LocostUSA.com

I believe the IMSA GTS (weak comparison) used to travel 63.5 / 25.5 mm in the front and 76 / 38 in the rear (say the Hub).
(even worse comparisons: Road Car 120 / 80 and 130 / 90 , Formula Ford 51 / 25.5 and Indy Cars 38/0 and 63.5 /25.5 (because of the tracks) )

When thinking about suspension I'd always consider usage of torsion bar suspension or single shock / axle suspensions - why not, Porsches are equipped with torsion bars until 964 series. Ferrari "rediscovered" torsion bars (combined with newish dampers) for the Formula One car (video: http://www.autobild.de/videos/f1-technik-1324031.html )

to avoid bump stops one could go with a mechanical solution that translates the force progressively or a special additional "spring" shown in second attachment

Update: http://www.racingaspirations.com/?p=292 nice calculator

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I use my car for street only. I bought 300# in front and 185# in the rear. My thought would be that all our sevens would be pretty similar in weight and stuff. I find that my car gets air born over bumps pretty easily. I have reduced (tire) air pressure to 20 # to keep it from bouncing all over the place. I'd like to go down in spring weight, but how much would be noticeable? Would I drop 25#, 50#, not sure how much to try first. I weighed my car on a scale the other day and it weighed right at 1500# but the scales had a hundred pound plus or minus rate at that weight, so not all that accurate.
Wayne

Carroll Smith said to go about 20% at a time.

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I'm a noob at setup, but wouldn't that entire "airborne" thing be due to shocks? Like the high speed compression valving is off somehow? Or that the shock(s) are binding, prohibiting movement due to impact spikes (as opposed to compression due to body/spring oscillation)? I once had a strut that, when it got warm, it started to seize up cause all sorts of funky handling.

My understanding is that the Stalker uses 350/175 F/R, and that many reported that the thing bottomed out causing bad butt bruises on rough pavement. The current owner of the company went to 600/300 in this post:

http://grassrootsmotorsports.com/forum/ ... 180/page1/

I sent him a private message asking him how it went, but no reply.

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Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

If you have less travel then an average street car, you'll hit the bumps at least a little harder. Get some perspective with some little skinny tiewraps around the shafts on your shocks. See how much they move up the shaft during going in and out of your driveway and also a smooth road with a stop sign. Then find a little bump and a bigger one, take note of your speed and see how much the tie wrap moves.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

I have 350 fronts and 200 rears and so far they are working out fine, but on the other hand I like your idea of the tie raps or in my case I have a bunch of mini zaps I can use, just to see where the shocks are really loading at.
I love simple these simple solutions/checks.

Al

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Super Seven 3.4

well i think i can chime in here. with my kids racing quarter midgets for the last 10 years i understand the connection between shocks and springs . my kids cars use on all 4 corners gas/oil filled coil over shocks.i have a adjustable shock that i use to find the correct dampening which goes from 1-5 . as my kids get older the shock will change stiffness (right now one runs 3s the other runs 4s) that said no matter what your shock angle is keep it simple. find the correct valving for a shock. go with a middle of the road dampening shock then start with the springs. if it only travels 1" to much spring. on my car that my dad built that i now own he was right there with my thinking. adjustable on all 4 corners ..... im new to the forum but i have been using these ideas for a long time. works for me.

I'm going through the same thing building my Centaur 7.
The front suspension is Mustang II and as a factory suspension it has A LOT of travel. My problem is with the Mii suspension I need coil springs that are 10" long that need to compress to 6" to reach the static ride height and the middle of the shock range of motion.

Doing the math this puts me at around 100 lbs / inch

I'm really concerned that will end up being too soft. Mine will be a street car that rarely if ever will see an autoX and never a track day. I don't want it SO stiff that it rattles my fillings out driving around town or back and forth to work. I don't want it so soft that it bottoms out on every bump

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Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216

this is the second time i have had to type this due to power outages.

the problem is the falling rate of the suspension, at full bump, the spring rate needs to be so high that at normal suspension loads, ride hight, the springs are too stiff.

take a spring of 100lbs per inch and a 200lb. 1/2 car sprung weight, if the spring was vertical it would compress progressivly and at 2" it would support the car, however i will assume that the mounting is such that the shock is at an angle of 45deg. and the ratio of wheel to shock is 2-1 which means that the spring is compressed to an actual load of 800lbs or 8".

