Competition Car Springs and Sway Bars - Setups

[260DET]

A couple of us locally have been trying some various spring rates and sway bar sizes which will still make the car reasonably comfortable to drive on the road yet will perform well on circuit race tracks. We have no defintive answers yet and probably never will due to some variations in body stiffness, overall weight, etc between various cars.

 

But it is looking as if there is is some merit in having slightly heavier springs up front compared with the rear. For example, 300 front, 275 rear. In conjunction with relatively light anti sway bars, for example 24mm front, 16mm rear. This for a fairly heavy car, not a stripped out racer, and not as yet conclusive.

 

The theory behind the 'heavier front springs than rear' idea is that it reduces nose dive under braking and enhances weight transfer to the rear under acceleration. Incidentially I tried the no rear sway bar idea on my car but found that, while there were some advantages in some situations with this setup, overall for the use outlined it was not the best way to go.

 

So, has anyone experimented along the direction we are heading in? I'm aware of what setups the competition people on this forum presently use but am wondering how they were arrived at and what their thoughts are on the above.

[JMortensen]

I used to drive my 240 everyday and take it to the track and autox as well. It hasn't been a daily driver for about 9 months, but I haven't ripped the interior out yet, so it is still 2350 lbs with a full interior. When I race I run Yokohama A005 slicks, they are way too hard for a Z IMO, but you can't complain when you get them for free...

 

I started with 250 lb springs front and back, 1.5 degrees neg camber front and rear, 0 toe front, and 3/16 toe in rear. I needed the car to turn in, and you do that with softer springs in the front, in my experience. In order to make that happen I reduced the front spring rate to 200, increased neg camber to 3 degrees, toed out 1/8", and increased caster to 6 degrees. I also increased neg camber in back to 2.5 along the way. The car still pushes a little, I think its the LSD more than anything else at this point. All of these changes took place over 5 years, one at a time.

 

I'm running a 15/16 (24mm) bar up front and a 7/8 (22mm) in the rear. The car still has a lot of body roll, and it was recently noted that I am lifting rear tires while slaloming. I am looking to go to a stiffer front bar, or possibly cut my ends off the existing bars front and rear and weld some plates so I can go to rod ends and have some adjustability.

 

I know a lot of guys run differently for the big track then the auto-x, and I've heard of people with Z's running stiffer springs in the front than the rear, and also running a small front bar and no rear bar. I think the guys that are doing that are running really stiff springs, like 500 lb. To make use of that kind of rate you have to have a full cage, and you would no longer be comfortable on the street.

 

I always use my pyrometer and some white shoe polish to check that my alignment settings are correct. Shoe polish over the edge of the tread onto the sidewall to see how far the tire is rolling over.

 

BTW, when I go to the big track I cut out some neg camber, to about 2 degrees and give it 1/16 toe in in front to get it to settle down a little. People who drive my car seem to think its tail happy, I think it still plows, FWIW. But I don't chop the throttle mid turn

 

Jon

[johnc]

The theory behind the 'heavier front springs than rear' idea is that it reduces nose dive under braking and enhances weight transfer to the rear under acceleration.

 

Funny that this should come up now. Erik Messley was (finally) able to do a comparison between a 240Z setup with bigger front/smaller rear springs vs. the smaller front/bigger rear springs at a California Speedway event last weekend.

 

His opinion of the bigger front/smaller rear springs is:

 

1. The car washes out a little on turn-in and feels sluggish.

2. Braking performance is reduced because you don't get a fast enough weight transfer to make full use of the front tires when they can provide the most braking effect. (FYI... spring rates do not affect total weight transfer, they just affect the rate at which that weight is transferred.)

3. Its much easier to lockup the front wheels under braking and adjusting brake bias rearward just reduces the overall braking ability of the car.

4. Steady state understeer in all corners unless the throttle is used (lift or power) to induce oversteer.

 

None of this is to imply that a car setup big front/small rear is slow around a racetrack. It just has a different feel then a small front/big rear setup. If you are more comfortable with a slightly understeering car then the big front/small rear setup may fit your needs.

