Thanks for all your help . I quess i just have to slow down when i see a curve and let the Honda Civic si with the fart pipe pass me

 

You are way out of line.

 

I put on bigger sway bars w poly bushings, re-valved shocks, camber brace & cross bar and the car is totally different from stock, and has lost most of the negative points listed above.

 

My ball point pen uses a coil spring. I can't believe they're using that 'technology' on cars.

 

Just wondering, with the camber brace and the cross bar, how does your car feel/handle with the top off?

 

Wow. When I was a kid, my baby tram had leaf springs... I can't beleive they use that 'technology' on Corvettes.

 

This is a very interesting thread, I'm learning a lot.

I recently came to the conclusion that the worst thing about my 88 vette is the handlng. In particular how it can't handle the 'washboard' type of road.

I have a bad back and live in an area of poor roads which of course magnifies the problem. When I drove my car around our capital city, Brisbane 2 years ago, it was as if it had completely different suspension because I was driving on smooth roads.

I have studied the C4 Suspension chart http://www.corvetteactioncenter.com/...usp_chart.html
It's amazing how different the spring rates were between some years. For instance my 88 Z52 has much stiffer front springs than 87 - 93.1 N/mm to 51.8N/mm. (BTW I understand the spring rate but can anyone explain the wheel rate please?)

I have had my Bilsteins re-valved as light as possible, this has helped the ride confort over bumps, but has probably made the washboard effect worse. I was following a lady driving a Mustang up a twisty range road, she appeared to be driving normally, but I couldn't keep up on the corners because of bouncing sideways at every little bump.

I thought coilovers might be the answer, but from this thread I now see that isn't so. I think lighter spring rates might help, or more wheel travel. Shocks appear to be very important, but how the heck do you work out which one is the right one - I want a soft ride and no bounce on the corners!!

S'nut

 

Recommended Reading:

Corvette From the Inside, Dave McClellan

Race Car Vehicle Dynamics, Bill Milliken

Competition Car Suspension, A. Staniforth (I think this is the updated version of the one I have, I will confirm)

These books will help go a long way to explain the science behind all of these issues.

 

It is an interesting thread (so is the other one) because springs are often misunderstood as some special multi-use part, something other than a device to hold the chassis off the ground (although a better description is a device to hold the tire on the road surface). Springs in the traditional sense (including the coil on a coilover shock) do not locate or determine any of the factors defining suspension geometry (other than a possible stretch of reasoning that they determine ride height).

The only real disadvantages of a leaf spring are size, weight, and friction in multiple leaf springs. Advantages are tunable spring rate and the ability to tune a progressive rising spring rate into the spring by changing individual leaf thickness and length (but modern man is lazy and a modern linkage can accomplish the same tuning). Take a low friction composite leaf and replace it with a coil of the same rate and force curve, and mount it at the same location, and it will perform the same (a force is only a force , of course).

Wheel rate is the force rate of change at the wheel. The spring rate is the force rate of change at the spring mount. Both are measured in force change per distance of movement at the measured variable. Springs are typically identified in pounds per inch (in the USA) and Neutons per millimeter (SI units), measured at the spring end. Wheel rate is measured at the wheel centerline. If the spring mount locates the spring force 1/2 the distance from the suspension pivot point to the wheel centerline, the wheel rate is 1/2 the spring rate. A 2000 pound force applied by the spring is reduced through leverage by 1/2 (with the leverage of this example) to apply only a 1000 pound force at the wheel centerline. Spring rates are often discussed but the wheel rate is what keeps the wheel (and tire) tracking the ground. What changes in most coilover conversions is the effective wheel rate and motion ratio between the spring travel and wheel travel (changing the efficiency of the spring force leverage on the suspension).

Your experience with shocks, and the lack of dampening to eliminate the high speed suspension travel over washboard is spot on. The shock valving is not tuned to dampen high speed motion of the shock shaft, probably the result of the overall reduced dampening you mention. Tuning the shock valving to the suspension forces expected, and ride you desire is needed to keep the tire in contact with the road. This improvement or loss is what most people feel when switching to coilovers, because coilovers require you to change the shock dampening (they have integral shocks, and usually high quality shocks).

Most people know that jounce (compression) and rebound (extension) dampening can be tuned independent of each other in a quality shock. Most however do not realize that low and high speed shaft travel can also be tuned independent of each other in a quality rebuildable shock.

If the tire sticks on a smooth track and does a good job at resisting transition motion (anti-sway) but fails at high speed washboard or fast bumps the valving can be changed to raise the dampening at high shaft speeds. Usually the result is an increase in dampening force at all shaft speeds, and the low shaft speed ride becomes to rough. You really need to keep the shocks jounce and rebound force at low shaft speeds reasonable and allow for more rebound dampening only at the short travel but high shaft speed washboard bumps. A good shock tuner can help (how you get what you want: fix it wrong, fix it wrong again, and then fix it right).

