LocostUSA.com

So the ones I have should be OK either direction then, good to know.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
viewtopic.php?f=33&t=18172

Here's a video from autocross today.
https://www.youtube.com/watch?v=piUP0nu ... e=youtu.be
Kristian

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V6 in a book frame build. Now registered.
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One of the guys got a series of pictures yesterday of me going through a set of corners. I think I need to do something about the body roll. I never realized how bad it was.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
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You've made some good progress, Kristian. Sometimes these small, but important items, are the hardest to tackle: 3 hours of dis-assembly, 2 for re-assembly for 15 minutes of repair time. I'll be looking for the video to appear.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

Are you currently running anti-roll bars?

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-Andrew
Build Log
Youtube

Not yet, but I might try stiffer springs first. Video is up on YouTube now.
http://youtu.be/piUP0nuruCI
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
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Been there, done that... Put a sway bar on it, Bro, you won't beeeleeeve how much it helps!!!

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JD, father of Quinn, Son of a... Build Log
Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom

From reading your build log, I believe you. But I do think I need stiffer springs too. I have a fair bit of preload on the springs to keep the car off the ground and it still sinks pretty good when I get in. It goes down about 3/4" rear and 1/2" or 5/8" in the front when I get in the car. The rear shocks are vertical and I think they are 175 lb/in springs. I don't have corner scales, but I think the weight on the rear axle is about 900lbs. The motion ratio at the front looks like 0.645, and I think the front springs are supposed to be 280 lb/in. When I lift a front tire with my jack, the same side rear comes up quite a bit before the other front tire lifts off.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
viewtopic.php?f=33&t=18172

Yes, the straight answer to what you need is most likely "both" in the end. The spring rate, or actually the wheel rate needs to be high enough to control pitch fore-and-aft as well as limiting body roll, then snuff the roll with a sway bar.... You'll get there, it's always kinda "trial and error" to those of us without an engineering staff, CAD and a wind tunnel...

JDK

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JD, father of Quinn, Son of a... Build Log
Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom

I think this build log is almost more of a reference for me than anyone else. I've gone back a few times to see what I did for certain parts of the car. So I will put the info on my shocks in here too. They are the Gaz adjustable that are available from Jack at Kinetic. The fronts are the 12"/3.5" travel and the rear are 14"/4.5" travel. I'm pretty sure the springs are 275 front and 180 rear that's what his site shows for options that make the most sense based on what I can remember. Before yesterday's autocross I adjusted the coil overs so the car was had only about 1/2" of rebound travel at all four corners and pushed the rubber bump stops all the way down. All four bump stops are pushed back to the top of the shock shafts.

I'm going to make some assumptions and some edumacated guesses and try plugging some numbers into a spring rate calculator on the hypercoils website. My car was 1320 before I put the aluminum fenders on and I weigh about 280, so I'm going to assume that with me in it the weight is about 1650 with fuel. There is a slight rear bias, so I get 803lbs on the front and 847lbs on the rear. I haven't weighed my spindles or anything, but the wheel/tire package is 30lbs. When I was bolting up the top of the shock with everything other than the wheel on it, it didn't feel too much heavier than the wheel, so I'll say 75lbs unsprung at each front corner for now. That gives me roughly 325 on each front wheel. If I use the 1/3 rebound, 2/3 compression and subtract 1/2" for the rubber bump stop, the spring calculator says I need 500lb/in front springs. For the rear I will say 220lbs for total unsprung weight. That gives 315 sprung per corner. The calculator says 235lb/in springs for the rear. Does this make sense to anyone else, or is it just me?
Kristian

Edit to add, I will take the bathroom scale out to the shop and get some more accurate numbers before ordering any springs. Another site has a calculator for suspension frequency that gives me 2.52 CPS front and 2.7 CPS rear with these numbers, might be a little too firm.

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
viewtopic.php?f=33&t=18172

I got some better numbers today using four bathroom scales. I don't have them leveled to check corner weights, but I can get the front/rear and the unsprung weights along with the total weight. Rear axle is at 190lbs, so 95 unsprung at each corner. The fronts are 58lbs at each corner, lighter than I thought they would be. The whole car is 1294lbs, 611 on the rear and 683 on the front. Last time I weighed it was at the local garbage dump, probably not the most accurate scale there, considering it will handle a loaded garbage truck. I'm pretty happy with the weight. Now I can figure out thenew springs a bit more accurately. The current springs are marked 8x300 on the front and 9x175 at the rear. With me in the car is pretty close to 1580, with 769 on the front and 811 on the rear.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
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You can measure your leverage ratios (motion ratios, installation ratios, static deflection, or whatever you want to call them) directly by raising your wheel centers a given amount and measuring the change at the shock shafts. I suggest two inches because that should be the extreme of bump under most circumstances. If you haven't done this already; you didn't say how you determined the 0.645 number for the front.

