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Thread: Designing and implementing a coilover suspension

  1. #11
    Registered Member chevynut's Avatar
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    Here's some info I found on front vs rear frequency....

    "The rear ride frequency must be greater than the front. This is due to the fact that there is time delay between hitting an obstacle by front and rear wheels. The rule that the rear suspension should have a higher spring rate (higher ride or natural frequency) rationalized the observation that vehicle bounce is less annoying as a ride motion than pitch.
    To minimize pitching tendency of vehicle one must plot the front vs rear ride frequencies in an amplitude vs time graph by considering the time lag. By performing various iterations of frequencies one can identify which two frequencies matches early so that there will be only bounce motion."

    "One common idea is to design for “flat ride,” which is to have the rear suspension frequency roughly 15% stiffer (or faster) than the front. The idea is that since the front hits a bump before the rear, the rear should be a little stiffer in order to settle at the same time. Flat ride was initially designed to improve comfort on vehicles with soft dampers, but it’s also useful for sports cars. Many racecars do not use flat ride and there can be benefits to higher front frequencies. Ultimately, the best spring rates for a race car are the ones that allow it to go fastest around a track. This rarely comes from plugging numbers into a formula, but suspension frequencies and flat ride are useful starting points. Many variables are not accounted for with these methods, including sway bars and alignment settings."

    "With equal or higher suspension frequency in the front, the pitching motion and out of phase front to rear motions will be more pronounced and the vehicle will have a tendency to pitch back and forth and not remain level after encountering some bump."
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  2. #12
    Administrator 567chevys's Avatar
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    Hello Laszlo for Posting this stuff , How do you find the time to do all the stuff you have been doing lately ?

    This stuff will help lot of people.

    Thanks Sid

    1955 2 DR Post
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  3. #13
    Registered Member 55 Rescue Dog's Avatar
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    I took a chance on my C4 55 and am running the softer stock transverse leaf springs and shocks front/rear from a 96 Grand Sport and don't think I could have picked better spring setup. GM has been using them through 4+ generations of Corvettes for a reason. The car just feels totally planted and balanced without being overly harsh. It absorbs the dips in the road better than anything else I've driven and stays flat front to rear with no pitch or double bounce from the rear like many cars. My stripped down 55 weighs more than I thought it would at 3400 pounds. Roll bar added around a 100lbs, and I still need to put the front bumper on and install door windows. I'm not using the rear sway bar yet, and don't think I really need to since the car can be driven hard into a corner without getting loose. I took it to one autocross to find out how the car felt pushed to the limits and was very happy how the car felt, and nothing broke or fell off. I could make it faster, but it is more than enough fun the way it is. It's like driving a tall Corvette on a stretched wheelbase.
    1955 Chevy autocross - YouTube
    Last edited by 55 Rescue Dog; 12-23-2022 at 07:25 AM.

  4. #14
    Registered Member WagonCrazy's Avatar
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    Good info. Thanks for diligently going thru it Laszlo.

    I need to go back and figure out the spring rates I put on the ViKing coilovers on my Nomad. Vague memory says 400# fronts (LS1 aluminum block so lighter weight than steel block) and 500# on rear. But in order to get the ride height I wanted, the rears adjuster nuts are near the bottom of the shock. So I suspect those may be too stiff and was going to buy a set of 450# to just try out and see.

    There's another thing to consider here. The changing overall vehicle weight.
    Weight of Driver (on left side)
    Weight of full tank of fuel vs. near empty. Fuel tank on side of vehicle or centered.
    Weight of battery (on one side or the other)
    Etc.

    Not sure how that would all factor in, but it's probably not enough to worry about when you're first setting up the vehicle. Your calculations should put you "in the sweet spot" as a starting point when you get it on the road and do the final suspension tuning.

    Another thing...my ViKings are double adjustable and I've done test drives after having played with compression and rebound settings. Big difference in feel when they both are set all the way to the extremes. The car rides just stiff enough now for my liking, but I still may put a 450# set of rears on just to play with it.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  5. #15
    Registered Member chevynut's Avatar
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    Quote Originally Posted by WagonCrazy View Post
    Good info. Thanks for diligently going thru it Laszlo.

