Coilover spring rate linear region

[dhutton]

Over what sort of percentage of it's length should a coilover spring be expected to remain linear in compression. For example, would a 10 inch spring still be at it's specified rate when compressed 2 inches? The reason I ask is I had some 10 inch springs that were very stiff when compressed almost 2 inches. I replaced them with some 12 inch springs (different manufacturer) and they behaved much better when compressed 2 inches.

Thanks,
Don

[79T/Aman]

were they the same rate?, could the 10" springs been coil binding or over extended during opperation?

[John Wright]

Over what sort of percentage of it's length should a coilover spring be expected to remain linear in compression. For example, would a 10 inch spring still be at it's specified rate when compressed 2 inches? The reason I ask is I had some 10 inch springs that were very stiff when compressed almost 2 inches. I replaced them with some 12 inch springs (different manufacturer) and they behaved much better when compressed 2 inches.

Thanks,
DonCurious....how did you check the compression to know that it was 2" during a drive? zip tie on the shock?


edit...or am I reading the question wrong?

[68sixspeed]

springs can vary mfg to mfg real bad, some brands like Afco use to guarantee a rate, we use to always test/check them for racing purposes and ended up on their stuff for that reason. The rate should stay constant/linear until you get to the point where coils start bottoming against each other, any 1/2 coils near the end will hit first causing an increase, then the mid coils should bottom together.

[dhutton]

Curious....how did you check the compression to know that it was 2" during a drive? zip tie on the shock?


edit...or am I reading the question wrong?

I think you are reading it wrong. I was referring to the preload on the spring. Sorry, I should have worded it better.

Thanks,
Don

[dhutton]

were they the same rate?, could the 10" springs been coil binding or over extended during opperation?

Spring rates were almost the same, 175 for the 10 inch and 185 for the 12 inch. I can't see how that amount of difference in the rate could make such a difference in ride quality especially when the angle of the coilovers is factored in.

What do you mean by coil binding?

Thanks.

[John Wright]

What do you mean by coil binding?

Coil binding = When the coil is compressed, the coils bind against each other. (read no spaces between them)

click here and scroll down to where it talks about coil binding
http://www.afcoracing.com/tech_pages/spring.shtml

[68sixspeed]

I think what you might be seeing is that with the soft spring rate you need to preload the spring a lot to get ride height, then getting coil bind on a bump. More typical rear spring rates are in the 250-300lb area. I run 275's on the street and I'm going to try 300 rears next to try and loosen the car up more. Probell's up to 400's on the rears. Note- if you have a rear roll bar you can keep a softer rate, but you still may bottom on hard bumps, compression in corner exit if you track the car, etc.

[dhutton]

I think what you might be seeing is that with the soft spring rate you need to preload the spring a lot to get ride height, then getting coil bind on a bump. More typical rear spring rates are in the 250-300lb area. I run 275's on the street and I'm going to try 300 rears next to try and loosen the car up more. Probell's up to 400's on the rears. Note- if you have a rear roll bar you can keep a softer rate, but you still may bottom on hard bumps, compression in corner exit if you track the car, etc.

The 175 pound springs are the ones that came with my G-Bar. The 185's work great, just trying to understand why similar setups behave so differently. I have been told that the 175 rate is a good match with the 550's I have on the front coilovers.

Thanks,
Don

[dhutton]

Coil binding = When the coil is compressed, the coils bind against each other. (read no spaces between them)

click here and scroll down to where it talks about coil binding
http://www.afcoracing.com/tech_pages/spring.shtml

Good link. Reading it over I think I may have had coil bowing. I noticed when I changed the springs that the label on the shock was badly scuffed. I'm going to check tonight to see if there are marks on the springs to indicate coil bind.

[68sixspeed]

Lets say you have a light car, 3400lbs with the driver, 55% front weight, thats 1530lbs on the rear wheels, 765 per shock, not taking into account the angle of the shock the 175 rate will compress the 10" coil 4-3/8" at static ride height. How much more can it have before it bottoms (coil bind)? With the angle I'd bet the coil is at 5" compression static, too soft of a rate IMO. Let alone what happens when you get some weight transfer under acceleration. Even the better leaf springs are in the 250-300#/in area... 175's would be more inline with a cobra kit car weight. -Dan

Ps- I might have some 10" 250's around if you want to test, not sure if I sold them at the swap meet or not.

