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Got a question for you fellows. This is what I have super-ride on the front I called ride-tech to see what shocks I needed all way around according to the cars weight front and rear I got a good front alignment car drives good tracks good. If you go over a rough place in the road hang on. Everything is good an tight got bout 7000 miles on the car.
Shock absorbers are simply linear de-acceleration devices, you just use the shock that has the correct compression and extension measurements for the suspension travel. For instance, with 4 inches of suspension travel, total up and down, you might use a shock with 5 inches of travel and install it with the rod pulled out 55% of its total travel (5 times .55 = 2 3/4"), so the shock would have 2 3/4" in bump and 2 1/4" in droop. Use any 5" travel shock, no matter the shock length. Fabricate the shock mounts yourself with the vehicle resting on its tires at ride height. A drive-on lift works well for doing the measuring and welding of the mounts.
TIP: Once you have the shock extended to the install length, cut a piece of fuel line rubber hose, about 3/4" long, slit it lengthwise and curl it around the shock piston rod right at the shock body. Wrap a worm screw clamp around the hose and tighten it down. This will allow the shock to remain at the install height so you don't change the length accidentally and make an error in the mounts. Ask me why I do it this way. :eek:
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I had a similar problem with mine, ride was good until I hit a good sized bump or rough spot in the road, then look out it would almost change lanes. Turned out to be the axle stops (rubber snubs mounted to the frame) were to long, trimmed a 1/2" off of them with a sawzall and no more lane swapping.
Good info there Tech!
39 Chevy, your rough ride is likely caused by the springs being too stiff for the weight of the car. As Tech points out, the shocks are there only to dampen the motion, preventing the "bounce" and do nothing for support. You might take the shocks off, and see what it takes to rebound the springs, looking for stops that might be too big while you watch it, like 36 Sedan pointed out.
Suspension stuff is interesting to say the least!
If you have a Heidts Super ride on the front, I would think that Heidts would have selected a spring rate that's not too far off. Heidts has already selected what should be the proper coil-over shock length. That should not have to be changed.
I've been going through this type problem with Ride Tech, but it was Ride Tech that selected the 450 lb/in spring rate for my Oze front suspension, that is a copy of the Super Ride II. I went to their spring calculator program and came up with a much softer rate of only 350 lb/in, using a guestimated 800 lbs on each front wheel. I've sent them an E-mail asking how they came up with such stiff springs for my car. It will rattle your teeth when it hits a small mismatch in the road.
One of issues that I'm dealing with is my shock mounts appear to be set to position the A-arms approximately parallel and horizontal, with a shock length of 11.8 inches. This works for their Shock Wave system, but not with their coil-overs. The 10" spring coil-overs have a ride height in the 12.2-12.6 inch range and the 8 inch model is 11.2-11.6 inches. One is too long and the other too short. I may end up cutting off my upper shock mounts and moving them up .6 inches, to work properly with the 10 inch spring length coil-overs that they recommended. They'll probably tell me to just set the length to 11.8 inches or maybe 12 and live with the reduced amount of available shock compression.
http://www.ridetech.com/tech/spring-rate-calculator/
One interesting thing that I noticed with their spring rate calculator is that changing from a 10 inch spring coil-over to an 8-inch changed the suggested spring rate from 350 to 450 lb/inch, with no other change to the input information.
I used adjustable mock-up bars to figure out the near-perfect shock length of 11.8 inches. If the length is any longer, the upper A-arm angle changes from horizontal to being angled down, at the ball joint end. Any shorter and the upper A-arm angles upward at the ball joint end. When I was driving the car this year, I had the shock length set around 12.6 inches. This caused the upper arm to angled down by 6-8 degrees, and it pinched the ball joint dust boot, noticeably. The springs were so stiff, that the shock length was overly long, even with no preload on the springs.
I've had no luck with the Ride Tech technical help folks. The guy I spoke to had no opinion at all about using a softer spring. If he was familiar at all with the spring rate calculator, he would have been able to tell me how much more preload I'd need with a 350lb/inch spring rate (about 1 inch).
The amount of preload that you're using can tell you something about the spring stiffness. In my case, I know that I've use zero preload and the shock length was not still not down to the perfect 11.8 inch length. If you have that situation, then the springs are too stiff. I'm confident that I can drop the spring rate down to 350 lb/inch and use less than 1 inch of preload to get the height that I need.
