The Strut thread - Koni / Illumina / Tokico / Carrera / Bilstein / Ground Control

[clarkspeed]

I think that's what he is saying. Tune to the temps, and you will end up about a degree "less camber" in the rear. (ex. -3 Deg F, -2 Deg R). Seems about right.

[heavy85]

Quick update (if you go back several pages) - the new Koni single adjustables feel very good both on the street and autox w/ 225F/250R springs. They actually seem smoother and less harsh than my old Illumina's. Between those and the slicks my car is now way faster than I am - now if my driving skills could just keep up. The two autox's this year I've been 2nd (behind SS Z06 who almost always gets FTDI) and 3rd (behind BM Lola and same Z06) in overall raw times and in the top 20% of PAX running a very streetable FP set-up so I'm very happy with the results so far.

 

Cameron

[johnc]

They actually seem smoother and less harsh than my old Illumina's.

 

Exactly! Street performance shocks (like the Tokico Illuminas) are designed to work with OEM or slightly stiffer springs so the increase in compression damping helps a bit. But, when you significantly increase spring rates (doubling them in this case) the increased compression damping hurts handling.

 

Because the single adjustable Koni's only adjust rebound damping, the compression damping remains the same. The Tokico Illuminas are a typical "street" performance shock where both compresion and rebound damping are increased as the adjustments are turned up. The give that driver that "stiff performance feel" but actually make the suspension less compliant, especially when the spring rates are raised.

[Wiisass]

Alright, I read through this whole thread last night, and I know I'm going to miss some stuff, but I did catch a couple mistakes. First off, it's a good guide for struts, I'm currently looking to put something together for another macp car and have been searching for take apart struts. Or at least a monotube strut that I could easily rebuild/revalve.

 

But a couple things that I noticed. Someone mentioned that they thought the HTS plot was in lbs on the y-scale and meters per second on the x-axis. I think that the y-scale is in newtons /10. Which would make the upper limit of the rebound side around 4000 newtons. This makes much more sense if you work out the numbers. Using 400lbs at 0.6mps would only get you a damping coefficient of somewhere around 16, while using 4000N at 0.6mps would get you a coefficient of 38lb/in/s. Which is a much more reasonable value especially if people are trying to run higher spring rates with.

 

Another thing, someone mentioned about the installation ratios and their effect on spring rates. Installation ratio is the ratio of the displacement of the spring/shock/roll bar versus the displacement of the wheel center. When it comes to comparing the spring rate or damping coefficient of the shock/damper to the equivalent rate at the wheel center, the installation ratio needs to be squared. This is important in order to calculate the wheel rate. So for example, you have a 1000lb/in spring with a 0.9 installation ratio. The spring will move 0.9 inches for every inch of wheel travel, but will have a rate of 810lb/in at the wheel center. This rate is known as the wheel rate and allows people to compare different vehicles more objectively. This wheel rate along with the sprung mass value allows you to calculate the natural frequency of the corner. The tire rate also needs to be included in this to get a better idea, but that adds another big variable.

 

Calculating the natural frequencies of the sprung mass is a way of normalizing the suspension model against other cars. Common values for the natural frequency that are important for racers are around 2.0-2.5Hz. The lower end of this is the upper limit of factory sports cars. The range above 3Hz is more reserved for race cars with full aero. The higher the natural frequency, the stiffer the car is.

 

I was wondering if anyone had physically measured the front and rear installation ratios of a 240Z? Also, what are common weights and distributions for the car? What's the normal unsprung weight at each corner? Also, I noticed that 225/250 seems to be a common spring rate upgrade, why is that? Is it just what several people have run with success or are there more reasons behind it.

 

You guys seem to have a really good discussion going, I would just like to keep it going and maybe even get more and more in depth if you guys are ready.

 

Tim

[JMortensen]

I can't address much of that, but the 225/250 I think I can explain. There are not too many struts available for old Z cars, and probably the best street car strut is the Tokico Illumina. It tops out at about 250 lbs, any more than that and there is a tendency to blow out the seals. 225 in front because Z's will turn in better with a lower front spring rate. I run 200/250, there are lots of guys running in the 175/225 or 175/200 range as well. It's not the best for racing, but it is about as stiff as most people want for a street car.

[johnc]

Erik Messley measured the installation ratios using some suspension geometry software. His numbers were .97 and .98 but I don't remember which is front or rear.

 

Also, I noticed that 225/250 seems to be a common spring rate upgrade, why is that? Is it just what several people have run with success or are there more reasons behind it.

 

That's a common rate recommended for a multi-purpose 240z (autocross, street, track) and its used often because its near the upper limit for the readily available (and cheap) Tokico Illumina shocks. More typical spring rates for track only 240Zs are in the low to mid 300s using Koni, Bilstien, Carrera, or Penske shocks. I do remember an old time CP racer claiming he was running 600 lb. in. springs on his car but he is the oulier in my small sample.

 

These spring rate numbers were worked out decades ago and most folks now use monkey-see, monkey-do engineering or a lot of track testing.

[Mikelly]

So I'm gonna order the koni singles this week. Who has the best price and availability guys???

 

Mike

[mom'sZ]

Who has the best price and availability guys

I got mine from shox.com... I think about 130$ a piece

[johnc]

Also try Summit Racing. Give them the Koni part number (8610-1437RACE).

