Struts and Springs Buying Guide

[ConchZ]

I've been doing a lot of research on this site and others to decide what combination of struts and springs to get. I've never seen a post that summarizes all the options, so I thought I'd write it up. I'm not an expert on the subject, so this post will be information drawn from the posts of notable experts. I'm hoping that writing this summary will help me organize my thoughts and perhaps draw out some advice on something I'm missing. So...here goes. First off, my car is stock, although it has fully poly bushings. My intended use is street use only. I may someday take my car to the track and get some lessons, but I doubt I'd ever be serious about tracking it. My comments will be geared to this usage.

First, let's discuss ride height - my 240z sits on sagging stock springs, and is already about an inch below stock ride height, at just under 6 inches at the rear of the rocker. I like this height, which is good, because it is the expected drop from most aftermarket springs. Many people experience different ride height results with aftermarket lowering springs. Sometimes this difference is attributable to accidentally swapping the front and rear springs, or even from installing them upside down. Some people think the newer gas charged struts will make a car ride higher, even with lowering springs. I guess results will vary a bit.

Next, let's discuss linear vs progressive rate springs - basically, progressive rate springs get stiffer the more they are compressed, while linear springs do not. The consensus opinion seems to be that progressive rate springs are the most comfortable, but they are not popular for track use because of their unpredictable dampening. Some even say they cause unexpected suspension movement, which results in control difficulty. I think this is only a problem if you are pushing your car to the limits on a track.

Coil Overs - these are available from various sources, in either ready to install kits, or a kit that will require you to do some cutting and welding. Prices run from a few hundred to about $1600, with the cheaper ones not including the struts and camber plate you also need to buy. The advantages of these are that you can adjust ride height, swap out springs, and install wider tires. Coil overs are best for someone who wants to race, and are not necessary for my intended usage.

Arizona Zcar springs - these are the only spring I can find that keeps your stock ride height. They are shorter than stock, but stiffer, so it works out to about the same height. I'm interested in dropping my height below stock, and these are also likely too stiff for my tastes. At 180lbs front and 200lbs rear, I believe they have the stiffest spring rate of all the options, although I can't find any numbers on some of the options.

Suspension Techniques springs - these lower the car about an inch. They are linear rate springs. I can't find the spring rates on these.

Eibach Pro-Kit - these lower the car about an inch. They are progressive rate springs. I can't find the spring rates on these.

Tokico Performance Springs - These lower the car about an inch. Be careful, because these are linear in the back, and progressive in the front. I may like this. The linear in the rear would stop acceleration squat, while the progressive front ones would be more comfortable. Their spring rates are 140lbs front and 165lbs in the rear.

That's it for spring options, so now let's discuss strut options.

KYB - they have one option for a 240, and they say they aren't for use with lowering springs. This rules these out, unless you go with the Arizona springs.

Tokico HP - these are the cheapest strut that will work with lowering springs. They are not adjustable. They are commonly referred to as "Blues".

Tokico Illumina - these work with lowering springs, and are adjustable. A set of them will cost roughly $200 more than the HPs. For that extra $200, you can adjust between 5 firmness settings.

Tokico D-Spec - these work with lowering springs, and are infinitely adjustable. Expensive, though.

Tokico springs and struts can be bought together as a kit, at significant savings. A popular Z-specific vendor that has a complete Tokico selection is Beta Motorsports.

When buying struts, it is important to make sure you get the necessary boots and bump stops. Most boots seem to have a bump stop integrated into them. Some kits seem to come with these boots, and some don't.

A final consideration is whether or not to spring;) for the bump steer spacers, if you are going to use the lowering springs. In terms that I understand, these keep your lower control arm parallel to the ground, which prevents extra under steer at cornering limits. Here's more info on bump steer. They are available from various vendors, and fit between the bottom of the front strut and the control arm. Be aware that many people report that they cause rubbing of the control arm on the inside of a 14 inch wheel (but not on larger wheels). Black Dragon sells some that claim to be ok with a 14 inch wheel. I have 14 inch wheels. I am not sure if want to spend the extra $70 on these, but I probably will unless someone here talks me out of it.

After reading up on lots of threads, here's my current thoughts. I plan to order a Tokico Illumina struts and spring kit and bump steer spacers. I probably don't need the adjustability of the Illumines, but for $200, it'll be a neat thing to play with, I guess. I'll always wonder, if I don't get them.