At the rear of my car I have 200 lb/in coil-overs at a 70 degree angle. The ride tech calculator says that 175 lb/inch springs will handle 725 lbs at each wheel, so I plan to reduce the rear spring rate, too. I know that I've driven the car with no preload on the springs, when I had the rear set to the lowest height that I ever tried. I didn't realize that I had no preload until I put the car up on my lift and noticed the rear springs were slightly loose. This is not desirable because the springs won't center on the top mount, without some help. You need at least a little preload.
Keep us updated after you make the changes, and good luck.
is your REAR suspension like?
Do you have ang pictures of your install/build?
Have you corner weighted the car? Does it vary much with passenger load and fuel quanity(pass 150-250# each and fuel 7 lbs/gallon)
Angles of your suspension arms, spring angles, shock angles-any known shock percentage ratings?
Tire sizes and pressure
and lets not forget the correct tire pressure in your tires for the weight of your vehicle. I know w/my 65 VW Notchback the only way I could get the rough ride out of it was lower the tire pressure in the front & rear. I don't care what anybody says, tire pressure does matter....joe
This is what Ride Tech said I needed shock 3.6 travel bearing upper an lower mounts 9.425"/ 13.025" coil spring 8" free length 375lbs. Shock 5.2" travel bearing upper an lower mounts 11.225"/16.425" coil spring 12.0" free length 225lbs
This is the weight each side of the car DS 761, PS 756 LR 874 RL 837 all of this is new to me this is my first time around. Setting aside not getting in to name calling I have grew up with the people that built most of the car I really thought they knew what they were doing with the name they have. I have had to rework everything they have done. We never get to old to learn had a 1st cousin tell me one time your friends is who you have to watch because your enemy's want come around.
If you want some answers, forget about bickering about your friends and give us some info-----------Do you have coil over shocks on the front?
What type suspension on the rear?
tire/wheel/psi?
length of any suspension arms
angle of suspension arms
measurement of where the spring/shock are on the arms----------
How about some pics of the under side??
Personally I'm thinking that your car may be too heavy for coil over type suspension at that travel distance-
Your suspension arm length is going to be considerably longer than where your springs/shocks are so the pressure/leverage? is much higher and you probably need at least double those spring ratings
a spring rate at the spring location IS NOT egual or even near the weight of that corner divided by the travel distance----
If all commenting haven't done so, taking a look at the Heidt's super ride II suspension at the website linked below will provide some answers. I have to assume that Ride Tech knows the A-arm dimensions and spring angle or 39 Chevy has provided them, to input into the spring rate calculator. Without those dimensions, there is no way to suggest a spring rate.
HEIDTS SUPERIDE II Front Suspension for 30s, 40s, 50s Fat Fender Fords, Chevy & Willys - HEIDTS
Spring Rate Calculator « Ridetech – Tech
The only way to get an idea if these suggestions might improve the ride is to compare the suggested new setup to the current one. If you can't get the spring rates on the current setup, there's no way to know if the springs are softer or stiffer than what you have now. Heidt's should at least know what they consider to be the most common spring rate for this front suspension.
I wouldn't think that Heidt's would sell a Super Ride II front suspension for a '39 Chevy if it was too heavy.
I gave Ride Tech everything they ask for that's where all those numbers came from. 4 link on the rear top arm center to center 16 1/2 bottom 24 1/2 245-40 ZR20, 235 40 ZR18 psi front 32 rear 34
Looks like something is wrong at the front, with that much preload on the spring. That would actually indicate a spring that's too soft and the adjuster had to raised way up to get the necessary ride height.
Did Ride tech ask for all of the dimensions on the spring rate calculator? If not, I'd be sure that they really know what they are. I've talked to some of their tech guys who seem to be clueless.
The length of the front shock should be no more than 11.6 inches at ride height.
I talked to the tech he ask for all of that info I called him back to make sure the info was put in correct that's what he said I needed. When I put them it seemed odd I was having to crank it up so high. I called back told him what I had after the install he said it didn't matter keep cranking if I needed to.
Sounds like a typical response. If they put the right numbers into the spring rate calculator, it includes an approximate preload value that's usually not much more than an inch. If the spring is much less than 7 inches long at ride height, that would seem odd, but the most critical thing is the shock length.Quote:
Originally Posted by 39 Chevy
The way it is now at ride height, spring is 5.25 long
That's means it's a soft spring IF that's what it takes to get the shock up to 11.2-11.6 inches. Seems like there would be a good chance of coil-bind under compression.Quote:
Originally Posted by 39 Chevy
edit:
Upon more thinking though, the shock is supposed to compress from it's fully extended length of 13 inches to at least 11.6 which is 1.4 inches. Since the spring has compressed by 2.75 inches, that means the preload is about 1.35, if the shock is at 11.6. That's quite a bit, but some of the softer spring suggestions for my car have just over 1 inch of preload.