Ask you shock tuner if he can set up digressive valving with the same low speed resistance you have now and increase the high speed resistance.

By the way, the only way a transverse leaf can transmit force from one wheel to the other is if the leaf center-mount pivots (like a late 1970 Triumph Spitfire). This was done to minimize the poor handling of swing axles and high roll centers and is not how corvette leaf springs are mounted (or desired). When the C4 came out this effect was discussed and quickly excused by the C4 design Engineers.

 

That's some great info, although I disagree on this point.

The rear spring is 99% independent, but the front spring is not. Compressing one end of the spring will also unload the other end partially. Grab a ruler and pinch it at two points equidistant from the center. Now hold your fingers up against a wall and put a load on one end, you'll see the other end move partially in the same direction. This is how the front spring works. For the same reason, it gives you some anti-sway effect.

The further apart these pivots are, the more this effect occurs (and the higher the spring rate is). Now clamp it tightly in two places close to the center, and you won't see any movement at the other end. This is similar to the rear spring.



The transverse leaf springs are both lighter than coils, lower c.g., and reduce the necessary weight of the sway bar by some degree. On paper, it is an excellent design. I'm just still waiting for someone to explain why it's flawed, or how it can be improved if this is the case.

 

Thanks Bogus for book list - the McClellan one is high on my want list.

63.340 - thanks, now I understand what the wheel rate is measuring, thanks also for info on valving, etc - this thread has given me new hope I can fix my suspension.

S'nut

 

Great discussion btw, let's keep on keepin it clean. (And the title is catchy too )

I think we're all learning something here...

 

Isn't a coil spring just a mix between a torsion spring and a leaf spring anyways? (or is it purely in torsion?)

 

A coil spring is a helical torsion bar.

Be well,

SJW

 

WHY??? The C4 can take corners with military like precision in stock form or Z51 set up.heck I removed the sway bars on my 86 some years back to do some cleaning and etc and the car still cornered very flat around tight turns.
The C4 is a fantastic handling car..why you would think a Honda,with its suspension designed to take the harshness off our roads as the driver feels it,would out corner a C4?



Seriously,heres a history lesson about the C4 set up...as you read,the first C4 was a handling marvel...BUT if the roads were bad,it was a nightmare for comfort.Keep in Mind,the C4 was designed in the 70's!
They had atari like computer systems back then,they dont have the stuff today so we cant compare the stuff today to years ago.Todays cars have alot of engineers using computer design to create the best possible product for types of cars.

So over the years,GM kept changing spring rates,sway bar sizes,shock rates and etc to try and please customers complaints about the kidney stone like rides the cars had over rough roads.

Tire size,profile,width,plus bad roads,also plays a role in how a car feels on bad pavement.This is true on sports cars that use low profile fat rubber and rims.

Btw,my mother loved to ride in my former Z51 86...she loved how it felt,rode and handle...when we hit bad roads,and the ride was harsh,I would apologize to her how the car felt rough and made her feel weird in the passenger seat...she said the best thing I ever heard..she said,"Dont blame the car,blame the roads".Its NOT the car's fault that so many roads are falling apart and everyone wants a top handling sports car to feel like a caddy over them.

So these days,since the C5 and C6,GM engineers have been designing handling around comfort..which is what we need because our roads in the good ole US of A fargin SUCK!!!!!!!!!!!!!!!

 

Good grief! It's a Corvette, not a Lincoln TownCar! You are going to feel the bumps and potholes in the road. The best suggestions that I've seen have prompted you to get a set of new, good shocks. Bilsteins at the least. KYB's are good if you're on a budget, but they suck on the twisties.

 

A ruler is composed of a uniform material strength and equal moment of inertia throughout it's length, two physical properties that are not shared with composite leaf springs.

One fantastic attribute of composites, and composite springs, is the material does not have to produce uniform strength or resistance to bending in similar size sections (not like steel), and can be formed to produce rigid or flexible material properties even with a constant cross section through a long manufactured part (a long part like a leaf spring). The center section of composite leaf spring can be manufactured to remain very rigid, to the point of resisting almost all deflection even as the moment of inertia remains constant.

The width of the pivot points on either side of the rigid section in the center of the composite leaf will allow adjustment of the resulting spring rate (the popular VBP springs for C2/C3 conversions), but does this adjustment demand that the center section of the spring be required to deflect?

How is the front spring (or should I say different "factory springs") engineered and manufactured? Is deflection of the centersection of the spring desirable, and has the evolution of the composite leaf front spring (from early C4 to C6) reflected a need for deflection throughout the leaf to produce an effect similar to "camber compensation" employed on swingaxle suspensions?