[dhutton]

Lets say you have a light car, 3400lbs with the driver, 55% front weight, thats 1530lbs on the rear wheels, 765 per shock, not taking into account the angle of the shock the 175 rate will compress the 10" coil 4-3/8" at static ride height. How much more can it have before it bottoms (coil bind)? With the angle I'd bet the coil is at 5" compression static, too soft of a rate IMO. Let alone what happens when you get some weight transfer under acceleration. Event the better leaf springs are in the 250-300#/in area... 175's would be more inline with a cobra kit car weight. -Dan

Ps- I might have some 10" 250's around if you want to test, not sure if I sold them at the swap meet or not.

I need to get you talking with Mark at SC&C. When I first started having this problem I asked him about going to 250 pound springs and he said that was too high. He mentioned some cars he prepped for a race series that used the heavier Dynacorn bodies and even then he only went to a 200 pound spring. He was also the one to suggest longer springs and that seems to have been the fix.

I'm not disagreeing with your calculations, just trying to understand and learn a little more.

One other data point is that Todd (Vegas 69) is still running the 175 pound springs on his G-Bar and has no issues while autocrossing and racing his car. And he drives it hard...

Thanks,
Don

[BRIAN]

Leaf rates and coil over rates aren't going to transfer over from one to the other.

I have a collection of coil over springs and can tell you from MFG to MFG there are differences even within the same length. Coil bow can be caused by cheap springs or the angle they are mounted.

If you look at the coil spacing on some 8" vs 10" you can see that in the center the spacing is even. I have been told to keep the spring in the center of its body by going to a larger spring as you did. Curious as to the shock that accepted both on that set up?

Everybody has a different idea of what ride quality is. He may be driving a 4x4 daily and you a ZO6. You have to set up for your likes and abilities. I would be more concerned with correct ride height and not over compressing spring causing bind or worse bottoming a shock.


That said Marcus knows his stuff so forget what I tell you and listed to him.

[dhutton]

[QUOTE=BRIAN;610991]

Curious as to the shock that accepted both on that set up?

QUOTE]

For the 10 inch spring I ran the adjuster nut up almost 2 inches. For the 12 inch spring I used a spring compressor to install it and the adjuster nut is at the bottom. So in both cases there is roughly 2 inches of preload on the spring. This is with the Varishocks that came with the G-Bar.

[dhutton]

I checked the 10 inch springs. No signs of binding but one of them has a large mark on the inside that indicates it was likely bowing.

That explains the bang on large bumps but not the general difference in ride quality. The new springs are definitely better, less harsh.

[Vegas69]

Hey Don, I'm just now running across all your problems with the rear spring rate. While I haven't had any problems and have done well on the track, I've found my spring rate to be to low as well. Funny, I went through the same excercise you did to find the base line spring rate today. I'm getting ready to throw in 220 or 250's. My calculation came out to 206 and with the angle it decreases the spring rate about 10%.

[dhutton]

Hey Todd. I got into a lot of trouble running those 12 inch springs mentioned above. I ended up going with 220 lb 10 inch springs with the help of Frank who put me in touch with Nick at Chassisworks. There is enough preload on them that I think I could have possibly gone with 250 lb springs. Let us know where you end up. Your ride height looks to be a little lower than mine.


Hey Don, I'm just now running across all your problems with the rear spring rate. While I haven't had any problems and have done well on the track, I've found my spring rate to be to low as well. Funny, I went through the same excercise you did to find the base line spring rate today. I'm getting ready to throw in 220 or 250's. My calculation came out to 206 and with the angle it decreases the spring rate about 10%.

[Vegas69]

I'm going to move my shock mounting point down .5 while I'm changing springs. I moved mine in due to the mini tub a long time ago. I had to remove the rear sway bar when I went to street treads, I think it's made the lack of spring come to light. I don't see any reason to change spring length. It should put me right in the sweet spot.

[Bryce]

This might be a good place for this.

When I choose spring rates I do (two) calculations.

First what is the weight of the car at that axle. Divide that number by 2. this gives you F (force or weight)

Since F=kx next is to determine the amount fo droop you want or the shock has. This amount of droop gives you the minimum preload on the spring at ride height. If you have 3" of droop you dont want the spring to become unloaded. take F/x=K. K is your MAXIMUM spring rate.

Now this is where personal preference comes in. I design around a 1G bump. How much travel do you have in your shocks from ride to full compression, this is your x for the next equation. Take F times 1G, or whatever number you want to design around. F/x=K this is you MINIMUM spring rate. Now you have a range.

The only way to adjust this is to adjust your shock length and your shock length at ride height.