Did I miss anything that I should be considering? Any corrections or additions to the above information? If so, I'll edit it and we'll end up with a nice buying guide that is written in layman's terms.

Matt

[John Coffey]

Since I was mentioned, let me add some information:

Spring Rates and Shocks

The rebound damping in a shock is closely tied to the spring rate. Shocks, even if they are adjustable, are designed to work within a specific range of spring rates. For our S30s the ranges are:

Tokico HP - stock to 200 lb. in.

Tokico Illumina - stock to 250 lb. in.

Tokico HTS (D-spec) - 150 to 300 lb. in.

Koni 8610-1437 - 225 to 400 lb. in.

Koni 8611-1259 - 225 to 400 lb. in.

Shock Adjustments

Shocks control chassis and suspension movement in two directions: bump (compression) and rebound (extension). They do this primarily through internal valving which in the case of the Koni shocks is rebuildable and can be modified. The valving in some shocks is adjustable (within a fairly narrow range) externally without disassembly. These external adjustments affect high speed compression and rebound and some very expensive shocks (Penske, Ohlins) allow adjustment of low speed operations.

Here's a summary of what the external adjustments affect and my opinions on each:

Tokico Illumina (5 settings) - A linear increase in compression and rebound damping from setting 1 to 5. This is typical of a street performance shock where the car is sprung near stock rates. The increase in compression damping helps give the car a tighter, more responsive feel at the expense of compliance and grip (on bumpy surfaces).

Tokico HTS (7 turns) - A linear increase in rebound damping with a very shallow increase in compression damping. Much better when higher rate springs are used that better control the sprung platform. Compression damping doesn't have to be used as a performance crutch for soft springs.

Koni 8610-1437 (2.5 turns) - A linear increase in rebound damping with no change in compression damping. Even better then the Tokico HTS for the reasons listed above.

Koni 8611-1259 (2.5 turns rebound and I forgot how many clicks on compression) - Double adjustable so that compression and rebound can be adjusted separately. The best of the off the shelf shocks for the S30 and really only used for racing.

Edited October 20, 2009 by John Coffey

[John Coffey]

More IMHO stuff:

Tokico Springs

The Advanced Handling spring kit for the 240Z has progressive front springs that have a working rate of 140 lb. in. and linear rate rear springs at 165 lb. in. This is fine for a basically stock 240Z and its what Tokico designed the spring for. I consider these stock replacement springs.

The Advanced Handling spring kit for the 260/280Z has linear rate springs front and rear with rates of 185 lb. in. front and 200 lb. in. rear. These can also be used on the 240Z but you will most likely have to cut coils to get the ride height where you want it. I consider these (and the Arizona Z Car springs) the first level of spring upgrade for the S30.

Eibach ProKit Springs

Progressive front and rear with working rates estimated at 150 lb. in front and 175 lb. in. rear. Again, these are fine for a basically stock 240Z I consider these a light "sport" upgrade.

Coil Over Springs

Hypercoils, Eibachs, etc. in 2.5" diameter. Rates available from 150 to 2,500 lb. in. in 25 lb. increments and lengths from 5" to 18". For our discussion we are looking at a rate range from 150 to 450. For any spring on a S30 from 150 to 250 lb. in. you'll need a 10" tall spring to keep from coil binding on a big bump or long corner. From 300 lb. in. and above an 8" tall spring works fine. An 8" tall 150 lb. spring as part of a coil over kit to clear big tires is a bad idea.

[Arne]

John, any idea what the appropriate spring rates were for the old Koni 82R-1716/82R-1717 inserts? Did they also just adjust rebound, and leave compression alone? Or how about the 86-1811/1812 set?

[John Coffey]

Don't know, never had one in my hands.

[Arne]

OK, just curious. I suspect those old red part numbers were designed for closer to stock spring rates, but have never been certain. Been considering a set for use with my Euro Stage 1 springs (about 110-120 lbs. rate, IIRC) instead of the KYBs I now use.

[mark belrose]

Since I was mentioned, let me add some information:

Spring Rates and Shocks

The rebound damping in a shock is closely tied to the spring rate. Shocks, even if they are adjustable, are designed to work within a specific range of spring rates. For our S30s the ranges are:

Tokico HP - stock to 200 lb. in.

Tokico Illumina - stock to 250 lb. in.

Tokico HTS (D-spec) - 150 to 300 lb. in.

Koni 8610-1437 - 225 to 400 lb. in.

Koni 8611-1259 - 225 to 400 lb. in.

