Opinions of 25mm rear swaybar

[wheelman]

I ran across this auction on ebay and wonder what all you guys think about it.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=7969655289&sspagename=STRK%3AMEWA%3AIT

 

It's a 25mm rear swaybar for an S30 chassis Z. The auction text states it's a good setup with a 22mm front bar for Auto-X and road racing. So is this true or just BS. Seems to me it would produce a rather tail happy car depending on other factors of course but I'd like some feedback from the experts.

 

This is the second time I've seen this on ebay. The first auction started at a higher minimum and received no bids and with 2 hours left it again has no bids.

 

Wheelman

[JMortensen]

1" rear bar seems awfully big, especially if used with a 22mm front bar. Also if it is for a 240 it doesn't have any brackets to mount it, which would be a problem. The bends look similar to the MSA front mounted bar for a 240, but the MSA bar comes with brackets. I suppose if you like to hang it out, a 1" bar could be made to work...

 

I believe the MSA bar is 7/8" for comparisons sake, and it is usually used with a 1" front bar. Also for comparison, the Suspension Techniques bar mounts to the rear uprights and is 3/4" FWIW.

[blueovalz]

I tend to agree with Jon. It's almost like he's got the sizes transposed between the front and rear. I've come close to same size front and rear, but that was with different springs and 2" wider tires in back.

[wheelman]

Thanks Jon, I appreciate the input.

I thought it sounded to big but had heard somewhere that a large rear bar would help with turn in and with the right front bar and camber settings could generate a nicely balanced setup. Seems a little counter intuitive to me, you'd end up with a tail happy car that would sometimes washout the front as well. I guess that would make for good 4 wheel drifts wouldn't it.

 

I went back and re-read the auction and it didn't talk about road racing but Auto-X and Slalom which have much lower speeds than road racing so might benefit from a larger rear bar without as large a risk of spinout.

 

I'm no expert so this is just speculation on my part.

 

I'm going to pass on this and go with a more conventional setup when I get to that point in my build.

 

Wheelman

[johnc]

That's a front bar, he's just got it sitting upside down on the pavement.

[johnc]

Ooops! My mistake. Nissan Motorsports lists a rear anti-roll bar part number 55611-E4622 at 25mm. It is a forward mount rear anti-roll bar and requires kit # 99996-E4010 for installation.

[260DET]

22F, 25R would appear to be a mismatch, unless you want to do a lot of rear end steering. Mine has 22F and 18R and will do high speed drifts on demand With 230 RWHP.

[johnc]

Your basically installing a live axle conversion kit with a rear bar that stiff.

[Phantom]

So with V8 power and an exactly 50/50 weight distribution what would be nominally good sizes front and rear? Mostly road courses and daily driving.

[JMortensen]

I think it has more to do with spring rates than the weight distribution. You can control body roll with really stiff springs and front sway bar only (more common roadracing setup) or you can go with softer springs and heavier sway bars front and rear (more common autox setup) or you can go somewhere in the middle. Heavy bars will change the ride and that needs to be considered if you're looking for bars for a daily driver.

 

Swaybar selection for Z's pretty much sucks. You can buy the "standard" sizes from MSA or Suspension Techniques, but nobody else seems to offer anything anymore. Saner advertises custom bars on their website, but I'll only email someone 3 times asking for price and availability, then I give up, and they lost my business. Nissan Comp used to have a BUNCH of bars available, but I believe that now they only sell the Suspension Techniques stuff. That's really about it. Not much selection at all anymore.

[Phantom]

Ok - so I'm currently running the European spec Nissan springs that are about 15% stiffer than the original stock springs - essentially same ride height - along with some cheap KYB gas struts and the stock front & rear sway bars with urethane bushings. Any reason to change if I'm not going to be competing a lot?

[JMortensen]

Just in general terms I think the Euro springs are too soft for competing, and I'd be looking at the biggest bars I could find to counter that problem, but if you like the way it rides and it's fast enough for you, then leave it alone.

[johnc]

No reason to change.

 

Here's one way to think of suspension tuning. Its very general but its get's you close:

 

Springs are used to tune the steady state cornering balance of the car. Basically you're shooting for a neutral balance in medium speed corners and a slightly understeering car in the high speed corners. Think of this as "the Platform"; the foundation that the vehcile's handling is based on.

