good stiff street suspension? need help and opinions

[Phantom]

You will be absolutely amazed at the difference in handling with your car if you just put in new OEM springs and struts. Your old ones are "sprungs". They are shot. I sent with the european spec Nissan springs that were supposedly 1/4" shorter than stock but they RAISED my car an inch over the original sprungs because they were so sagged. Car hanldes very nicely now - stiff but not harsh.

[260DET]

LedFoot, congrats on your sensible approach. Wish I had done the same instead of learning the hard (expensive) way.

 

Can't really answer your question on wheels although the topic has been discussed on this great forum in the past. The fronts are the problem, particularly if you fit four spot calipers which often require the wheel to be moved out to clear. Which can be easily done by using Datsun 240K hubs which will gain about 10mm 'outset'. In which case with 15" wheels the front guards will usually have to be rolled using tyres around 215 X 60 size. Which is what I have done.

 

So you can see that you need to consider any brake upgrade at the same time. A possible brake solution is to use two spot sliding calipers which may not require more outside clearance so you can use stock Z hubs.

 

Let us know what you come up with if you can.

[Guest LedFoot]

Thanks 260DET,

 

What I'm trying to do is put the largest possible set of tires on that don't require flares. This way the car looks somewhat stock but in reality isn't.

 

The other reason I'm trying to get as much rubber to the rear is that I'm planning to put an Eaton MP90 or Yella Terra supercharger on as well. Now I know that a lot of people will tell me to go for a turbo b/c it's cheaper and they are probably right, but I like the idea of truckloads of tourque and power all the way from the low end. At this stage I conservatively estimate 220-240kw at the rear wheels at around 16psi boost. Therefore I need rubber (lots of it!) and also some beasty brakes!

 

So I'm trying to find out how to get at least a set of 225's on the front, and 240+ on the rear.

 

Time to break out the ruler and graph paper soon! I heard some good tips on setting up front suspension the other day. Apparantly when you put wider tires/wheels on it is important to ensure that you adjust your offset or strut geometry so that the following occurs:

 

1) Draw a line that extends the axis of the strut to the ground. (where the strut points to)

 

2) The point at which this line intersects the tire and the ground should be in the centre of the tire.

 

This is the point on which the wheel pivots. If it is closer to one edge than the other then if an object or bump strikes the side further from the pivot point, it will exert more tourque on the pivot point and therefore pull the steering wheel around harder in your hands. For example if you had your pivot point hard up on the inside edge of the tire and you hit a rockon the outside edge of your tire then the wheel would fight you with twice the force that you would normally get if you had the pivot in the centre.

 

Most of you probably already know this but if not it could be usefull to any newbies (like myself!) who are looking to set up some suspension!

[cygnusx1]

I have Tokico 1" lower springs (200# or 250#), Tokico Illuminas (usually on 1), poly bushes in the front control arms, poly T/C rod and sway bars bushings. Sway bars are Suspension Techniques 1-1/8" Front and 7/8" rear and I use bump-steer spacers. I installed front and rear tower bars. I use 225/50-15 tires and with all that^ it handles AMAZINGLY well on a smooth road. Not much can stay with my Z in the curves. It gives Super neutral and predictable handling. When I encounter bottle caps, I shudder with fear. DON'T go this stiff for just the road! I feel for the unibody. I am planning on taking the suspension stiffness down a notch with easier springs soon.

 

Anyone have any suggestions for a good street spring?

[260DET]

I have Tokico 1" lower springs (200# or 250#)' date=' Tokico Illuminas (usually on 1), poly bushes in the front control arms, poly T/C rod and sway bars bushings. Sway bars are Suspension Techniques 1-1/8" Front and 7/8" rear and I use bump-steer spacers. I installed front and rear tower bars. I use 225/50-15 tires and with all that^ it handles AMAZINGLY well on a smooth road. Not much can stay with my Z in the curves. It gives Super neutral and predictable handling. When I encounter bottle caps, I shudder with fear. DON'T go this stiff for just the road! I feel for the unibody. I am planning on taking the suspension stiffness down a notch with easier springs soon.

 

Anyone have any suggestions for a good street spring?[/quote']

 

There is an assumption in your conclusion ie that it is the springs which are giving you a hard ride. Could I suggest that it is your sway bars that are the problem? Eg you may like to try using a say 22mm stock front bar together with a lighter stock rear bar and keep your existing springs. IMHO a 28mm front bar is way too heavy, it is surprising that when making a sharp fast turn that your front tyres are not at least chirping, or bouncing a bit if the road is a rough or uneven.

