Coil over front springs
I have been autocrossing my Zink and the front end tends to push. I believe I need to put coil over springs on my front shocks but don't know what "rate" springs I should use. I want the front stiff. I see every rate font 95lbs up to 300+lbs.
I scaled my car a while back with me in it and the front weight was 250 and rear was 350 each wheel if that matters.
Suggestions?
What model Zink?
Not sure...Originally Posted by S Lathrop
http://www.apexspeed.com/forums/show...highlight=zink
You have a Z4 or C4. This is the original Zink FV. The chassis is was built after 1969 and maybe as late as 1974.
With a vintage legal FV motor and original wheels, your car is probably worth way more money than you realize. It would be eligible to run at INDY this weekend with the vintage show.
Way simpler than trying to do coil overs would be to get shocks that you can remove the tops and use Dynamic bump stops to supplement the springs you have. The bump stops are something less than $25 each and you probably only need 2 per corner. Additionally you need shocks that have top out bumpers inside in order to limit shock travel.
I suggest that you limit your modifications to things that do not decrease the value of your car as a vintage FV.
How much are you offering me for it? ;-)
Anybody else have any suggestions for me?
I have enough parts in my barn to build a C4. Don't need another race car.
I have used bump stops for decades as an integral part of the suspension system on every thing from FV to Indly Lights. I have used them for bump and rebound control. I have a car right now running in F2000 that is using 12 bump stops.
The virtue of bump stops is that you can get rising rate springs that are self damped. F500 use a type of bump stop for their entire springing system.
What makes you think a stiffer front end is going to correct the push issue?
What tires and sizes are you using?
Brian
9" tires in front. I have pictures of the front a-arms in action around a tight braking corner.
Do you have a link of what you think I might need?
9" tires in front???? 9" wheel, cross section, thread width????
You want some answers, you are going to have to layout all the details.
What tire brand, compound, size, and age/heat history… front and rear?
AGIAN, what makes you think that a stiffer front end is going to solve the push?
Brian
13" dia rims. 9' wide front 10" wide rear. Hoosier 25B. Current fronts are less than 1 year old.
I can do high speed turns (85mph) with little to no drop of front end with NO push. My problem comes in when I do tight braking corners. LOTS of push. I see the trailing arms in the front "raising" because of front end dip.
Rear has coil overs already. The back end is like driving "on rails". I can't do anything stupid enough to make it even start to brake loose.
I know from past experience that when the front end changes height that toe and camber changes a LOT.
I wasn't asking for help fixing my "problem". Was asking help from anyone that had experience with different spring rates on a Vee and what rates I should start at.
1) What % of your lap time is spent in 75+ mph turns on average over the season? Are you willing to give up high speed performance for low speed? Generally speaking, you need to introduce oversteer to the setup. Can you handle a car with high speed oversteer?
2) All things being equal, stiffening the front end is going to increase the understeer. Chassis roll/camber change (camber un-gain in this case)at the front, will be greater at high speed. Should not be the issue. Toe change is a possible issue. Have you tried static toe out? Have you made any changes to the Ackermann/dynamic toe change curve. These cars were not originally designed for slow tight turn. They are almost never operated below third gear for example.
Using stiffer front springs is simply the wrong approach.
3) I am not sure any rules allow coil over shocks, so we really do not have knowledge about them on a FV. Are you use one spring pack or two at the front? One complete spring pack has a spring rate of about 40-50 lb/in. If a sway bar, what size?
4) The correct way to reduce the understeer would be to allocate more roll resistance to the rear. I would say reduce the force on the Z bar and let the coil overs at the rear carry more of the load. This will make the car looser at all speeds.
Brian
Sorry but just wondering...did you read that I am autocrossing the car?
I understand the "normal" thinking that adjusting the rear will change the front.
If I change the rear I will have to change the springs because they are close to maxed out now.
Yes, I understand your activity…. You are taking a car designed to operate between 50-100mph and operating it at 25-75mph.
Adjusting the rear will not change the front… it will change the balance of the whole car.
I would propose changes to the front if there were any options other than a larger front tire. I assume you are using offset front bushings to get 1-2deg of negative camber. You really have no choice but to work with the rear. Take some of the cornering load off the front and put it on the rear. How is it cheaper to buy front springs and collar systems than just replacing the rear springs?
Precisely how is the Z bar and rear springs setup? Where did you get your knowledge about how this cars Z bar rear suspension is setup?
Brian
Last edited by Hardingfv32; 06.07.15 at 11:45 AM.
Carl Haas Auto: http://www.haasauto.com/home.php
You can get a rate chart for the bump stops from them. I have tried a lot of bump stops and the Dynamics are the best and they have a very wide range of rates available.
Next: do you know how your front springs are setup. The stock VW springs give a front ride height that is too high. Common practice was to cut 2 of the leaves in the spring pack to reduce the spring rate and get the proper ride height. An alternative is to use a full set of leaves and bend the springs to get the correct ride height. You do this by putting the trailing arm on backwards and putting a pipe over the enf of the link to get enough leverage. The last cars I build, I replaced the 4 outer leaves (half width0 with full leaves to get a higher spring rate. I then bent the spring to get the correct ride height. In FV these days you can modify the mounting block in the middle of the beam to allow you to adjust the ride height.