[Doug71zt]

Will the 8610-1437RACE require revalving or are they good to go out of the box for a street/strip/track car (in that order)? I'm running 175/200 with the sectioned-tube Illuminas in my 71ZT and am not too happy with the impact harshness that it has now with 225/45/17's. I am also going to take a step back on the bars to 25mm on the front and a 17mm on the back. It has a monster 28mm bar on the front now. Down to a 16 inch wheel also, with more rubber on the rear.

 

John - I'm curious why you are going with the Tokicos on your personal car instead of the Konis?

 

Thanks for this thread - It has definitely helped me out to understand why I am unhappy with my current setup.

 

Doug

[johnc]

Will the 8610-1437RACE require revalving or are they good to go out of the box for a street/strip/track car (in that order)?

 

With the spring rate you mention the rebound valving will probably be too stiff even at its lowest setting. The shock might tend to pack down the spring over a series of bumps on the street.

 

John - I'm curious why you are going with the Tokicos on your personal car instead of the Konis?

 

The spring rates (too low a rate for the Konis) and the price.

[JustinOlson]

Has anyone tried the P30-0032 Bilstein without revalving for a dual purpose street/track car? I'm thinking of trying them out with 225lb Front and 250lb rear springs. For the money I could always have them revalved if that doesn't work right.

 

Regards,

Justin

[katman]

I'd proly go with an Illumina and slightly lower spring rates for a dual pupose car.

[JustinOlson]

The only real street driving my car sees is driving to the track and to the grocery store once a week. I'm looking at either doing Koni 8611 double adjustables, AZC big shaft suspension or bilsteins.

[johnc]

You're kind of in this no-man's-land regarding shock choices. Spring rates in the mid 200s are "in-between" a full track setup where the Konis/Bilstiens start working well and where the Tokicos stop working well.

 

You can revalve the Konis/Bilstiens to get them to work at the spring rates you're selected. Talk with Koni and Bilstien directly and give them all the information you can about your car. They will make some recommendations and probably charge about $100 per shock.

[katman]

John's right, of course, you're a "tweener". And Koni/Bilstein will proly not want to put in the time to really figure out what you need- they're dig up some ole full race or hot street recommendations. Face it, we're talking old cars. I'll offer up my "old guy who spends more time in a Caravan than a Z" opinion again: For anything that doesn't get to the track on a trailer, I'd err on the side of soft and here's why.

 

First, I've /owned/driven/built several nice 240Z's that were in the 115R/145R-185F/185R range with typical "other" street mods on several race tracks at various times and have had as much or more fun as I have in a full out ITS car. And been nearly as fast. Tires have more to do with cornering speed than another 50-100 in/lbs of spring at the level of driving most people we be doing on "track days".

 

Second, it's a lot easier to get up to speed during a weekend in a softer car than a stiffer car. It might not be the ultimate potential of your car, but let's be realistic about the point of a track day. Fun, not tenths.

 

Third: shocks for a streetable car are easier to come by, cheaper, and not as critical as shocks for a stiffer car. I doubt anybody in the 200-250 range really has the shocks that are "best" or appropriate. I bet damn few ITS racers are capable of knowing what they have or need either.

 

Fourth: I don't like the long term affects that stiff springs have on Z chassis' and other parts. The shock loads are huge (for the right shock).

 

and finally: If the vavling isn't spot on, and you're actually good enough to know it, you're in for another revalving, and maybe another... [aside: this really really pissed me off when SCCA caved to the class whiners and outlawed remote reservior adjustable shocks for ITS].

[JustinOlson]

Thanks for the advice from those that have been there and done that. I guess I should just start out with some cheap "street" shocks and go as far as I can with them.

 

Now, another topic, lightening up the strut tubes. Have people gone to lighter thinner walled material for the strut tubes? How about going to a strut tube that is thread the whole length to eliminate the need for sleeves. Has anyone machined lighter hubs and such. When I was at Rusch motorsports I picked up a sectioned strut tube and that thing was heavy as hell without the brakes caliper or rotor attached. I think on a "no rules" car you could take a lot of weight of the suspension pieces.

 

Regards,

Justin

[johnc]

Now, another topic, lightening up the strut tubes.

 

The castings are the heavy part, not the tubes. When I built the Penske setup I used the Penske steel threaded shock bodies instead of the aluminum ones based on Penske's recommendation so I would be reluctant to shave down the strut tubes.

 

Is the car you're building an engineering exercise?

[74_5.0L_Z]

Be careful with that last statement. Don't be too cheap. Stay away from the KYB gas struts. They are cheap, but are way too stiff in bump and too loose in rebound.

 

I am using the Koni 8610-1149 with 250 lb/in rear/ 200 lb/in front. I don't find the ride very harsh, although I don't drive it on the street very much.

 

If your going cheap then get the cheap konis or illuminas.

[JustinOlson]

The castings are the heavy part' date=' not the tubes. When I built the Penske setup I used the Penske steel threaded shock bodies instead of the aluminum ones based on Penske's recommendation so I would be reluctant to shave down the strut tubes.

 

Is the car you're building an engineering exercise?[/quote']

Well, every car I have ends up being an engineering exercise. I just like to look at all kinds of different angles and try to do things differently.

 

So what can we do about the castings? CNC aluminum anyone?