Cutting my Festy's springs

[Dragonhealer]

How long are stock rear Miata springs? Measured just sitting on the ground. Same diameter as the Festy's?

BTW, when the VW KYBs came in they had very short, hard bumpers and a short, hard, smooth cover, not a bellows type. They are inadequate. Get the SB118.

The early Miata rear springs, paint code yellow/yellow, 1990-1993, are 9-1/2 turns absolute, 8-1/2 turns working, of 10mm coil stock. ID is apx 3-1/4, OD apx 4-1/8, a snug fit in the Festiva perch. Free lengh is apx 14-1/2, as fitted to Miata under load apx 8" as fitted to rear of Festiva apx 10-1/2
Best setup for this includes strut bump stop 1J0 512 131B from Rockauto.
use 65 to 90lbs. Toung weight, rear cabin ok to +300 lbs.


+1 Tom!

[TominMO]

What is Ryal's screen name? What is the rate of the rear Miata springs? I think the fronts are ~140, so I'm guessing ~110 for the rears.

[Advancedynamix]

Ryal is the man to answer that question. I am pretty sure they are the same diameter as festy/aspire springs. Ryal has them on his 91 that he uses to tow race cars and garbage around (trashwagon).

[TominMO]

Good stuff here! Another note too. Miata rear springs are a heavier rate than the aspire rear springs. This is helpful info if you tow heavy loads with your Aspire or Festiva. This info is courtesy of Dragonhealer.

How long are stock rear Miata springs? Measured just sitting on the ground. Same diameter as the Festy's?

BTW, when the VW KYBs came in they had very short, hard bumpers and a short, hard, smooth cover, not a bellows type. They are inadequate. Get the SB118.

[Advancedynamix]

Good stuff here! Another note too. Miata rear springs are a heavier rate than the aspire rear springs. This is helpful info if you tow heavy loads with your Aspire or Festiva. This info is courtesy of Dragonhealer.

[TominMO]

My VW KYBs ('91 Cabriolet, $33 each) came in today, so off to the McParts store to find a short exhaust pipe piece to raise the spring perch. The KYBs are built differently than the Bilsteins. The Bilstein body is 2" diameter, the KYB's is 1.5". The proper pipe turned out to be 1 5/8" ID; but it needs to be flared at the bottom for a proper fit, and shortened an inch or two at the other end. I will take it to an exhaust place to have them flared, along with the strut for test-fitting as we go. They can probably cut it easier and more precisely than I can, so I'll probably have them do that too. I'm guessing $10 total; we'll see. Pics tmw or Fri. The two pipe pieces cost me ~$7.

It occurred to me that I could just squeeze the bottom of the extension pipe I used on the Bilsteins, to get it to fit on there without using the spare spring perch, which looks tacky. Might try doing that by using an exhaust U-bolt fastener to squeeze it.

The bottom of the VW KYB is quite different from what we are used to on the Festy rear struts. There is a long metal tube sticking out of each side of the narrow rubber piece at the bottom of the strut. As Charlie says, cut 1/8" off the side that will go to the inside of the car, for more clearance. You could even cut more and use washers on the other side for a few mm more clearance, like he also said.

The spring perch KYB provides is perfect. Like the Bilstein's, you install it "upside down" compared to what our spring perches look like.

For all Festy front and rear struts of any brand, strongly recommend the KYB SB118 strut bumper and bellow. These are the good German ones. I tried it on the VW Bilsteins and KYBs, a Festy front KYB, and a Festy rear Monroe. It works well with all of them and easily fits inside both front and rear springs. Long bumper and long bellows keep out the water and grit from the strut shaft; and the bore of the bumper is large enough to fit all of these struts. On rear-strut applications, I used an extra rubber upper mount donut thingy to space the bumper/bellows assembly downward enough to put a little compression on the bellows, so it stayed permanently below the bottom of the shaft. For fitting onto the front struts, you might want to cut the topmost section (of four) off the bumper; it seems a bit long for the front. At Rock Auto, they list the SB118 for these cars. It's under $14.

MAZDA	323	(1986 - 1994)
MAZDA	MX-3	(1992 - 1995)
MAZDA	PROTEGE	(1990 - 1998)
NISSAN	ROGUE	(2008 - 2012)

[TominMO]

Just ordered the two VW KYB Gr2s for my Aspire. Gonna leave the stock tires on (155/80-13 Kumho Solus KR21), which will give me a direct comparison of the effect of the struts with no other changes. After trying this out, I will then cut the front springs one coil, to lower the front as well.

[Advancedynamix]

Yeah, kyb uses a thicker sleeve than that clip on the bilsteins. It should hold your spacer better and you won't need the other perch. If you buy 2 and they don't work I'll buy them from you. Running 2 completely different setups on the back is not really safe. The shocks are drastically different lengths and dampening rates. Under braking (when the rear becomes light) it could cause the car to drift heavily to one side. In an emergency, this could be a disaster waiting to happen.