FYI John I finally gave up on the Advance Design inserts - never could get them to work correctly with any of the 250-325 lb. spring rates I was using. I'm changing over to Koni 8611-1259s next season.

Mark

'70 240Z C Production restored privateer

[jmortensen]

FYI John I finally gave up on the Advance Design inserts - never could get them to work correctly with any of the 250-325 lb. spring rates I was using. I'm changing over to Koni 8611-1259s next season.

What are you going to do with those crappy Advance Design struts then? Just curious.

[motorman7]

Boy I have a lot to say on this issue. One other factor that must be considered is the tires and rims that accompany the spring shock set-up. These also play an important factor in the ride and handling of the car. Another factor is personal preference, of course. I think my son and I are at opposite ends of the spectrum. He wants a car that rides on rails around the race track, and I want a car that I can drive everyday without getting beat up.

Over the last month I have done one tire set change out, and 4 spring configuration changes (yes, that equates to 16 spring swap outs. I am pretty good at it now). All this was done in the effort to produce a decent ride for my daily driver, a 1971 240Z with an L26, 5 speed and LSD. I was looking for something that was both comfortable and yet sporty.

The initial configuration was the Tokico Illumina adjustable struts, Tokico 5020 Springs,195/50 Yokohama H4’s(AA traction Rating) on Konig 14” rewinds, 1” diameter Anti-sway bars front and rear, and front and rear shock tower support bars. In this configuration, the handling of the car was incredible. I could rip around corners way faster than I thought possible and the tires would not chirp or make a sound. The car remained flat and had no problem doing more than double the posted speed limits around turns. The ride was like that of a go kart, very stiff. The negative of this set-up is that I spent most of my time trying to dodge potholes and maneuver around speed bumps during everyday driving. On speed bumps, I would get the occasional scrapping. Bumpy roads were brutal . On some speed bumps, I would bottom out, so had to be very careful in parking lots. So, the car was great down the backroads, but not practical as a daily driver.

The first change, and very significant, was the tire/rim change. I replaced the 14” Konig Rewind set-up with 16” Panasports and 205/60 Yokahama YK520’s (A traction Rating). This was a big improvement as I no longer had to dodge the speed bumps. They also softened the ride up a bit. In spirited driving, however, I could here the tires groan a bit and also felt a bit of mush that I did not feel with the earlier set-up. I also liked the final 5th gear drive ratio for freeway driving. With the ~15% Diameter increase I now am doing about 2800 RPM and 80 MPH (Typical CA freeway speed). This is pretty nice for gas mileage I am thinking. The Konig set-up was doing 70 at 2800 RPM. In spite of the improvements, I still wanted a softer ride. So, I decided to take off the Tokico springs and put on some Suspension Techniques (ST) Sport Springs.

While putting on the ST springs, I was a little spooked by the loose fit of the springs on the fully expanded strut on the fronts. So, I ended up running the ST rear springs in the front (They fit better) and keeping the Tokico springs in the rear. This was not much different than the four Tokico’s and offered no improvement.

After getting some reassurance on the ST spring fit, I installed all 4 on the car. The front of the car sat about the same height as the Tokico’s but the rears sat way low, about 2” lower. The top half of the tire was hidden in the wheel well (wrong springs?). This definitely would not do, so I put in a two inch spacer to get the rear height correct. With this configuration, the ride was a bit softer than the Tokico’s, but not much. Still not what I wanted. Found myself still dodging potholes and large bumps.

Finally, I opted for the stock springs in this set-up. This is what I want! Soft enough to drive every day, but solid enough to take a spirited drive down the long windy roads. It is a very nice compromise. In addition, I can now use the adjustability of the Illumina’s. On all the previous set-ups, I had them on the softest setting (1) . Now I can dial them in. I currently have the fronts set at 3 and rears on 2.

So, just thought I’d share my thoughts on this for anyone interested.

[mark belrose]

What are you going to do with those crappy Advance Design struts then? Just curious.

Jon, I gotta very very good deal for you. Seriously though, they'll probably get put on Ebay; they'll buy anything over there.

Mark

[motorman7]

ST Springs with 2" spacer

[jmortensen]

ST Springs with 2" spacer

You ought to seriously consider returning that poly isolator. It's a bad idea to use polyurethane in that spot. It is too stiff, and requires too much force to change the angle of the strut. Rubber isolators are much better.

Mark, I'll be running spring rates that work better with the AD struts. Let me know when you put them on ebay.