Swaybar dilemma

Well,

 

I went to install Perrin 22mm F&R swaybars this weekend and after installing the rear and unpacking the front, I noticed the diameters were not the same. It ends up that I received a 25mm rear in the 22mm box and I'm afraid to install the 22mm front because of the mismatch. The car is a bit oversteer happy now (with the stock 21mm front) and I am wondering if I put in a 25mm bar in the front that the ride quality will be unacceptable? Is anyone running 22mm F 25mm R? The suspension is set up as follows:

 

Prodrive PFF7's with 225/40/18 Cooper Zeon tires (They ride like they have cement in the sidewalls)

 

USDM Spec B Bilstein struts with STi Pinks (F:ST2033021000 / R:ST2038021020)

 

Is anyone running a setup similar to this on a LGT A/T wagon with a 22mm (F) 25mm ® or 25mm all the way around? The torque specifications between the 22mm and 25mm bars is scary:

 

FRONT SWAY BAR % INCREASE BASE ON DIAMETER ALONE

 

Stock Diameter PERRIN Sway bar % Increase

21mm 22mm 120%

21mm 25mm 214%

 

 

OEM 21mm BAR ONLY SETTING

EFFECTIVE RATE 480 LBS/IN

PERRIN 22mm BAR SETTING #1 BAR SETTING #2

EFFECTIVE RATE 610 LBS/IN 740 LBS/IN

RATE INCREASE OVER STOCK 125% 155%

 

PERRIN 25mm BAR SETTING #1 BAR SETTING #2

EFFECTIVE RATE 1030 LBS/IN 1260 LBS/IN

RATEINCREASE OVER STOCK 215% 260%

 

____________________________________________

 

 

Legacy SWAY BAR % INCREASE BASE ON DIAMETER ALONE

Stock Diameter PERRIN Sway bar % Increase

15mm 22mm 462%

15mm 25mm 772%

 

OEM 15mm BAR ONLY SETTING

EFFECTIVE RATE 35 LBS/IN

 

PERRIN 22mm BAR SETTING #1 BAR SETTING #2

EFFECTIVE RATE 170 LBS/IN 205 LBS/IN

RATE INCREASE OVER STOCK 480% 580%

 

PERRIN 25mm BAR SETTING #1 BAR SETTING #2

EFFECTIVE RATE 290 LBS/IN 345 LBS/IN

RATE INCREASE OVER STOCK 825% 985%

 

Any help is greatly appreciated!

 

 

Rob

You could try running the front on the stiff setting and the rear on the soft setting. But it will probably still be tail happy. I would just send it back for the matching size.

You don't want to run much stiffer bar in the rear - means tail happiness. Typically matched set have front bar stiffer - e.g. Cusco, Swift.

The torque specifications between the 22mm and 25mm bars is scary:

 

Rob

 

 

Why? They are lbs/inch, not lbs/ft

Why? They are lbs/inch, not lbs/ft

I'm guessing you're thinking ft-lbs which is torque. lbs/in is the standard unit of measurement for spring rate and a swaybar is essentially a spring. So to compress the bar one inch it takes 480 lbs or whatever.

 

Most springs aren't a foot long plus you'd exceed the elastic region of metal deformation which is where you'd like to keep the spring as once you're into the plastic region the metal permanently deforms and is no longer functioning as a spring. Typically to make the measurement you don't even go to an inch of compression as it might push the spring into the plastic region so just multiply the distance you did compress by however much to get an inch as it's the Imperial system's smallest whole unit of length measurement (metric uses kg/mm). Even if you did multiply the measurement to get lbs/ft, the numbers would get absurd like 5760 lb/ft. People can probably picture 480 lbs but 5760 lbs is a little harder.

Typically a stiffer bar in the front than the rear causes understeer. The point of going with sways is to decrease body roll and reduce understeer. Hence the 25mm rear sway.

putting a bigger bar up front will take some of your oversteer away.. larger front bars will also help on the turn-in, but if you over-drive the car, it will create understeer.

 

i used to run just the rear upgraded bar, then realized the car was snappy enough in the rear to get the car to rotate, but there was not enough bite up front for the car to catch the direction I wanted to go after the flick.

 

There's nothing wrong the "mismatch'.. heck even the car in stock form is already "mismatched" if you are purely looking at size. While you are looking at the torque specs on them, it's really your shocks that need to be able to hold its ground first before the bar can be effective. Once the tires leave the ground, that sway bar is useless.. It would be truly effective if you had short-traveling high performance shocks that can keep the car from rolling over.

 

Overall, the bigger the sway bar, the more snap you will get IF you start over driving the tires' limits and start lifting the tires off the ground during cornering.

 

On some of the earlier test and tunes at autocrosses, I completely disconnected the front stock sway bar and installed the a rear 23mm solid bar in the rear hoping that it would rotate.. unfortunately, it was only biting IF I was on the throttle and not overdriving the front wheels. I eventually put a larger bar up front so that I can get the car to bite into the turn and allow the car to pivot around the front end.. to me, the rear bar was just another piece that was there to make it easier for me to break traction when i decided to flick the car around...

Thanks guys!

 

I was only saying it was scary from the #'s over the stock bars on how it changes how the car handles. (825% stiffer vs. stock is a big # for the rear. I should have worded it better.) I was also worried about going to a 25mm on the front also and the suspension being too stiff on uneven surfaces as a result for a DD. I was also worried about the drastic shift from understeer to oversteer tendencies. (My fear is my wife hurting herself by wrapping the car around a tree on the very rare occasions when she drives it.)

 

I got through to Perrin finally and they advised against using the larger bar and said it should be a matched set then make the adjustments from there. Perrin also said that the 25mm bars are also fine for the street when matched. I bought the last two 22mm (With the "bonus" 25mm in the 22mm box) sets from Jeremy over at Fred Bean's so swapping at the time was not an option. It was looking like my only four choices were going to be:

 

Run the 22mm FSB and 25mm RSB.

Put the stock RSB back on.

Return the 22mm FSB and get a 25mm FSB.

Buy a 22mm RSB from another party and try to return the misboxed 25mm RSB

 

Jeremy was able to get in touch with Perrin and get the proper 22mm rear shipped for me so my worries are about over. Now I just have to hope it doesn't rain this weekend...

 

Hopefully i'll have better luck with the twinscroll install.

 

Thanks again to everyone for all of your advice.