coilover springs, shorter or longer?

So 2 very simiar cars...2 different brand COs.

One has 2.5x8" springs, the other uses 2.5x7" (might be 6, I forget but I think its 7)

Same spring rate, same spring brand, different company dampers.  Only real difference in the cars is the short springed car has the front sway bar deleted, thats my personal Tercel build, the other car is a Sera ( a friends car Im working on), which does have a slightly shorter wheelbase, otherwise identical chassis and retains the stock front swaybar.  

Im not going to state brands as I do not want to stir up confusion.  Both are excellent pieces, I'm just trying to learn tricks here.

The Sera just recieved COs with manufacturer recomended spring rates (6k/4k).  I requested a different (lower, 5k/3k) rate to the owner.  They sold him on the existing catalog rates.  The car is more back road fun car then track beater.   I have alot of experience chasing my tail trying to sort these cars out in what works well and not, (pretty sure I have a better idea then most of these suspension people on THIS particular chassis).  Anyways, put them on...yes its a rough as predicted...but better then mine and even at very low damper settings ( 3/30F, 2/30R), virtually no extra spring oscillations.  Takes large bumps extremely well.

On my Tercel, it has a older generation, different brand CO kit, same 6k/4k springs just shorter.  And its pretty good overall.  However Ive had to run my settings pretty high up front to control the springs, 16/24F, 4/24R.  It also rearranges my face on some decent bumps and gaps in the road.  My one particular favorite test bump, the car pretty much gets airborn, and damn near out of shape going thru it (the bump is a bad whoopdie woo at a small bridge mid corner).  Its entertaining, but also hurts and is basically unsafe. 

The Tercel is almost at stock ride height, the Sera is "lowered" but not dumped.  Tercel also has more aggressive toe out and camber then what I had the Sera set to.  Tercel also dailys on regular tires vs the Sera is on RE71s (both same size).

SO the biggest difference is the brand of damper and the length of the springs.  Can the length be of any ride influence?  The dampers on the Sera are cheaper then the ones I have on my Tercel.  I am considering changing my springs to taller slightly softer rates.  None of them bottom out and the coilovers are full height and preload adjustable.

The shorter the spring, the more easily it will coil bind. The higher you set your ride height, the more likely you are to coil bind. I suspect that might be what you're experiencing with the Tercel. A bound spring is a piece of solid steel, it locks the suspension up.

You can check for coil bind pretty easily visually. Just look for a mark where the coils come together.

In reply to Keith Tanner :

I will have to check...that could be why its borderline violent on large bumps, infinite SR!

I'll drive it into the shop tomorrow and take a gander for sure.

Sera as it sits

Tercel;

I want a Sera just for the doors. 

Ive never seen a sera vefore now, and i think i hate you for the amount of lust i now feel.

 i think i hate you for the amount of lust i now feel.

Well I don't have anything to contribute on spring rates but I've never seen a sera before and I must say, great looking car. 

I was unaware of the Sera. Cool car. Wikipedia says the first three years are 25+ years old. 

Seems like window tint would be useful with so much glass. 

T.J. said:

I was unaware of the Sera. Cool car. Wikipedia says the first three years are 25+ years old. 

Seems like window tint would be useful with so much glass. 

 

the owner did have the car recently tinted with good 3M stuff more for UV then looks.  I think its 50% iirc

My gut says coil bind, Masking tape around a coil will also help show it if there not nicely fresh painted springs.  If it cuts the tap you know you've touched the coils.  Cheap tie wraps around the shaft work great as travel indicators as well but then you have to do the math.

In reply to 44Dwarf :

Mine are fully dust covered.  A bit hard to to reveal the shaft (heheh)

I like the tape idea.  The COs are significantly shorter then stock I really hope i aint bottoming out my ride height atm.

If you are binding, longer springs are a good answer. Get a spring that's x" longer, drop the perch by x". Your ride height stays the same but you will gain more compression travel before coil bind. There will be physical limits such as adjustment range or interference with chassis components.

In reply to Keith Tanner :

Pretty much my plan.  Thanks guys for the ideas

Finally got my car in the shop...the springs are definitely closer together.  I confirmed they are 7" springs on mine.  There is an easy 3.5>4" of bump travel to the body.  I could not feel the bump stop...i can only assume its about half that bump distance.

Here is the Sera.  Since its a little lower it was hard to get a really good picture

There is a 5/8" gap between my springs.  I really couldnt get my hands and tape measure in the Sera to measure...but Id say they had an easy 1/8-1/4" more gap

Are those Fortune Auto coilovers? The ones with the green perches. If they are, your spring rates probably aren't stiff enough to keep it from blowing through the available bump travel. You will probably also want much more spring preload then they say, then you can adjust the ride height back up with the shock overall length. Also consider installing longer and softer polyurethane foam bump stops because the rubber pucks they put are awful.

My s2000 has FA coilovers with obscenely stiff spring rates and it actually rides really nicely. But the caveat here is obviously if the bumps are larger than your available wheel travel then you will experience some discomfort. And that applies to any suspension setup.

I just went from 7 inch springs on my racecar to 6 inch springs in order to get the ride height I wanted (I was bottomed out on the perches).

Longer springs are better.  The only reason to run shorter springs is if you have physical limitations.

In reply to freetors :

Yes they are.  And to be clear im not complaining.  I just think I could make improvements more biased for my desires.

I am set at what they recommended 1/4" preload up and 1/8" rear.  I also set up the suspension on the Sera the same way...the fronts were almost loose when they arrived.

I am set to go longer and softer on my springs when time allows.

This thread brings to light an issue I may be having with not enough pre-load. good information to know.

Well nothing new with this as my car hasnt run in over a year due to me dragging ass on finishing the engine swap.  

The car will definetly need softer springs since up front Ive actually lost closer to 170lbs.  And I can see with my little trick on my lift I have no compliance up front vs my rear still compresses slightly.  Before the motor swap I had the ever so slightest movement.

Its something Ive noticed with my drive on lift.  When lowering a car down and i can pulse the valve to make the lift stop abruptly.  Essentially cycling the suspension under vehicle weight slightly.  Every car that shows some compliance rides well on the street.  The ones that dont show any movement generally dont. 

Its crude...but it's pretty consistent results on my end.