    I need to go back and figure out the spring rates I put on the ViKing coilovers on my Nomad. Vague memory says 400# fronts (LS1 aluminum block so lighter weight than steel block) and 500# on rear. But in order to get the ride height I wanted, the rears adjuster nuts are near the bottom of the shock. So I suspect those may be too stiff and was going to buy a set of 450# to just try out and see.

    There's another thing to consider here. The changing overall vehicle weight.
    Weight of Driver (on left side)
    Weight of full tank of fuel vs. near empty. Fuel tank on side of vehicle or centered.
    Weight of battery (on one side or the other)
    Etc.
    Thanks for the feedback Paul. I included all the weights of the things you mentioned, and my spreadsheet is flexible for added weight, but they're really pretty small when you're talking about a corner sprung weight of around 800+ pounds. Notice that the frequency calculations aren't affected by the type of shock or length used. All you need to know is the corner sprung weight and the wheel rate.

    At the time we did your build, I was still unsure about how to calculate the effect of motion ratio and when it should be squared in the calculations in my spreadsheet. It's now very clear to me and I modified my spreadsheet accordingly. Also, Wade gave me feedback that a 600 pound spring wouldn't work on the rear of his car and it sagged badly. So I used his information to develop my first pass spreadsheet. As I mentioned, I had a lot more rear shock angle on his frame than on subsequent frames. I think I moved the top rear shock mount outboard right after his build. I'm not sure where yours is but I think it's the new orientation.

    At 400 lb/in in front you should be at a wheel rate of 232 lb/in with a late C4 suspension. I have actual weights from Wade's 57 Nomad with LS/4L60E and his was 1870 pounds in front, or 935 per corner. I just went through the numbers and made a better estimate of unsprung weight and came up with 103 pounds in front with my wheels and tires. So your front corner un-sprung weight would be about 832 pounds. This results on a frequency of 1.64 Hz. Adding 100 lbs. to the front corner weight for a driver drops the frequency to 1.57 Hz. A 350 lb/in spring would drop that to 1.47 Hz so that gives you an idea of the ranges and sensitivity.

    Going by the suggestion of 15% stiffer in the rear, assuming you like the front as-is, you should be running about 1.89Hz in the rear (no passengers). Wade's Nomad's rear weight was 1816 pounds and I come up with an un-sprung weight of 97 pounds with my wheels and tires. Using those numbers, you should run a 400 lb/in rear spring to get to 1.88 HZ.

    I don't think dropping to 450 in the rear is worth doing. I'd go to 400 if you like the front where it is. If you want the front softer, I'd do that before I picked a rear spring and go through the calculations again. It would be better if you could actually weigh your car front and rear to get an actual weight but I'll bet these are close.

    One more note....the tires also act as a spring so a wider tire with a larger sidewall will ride softer than one with a shorter sidewall. This doesn't affect the static wheel rate, but it does affect the dynamic wheel rate as the tire compresses over bumps or going into turns.
    Last edited by chevynut; 12-23-2022 at 09:56 AM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #16
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    I took a chance on my C4 55 and am running the softer stock transverse leaf springs and shocks front/rear from a 96 Grand Sport and don't think I could have picked better spring setup.
    Do you know the spring codes for your springs? There were two different front springs on the 96 Grand sport, the HA and the FSR springs, at 343 and 418 lb/in respectively. These had 109 and 137 lb/in wheel rates so quite a bit different. There were also two different rear spring codes. I think GM moved to softer springs due to complaints from owners over the years, those who should have bought Cadillacs instead of sports cars . A 109 wheel rate is about equivalent to a stock Tri5 front wheel rate so the swaybars are important to limit roll. They even decreased the swaybar size on some of the later cars to 24mm so they likely have more roll than the earlier ones. I doubt performance improved with those changes.

    GM has been using them through 4+ generations of Corvettes for a reason.
    I think GM used the composite transverse leaf springs partly because they're cheap, but effective. I'm sure a composite spring is cheaper than two quality coilovers and springs. GM finally wised up and went to coilovers front and rear with the C8. Ferrari, Lambourghini, Pagani, Koenigsegg, Maserati, Porsche and others use coilovers for a reason. Nowadays they often use levers to move the coilovers off of the a-arm to reduce unsprung weight, but the coilovers work well and are more adjustable than the Corvette suspensions. Morrison, Roadster Shop, Detroit Speed, and most other high-end chassis suppliers use coilovers and there's also a ton of C4 coilover conversion kits on the market for a reason.