Any used VW springs you get will not be even side to side. So I would suggest that you bend any set of springs us use to at least get the ride height even side to side.
I have experimented with bump stops and droop limiting on the front of FVs. We found that the bump stops on the front made the car too reactive. But that was before the Dynamics bump stops were available. I believe that this is exactly what you want to look at. And droop limiting will be desireable as well.
Finally, you can balance any car. The idea that the rear works good so you don't want to change it is common and not correct. What is happening is that as you start to turn the car, you are loading the front tires more rapidly than the rears. As you turn the car more, you get to the limit of the front end of the car without ever asking the rear of the car to get into the game. If you simply raise the rear of the car, for a FV this is reducing the rear camber, you will get a better balance of the cornering loads between the front and the rear of the car. Once you get the car balanced, you then work on the other issues that keep the car from being what you want. You may find that the issue then is the rear. Or you need a lot more front sway bar or a way stiffer rear Z-bar. But you need to find out what the car does when it is in balance and then start to fix things. As you raise the rear of the car, you need to disconnect the Z-bar raise the rear then reconnect the Z-bar with the same amount of preload. Otherwise you will make 2 changes at the same time and not have a clue what helped.
Just curious... what size anti-sway bar is in the front axle tube ?
I found too small of sway bar allowed too much front-end roll (weight shift) and produced a push in a Caracal-C... not sure how much it would or could cause in a C-4.
Have to believe those huge tires are affecting the car's natural characteristics.
Glenn
1) Does running on the front bump stop reduce the load or just stop the chassis roll? In the car being discussed, how is hitting the front bump stop going to effect the car's neutral balance at the 85 mph speed range?
2) How does the rear jacking in the corners going to effect a proposed reduction in rear camber? Could we assume that there is less jacking, less camber reduction, in the slow turns where this car's imbalance is taking place? I would thing that reduced static camber would make the issue worse.
3) Maintaining the same rear ride height after adjusting a Z bar car:
Does reducing the preload on the Z bar increase rear roll resistance? This assumes that the rear springs are adjust to maintain the ride height.
Brian
1. The bump stops have a progressive spring rate: 3mm = 5.6 kg, 4 mm = 11.6 kg, 5=22, 6=35, 7=60 ( for the softest). If you double the bump stops, you get half the spring rates. This is added to the spring rate for that wheel. Being stiffer, the tire will react to the steering input quicker up to the point where you exceed the cornering potential of the tire. Because the track surface is never perfectly flat, you can think of this as using the bumps to help turn the car. That is why you have packers to tune the effect of the bump stops as you are turning the car.
2. The rear does not jack because of the Z-bar prevents both wheels moving down together. My advise about disconnecting the bar before raising the rear of the car is to keep the spring load from the z-bar constant. It may be that you need more spring load from the z-bar. In that case you add more z-bar load but adjust the ride height to compensate.
3. Raising the rear will cause the cornering loads to build in the rear faster. The maximum cornering potential is when the front and rear tires are near their respective maximum. One definition of a balanced car is when the slip angle of the front and rear tires are equal. Raising the rear of the car does 2 things; it raises the rear roll center and it raises the rear CG. Both changes cause the weight of the cornering load to transfer into that tire faster.
When a FV corners, the rear rises until the cornering forces and the resulting jacking forces are in balance. The motion of the rear end over the track is a combination of rolling and bump movement. If the car wants to corner harder, you will need more Z-bar load to offset the jacking forces. Given that this car is running much larger tires than what the FV suspension was developed around, The Z-bar may be way under sized. that is offset by keeping the rear ride too low and dealing with push all the time.
Decades ago I built a bolt on zero roll setup for this car. Something like that may be the only solution to the real problem here.
1) Since it has been stated that the car is low speed under steering, can we not say that the front tires are exceeding their potential?
A stiffer front end could provide better turn in by heating the tread faster, but what happens to the rest of the turn, are we not going to see the tire over worked, getting too hot, in the middle and exit sections increasing the under steering issue?
2) The Z bar is there to limit jacking, some amount of jacking always takes place as the Z bar is a form of spring/torsion bar. The camber is going to move in a positive angle direction, say -4 total to -2 total at the rear as the rear jacks.
3) Raising the car does THREE things: it raises the roll center & CG, but also reduce the amount of total rear camber.
It would be my opinion that camber has a much getter effect than the changes to the roll center & CG in this case. Do you have any research one way or the other on this subject?
Brian
I will argue that the camber is not as big a deal as you might think. The rear of a FV jacks. It jacks to the limit of the suspension settings as the car corners. The more static camber you set, the longer it takes to get to its cornering attitude. If you look at pictures of a FV cornering, you don't see a lot of negative camber in the rear. And in fact you possibly see some positive. Mostly caused by the distortion of the rear tire during cornering. What I found critical and it is reflected in the rear camber number is the amount of travel you have in the rear suspension. That I measure by taking a camber reading of the car loaded, on the ground and the camber of the rear wheels when the car is jacked up. I found that keeping the net change constant was more important than what the actual static camber is set at. It is possible that the front anti roll bar might have a larger effect on rear camber in cornering than the static rear camber.
