Front and Rear Sway Bar Effects
 

Hey All,
How does the rear sway bar effect the front sway bar or vice versa ?

I am about to switch my bars out to the suggested 23mm Nissan comp front and the 3/4 " (20mm) rear housing mounted Suspension Techniques bar. I am currently using a 1 1 /8 " front and a 7/8" rear. I have bad understeer in the front using the big bar and stock/worn struts. One thing I have noticed with the rear is that I don't have the huge body roll causing the outside tire to lift and spin freely (open diff). Once the LSD goes in some of that problem will go away.

I just wasn't totally sure how the front and rear bars effect each other.

Thanks,
Mike

New brake parts should be here today :)

Sway bars are a good way to tune your car for understeer/oversteer. Changing just one will effect the overall handling of the car. For your application, I would want to stay with fairly large front/rear bars. The larger front/ smaller rear bar usually will produce an understeering car. I would try to install a smaller front then rear bar or same size. Another cheaper way to adjust your car is to use your existing bars and loosen up your front end links a little(I think...maybe rear) to tune in some oversteer.
Hope this helps.

To dial out understeer you need to loosen up the front, wether shock/spring/sway/tire pressure. You may be successfull in using more or less tire pressure, so that one is not so simple. You'd have to observe treadwear, or get a thermal probe/pyrometer.

http://www.whiteline.com.au/faqsusp01.htm
http://www.teammatrix.com.my/Setup/damping2.htm

You mentioned that you have worn / stock strut inserts and will be making a sway bar change to get rid of some understeer.

Might I sugest that you update the shocks before making a bar change. After that I would make a bar change on one end at a time.

After the shock change take a look at how the car is doing in each part of the turn. Is it pushing on initial turn in? Does it roll well in the middle? Do you get oversteer on exit? Does the inside front wheel come up during corner exit?

Do you have rod ends on the bars to take out pre load? Do you have coil overs? If so has the car been corner weighted? You will want to take care of these areas before making many changes also.

There are printed guides to help you through the tuning process. A friend with a camera taking shots of the car at the different parts of a corner can help too. One corner with three different shots of the front of the car. If you run the same course later in the season you can do it a gain to measure improvement. A skid pad could help here too.

Alan

Thanks Alan !!

My New front strut inserts came in yesterday :) I also have a Energy Suspension Master Urethane bushing set to install as well.
Along with adjustable control arm bushings .


I will change the front out first to the 23mm bar. I agree with Erik from EMI that the 1 1/8 " is to big for my application. I am not running coil overs at this time. That will be my next step this Summer.

The car understeers most noticeably now at corner exit. It was a problem before tire change in the any long sweeper , but seems to have improved with race tires .

Once the strut inserts and bushings , and sway bar go on I am going to put the car on my friends scales to get a corner weight.
I will only be able to shim the sway bar ends to get the corner
balance close since I won't have adjustable bar ends. The guy that has the scales has a set of Saner Performance adjustable
sway bars for his Z that he just got. That will probably be an option for me by the end of Summer.

I will position my video camera in a corner that I seem to have problems in and I can then capture the images one at a time to
see whats going on. Have to love the new video editing technology :D

Again thanks for all your help !!

When you corner weight the car make sure that you use a set or corner weight wheels (rigid with no tire). This is a common mistake most people make when putting a car on scales. You need to make sure the radius is the same on all four corners or you can end up out of whack from very small changes in diameter. There's a reason why you see those skinny wheels on most formula cars. It really matters.

I know the standard advice is that a smaller front bar will give you less understeer but that's not always the case. A mac strut car, like the Z, cannot gain camber quick enough on the outside wheel to make up for roll and you can sometimes find a net gain by going with a larger front bar. I've also found by experience that 240Z don't like large front bars and slicks as they often rip out the sway bar mounts unless reinforced. Just one more thing to think about.

If you can I'd look really hard at running a setup that relies more on springs and less on sway bars. It will help when putting the power down and in transition.

For autox I've found that you often have faster times when you run enough camber to make the inside edges of the tire 10 to 15 degrees hotter. This is best left to testing. If you run a lot of camber you can get false readings where the outer edges cool in the air. It's best to come right off a hard corner and then check the temps.

Alot of AutoX folks that I come across go for soft springs, big bars. Road racers or open road, the opposite, more spring, less bar.