokes, and more and more i find myself working a little calculus (aka magic) and a TON of algebra rearranging equations and working about getting this more solid than that graph i posted. what i'm working on now makes that one seem useless. i will now know EXACTLY how the weight of the vehicle will affect it, rather than making the conjecture that the car will sit down into the first inch and provide a guess spring rate. so yeah, all of my spring rates are going to be way off now that i'm thinking smarter.

on the beta testing front, i saw a GORGEOUS 2002 Honda Rebel (tiny 234cc cruising bike) with not even 2,800miles on it and bought it (yes, i'm a bit of an impulse buyer, but my 240 was an impulse buy as well), so money may be quite cramped for me, at least for the next month or two, so movement may be very slow there unless i can buddy up to somebody with a welder. i know the dimensions of my [future] cylinders, so i could fabricate mounts very precisely if i wasn't paying some shmuck $50/hr+ to do it. in the meantime there is still a LOT of work in the physics still to do before i can say i have enough real data to put the system into motion realistically. i mean i could just wing it with rough numbers, but without really knowing what's going to happen, i'm hardly any better than the rest of the air ride crowd. like adding cams and feeling fast then finding out you lost 20whp b/c of a lack of tuning. it could be stiff and feel decent, but anything would feel better than my bouncy, worn stock shocks (and blown right rear one).

[95lstegman]

mods, please move this to the nissan engineering forum.

hey, does anyone know where i can find, say, a nice spreadsheet that calculates weight transfer under acceleration (which can be sideways, like when you're turning) from side to side at least, and maybe front to back? i'll start working on one but if somebody turns one up that would save me some time.

since air springs' spring rates follow exponential functions and linear springs' spring rates follow linear functions, i need to know what area on the curve i want the air spring to mimic a linear spring of given spring rate.