[TominMO]

I don't know if you'd want to just use 1. Lol. The mismatch may give a very unbalanced ride. 33 bucks a shock is a great deal btw. Kyb shocks seem to last forever too.

Yeah, I wasn't going to use just one, but didn't want to invest in two if I couldn't make it work. But the more I think about it, it should work fine even with just one spring perch. The right size of connector tube would fit under the perch, raising it to a usable height. KYB does this differently than Bilstein. But we'll see. I'm gonna order it. One of my rear Festy KYBs on the Aspire puked its oil out after a few years, which is why I stuck a Monroe in there temporarily. But my front Festiva KYBs on the Festy are still good after five years or so. I just put the Rio struts on as an upgrade, and will save the used KYBs for the Aspire, which also has them, when they go out.

[Advancedynamix]

I don't know if you'd want to just use 1. Lol. The mismatch may give a very unbalanced ride. 33 bucks a shock is a great deal btw. Kyb shocks seem to last forever too.

[TominMO]

I can vouch for the vw kyb gas adjusts, they work really well. I bet that even the cheapest replacement VW shocks will be an improvement over the stock fitment Festiva shocks (unless you don't want to lower the car, then stick with the stock stuff). Bilstein has a lifetime warranty though.... haha

The rear KYB GR2/Excel-G strut for a 91 VW Cabriolet, part #341007, is only $33 at Rock Auto. It appears to come with a new bump stop and cover too. This sounds like another very good way to go. I think you could use the exhaust-connector method on this one, to raise the stock spring a bit. I might order one for my Aspire to check this out. One of the rear Festy KYBs on the Aspire died, and I replaced it temporarily with an almost-new Monroe I had laying around, which came off Matthew when I scrapped him. The Aspire already has skinny tires (155/80-13s) on Aspire alloys.

[Advancedynamix]

I can vouch for the vw kyb gas adjusts, they work really well. I bet that even the cheapest replacement VW shocks will be an improvement over the stock fitment Festiva shocks (unless you don't want to lower the car, then stick with the stock stuff). Bilstein has a lifetime warranty though.... haha

Why must I spread some rep around before giving it to Tom again? That's dumb!

[TominMO]

There is a big problem with lowering the car on factory rear struts. Even with stiffer springs you'll get more body roll. This is because the shocks have too much sag. The inside shock will work with inertia to lift the inside of the car and remove valuable weight/traction from the inside front wheel. The biggest advantage to the VW setup is that they are nearly 3" shorter than stock fitment Festiva/aspire Shocks. That means 3" less sag, which controls the body roll without the use of stiffer springs and sway bars. It also places the shock in it's appropriate working range. Lowering the car on stock length dampers adjusts the static ride height into the incorrect portion of the shock travel for correct dampening.
I tested stock fitment kyb gr2 shocks with cut springs to lower the car and I then cut 3" out of the shafts of those same shocks. The difference is astonishing. The valving is also extremely important, but if your travel is working against you then you're fighting a losing battle. Bilstein shocks have variable valving built in. They sort of auto adjust. I've thrown out plenty of double adjust dampers in favor of non adjustable bilsteins and have never regretted it.

OK then. Everybody just buy Bilsteins. But the VW KYBs should still be pretty good too, given that they are physically just like the Bilsteins. The valving will be different of course, but still.

[Advancedynamix]

There is a big problem with lowering the car on factory rear struts. Even with stiffer springs you'll get more body roll. This is because the shocks have too much sag. The inside shock will work with inertia to lift the inside of the car and remove valuable weight/traction from the inside front wheel. The biggest advantage to the VW setup is that they are nearly 3" shorter than stock fitment Festiva/aspire Shocks. That means 3" less sag, which controls the body roll without the use of stiffer springs and sway bars. It also places the shock in it's appropriate working range. Lowering the car on stock length dampers adjusts the static ride height into the incorrect portion of the shock travel for correct dampening.
I tested stock fitment kyb gr2 shocks with cut springs to lower the car and I then cut 3" out of the shafts of those same shocks. The difference is astonishing. The valving is also extremely important, but if your travel is working against you then you're fighting a losing battle. Bilstein shocks have variable valving built in. They sort of auto adjust. I've thrown out plenty of double adjust dampers in favor of non adjustable bilsteins and have never regretted it.

[TominMO]

Tom did you have to "narrow" these shocks at the bottom like the kyb's ? I was going to go kyb's but if these don't need modding I may go this route.

Yes, about 1/16" on each side. It will be the same with the VW KYBs. The KYBs are about half the price, and no doubt also do a good job. It would be interesting to compare the two.

I think the easiest/cheapest solution, bang-for-buckwise, would be Festy rear KYBs; cut the spring 1.5 coils at the bottom; install good long bump stops to protect against bottoming. That would give you a body lower than stock, comparable to what I have, with a slightly stiffer spring rate, and decent struts. They won't be Bilsteins, but a good inexpensive upgrade. Get the same tires I have, which will easily clear any Festy or Aspire rear strut without a spacer.