For a solid axle, you'll need to raise both rear wheels the same amount. Two wheeled bumps are more representative of ride motions. If you want to use a calculated number instead of measuring, or to check your measurements for reasonableness, use the distance between your shock mounts for Dimension A on the Hypercoils worksheet and your track width for Dimension B.

There are calculators around for calculating a rear suspension frequency that will cancel out pitching oscillations at a given speed, say 65mph for a road car so that ride motions on trips will not be annoying. For a track car you may not care about this.

Re: goals for natural frequency, I read an Alan Staniforth book many years ago in which he experimented with natural frequencies in a number of cars. Results were that 120cpm felt more comfortable for the drivers but 135cpm or so gave better lap times. There's also a paper floating around by Robert Q. Riley in which he made a strong case for 120cpm being pretty much a minimum for light cars lest ride motions suck up available spring travel. So, I have always thought that I would start there. Remember that adding anti-roll bars will increase your natural frequency when in roll, so if you think you will be adding them at some point, you may want to aim towards the low side now.

FWIW, so long ago that I have forgotten how to do the math and have lost my notes, I calculated roll stiffness for a typical book locost and came to the conclusion that at least a front anti-roll bar is a must if you want to corner nice and flat, say a couple of degrees roll at 1g. From what you are saying about how much the suspension deflects when you get in the car, as well as the roll we see in your video, I'm sure that just having stiffer springs will make a world of difference from what you're experiencing now.

One last point is that you might want to add some weight to the rear for a passenger, maybe half a passenger if you want to hedge your bet. I see you have company in your video.

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Dreaming the dream since 2003. Haynes chassis, Miata uprights, everything else from 1987 NA RX7 donor.

I figured out my motion ratio by plugging my front suspension numbers into the calculator on the Hypercoils website.
http://www.hypercoils.com/spring-calculator

Then I put my numbers into the frequency calculator here.
http://www.racingaspirations.com/mods/kuhe8zbu
And here.
http://www.racingaspirations.com/mods/7qvvjb1n

From what I have read about suspension setup, I should shoot for a frequency of about 2.2Hz front and 2.5Hz rear for an autocross car. I am currently at 1.96 front and 2.38 rear, which feels like it rides pretty soft to me. I have also read that when people start at 2.2/2.5 they end up going stiffer a lot of the time. 400lb/in front and 200lb/in rear will give me 2.26/2.51Hz. 450lb/in front, 225lb/in rear will give me 2.4/2.66 Hz, which still doesn't see like a huge jump from where I am now.

I wonder if I should order both or just go straight to the stiffest set? I'm kind of leaning towards the stiffer setup. It should still ride softer than my pickup, which I put about 75000 kms a year on. It's an F-250 with rear springs that have 3 times the payload capacity of the stock ones, so I'm used to feeling every imperfection in the road. I've found with work trucks that a stiffer suspension might ride rough when going slow, but it really does work better when you crank up the speed on rough roads.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
viewtopic.php?f=33&t=18172

Trading some ride comfort for better handling is a tough call Kristian. Would it not be worth exploring the swaybar/anti roll bar option in conjunction with some progressive rate springs instead of the linear ones you have at present.? Going too stiff on the rear springs with a live axle may unsettle the car.Just thoughts

Bob

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Build Log viewtopic.php?f=35&t=16640&p=187700#p187700

Mancave http://s1116.photobucket.com/user/mypic ... ow/mancave

Hey, Kristien, your rear motion ratio is not 1. It is the distance between your shock mounts divided by track width, so something like 40 divided by 56?

I was fooling around with the weight transfer worksheets, and found that a car with a solid axle will transfer enough weight through the rear roll center to the extent that much stiffer front springing is required to balance the car.

So, I think a 450lb spring in front and 2.37HZ is fine, and suggest 250lb for the rear, which should give a frequency of 2.01Hz.

I guesstimated a lot when it came to CG heights and so on, but am estimating that that even though front and rear roll stiffness will be 60/40, the distribution of front and rear weight transfer will be 48/52. I'd be glad to send you the worksheets, of course.

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Dreaming the dream since 2003. Haynes chassis, Miata uprights, everything else from 1987 NA RX7 donor.