Looking at the photos first and fourth pics-it seems that you have some issues with the left rear-upper link heim is almost all the way in and lower rear heim is screw ed way out, plus front one is way more screwed in. aren't the liks right and left hand threads????
Looking at your tire size/air pressure/ wheel size I can see where some of the ride harseness comes from .
Wher do you have the schock valve stings set???
By the way-nice clear pics that show the detail very nice and clear.
Here's an article that discusses spring rate and motion ratio. One of the downsides to the 8" spring length coil-overs is an increased spring rate to keep the shock from bottoming out, since the shock has so little travel. On my car, choosing an 8" spring instead of the 10" spring that I now have, increases the suggested spring rate from 350 to 450 (same as I have now). Since my car rides so harsh in the front, most likely, I'll be moving my upper shock mount up to get the proper A-arm angles, while keeping the longer springs.
Choosing the Ideal Spring Rates and Spring Tech
The threads are R & L hand should they be adjusted till they are about half & half? The valve setting is at the light as they will go. I had already figured the tire size was some of the problem. What should the A-arm angle be ?
Yes, most bars have right and left hand threads, so the bars can be adjusted without unbolting one of the ends. I've got triangulated 4-bars with rubber bushings that should yield a better ride, but only one end is adjustable, so it's a real pain to make any changes. I'm thinking of changing that too, but not to heim joints, maybe polyurethane bushings.
The A-arms are supposed to be approximately horizontal and parallel at ride height. When that's achieved, you've got the "ride height" that's built into the suspension. In my case, it's about an inch lower than the height that I had been using, since my shocks are too long. I set mine up by the shock length. The lower height will require some slow driving when turning the wheels and going over a ramped road into a parking lot. The tires can hit the wheel opening, easily. When going straight, there's lots of room for tire travel.
The tech guy at Ride Tech suggested that I start with shock adjustment at mid-point. I had always had mine set mine very light (knob screwed out most of the way). By that time, my car was partially torn down and out of service (until it's painted and reassembled).
From looking at the Spring Tech article I also read the sway bar article. From reading that it looks like that could be part of the problem also.
My A-arms are about 1" out of parallel setting high at the inside of the wheel.
If the A-arms are angled upward, at the ball joint end, that would mean that the car is sitting lower than intended. If the shock length is proper - in the 11.2-11.6 inch range, it means that the A-arms pivots were welded to the frame to work at a greater ride height and the shock length is wrong. Ideally, the shock length should be set to allow 50-60% of the travel in compression and the A-arms should be horizontal and parallel, all at the same time.
At least with my car, sway bars are not an issue because I have none. I detected very little body roll during my 1200 miles of test driving last year, but I have thought of trying to adapt a Heidt's sway bar to my front suspension, while I've got it torn apart.
In the pics of both rear springs it appears that the top mounting bolt isn't centered in the shock upper end and that the springs are not centered around the shock body-is this because the springs have a larger id than the mounting components are designed for???( wrong spring ID )
Hi, I understand this is an older thread, but I wanted to drop in and give my two cents since someone referenced one of my articles above (sways and the spring article).
My Recommendations
The front springs are under-rate for what I perceive to be the motion ratio. (~78%)
Be aware that increasing the front rate (and ride height) will cause additional static and dynamic weight on the front. Adjust accordingly.
Running a fixed height shock for this application is a really mediocre solution. Adjusting the ride height with an adjustable base mount would give you full travel without having to do janky stuff to get the geometry right. This would let you reduce the spring rates considerably.
Tie a small piece of string to the base of the shock shaft, drive around, and then see where the string is now located. If it's at the top, you are beating the shock to death. Increase dampening considerably.
The golden ticket is adjusting the front and rear harmonics to be near each other. Milliken & Milliken found a 20% lower frequency in the front worked well.