 

There's a short video here of my car going around a track. The car is setup neutral to slightly oversteering with 275 front and 300 rear springs. It rotates very well which you can really see in the corner where the M3 goes of the track:

 

http://www.hybridz.org/phpBB2/viewtopic.php?t=24602

[blueovalz]

I recently changed the spring rates around for a stiffer rear spring verses front (now it has 265 R and 225 F), and once the sway bars were sorted out, I found the turn-in was much improved, yet oversteer was more predictable. So far, I've found no area in the handling characteristics that were hurt by this move, and a lot of tiny, but noticable improvements that made the car much more enjoyable at the limits of traction than before. This is not to say the car had the ideal set-up before going with the stiffer rear, but I'm finding this set-up easier to sort out than when it was the other way.

[Guest MistressMotorsports]

Hey John, whose car were you referring to? Yes, Erik and I are going to try to swap springs for the next event and put the 275's on the front and 300's on back. The one big unmentioned item is the unknown front sway bar rate. We have no idea what brand of sway bar is on my car, what it's rate is, or anything. Although this would not impact braking, the sway bar has a large effect on turn in and steady state. We didn't have a lot of time to play with bar adjustments to see what we could do to improve cornering. The car was close enough to neutral, however, that just swapping the springs will probably create a steady state loose condition, which needs to be addressed via a new or tweaked bar.

 

Mike

[johnc]

Your car. Erik did mention the front bar as a big unknown. Also, Erik tends to prefer a very loose car ("lively" is how he describes it) so mere mortals like us would prefer a chassis closer to neutral. Someday I'll tell you what it was like to race my white 240Z right after I bought it from Erik back in 1998.

[260DET]

Thanks all for your responses and input. So it looks like 275 front springs, 300 at the rear, is worth a go. Which is good because presently they are 250 front, 300 rear on my car.

 

And maybe then if the above seems right try a 25mm (1") adjustable front bar in place of the 27mm (1.1/16") which is the cause, I think, of some low speed front end skip/bounce and heavy outside front tyre wear on slow sharp corners.

 

Then, stage three, consider the present 22mm (7/8") adjustable rear bar. How does all that sound?

 

Incidentially, shocks are adjustable rebound Koni yellows, wheels 15x7 with 205x55 Dunlop DO1J soft compound road legal grooved slick type tyres, and yes, they should be bigger.

 

BTW, great video John, the Z looked more composed than the chaser sounded.

[260DET]

Some further observations and revisions. I clamped the 27mm bar in a vice and tried to twist one leg using a long piece of pipe over the end, it would not move. Conclusion: a bar anywhere near 27mm essentially converts the independant front suspension to a beam axle. Not good.

 

So I'm going to use a stock 22mm bar on the front. Then I have been offered a 16mm bar to try on the back so that will be given a go as well.

 

As far as springs go, I have been offered a pair of 275 springs to try as well. So they will be used with the 300's I already have. Which springs will go where has not been decided yet but, given the swaybar sizes, the 300's will probably be tried on the front first. Mainly because the bloke lending me the bits wants to see how that setup works.

[pparaska]

My car is in no way sorted out. It also has an iron headed Chevy V8 up front (but with AL water pump and intake manifold). The bumpsteer still needs adjustment, and the Momo wheel and short knuckles make it twitchy on the street.

 

I've moved from 225/300 F/R rates to 225/225. I have the Illuminas on 2 (a bit soft, but 3 is a bit harsh for street driving, IMO).

 

The car doesn't buck as you think it might over tar strips, etc.

 

I have know idea about corner or crosss or total weights.

 

I do know that 300 lb/in was not comfortable to drive on the street. And it was hurting acceleration traction.

 

Just a really bad data point, I know, but the one piece of info that might be of interest is the 300 lb/in springs on the rear were pretty tough on me and the car on the street. That and the Illuminas needed to be on 4 to keep it from pogoing.

[johnc]

Another thing to remember, unless you have a roll bar (for the rear) or a roll cage tied into the front strut towers going over 300lb.in. on either end of the car starts to turn the Z chassis into a spring. It flexes.