aftermarket rear swaybar, stock front, bad idea?

[cdlong]

just got a '95 base 240sx and found out it doesn't have a rear sway bar. i want to add one for autoX this summer and i figured it would be a good time to upgrade. i want a whiteline for the adjustability but i'm worried the extra stiffness in the rear will make the car too *** happy.

is the range of the whiteline close enough to stock that it will be alright or should i just get a stock bar and worry about upgrading both later? they come in 20 and 22mm but i've only seen the 22mm one.

[skydragoness]

S14 Stock (data from CourtesyParts)Front 27.2mm Rear 15.9mm

Whiteline Adjustables (data from PDMRacing.com)Front 27mm Rear 20mm (22mm available as well)

^ Taken from the Suspension FAQ that Exar made a sticky of

I got one word for you: oversteerYou may even pick up the outside wheel while taking turns autoxingJust get both Whiteline swaybars and call it a day, (or the cheaper Suspension Techniques are good too)

[Red coupe]

S14 front swaybars are 2mm bigger then S13? I just replaced bushing on my swaybars today and the front measured 25mm by the little messuring tape ... also why would buying just the rear make him oversteer more then buying both if stock front is thicker by .2mm? he would be buying basicly the same size bar...Id suggest getting the rear first and CAREFULLY try driving it, just driving around town even if you knew it understeered a bit you could just take it easy and youd probably be fine untill you could get the front. That way if the whiteline isnt any stiffer metal then oem you wont have spent so much money replacing stock with an aftermarket equivilan.

[Q45tech]

15.9 mm is roughly a 12-14 pound/roll inch increase in roll stiffness at the tire road interface with oem bushings end links........roughly 7-8% increase divide this by ~~ 2 to calculate the rearward % shift in roll couple.

A 20 mm is roughly 2.5 times stiffer or roughly 40 pound/inch increase over springs. Still only creates a ~~20% rearward shift in roll couple ratio.

Without a rear bar the front is usually 75-80% of total roll stiffness, so shifting 20% to rear makes the front now 55-60% ---ideal based on weight differences front to rear. A 22mm get you too close to neutral and snap over steer in poor traction conditions.......of course you can stiffen the front bar but this just loads the front tires more making matters worse from an ultimate G perspective.

Probably the ideal size [20mm] if you consider the effects in the rain or snow/ice.

The rule of thumb is the rear sway bar should never be 50% of total rear stiffness and a 20mm will be ~~40% [probably 33% with oem rubber bushings].

[cdlong]

Probably the ideal size [20mm] if you consider the effects in the rain or snow/ice.

so the 20mm one would feel good with a stock bar up front? assuming i put it on the softest setting for daily driving and stepped it up a little bit for the track/autoX.

oh, and i'm not made of money, that's why i don't want to buy both front and rear. and i might be able to get a stock rear bar easily if i act on it in a few days so i need to make a decision now.

[Q45tech]

On the Q45, Nissan decreased the front oem bar by 1mm whenever they added a rear bar to help unload the front tires. The 1mm [29>28mm] reduced the front bar by 13% [18 pounds per inch] and the front bar was 50% of roll stiffness [146 in/pound springs] so a ~~6.5%/2 or 3.35% rear shift in % of total roll stiffness ratio from a smaller front bar.

This added to a only 12 [Q45t] or 40 [Q45a] pound inch increased rear stiffness meant less rear harshness, less front harshness.........yet more ideal balance...................minus 18 plus a +12 or +40.

A perfect car would have a roll stiffness ratio equal to the weight distribution ratio [54/46......52/48].......unsafe because when you accelerate the rear tires must share friction so less available for handling.

Why manufactuers start with 75/25 and work closer to 54/46 [in tiny increments] as the level of desired performance rises. You will never see much below 60/40.

You almost never need a stiffer front sway bar unless you use significantly stiffer front springs. Eibachs are only 10-15% stiffer so no change is necessary other than matching shocks.

Notice that most adjustable front bars have a stock or slightly less than stock setting available.

[cdlong]

On the Q45, Nissan decreased the front oem bar by 1mm whenever they added a rear bar to help unload the front tires. The 1mm [29>28mm] reduced the front bar by 13% [18 pounds per inch] and the front bar was 50% of roll stiffness [146 in/pound springs] so a ~~6.5%/2 or 3.35% rear shift in % of total roll stiffness ratio from a smaller front bar.

This added to a only 12 [Q45t] or 40 [Q45a] pound inch increased rear stiffness meant less rear harshness, less front harshness.........yet more ideal balance...................minus 18 plus a +12 or +40.

A perfect car would have a roll stiffness ratio equal to the weight distribution ratio [54/46......52/48].......unsafe because when you accelerate the rear tires must share friction so less available for handling.

Why manufactuers start with 75/25 and work closer to 54/46 [in tiny increments] as the level of desired performance rises. You will never see much below 60/40.

You almost never need a stiffer front sway bar unless you use significantly stiffer front springs. Eibachs are only 10-15% stiffer so no change is necessary other than matching shocks.

Notice that most adjustable front bars have a stock or slightly less than stock setting available.

that's the longest answer to a yes or no question i've seen. i assume the answer is yes? thanks, i was going to pick up a stock bar today.

[Q45tech]

Not a good idea to rely on a simple yes or no, without understanding the simple math and how the answer is derived.

The main problem with most adjustable bars is they have only 3-4 adjustment positions on the right angle bar.

But as you see from the examples above, it is the SUM of the 2 stiffnesses [coil + bar] and the ratio between front and rear that counts.

100% stiffer than stock is meaningless without knowing what stock is and how it relates to the real at tire stiffness.

What's scarey is they just copy oem design with all convolutions and bump up the diameter ...........assuming the the [^4 th power formula] functions the same with differing materials.

[Q45tech]

The purpose of all the drawn out discussion is to teach people how to make their own suspension decisions...........not to be manipulated by advertising.

For years to come most cars will have springs, shocks, and sway bars might as well take the time to understand the engineering WELL.

[elwesso]

if you can pick up the OEM rear bar, I think that mgiht be a good place to start.... Remember you can always loosen the front bar some (on the end links) to make the rear bar seem stiffer...

To get the most out of that tiny 15.9mm bar you can use poly bushings or OEM bushings with washers, to reduce the amount of play they have...

I personally would get that, and play with the torque on the front and rear. Remember with nissan you cant just screw the things in all the way!! Very sensitive and 1/4 turn can make a world of difference!