Cutting my Festy's springs

[TominMO]

Had some new 2001 Rio front KYBs I've been wanting to stick on the Festy, and now it's warm enough to work in the garage again, so I went for it today. I'm new to suspension tinkering, so bear with my ignorance.

Rio KYB shaft thickness = .792".....Festiva KYB shaft thickness = .707". The idea here was to find a strut with better dampening.
Original ride height with my tires was 23 7/8", measured from the ground to the fender arch.
Put 'em on with the Rio springs; ride height was 26".
Put 'em on with the stock Festy springs (which are taller than the Rio ones); ride height was also 26"
Cut the Festy springs (cutoff wheel, ~10 seconds per spring) by two coils; too much! Ride height was only 23" after a short drive to settle the springs. Also, the ride was terrible over little bumps and depressions like for manholes. Not sure what the spring rate is now with them cut. The Rio struts should be better at dampening, but apparently not enough to make up for the springs.

I have two sets of front Aspire ~110-lb springs and also a set of the Rio 175-lb springs. Thinking of cutting the Aspire ones maybe 1 coil, then 1.5 if needed to get the ride height back to 23 7/8" or 24". Maybe fool with the Rio springs. Any thoughts?

Not doing anything with the rears right now. I have ordered various metal and rubber spacers to fit between the rear coils, just to experiment.

This was all very much easier to do with my cordless impact wrench on the spring compressors. Saves lots of time, and the lower back.
I used the cordless impact on the center nut to remove the springs too. Strut on the ground, bottom of the strut against the wall, and held on to the top hat with one hand to dampen how far the parts went when the nut came off. Put a couple of boxes in front of the top of the strut to capture the parts (mainly the nut). Worked great, and no damage to me.

[Gomez]

I am not sure what ride height was when I did the Rio front swap on my other car. I cut 1.5 coils off the Rio spring and ride height looked a bit lower than stock. Ride was definitely firmer BUT waaaay more pleasing in just about every aspect. I always avoid holes in the road and generally the roads here are acceptable. Somehow I remember someone doing the math on 1.5 coils off the Rio to be in the area of 185 lb/in (may have been in the area of 200 lb/in though). Would be perfect with a stiffer rear end.

[drddan]

So, what you are saying is the Rio strut raised the height no matter what spring was put on it? Curious. So the strut, in effect, has more to do than just dampen things?
Is there height difference in spring perch? I imagine the Rio strut is longer. I am on a learning curve here. I have been wanting to check out the Rio's, haven't yet.
Thanks for posting, Tom. :happy1:

P.S.
How did you find the # rating of the springs?

[TominMO]

So, what you are saying is the Rio strut raised the height no matter what spring was put on it? Curious. So the strut, in effect, has more to do than just dampen things?
Is there height difference in spring perch? I imagine the Rio strut is longer. I am on a learning curve here. I have been wanting to check out the Rio's, haven't yet.

P.S.
How did you find the # rating of the springs?

I put the Festy KYB next to the Rio KYB. Exact same spring perch height. I looked at the top pieces too. Didn't see anything obvious that would explain why both were 26" on the car. But I didn't drive it with either uncut spring on it; I only drove with the cut springs. So maybe the uncut ones would have settled down somewhat, but definitely not to 23 7/8".

In a thread called "Spring rate calculator", zoom zoom posted spring info. I'll try to find it again and add the link.
Here it is; see post #5: spring rate calculator

[bhazard]

The Rio struts are too long. Charlie can chime in on this.

[drddan]

Aw, I screwed up those numbers! 574 and 537 are incorrect. Its late, i'm going to bed before I make it worse

images0SCEDIM2.jpg

[TominMO]

The Rio struts are too long. Charlie can chime in on this.

Since the spring perch height is the same, I'm thinking what is too long is the travel of the rod itself? How does that affect spring action? I wonder if I can use washers on top as spacers (between the two top pieces) to give more compression, if that is the problem?

But how can it be too long? By cutting the spring, I ended up with 1" less overall ride height.

[Gomez]

He means extended length is to long. That will effect handling several different ways but not ride height.

[TominMO]

He means extended length is to long. That will effect handling several different ways but not ride height.

OK, didn't know the term but that makes sense. What I don't understand is how that would affect handling. With appropriate-length springs, and the sprung weight bearing down on the strut from the top mount, how does it matter? Plus, my Festy springs should have a higher spring rate now that two coils have been removed. I was expecting a much better ride, with heavier damping (since the strut was designed for a heavier car) and somewhat-stiffer springs, maybe 120ish lbs.

The Rio springs are shorter than the stock Festy ones, so with longer strut action i would think they would need longer springs--or stiffer ones, which the Rio has. I'm thinking I might be able to make this work by cutting maybe one coil off the Rio springs. Still would like to hear Charlie's input tho; might save me a lot of wasted time. Good learning experience too.

My Festy KYBs are still good. I wonder if the best setup is to use them, with maybe early Miata front springs, either cut or uncut? Anyone know anything about this?

Edit: looking at Miata front struts on RockAuto, I wonder if they can be used on the Festy rear? There is an adjustable KYB that looks like it would be fun to have.

[TominMO]

A useful thread on Miata springs.

A Miata sport parts website, GoMiata.com.

The KYB AGX 90-97 Miata front shock, as a possibility for the Fespire rear. It's $87 at Rock Auto. I'm thinking Festy/Aspire front spring. Not sure about the spring perch height, considering wider tires, and maybe it has too-long travel IDK, but it would be exciting if it worked!

[drddan]

Coil spring calculator

http://www.therangerstation.com/tech...ringrate.shtml

[TominMO]

Nice find! Do the springs have to be clean when calculating the rate?

[Advancedynamix]

I haven't looked at Rio shocks, but if the extended length is longer than a Festiva, you'll want a longer than stock spring, with a softer initial spring rate. This allows for the spring to compress more and settle in at the desired ride height. The spring rate rises as the spring is compressed, so the dynamic rate will be similar.
When you cut a spring you not only raise the initial rate, but you also quicken the ratio at which the rate rises. This is what you are feeling when driving the car. You don't feel the initial spring rate.
In other words. A 100lb spring and a 200lb spring can both deliver the same 250lb dynamic spring rate on the vehicle. The 100lb spring will just need more compression to get there. If the 100lb spring has less windings than the 200lb spring, it may actually offer a stiffer ride because it's rate rises faster than the 200lb spring.
All of this spring talk though is useless without understanding that the springs are not what is most influential to control of weight transfer. The shock valving itself is what will give you the ride quality and vehicle control you desire. All to often, the emphasis is given to spring rates and sway bars and the most important part of the equation is ignored.

[TominMO]

Thanks for the tutorial, Charlie. IIRC the extended length of both the Rio and Festy KYBs was the same. I will re-check. The Rio strut was definitely bottoming on even small irregularities, due to the missing two Festy coils. I will try cutting one Aspire coil, and one Rio coil, to experiment further. I'm only guessing on the Rio's strut having stiffer valving, based on the Rio being heavier, and the strut having a thicker shaft. But first I will try a stock uncut Aspire coil, and test-drive it before moving on to the next test. That will give it opportunity to settle in to its natural ride height, something I didn't realize earlier that I should do.

[Advancedynamix]

You can roughly guestimate valving by pushing and pulling the shock shaft by hand. Strangely enough, I prefer this than the figures I get from the dyno tests. But then again, I prefer to tune by feel.