[cygnusx1]

With those heavy bars, it does not handle well unless the road is smooth. From what I understand, in order to keep the tires flat on the pavement in a Z, you need to minimize body roll. The Z does not benefit from a modern multi-link suspension so roll causes uneven loading across the contact patch. I do realize that springs can also control roll. So you suggest leaving most of the roll control to the springs rather than the swaybars?

[johnc]

There are generally two schools of though regarding springs/anti-roll bars:

 

Stiff springs, soft anti-roll bars

Soft springs, stiff anti-roll bars

 

Use the first if you've got good shock control (Penskes, Ground Control AD, Koni 8610s, etc.). If you are running off-the-shelf shocks (Tokico Illuminas, KYBs, Bilstiens, etc.) then soften the springs and run bigger anti-roll bars.

 

BTW... Springs under 250 lb. in. are considered soft springs on a racing 240Z.

[Guest 1975yellowBSPZ]

John et all,

My sway bars are what I guess would be considered to be big (1 1/8†front and 7/8†rear) and my springs are 182 lbs ft and 202 rear, This is the standard Suspenstion Techniques setup if anyone was wondering what their specs are. I was affraid from what I have seen on these boards, that I had too much bar (esp in the rear), and the springs would not be stiff enough to be effective in autocross. You said that there is a school of tought that this setup may be effective? I was going to get the tokico adjustables just because they are in my price range currently. Would this setup be workable for a regionally competitive bsp entry, and does anyone know what would I look for in tuning/driving with the stiff bars soft springs type of a setup?

 

Bryan W

[JMortensen]

Tom Holt ran 150 front 250 rear (I think???) for years and was competitive at the national level. I remember thinking "Wow, that's is really really soft in front." I think the key is to get the spring rates set up front to rear in a way that allows you to rotate the car with your driving style.

 

I don't believe that there is a "right" answer for spring rates and sway bars, because so much depends on the driver input, weight of the car, tire size, etc.

 

Unfortunately, changing spring rates isn't as easy when you are running the stock perches, because you are limited to what is out there already. Coilovers gives you a HUGE choice in spring rates, plus added adjustability of ride height and corner weights.

 

I don't know why there is seemingly such a push to use stock or no bars on this list. I can say from personal experience with a 1" front and 3/4" rear bar that I am seriously under barred in front on slicks. My car leans way too much up front, and occasionally picks up a REAR tire in a slalom. It is probably a street vs race thing, my car doesn't lean much on street tires.

 

I think the main issue with running soft springs is you don't want the suspension to bottom from roll, so stiff bars are required to ensure that doesn't happen, or as JohnC said, super stiff springs (but then you need the big $$$ struts to control the springs). Sectioning the struts probably wouldn't be a bad idea either, 1975, but if you're going to that much hassle you might as well switch to coilovers so you can play with the spring rates more easily.

 

As cygnus said, in order to keep the tire patch flat you need to minimize body roll. But you can also decrease camber! I started out autoxing my Z 6 years ago with 1.25 degrees front and 1.5 degrees rear at the advice of a long time autocrosser. Now I am at 3 degrees front and 2.5 degrees rear. Use the pyrometer, use the tire pressures, and if you think your tires are rolling over too far, use some white shoe polish wiped over the edge to see just how far they are going. If they roll onto the sidewall, you can up the air pressure or decrease the camber, or increase the roll stiffness or increase the spring rate.

 

Another $.02,

 

Jon

[johnc]

I don't know why there is seemingly such a push to use stock or no bars on this list. I can say from personal experience with a 1" front and 3/4" rear bar that I am seriously under barred in front on slicks. My car leans way too much up front, and occasionally picks up a REAR tire in a slalom. It is probably a street vs race thing, my car doesn't lean much on street tires.

 

Anti-roll bars turn an indepent suspension into a dependent suspension by affecting both sides when load is applied to the bar. If the load applied is just body roll, then things are OK. But, when the load applied is a bumpy track surface (of which we have lots out here on the West Coast) anti-roll bars reduce compliance and cause conrering/braking problems.

 

With more advanced shock designs moving down to a more "moderate" price range it becomes easier to decouple left and right side suspension with smaller anti-roll bars. Low speed compresison and rebound control on a shock provides better body roll control then anti-roll bars through transitions (corner entry/exit, slaloms, etc.) and working in conjunction with smaller anti-roll bars you can hit the same amount of roll control in steady state corners as a 100% larger (rate, not diameter) anti-roll bar.

 

That's why lots of people are starting to run smaller anti-roll bars. They've just spent lots more money on shocks. FYI... I'm running a 23mm front and a 18mm rear anti-roll bar and I still think they are a little big.

