Cutting my Festy's springs

[Festiva_Fred]

Good info!

[Advancedynamix]

Suspension tuning on these cars can be very rewarding. Many people will never know how incredible the WA (Festiva) chassis is. The suspension that came on these cars was tuned for third world roads on 12" wheels. It is so far off the mark that just about anything improves it.

[Advancedynamix]

Also, I don't think Miata shocks will fit a Festiva without lots of work. I was helping set up an NA last weekend, so I've had my hands on a few sets of them. The MK1 VW shocks are your best bet from what I have seen. The MK1 VW is a great choice as well because it has a very similar suspension setup to the Festiva, so you are getting a shock which is valved properly for a trailing beam.

[TominMO]

Also, you may want to experiment with quality rising rate bump stops, like those made for German cars. The bump stop can be used as a supplemental rising rate spring to aid in bottoming resistance. Febi/bilstein makes the best quality ones that I've seen.

Ah, good tip and reminder.

[Advancedynamix]

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.

Also, you may want to experiment with quality rising rate bump stops, like those made for German cars. The bump stop can be used as a supplemental rising rate spring to aid in bottoming resistance. Febi/bilstein makes the best quality ones that I've seen.

[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.

[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]

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]

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

[drddan]

Coil spring calculator

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

[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!

[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.

[Gomez]

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

[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.

[drddan]

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

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