    The transverse front springs offer very little ride height adjustability and to do it is a huge pain in the ass, and to me that's a big downside. There is an adjustable C4 front spring on the market only with very high spring rates of 1000+. I like the fact that I can tweak ride height in minutes and make spring rate changes quickly with coilovers without tearing the entire car apart. In the rear it's a lot easier to adjust the ride height with the transverse spring, but spring rates are fairly limited although perhaps adequate.

    My stripped down 55 weighs more than I thought it would at 3400 pounds.
    That's about the curb weight of a stock 2-door sedan. The C4 suspension should have shed at least 150 pounds from the chassis compared to a stock '55 so there's added weight somewhere. Wade's 57 Nomad weighed 3686 pounds finished compared to a stock one at 3600 ('56). I estimate mine will weight 3850-3950 pounds with the BBC, full interior and power everything, but it's not a race car so I really don't care. That's about the same as a new convertible Camaro and lighter than a new Challenger, and with around 640 ft-lb of torque and a 4.10 rear gear it probably doesn't matter that much.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #17
    Registered Member 55 Rescue Dog's Avatar
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    I have the HA spring in the front and believe me it doesn't ride like a Cadillac or a stock tri-five. The geometry is totally different for one, and the front spring adds roll stiffness by itself. I originally drove the car without a front sway bar, and it cornered surprisingly well. The ride height is right where I want it, so I'm not concerned about adjusting it anyway. I don't know how your car will be under 4000lbs, because on mine I have an aluminum head LS, manual brakes, no inner fenders, no heater, no air, no radio, no back seat, no power anything, no interior to speak of other than carpet and fairly light seats, and an 8-pound Woodward collapsible safety steering column. The battery is in the center of the car behind the driver's seat. The only thing I added was a S&W 4-point rollbar that I designed to bolt to the chassis. Here is a good article explaining why they used leaf springs, which wasn't cost, and some of the advantages of coilovers for track cars. They also have light axillary coilovers that can be added to the transverse springs if needed. I saved a ton of money using a proven stock setup and it handles/rides great.
    C5/C6 Corvette Suspension Tech: Coilovers vs. Leafs - LSX Magazine
    Last edited by 55 Rescue Dog; 12-23-2022 at 12:46 PM.

  8. #18
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    I have the HA spring in the front and believe me it doesn't ride like a Cadillac or a stock tri-five. The geometry is totally different for one, and the front spring adds roll stiffness by itself.
    The HA spring has a 109 lb/in wheel rate (according to Corvette guru Hib Halverson)...that's identical to the most common stock tri5 front spring in stiffness. That's really soft compared to most performance suspensions. Wheel rate is wheel rate no matter how you get it. I have explained that the wheel rate combined with the sprung weight (frequency) is what determines the ride quality (softness or stiffness). So yes, you are getting a relatively soft ride of around 1.3 Hz if that's actually the wheel rate. If it's not, ask Hib Halverson about it or measure it yourself. Handling is much improved with the C4 front suspension geometry, as I argued with you a long time ago before you bought yours, when you were claiming the C4 suspension was out-dated and sucked.

    The ride height is right where I want it, so I'm not concerned about adjusting it anyway.
    That's good for you. Based on the pic in your avatar, your car seems to sit awfully high to me. It almost looks like stock height. Brian's car looks like sits lower and mine is much lower. Not sure why one would want to put a C4 suspension at stock tri5 height, but there's all sorts of different preferences. Most guys want their cars as low as they can practically get them these days for looks and performance, so that's how we built our frames.