[Guest 1975yellowBSPZ]

Thanks for your input.

As my plan is to switch to coilovers as I get the feel for the car and autocross in general, I am just trying to get the car where it is reasonable for the time being. I have to do some motor work and go tire shopping ($$$$) so I just am trying to band aid the the current suspension until I can justify the coilover setup. I am feeling pretty good about going with the tokicos for now, (unless a coilover set falls into my lap at a deal I can't pass up) and getting everything else in order. Of course The cheaper I can get my motor finished the more options I have...

 

I am new to this car and motorsports, and greatly appreciate all of the input you guys have given me.

 

 

BW

[gramercyjam]

Tom Holt ran 150 front 250 rear (I think???) for years and was competitive at the national level.

 

Ok, I'm going to chime in, just so people don't get the idea that 150/250 somehow is a desireable setup.

 

Maybe he ran those rates, but I don't think he was ever happy with that setup. He has run for at least the last two years 400/400 (on the advice of Vic Sais I believe) and Advance design shocks. He is satisfied with the setup, at least for now. Spring choice for a competition car can be a function of budget (it is for me) - 400 lb springs can't be controlled by budget shocks.

[JMortensen]

JohnC, what you are saying makes perfect sense, and I wish I had the $$$ to do a setup like you've got (I hope read this as envy, because it is, believe me ). But I was referring to a more general dislike of swaybars because they make the ride harsh in a street car, not because they have 500 lb springs in the car. With soft springs I think big bars are necessary.

 

Gramercyjam, when I emailed Tom a few years back he didn't seem the slightest bit disappointed with his spring rates, FWIW. I'm not exactly a good friend of his or anything, so maybe he just didn't tell me the whole story. When we were talking he also said that he was somewhat surprised at the stiff spring advice (which I think came from Ground Control).

 

I wasn't trying to say that 150/250 is the ultimate setup, only that he was able to make it work on the national level. I still think that there are varying setups which can be made to work, regardless of what the "proven" setups are. And I stand by the idea that the rest of the car, tires, suspension, weight, and most importantly the driver can make a setup great for one person and horrible for the next.

 

Case in point: Every time one of my friends drives my car he spins. Every single time without fail. The only way I can get his car to turn is to turn in, chop the throttle, and stand on it all the way through the corner. We have both been autoxing for a while (8 years or so for me, probably 14 years for him), and our cars post VERY similar lap times on the big tracks and at autox. Put either one of us in the other one's car and we suck. Given more than 2 or 3 laps to figure it out, I'm sure either one of us would adapt to the other's car, but we always swapped at autox, so we would only get 50 seconds in the other's car, not enough to figure it out. Still, we have built our cars to perform the way we want them to perform, and that's why they drive so differently.

 

Jon

[gramercyjam]

I still think that there are varying setups which can be made to work, regardless of what the "proven" setups are. And I stand by the idea that the rest of the car, tires, suspension, weight, and most importantly the driver can make a setup great for one person and horrible for the next.

 

No disagreement from me on that. Especially about the driver. A good driver makes all the difference.

[260DET]

Here is some data on anti sway bar rates which may be compared with spring rates so as to judge the effect that a sway bar has. The sway bar rates were provided by a contributor to this forum and take into account the leverage factor. To compare various sway bars I have used the Diameter Conversion Chart from http://www.whiteline.com.au.

 

Front : 22mm bar - 268 inch/lbs, 23 mm - 321.

Rear : 20mm bar - 86 inch/lbs, 21mm - 105, 22.5 - 139.

 

Using the Diameter Conversion Chart, substituting a 28mm bar for a 22mm will increase the rate by 162%, ie from 268 inch/lbs to 702, if my maths is correct. Which nicely illustrates the huge influence a large sway bar has on suspension rates compared with the spring rate itself.

 

Plus, as johnc indicated, consider the effect of coupling the independant suspension together with any sway bar, particularly a large bar that exceeds the spring rate by several times. To every action there is an equal but opposite reaction applies with a vengance.

[74_5.0L_Z]

Just to muddy the waters further, I'll post my set-up.

 

250#/in rear

200#/in front

koni reds single adjust struts

1" front anti-sway bar

no rear sway bar

 

I autocross the car, drag race it, and drive it on the street. The car is well balanced IMO, is not too uncomfortable on the street, and still cut 1.8 sec 60' times on street tires(Dunlop SP8000).

 

Stiff for the street is what my set-up is. If you go much stiffer, the car will beat you and itself to death, and will scim across bumpy corners like a stone. Another thing to consider is that the Z is pretty flimsy unless reinforced. Spring rates greater than about 250 turn the car are too stiff for the stock chassis.