if we look at the angle of the shock at full bump, the angle ratio may be as much as 30deg. this would require a spring load of 1200lbs, or 12".

therefore the spring would have to be compressed on installation by 4" if the ride hight were at mid point of travel thus requiring a shock travel of 8" and a spring of 12" in length for a 1" per 100lb. spring.

this spring however would be in coil bind before this point is reached so a longer spring is required, to permit a spring with 12" of compressable length to be fitted the shock needs to be long enough to be able to initially compress the spring by adjusting the seat 4"

the above may be impractical so a spring with a higher rate must be substituted, alas that means a stiffer ride.

if we were to work out the senario a slightly different way, and started with a spring that was fittable to the shock, say 8"compessable length, then we would have to have the same load of 1200lbs at full bump but in 8" of compression, this would require a spring rate of 150lbs. and at ride hight would be loaded to 600lbs. and to acheavehe 800lbs required to support the car at 50% travel the spring rate would need to be 200lbs per inch, thats 4" of travel, spring resistance would increase above that required for any travel beyond ride hight so worsening the situation.

the result of this would be a 100% increase in suspension resistance to deflection so if you were to hit a bump with the original 12" compession spring at 50 mph, in the second senario it would feel like hitting the same bump at 100mph.

both senarios have the same amount of travel in the shocks.

THIS ONLY ILLUSTATES THE DIFFERENCE IN SHOCK ANGLE CHANGES AND DOES NOT CONSIDER THE EFFECTS OF IMPACT ON THE SUSPENSION

having read this, why would you use falling rate suspension?

i didn't

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and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

Since this is an on-going spring thread I will ask for help here:

My rear is 1" too high. Mounting points are fixed. Currently running 12", 200lb/inch coilovers mounted vertically on solid axle. With 190lb driver and not much fuel, springs are at 10.25". Fuel load is 100lbs, passengers don't matter.

So if I want to drop the car 1" in rear at 1/2 tank I want 140-150lb/in springs right?

Also, preload was at 0.5", sound about right?

Thanks,
Cory

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Build log: viewtopic.php?t=9291

If your ride height is too high take out the pre load first. The springs are loose in my coil overs and I just have them wired to the top perch

Go for softer springs if the ride is too hard or the handling needs adjustment. otherwise use the coil over adjustment. Are they not adjustable?

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Use your spring perches to set the ride height and spring rates to set your ride and handling. I don't know when this idea of preload became such a big deal, but it's not. I had some kids do the corner weighting on my Locost last fall and they ended up with the front end 1/2" higher than the rear. Same excuse, preload. I took the car home and lowered the front end.

For the record, my 1500 lb. Locost has 350# front springs and 160# rear. Ride is firm but not jarring, and handling is absolutely perfect.

The top part of my coilover that contains the spring will fall off if there is no spring tension on it so that's not an option. Only adjustment is pre-load, not ride height. I'm going to try a softer spring first and see how it handles. If too soft I will have to redo my lower bracket somehow to get it lowered.

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Build log: viewtopic.php?t=9291

Make sure you have enough tire to fender clearance. Besides changing the ride stiffness:

1) you will reduce the static clearance by 1"

2) by reducing the spring rate, the same "bump in the road" will move the tire further upward than before possibly contacting the fender, possibly bottoming the shock.

Based on the info provided, 150# springs with ~.25" preload will get you close to 1" lower ride height than you are now.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Hi Cory, I took a quick look at your build log to find a photo. I'll read the log later but it looks interesting. Do you have a thread in the Completed Builds section? That would be great, we need to convince people that these projects are doable.



Nick is right. Your shock has a ride height adjuster, not a preload adjuster. It can preload the spring, but that is neither here nor there - more of an issue of spring design and it's free length. Your springs appear to have a free length several inches longer than you need or maybe want.

I went out and looked at my formula car in more detail and will get a picture for you in a little while. You're right the parts at the top of the shock (perch) do get loose at full drop. In fact the perch and spring are both hanging now from safety wire that holds them to the shock eye.

You should have bump rubbers installed on your shock's piston rod. They come in a variety of shapes (heights and tapers ) to give quickly rising rates etc. They really are required to protect the shock from damage during bottoming. The bottoming can be both a safety and money issue, because sudden bottoming can also cause sudden handling changes. You want bump rubbers. Then look to see if you are bottoming and use stiffer springs.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.