    I don't know how your car will be under 4000lbs, because on mine I have an aluminum head LS, manual brakes, no inner fenders, no heater, no air, no radio, no back seat, no power anything, no interior to speak of other than carpet and fairly light seats, and an 8-pound Woodward collapsible safety steering column. The battery is in the center of the car behind the driver's seat. The only thing I added was a S&W 4-point rollbar that I designed to bolt to the chassis.
    Well, it's quite simple. A stock 56 Nomad weighs 3600 pounds with 776 pounds of dry weight for the iron engine and iron PG transmission. My engine is 650 pounds and my trans and flywheel is 190 for 840 pounds total or 64 pounds over stock weight. The aluminum suspension drops about 170 pounds so that makes the car 106 pounds less than stock. I added an estimated 400 pounds in engine accessories, power window regulators, console, armrests, power seats, stereo, etc. and I get to 3894 pounds. I don't know if I over-estimated or under-estimated that 400 pounds because a lot of my interior is aluminum. Another data point is Wade's finished car weighed in at 3686 pounds with an LS-1 and 4L60E. My BBC is probably 250 pounds heavier than his is and my trans is a little lighter so call it 225 pounds heavier. That's 3911, so about the same. If I hit 4000 pounds so be it, but I doubt I added more than 500 pounds over yours. I don't know why yours is so heavy.

    Here is a good article explaining why they used leaf springs, which wasn't cost, and some of the advantages of coilovers for track cars.
    They also talk about some of the disadvantages of the transverse leaf, and in the end they say that coilovers are actually better for tuning and flexibility. The "crosstalk" issue is real, but it only matters on top-end cars.

    "The stock suspension is great, but all of the premiere race cars will make the move to a coilover for a reason, and that is to really make the suspension fully independent, and to gain the ability to fine tune the spring rates on all four corners with an almost infinite variety of springs and rates that are available for coilovers.”

    And one has to question the knowledge and credibility of the article's author when he says bullshit like this:

    "When GM first used a transverse composite leaf in Corvettes that were introduced in 1981, they were able to replace a ten-leaf steel unit that weighed 41 pounds with a single composite leaf that only weighed a paltry 8 pounds. Because the composite leafs have a strength to weigh ratio five times higher than steel, they were able to achieve the same spring rates while shaving off a significant 33 pounds of un-sprung weight from the Corvette."

    The transverse spring is not unsprung weight.

    GM kept the transverse spring through C5/6/7 because they essentially used the same platform for those cars and re-tooling everything would have cost a lot. I'm sure part of the reason was the lower cost of the leaf spring versus the alternatives and it wasn't a bad solution as I said. The article said a part of it was packaging, which isn't really an issue on a tri5. We know GM abandoned the transverse springs in the C8 when they re-designed the whole car.

    One has to ask, if the composite transverse leaf spring is so good why hasn't everyone else building high performance cars been using them? Why did they drop it in the C8? There must be a reason.

    If you're happy with your suspension setup, that's great. I have recommended to some of my customers that they use the stock rear spring to save cost, because ride height adjustment are easy in the rear and it works fine, but the front is a different story. I just think coilovers are better and they have the added benefit of flexibility and ease of adjustment and tuning. I won't do a lot of tuning on my car, but I like the fact that ride height adjustments are very easy. In the rear of my car, I couldn't use the stock transverse leaf because of the 3" narrowed rearend (no BS comments about that please), so I went with coilovers which is a better solution to me anyhow and cost wasn't an issue.

    This thread wasn't intended to argue about whether a leaf spring or coilover is better, only how to choose the right coilover shocks and spring rate, but I expected nothing less from you.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #19
    Registered Member 55 Rescue Dog's Avatar
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    Thanks for taking the time to make a thoughtful response, but I didn't bring up transverse springs, and coilovers are not magic bullets, or they would be standard production springs on every car built nowadays. A Mcphearson strut is basically a coilover like many other designs. The basic subject I thought should be finding the right spring rate for any given car, since it is all related. The main advantage of coilovers is the ability to adjust corner weights on track cars to make changes for different track conditions, not for how the ride height looks. I've seen race car trailers with 20 different coilovers hanging on the wall to quicky change the setup for the track. You can only adjust ride height up/down so much anyway, or you end up with other issues. My ride height puts the suspension near the center of its compression/rebound travel, and if I lowered it then I would run out of compression travel and mess up the suspension angles. As it is I can drive it anywhere without having to worry about dragging the bottom of the car. The front will still come down a little when I put the bumper on.
    You have been working on C4 chassis and selling them for many years, but have you even driven a C4 tri-five? I have driven mine a lot and know how they really work.
    Last edited by 55 Rescue Dog; 12-24-2022 at 08:08 AM.

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