With push rod bell crank zero roll system used a many cars, you can make small tuning changes with the push rods and not change the travel limits set with the shock and the droop limiter.
I don't have a front sway bar.
Are you sure? Do you have spring packs in both tubes? You either have a spring pack in both tubes or a sway bar in one of them. Since your original post was about trying to increase your spring rate, it seems doubtful you have springs in both tubes as that would be twice the spring rate as one tube only. There has to be something to hold the torsion arms in place, springs or sway bar...I don't have a front sway bar.
Perhaps you have a sway bar and did not realize it? It is common on a FV (most if not all) to remove one spring pack and replace it with a sway bar.
How can I tell?
Sway Bar
If you look at the square opening in the ends of the trailing arms where they come out of the axel beam, you can tell which tube has the spring and which has the sway bar.
The springs will be a stack of flat plates that are about 3/4 inches wide and an 1/8 inch thick. The sway bar will be a square block that has a hole drilled through. The sway bar is inserted into the hole and the end is welded. What you can't tell about the sway bar is what diameter it is. In the case of a Zink bar, it was likely 5/8 diameter stainless steel.
The sway bar will also have bronze spacers between the beam and the trailing arm to control the position of the trailing arm. The springs will have a rubber seal instead of the bronze spacer.
You should see if you can find some experienced FV racers in your area to help you get up to speed on the care and feeding of a FV. Those guys know a lot about setups that will certainly help you solve many of the issues you are having. Things you should know such as how to set the front with negative camber and how to do a setup with a Z-bar rear end. Your car is way different than what is raced as a FV but the fundamentals are the same. Also, these guys can help you understand a lot of what has been discussed in this thread.
Steve answered that question, but it is safe to assume you have a bar in one of the tubes. Given the fact that you are unsure what you have, I would not assume you are going in the right direction by increasing the spring rate. My suggestion would be to first make sure you have a standard FV front working properly, then make any further decisions. While a fairly simple design, there are many things that could be wrong. Getting the front setup properly would be your first step. The first check I would make would be to disconnect the front shocks and see if the front is "free", does it return back to normal when you push it down/pull it up. This is just to check if your link pins are set up somewhat correctly. I would start by disassembling the front, checking the linkpins and kingpins for wear, and the torsion arms for wear/slop. At this time you can check and see what you have for a spring pack and roll bar diameter. Check the link pin bushings to see if they are offset for neg camber. If you do not have a VW manual, get one. Once you know what you have, assemble it for a test fitting. Then come back and ask specific questions.How can I tell?
You really need to know what you are starting with and if it is all working properly.
Late to the party and I'm coffee'd up, so a +1 if anything has already been mentioned.
When first autocrossing my vee, it had push everywhere. Corner entry and mid corner were particularly bad. Forgiving for some situations I suppose, but lazy for autocross. Going to 10" width tires were probably greek to the existing chassis setup as well.
I went 1/8" toe out and raised the rear a bit which also removed some neg camber. I'm still around 2-3 degrees total neg camber in the rear, and aggressive (but gentle) droop limiting keeps things in check. Also set my rear toe around 1/8" in. Since your most severe push is under braking, check your bump steer. You may be going far toe in when the front squats. Get a second set of hands, stretch a tape across the front wheels, and stand on the front end.
Check this website for some help At least establish that something isn't way out of wack, then go from there.
Cars are different, but these things worked for me and my zero-roll. Some or all may apply to your setup. Don't discount something as simple as tire pressures either. Mine are only around 15f and 16-17r. Good luck.
By the way, I picked up that vee in Lafayette that you had your eyes on a few years ago. You wouldn't recognize it now.
Thanks. Good info. I will check the link.
Got pictures? I didn't buy it because I couldn't get my shoulders in it.
Late to the party and I'm coffee'd up, so a +1 if anything has already been mentioned.
When first autocrossing my vee, it had push everywhere. Corner entry and mid corner were particularly bad. Forgiving for some situations I suppose, but lazy for autocross. Going to 10" width tires were probably greek to the existing chassis setup as well.
I went 1/8" toe out and raised the rear a bit which also removed some neg camber. I'm still around 2-3 degrees total neg camber in the rear, and aggressive (but gentle) droop limiting keeps things in check. Also set my rear toe around 1/8" in. Since your most severe push is under braking, check your bump steer. You may be going far toe in when the front squats. Get a second set of hands, stretch a tape across the front wheels, and stand on the front end.
Check this website for some help At least establish that something isn't way out of wack, then go from there.
Cars are different, but these things worked for me and my zero-roll. Some or all may apply to your setup. Don't discount something as simple as tire pressures either. Mine are only around 15f and 16-17r. Good luck.
By the way, I picked up that vee in Lafayette that you had your eyes on a few years ago. You wouldn't recognize it now.
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