Shock dyno graph/spring rate advice

[Dimman]

I'm looking for some expert advice on matching shocks to springs for a custom coil-over build.

My spring rates are probably going to be 650lbs front and 475lbs rear.

The shocks I'm looking at have these two curve options, but I don't know what I'm looking at when I see a shock dyno graph.

Curve 1:

Curve 2:

They are not adjustable but can be valved from the factory in any combination of compression and rebound settings on the graphs. Closest to center (green lines) are setting 2 and extreme ends (red lines) are setting 8.

They also have a tuning kit available to re-build and re-valve them myself.

Which curve and then which settings for compression and rebound would be a good starting point for the above (650 lbs front/475lbs rear) spring rates?

Thanks,
D

 

[spencyg]

+1 on this question...about to rebuild a set of coilovers myself and the exact same ponderings were rolling around in my head...

SG in NE

 

[Dimman]

Here's the starting point of what I know (think I know) so far. The car rolling, squatting and diving movements are controlled by the area of the shock that is around 4"/sec and under. As the movement of the wheel gets more violent, the larger numbers are used eg: 6"+/sec is usually a bump, or pothole or something, faster hitting same bump at faster speed is more "/sec.

But how does (if it does) the force number relate to a car's spring rates? More force on the graph is more damping or controlling the spring's movement, so is the amount required easily calculated (or can be put in a good starting point) by the spring rate and the car's weight/balance? Or is is one of those super-complex math problems because the forces are continuously changing all the time?

And does the anti-roll bar choice need to be accounted for as well?

 

[spencyg]

Very interesting discussion on the effect of valving (and graphs) in the real world. I think I need to build one of these cheap shock dynos.

http://www.honda-tech.com/showthread.php?t=2415915&page=3

 

[Dimman]

Very interesting discussion on the effect of valving (and graphs) in the real world. I think I need to build one of these cheap shock dynos.

http://www.honda-tech.com/showthread.php?t=2415915&page=3

Interesting? Yes.

Correct? I have know idea. Hence the post.

I was sort of anticipating this, as it's a teensy bit more complex of a question than the typical "Should I get Tein or Megan coilovers???" questions...

Probably going to need some patience.

 

[spencyg]

Well, to really delve into the specifics of what areas of a particular dampening curve play a part in various aspects of both driving/handing characteristics as well as suspension component selection, I think reading a few "primers" on race car setup is in order. I have a few books at home on the subject of suspenion design and I'm certain they have some of this info...I just haven't had a minute to pull them off the shelf in the shop to have a look.
One thing to note is that the X axis of the graph is the velocity of the suspension link directly attached to the shock (at a 1:1 ratio), and the Y axis is the instantaneous reaction force which the shock provides to that suspension link at that particular point in time. Needless to say, a shock absorber is there to control the motions of the unsprung weight more than the sprung weight, so as you're figuring out what kind of reaction forces you might be dealing with, you need to take into account the following:

Wheel weight
Knuckle weight
1/2 of all control and link arm weights
1/2 of the strut weight
Spring constant
Suspension geometry as it relates to the lever arm ratios of the forces involved.

As you look at the amount of force exerted back into the suspenion link by the strut, you need to keep in mind that smaller velocity motions (closer to the origin of the graph), are representative of small dampening actions due to smaller imperfections in the road surface as well as body lean and cornering reactions. The larger velocity motions (farther out on the graph), represent the gross dampening of larger imperfections (railroad tracks, potholes, etc). I think this partly boils down to some basic math to figure out what kind of forces are present in your particular vehicle which require dampening, and then it partly boils down to personal preference. I think this is why it is a rather difficult topic to write on. What feels right to me might not feel right to you, and what I consider good handling might go completely against what you consider good handling.

Obviously this paragraph hasn't answered your question at all....I'll try and take a look at some of those books this evening to see if they have some forumulas and discussion which might be helpful.

SG in NE

 

[Dimman]

Well, to really delve into the specifics of what areas of a particular dampening curve play a part in various aspects of both driving/handing characteristics as well as suspension component selection, I think reading a few "primers" on race car setup is in order. I have a few books at home on the subject of suspenion design and I'm certain they have some of this info...I just haven't had a minute to pull them off the shelf in the shop to have a look.
One thing to note is that the X axis of the graph is the velocity of the suspension link directly attached to the shock (at a 1:1 ratio), and the Y axis is the instantaneous reaction force which the shock provides to that suspension link at that particular point in time. Needless to say, a shock absorber is there to control the motions of the unsprung weight more than the sprung weight, so as you're figuring out what kind of reaction forces you might be dealing with, you need to take into account the following:

Wheel weight
Knuckle weight
1/2 of all control and link arm weights
1/2 of the strut weight
Spring constant
Suspension geometry as it relates to the lever arm ratios of the forces involved.

As you look at the amount of force exerted back into the suspenion link by the strut, you need to keep in mind that smaller velocity motions (closer to the origin of the graph), are representative of small dampening actions due to smaller imperfections in the road surface as well as body lean and cornering reactions. The larger velocity motions (farther out on the graph), represent the gross dampening of larger imperfections (railroad tracks, potholes, etc). I think this partly boils down to some basic math to figure out what kind of forces are present in your particular vehicle which require dampening, and then it partly boils down to personal preference. I think this is why it is a rather difficult topic to write on. What feels right to me might not feel right to you, and what I consider good handling might go completely against what you consider good handling.

