Ultimate Street suspension guide

[bhazard]

Quick question this doesn't relate to the quote I'm using but you shortened the length of the shock what 3"? How did you shorten this the bit of info I just can't find

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Most of the info in this thread is obsolete. The current technique is to use the rear struts for a mk1 VW rabbit/golf. They are already shorter.

[Festiver]

I was only saying that comparing 2 completely different spring designs by the pressure rating confuses the issue. A bulk of the questions I get concerning peoples suspension setup is based on this confusion that spring rate numbers are the only thing to consider when choosing a spring. The only reason I can recommend the rates that I do with the Southwest speed springs, is because I've tested everything from 105-200 lb of their particular spring product on several Festivas. That doesn't mean I know what x (insert other random kind of spring) will behave like on x (insert other random shock absorber). When people use my spring rate suggestions to select other springs to put on another type of shock, they are on their own. I can only vouch for the products I have personally tested.
The Miata springs you have been using seem to work great with the stock replacement KYB aspire shocks that you have been using. They may also work with the VW mk1 kyb shocks, except you won't have enough tire clearance for the large tires that you run. I theorize that a set of 150lb Southwest speed springs on the VW KYB shocks will work as well, or better than the setup your running, but we won't know until you try it. I fear that this setup will have too low a ride height for your liking though. The 150lb 1 7/8 springs on stock replacement KYB shocks are a little bouncy. That is what is on Tweak, and you've seen the difference first hand on a track. Towing a trailer may not yeild the same results though.

Quick question this doesn't relate to the quote I'm using but you shortened the length of the shock what 3"? How did you shorten this the bit of info I just can't find

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[Dragonhealer]

I think you are right to both, will machine up a pair of tophats to compensate for the shorter spring. Anxious to see the difference with the VW shock.
The extra advantage of lowering the rear when unladen would be cool too!

[Advancedynamix]

I was only saying that comparing 2 completely different spring designs by the pressure rating confuses the issue. A bulk of the questions I get concerning peoples suspension setup is based on this confusion that spring rate numbers are the only thing to consider when choosing a spring. The only reason I can recommend the rates that I do with the Southwest speed springs, is because I've tested everything from 105-200 lb of their particular spring product on several Festivas. That doesn't mean I know what x (insert other random kind of spring) will behave like on x (insert other random shock absorber). When people use my spring rate suggestions to select other springs to put on another type of shock, they are on their own. I can only vouch for the products I have personally tested.
The Miata springs you have been using seem to work great with the stock replacement KYB aspire shocks that you have been using. They may also work with the VW mk1 kyb shocks, except you won't have enough tire clearance for the large tires that you run. I theorize that a set of 150lb Southwest speed springs on the VW KYB shocks will work as well, or better than the setup your running, but we won't know until you try it. I fear that this setup will have too low a ride height for your liking though. The 150lb 1 7/8 springs on stock replacement KYB shocks are a little bouncy. That is what is on Tweak, and you've seen the difference first hand on a track. Towing a trailer may not yeild the same results though.

[Dragonhealer]

Still apples and bananas, I know. 10" vs 12", small diameter spring vs large diameter spring, small coil stock vs much heaver coil stock, high energy density vs much lower energy density. But at 12% difference, I thought it worth a try. Scratch the 12%, there is a square function in the density formula. but the spring frequency should be within 12% or so, and the loaded ride height (and associated bump and rebound travel) are about right.

Just not sure why it works!

[Dragonhealer]

Perhaps so, my memory ain't what it once was, but I'll bet I put the NB Miata front springs in the rear of Rosie after you posted this, from: Advanced Suspension Mods, Post #435; (bold added for clarity)

http://i1094.photobucket.com/albums/i443/advancedynamix/NCM_0992_zpspjfbttdi.jpg

Then I use a 10" long 1 7/8 diameter springs from southwest speed.
I used 105lb springs on this car, as a test. This spring will allow for 7" wide wheels and 4 degrees of negative camber in the back, while still being able to ride 4 or more inches lower than stock. For a car that's only running 2-3" lower, with a typical festiva load, I'd suggest 120lb springs. For a car being used to tow or carry extra weight in the back I suggest 150lb springs.

The base spring rate effects the rate at which the spring rate rises. Running too stiff a base rate will cause the car to ride too high and feel stiff and bouncy. These VW shocks have a lot of rebound dampening, so 150lb springs won't feel bouncy, but they will give a very firm ride and could cause the car to tend to drift.

Last edited by Advancedynamix; 10-21-2015 at 10:29 AM.

[Advancedynamix]

Thanks Charlie, a timely warning.
Can you just delete this post to avoid confusion in what is a great thread?

I'd rather leave it. You brought up a great point, that needs to be discussed. Spring tuning is not a "paint by numbers" picture. You and I have dealt with this many times on race cars, but most people don't hear the facts about chassis tuning.
Your suggestion is extremely valuable. You've really dialed in a Festiva for towing. I am amazed that you safely tow loads that outweigh the car your using to tow with, at freeway speeds, in the middle of the desert! I've seen it work, time and time again, and it never ceases to drop my jaw. Your setup is perfect for Ryan, or anyone else who wants to tow a heavy load over rough terrain. It does fall into the category of "ultimate suspension".

[Dragonhealer]

Thanks Charlie, a timely warning.
Can you just delete this post to avoid confusion in what is a great thread?

[Advancedynamix]

85/150 for 2500 pound trailer?
Ryanprins13 asked me what I had set up on Rosie to tow a vastly overweight load, and I wasn't sure so I took it apart and measured.
Suprised me too, towing it is very solid, but feels nervous when empty and a little dicey.
Aspire swap front and rear,
front and rear struts are GR2's for Festiva, front spring is Festiva 85lb/in, rear spring is 1999/2000 Miata FRONT spring 150lb/in with the long VW bump stop which adds to spring rate after 1 inch of travel .
I'm not sure why this works, less weight on the front axel when 400 pounds on the hitch?