I once was bold enough to ask Dick Guildstrand if leaf springs were a dead end in technology (during his success with the coil spring C3 Camaro consulting and preparation for GM). He quickly explained how composite manufacturing of a leaf spring allowed the Engineer to design the exact wheel rate desired, without the limitations of linear rate coils or progressive rate tapered torsion stock and without a complicated cam or rocker linkage. The composite matrix determines the deflection and force properties, not the raw material stock or thickness and heat treating. This was (and is) a radical change from the limitiation of working with a isotropic material like steel. Now if all of us enthusiasts had an autoclave and composite manufacturing shop to build custom springs we could exploit these benefits (something where it appears only GM & Aerospace Contractors have the resources to fabricate custom composites).

The early C4 ride harshness was as much shock design and technology as it was spring rate related. The early C4 era demanded the compromise of stiff spring rates to produce superior cornering performance (low travel for minimal camber at the traction patch). Usually high spring rates demand extremely soft jounce dampening and rather rigid rebound dampening. Unfortunately this did not produce good low shock shaft velocity dampening to deliver a quality transient response. The low velocity jounce and rebound dampening force had to be high to minimize the transient responce time with near zero friction composite leaf springs (the suspension engineer could not rely on leaf friction to dampen low speed transition deflection), and shock valving technology had not evolved enough to be able to accomplish this without providing extremely harsh high velocity jounce dampening. The choice was poor transient responce on a smooth road (like on a racetrack where the car was often tested) or reduced tire contact with the road over fast washboard (typical poor street conditions).

Since Carrol Shelby's early 80's budget minded "goes like hell" Dodge turbo products were already cornering in excess of 1G on skidpads and magazine shoot-outs the decision to sacrifice rough road handling was easy. The shock dampening force was increased to maintain a high resistance to low velocity shaft travel, and the dampening resistance at high shaft speeds increased (to the point of harshness).

Modern shocks can be tuned to have high dampening force rates at low shaft speeds (for both jounce and rebound), and not have excessively high jounce dampening at high shaft speeds with relatively high rebound dampening. The low shaft speed dampening allows the suspension to keep the tire on the track as weight is shifted from one corner of the car to another in a smooth fashion (like with a good driver on a smooth racetrack). The high rebound dampening at high shaft speeds sucks the suspension down into the range where the spring force is high, and the low resistance high shaft speed jounce dampening allows the resulting compressed spring into a range where it can force the tire away from the chassis to follow the road between bumps. Once the shock technology caught up with the suspension design, the springs no longer needed to be extra rigid to keep the tires on the pavement, and the compromise that demanded excessive stiff spring rates and dampening resistance was eliminated (much more so with active ride control).

Returning to springs, does a coilover spring manufacturer offer a tunable progressive rate coil to fit the common coil over sizes (60/70mm, 2", 2.25",2.5" and 3" ID coils, from QA1 or Eibach or ??)? My 2004 catalogs do not list one (maybe they do today) to provide a progressive rising spring rate as the spring deflects (something the composite leaf is engineered and fabricated to produce). Any modern coil experts find one?

 

More top info, thanks. How, or who, makes them?

also - I was looking at the Spring chart again http://www.corvetteactioncenter.com/...usp_chart.html

The 94-96 spring rates are 60F/26R N/mm compared to my 1988 Z52 which has 93F/39.9R N/mm - that's about one third softer- surely that's got to help with ride comfort?

I don't know if those springs would fit my 88, but if they do fit, I'm wondering if the softer springs and better valved shocks would improve my ride comfort and still give me better handling than I have now?

S'nut

 

63 340hp

 

The 84-87 leaf spring has the same crosssection throughout, although less arc in the middle in a free state.

I don't know what it looks like compressed, but I'd be very surprised if there were anything creative done with the fiberglass layup to give a different stiffness on the outer vs inner sections to effect how much anti-sway it gives us.

I don't know much about composites beyond the textbook and some basic materials testing, but I don't see how a spring, composite or not can offer a progressive rate when the loaded points of the spring don't change during it's travel.

You can taper a spring all you want, tie a bunch of different rate springs together, but ultimately all you get is a constant rate spring (until part of the spring bottoms out) if I'm wrong here, let me know.




As far as shocks go, do you have any real-world suggestions on how we can improve? My 85 Z51 is probably the softest sprung Z car made, but I'm considering upgrading some of the rest of the suspension linkage to spherical joints to make it more compliant than the poorly done binding stock bushings. I would also either rebuild the bilsteins or replace with something a little more modern like you mentioned that can take up these high frequency loads, but still be firm on the low speed ones. The rear end does tend to skip around more than I like, and the car is only going to get lighter.