Obviously this paragraph hasn't answered your question at all....I'll try and take a look at some of those books this evening to see if they have some forumulas and discussion which might be helpful.

SG in NE

It could be worthwhile to gather all up this info specifically for the Mk3. Stock weights, and the linkage distances/angles. Accumulate data on common brake swap weights, too. We could all probably figure our own wheel/tire packages out.

 

[supraguru05]

Your front spring rate is rather low. for every 1 inch of front wheel travel the shock only travels approximately 0.64 inches. This significantly decreases your installed spring rate. I would recommend a minimum of 800 lb.in front springs for entry level racing on street tires. Also the front unsprung weight on one corner of my car is around 100 lbs with 275 tires.

 

[Dimman]

Are the shock curves and spring rates related? The reason I'm asking this is that the springs that this company sells max out at 650lbs.

If the fronts are too soft is that going to cause oversteer issues then? So could I reduce the rears, if it's a balance issue?

If the shocks are ok for the 800lbs, I can get Eibach 2.5" ID race springs.

As for the curves, I can eventually sort out what I like on my own. However these need to be removed and re-valved to adjust them (deflective-disk stacks) so it's a bit of a chore. An understanding on how the spring rates and the force/velocity curve interact would help me make a better initial valving choice.

Thanks for your help.

 

[spencyg]

The spring constant (i.e. lbs/in, kg/mm) has a direct effect on the loads which the dampener is required to slow down. The shock structure should be able to handle higher spring rates, it would just mean re-valving and/or using a thicker viscosity shock oil. One factor which will come into much more play when dealing with very stiff springs is the heat generated by the dampener to absorb the forces involved. A strut which stays relatively cool with a 600 lb/in spring could be too hot to touch with an 800 lb/in spring. I am going to be adding reservoirs to my struts eventually to account for this issue by adding to the oil volume and providing more surface area to bleed off heat.

I can't comment on lowering your rear springs to account for deficient front spring rates, but intuitively speaking, it sounds rather backwards if you're trying to really get a stiff race setup.

 

[Dimman]

It's for a performance street setup.

According to the sticky stock pre-89 is 461lbs front and 180lbs rear.

So the rates are more than the stock rates, what I was thinking is if he said the fronts are too soft (implying the rears are ok), then the balance was off. So reducing the rears would balance out more? Also reading through here, the race setups like to be in the 800lbs-1000lbs front area and 600ish in the rear.

If I go 650lbs front and 375 or 400lbs rear is proportionally closer to a 1000lbs/600lbs f/r setup. (Come to think of it, I thought I did my math better, I don't know where the 475lbs came from, maybe I typoed 375lbs...) I was thinking this would ride a bit nicer than a harder race setup.

Then I was looking at using a Whiteline front bar at full stiff (207% stiffer according to the sticky) paired with a Tanabe rear bar (220% stiffer). So this is effectively making the spring rates stiffer only under cornering loads.

What I am looking to do is tighten up the handling without upsetting the stock balance too much or making it too harsh. The slightly increased proportional spring rate in the back and a bit more rear bar stiffness should also reduce a bit of the understeer.

As for the shocks, they are financially an attractive piece if the can be valved to what my setup needs as they will likely be 'set and forget', and are about half the price some double adjustables (separate compression and rebound) from the same company. Plus they are user rebuildable and revalveable.

 

[supraguru05]

if this is a street setup I see no need for this level of damper. I would buy the oem bilsteins and run something like eibach springs and call it good. If you dont like the progressive eibach springs you can order custom wound springs in a linear rate.

Can you post which damper you are considering?

 

[Dimman]

if this is a street setup I see no need for this level of damper. I would buy the oem bilsteins and run something like eibach springs and call it good. If you dont like the progressive eibach springs you can order custom wound springs in a linear rate.

Can you post which damper you are considering?

They are actually QA1 circle track dampers.

http://qa1.thomasnet.com/viewitems/...dy/aluminum-threaded-body-shocks?&plpver=1001

Any standard 2.5" spring will fit their coil-over kit. They also have small-body aluminum shocks that take 1.875" springs, with the same curves that have an assortment of different overall lengths and strokes, so fitment won't be an issue.

The price is right, and they are fully rebuildable and revalveable so I figured, why not? In the circle track community these are a legitimate Bilstein competitor. Weights of most of the stock cars run close to the Mk3.

The only issue is mounting, but I will be fabricating some brackets for the upper spherical bearing to mount to, that bolts up to the stock location. Not an issue for me.

So is this a reasonable idea or waste of time? Right now I have two Supras, one a JDM 1JZGTE car that came with Cusco coilovers, and the other is a bone stock, 4x4 ride height 7MGE, so this coilover idea is more of an experiment for the stock car.

 

[spencyg]

QA1 makes some nice stuff. With a little fabrication you really can't go wrong there. Obviously you'll be on your own as far as valving is concerned, but once you get the hang of it and play around with enough combination, you should be ok. I really would suggest getting some reading material on the finer points of race suspension application and tuning before spending any real money though. The $50 you'll spend on a couple good books will pay for itself immediately.

Sg in NE

 

[supraguru05]

I would talk to AFCO. They make both a single and non adjustable aluminum threaded body shock in the same dimensions as QA1. the benefit is you can talk to Speedway motors and they can valve them for you for your application. Also AFCO has experience with asphalt road race cars.