This does not apply to the springs we use on these coilovers.
Spring rate numbers can be very confusing. The rate numbers are meaningless without a full explanation of the springs (ie wire diameter, distance between coils, length of spring, and winding diameter.) A 150lb rear 1 7/8 I.D. spring will be behave much differently than a 150lb OEM spring because the 2 springs are different shape, length and diameter, as well as being made of different wire.
The spring rate tells very little about the actual tension of the spring when installed and compressed, or how it will behave when compressed 4 or 5 inches. We should never use rate alone to compare 2 completely different spring designs, because this is misleading, and will confuse people.

[Dragonhealer]

120/105 with stock engine placement. 150/105 for g series.

150/120 for heavy loads.

85/150 for 2500 pound trailer?
Ryanprins13 asked me what I had set up on Rosie to tow a vastly overweight load, and I wasn't sure so I took it apart and measured.
Suprised me too, towing it is very solid, but feels nervous when empty and a little dicey.
Aspire swap front and rear,
front and rear struts are GR2's for Festiva, front spring is Festiva 85lb/in, rear spring is 1999/2000 Miata FRONT spring 150lb/in with the long VW bump stop which adds to spring rate after 1 inch of travel .
I'm not sure why this works, less weight on the front axel when 400 pounds on the hitch?

[Advancedynamix]

I've seen those on my Festivas too. They do go between the strut mount and the body of the car.

[bravekozak]

Why were these gaskets only available on Aspires?
Do they go in between the top hat and tower?

[Advancedynamix]

That pretty much explains it! Thanks a lot! I'm surprised the front coilover valving matches up the rear so well too.

Yes, we are really lucky here too. The length and valving rates work better on the Festiva with these light spring rates than they do on the VW cars with the springs they come with. Lol. I've driven more than one VW on Raceland coilovers, and they aren't very impressive. The spring rates are too high and the valving is too soft for the MK2 and way too soft for the MK3. Kinda funny how they are perfectly matched for a car that these companies don't make a shock for. We're also very lucky that these are the cheapest threaded body coilovers for any car anywhere. Try to find a 200 dollar set of coilovers, brand new with free shipping! Ha! And the quality of the parts is on par with much more expensive setups.
I just hope the price keeps going down and we don't lose this source any time soon. With proposed terrifs on imported goods, I have a feeling this is going to be the lowest price we will see ever again though. I don't even know how they make these things and ship them so cheap.

[chrisofna]

That pretty much explains it! Thanks a lot! I'm surprised the front coilover valving matches up the rear so well too.

[Advancedynamix]

^ yeah, they are a lot longer.

So here is the deal with the MK1 vw rear KYB shocks and why they are a lot better than a threaded body coilovers for our cars;
1. The length does matter.
The stock (Aspire/Festiva) fitment KYB shocks are not a bad match for the Festiva, but they are too long. Even at the stock ride height, the stock shocks have too much droop distance (The distance the suspension drops when you raise the car). This droop is the number 1 cause of excessive and uncontrolled body roll. Reducing the droop, will reduce the body roll without the need for stiffer springs or anti roll bar. This means you can have a nice soft ride and still rail corners like a slot car. The mk2 rear coilovers are actually longer than the stock Festiva shocks, so that means they are worse than stock. The mk1 golf KYB shocks are about 3" shorter than stock FESTIVA shocks, which is just right for most street cars and track cars.
2: Girth isn't helpful in the rear.
The rear threaded body coilovers use 60mm springs. These springs take up valuable room that we need for our tires. These cars don't have much room in the rear wheel arches and wider springs, on wider shocks is a lose lose situation.
The KYB Mk1 vw shocks are very thin, and that allows us to fit the small body adjuster sleeves on them so we can use the skinny 1 7/8 diameter springs. This means we have enough room to fit wider wheels and tires if we want to. This is very important if you want to put track tires on your car, as the only commonly available size that fits the fenders of a Festiva (sorta) is 185/60-13.
3.Control that motion.
The shock valving of the MK1 VW KYB shocks is good. I mean it's really really good. It's by total coincidence that these parts work so well together, but they do. I've driven a lot of professionally set up race cars and this combo never ceases to impress me. We got lucky here. You can build rear shocks for your car for under 200 bucks that make a bigger difference than paying Moton to build 10,000 dollar shocks for your GT3rsr. Yes, I've driven both. No, I don't get kickbacks from KYB or southwest speed. I do get my kicks from this setup though.
4: Throwing the weight around.
These cars benifit greatly from reducing weight in the rear end. Sir Mix a Lot wouldn't like going all out in a Festy, but the rest of us love it. The more weight that's in the rear, the more likely the car is to oversteer when pushed to it's limits, and the harder that oversteer is to control.
Oversteer, in a FWD car? What? Ooooooh yes young Skywalker. The force is strong and it will spin you to the dark side if you don't know how to use it. The MK2 (or even MK1, or Tien for the Festiva) rear coilovers are much heavier than the kyb mk1 shocks with small body sleeves and 1 7/8" springs. This setup is lighter than stock. Think of them as double lite sabers. It's like cheating.
5: Fitting all that in there.
The bottom shock mount of the Festiva is about an eight of an inch narrower than the VW. This requires that you grind off almost a quarter inch from one side of the VW mk1 kyb shocks and put the supplied washer/spacer on the other side to space the shock inward. The mk2 coilovers will be harder to fit, because the rubber bushing is too wide and then the shock body hits the beam if it articulates (that's assuming that you're running the suspension high enough for the shocks to even work at all, which would be higher than stock.)