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Shock travel is not always limited by the stroke length of the tube itself. There is barely 5" of compression travel in a 8" long spring, nor is there enough compressive force at that motion ratio to even remotely achieve that without trying your hand at the Duke's of Hazard driving school. You have to consider a few things:
- Spring Rate & Spring Compression Travel
- Shock Compression & Rebound Dampening
- Shock Gas Pressure & Design
- Force Input Speed & Duration
- Unsprung Mass
- Tire Dynamics
Tires
When you hit a bump in the road the tire is compressed. The amount the tire is compressed is due to the resistance (damper / spring) and the inertia (corner weight / unsprung mass) acting to deform the tire. How rigid the sidewall is and the load bearing capacity of the tire also have an effect, a rather large one. A taller sidewall, larger load rating, non-reinforced sidewall (or lower plys), and lower pressure all allow for greater tire deformation, which acts to dampen the blow. A stiffer tire will deliver more force and with a sharper duration ("impact" loading).
The force accelerates the unsprung mass (wheels, tires, brakes, etc.) upwards. There are a couple of very vital components at this point, the speed of the unsprung mass and the weight of the unsprung mass. That's because velocity x mass = inertia.
Suspension
So up comes the wheel into the wheel well. The second the force starts to move the wheel the suspension is acting to counter the force. This counter force comes from several sources:
- Shock Compression Dampening
- Heim Joint Bearing Friction
- Spring Force
- Sway Bar Spring Force
- Suspension Geometry
Initially the upward movement creates a very fast piston travel speed within the damper. This causes the compression dampening to be considerably higher (stiffer) which creates a large resistive force to the unsprung mass traveling upwards. This has a second effect of low shock compression and delivering the load to the chassis. This causes the front to pitch upwards, and ultimately downwards. It is this upward / downward sine curve that the body perceived as the harshness. (It should be noted that rear frequencies are perceived as harsher than frontal frequencies).
Concurrently the coil spring is compressing from the same movement. The linear Hyperco spring above will produce, say 350 lbs. / in. of travel. Meaning, the first inch absorbs 350 lbs of force, and two inches absorbs 700 lbs of force. This force is transmitted to the chassis, but also acts to accelerate the unsprung mass on it's downward rebound travel with the same force, minus losses. Hence why we run shocks. During the rebound moment the piston travels back through the fluid which causes different flows through the valve stack, creating rebound dampening. In this case, the high speed rebound dampening region, which is a high amount of force.
This force travels back and forth several times until the shock (and other losses) overcome the force. This creates a decaying sine wave of body movement (vibration). Both overdampening and underdampening can cause excessive body movement which will be perceived as harshness.
In NVH studies, harshness is measured in Hz and kept to a specific range. Some people may experience discomfort at different thresholds depending on their relative tolerance to it. This is why I don't care much about running 600# springs on my car while my dad enjoys spring rates in the 300# range.
It should be of note here that a "5-inch travel shock" is a very limiting descriptor. If Shock A has very low force dampening, it will cover that 5" very quickly. If Shock B has very high force dampening, then it may not ever use it's 5" of travel.
Furthermore, a 8.00" coil spring with 6 - 0.500" coils only has 5.00" of travel before it is completely closed. At that point, any additional compressive load is transferred to the mountings as an impact and the bending stresses on the suspension immediately ramp up. It should be noted that packers, bump stops, and spring solid height should ALWAYS be used to limit suspension travel to avoid damage to the shock and/or control arms.
Sway bars only really add forces when one side moves in a different direction. So if you hit a pothole, for example, on the left side, it will add spring rate to that corner. The amount of rate depends on the sway bar setup (thickness, material, lever arm length, etc.) It should be noted that offset hits to both axle wheels creates a lot of torsional / weird movements that are perceived as very rough (because they are annoying). A sway bar makes this even worse because rate is quickly shared.
Lastly, you need to heavily consider the angle of the shock as it has an effect on the motion ratio. The further away from 90 degs. it gets the higher the necessary rate.
Suspension geometry affects shock piston speeds and effective spring rates, as well as other dynamic concepts.
Welcome to the forum, and thanks for taking time to post. I hope that you'll stick around and help us with suspension issues, as questions arise.Quote:
Originally Posted by Rennmeister
Ditto Fascinating read!
Welcome Renn- Now some one can maybe see why its taking me some time to write up thread on suspension and steering
A typical 8" spring coil-over only has 3.25 inches of total travel and it's usually set up to have 50-60% of that in compression. The shock will bottom out long before coil bind occurs, unless the springs being used are way too soft and a lot of preload has been applied.
Modern springs have a lot more space between the coils, than they used to. I saw examples this weekend, where some open wheel cars had springs with the coils almost touching, at normal ride height. You won't see that with a modern ride-tech coil-over.
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