 

Antiroll bars are used to tune the transitional balance of the car and fine tune steady state cornering balance. ARBs fine tune the Platform's balance and adjust that for track and driver specific needs.

 

Shocks are used to fine tune the transitional balance of the car and control the Platform's natural oscillations (sprung and unsprung). Its the last, most granular level of tuning for the Platform and is the finest tuning tool for the track and driver preferences.

[Phantom]

So if I were generally set up for track courses but decided to go autoX for a day I could "adjust" for it somewhat with adjustable struts? I assume Asb's would be the better route but, in lieu of that, the struts would help some?

[johnc]

Well, there's a 4th item that I didn't put in the list above, and that's alignment. The different parameters covered under the term "alignment" affect all aspects of handling.

 

Adjustable struts (I assume you mean adjustable lower spring perchs) affect two alignment items: ride height and corner weights. In general, those items affect hows the springs do thier jobs so its part of setting up the basic Platform.

 

So, to answer your question, in most cases you will not be adjusting corner weights and ride height when transitioning from the track to an autox course. Shocks, ARBs, and alignment settings are the more common items changed when going from one type of competition to another.

[JMortensen]

No reason to change.

 

Here's one way to think of suspension tuning. Its very general but its get's you close:

 

Springs are used to tune the steady state cornering balance of the car. Basically you're shooting for a neutral balance in medium speed corners and a slightly understeering car in the high speed corners. Think of this as "the Platform"; the foundation that the vehcile's handling is based on.

 

Antiroll bars are used to tune the transitional balance of the car and fine tune steady state cornering balance. ARBs fine tune the Platform's balance and adjust that for track and driver specific needs.

 

Shocks are used to fine tune the transitional balance of the car and control the Platform's natural oscillations (sprung and unsprung). Its the last' date=' most granular level of tuning for the Platform and is the finest tuning tool for the track and driver preferences.[/quote']

I disagree. I think a stockish Z with Euro springs and KYB's will suffer from excess body roll and pushed hard will be rolling off the tread and onto the sidewalls in heavy cornering. That's been my experience anyway. You can jack up the tire pressure to 50psi to try and keep the tire on the tread, but I think the car might go faster with a set of swaybars.

 

I should say I do agree with everything that John said, but I think the swaybar performs more tasks than solely affecting the balance in a car. It is responsible for controlling the camber change during cornering as well. On a fully adjustable car we can adjust caster and camber independently to suit our needs, but on a stockish Z adjustments are pretty severely limited. A different set of swaybars could theoretically be 1000% stiffer, yet still yield the same balance if they were proportional to one another. Despite the fact that the balance didn't change, the handling would change in a pretty dramatic way.

 

Here's a good explanation of swaybars:

http://www.grmotorsports.com/swaybars.html

[johnc]

Jon, you're right. My explanation above was a theoretical view assuming everything in the suspension can be changed. In the real world compromise is the name of the game. You often have to do something somewhat unnatural with the suspension to get the car to go fast around a track.

 

Previous generation VW VR6 GTIs are a classic example. In the stock racing classes they actually went faster and had reduced levels of understeer by installing insanely large front ARBs. The reduction in camber loss in roll more then offset the increased tire loadings. Ideally, you would have achieved the same and gone even faster with a bigger rear anti-roll bar, but the stock class rules didn't allow touching the rear bar.

[Phantom]

I guess there really is no firm answer. I logged a couple hours at Texas Motor Speedway and have plenty of photos and video of the car in corners indicating the body was about 1"- 1 1/2" higher on the inside than the outside. It didn't make me uncomfortable but it was definitely more than I thought it should have been. I was running 225/50 series street tires so the lean was probably less severe than if I'd had a good set of track tires. The video did garner a comment about the car needing bigger sway bars. The suspension was in dead stock settings. I know what to do if I were going to build a pure track car but this one is 99% daily driver and just periodically forays onto a track. I do feel good about pushin a Lotus Esprit really hard one session. would have taken the RX8 in the next session but brakes were completely toasted and I was low enough on fuel that I was losing motivation coming out of tight corners.