Home | Mailing List | Specifications | Care and Feeding | Modifications | Vendors | Literature

 

Rear Sway Bar

 Thanks to Sheriff Buford T. Justice:

updated 7/30/01


One frequent modification giving high satisfaction to 3rd Gen owners is replacement of the rear sway (anti-roll) bar. In hard cornering sway bars take the force that drives an outside wheel up into the car and distribute it to the inside, so the car leans less and the tires stay flat - in better alignment - to better conduct forces to the ground. Each axle has it own sway bars and balancing the relative size of the two is important to keep a car's handling safe.

Few modifications (save correct tire inflation) give more improvement per dollar in handling than larger sway bars, and with fewer undesirable side effects. Even in winter when my 17" rims are off, the fatter rear sway bar stays on giving me a hidden advantage. 


On front-wheel-drive cars, the large bar goes on the rear, not the front. Because the driving wheels are at the front of the car, you want the increased roll stiffness at the rear. This improves traction at the driving wheels and reduces understeer which front-wheel-drive setups always seem to have. An anti-roll bar or a larger one would be used at the front of a front-wheel drive car only if the rear wheel lifts during steady-state cornering, and if the car leans too much. So use a front bar with caution unless you like heavy understeer on your front-wheel driver. - (pp. 149, How to make your Car Handle Fred Puhn)



Colored from Helms, Blue indicates the rear sway bar, Red shows bushings, brackets and end links.

All SHOs 89-99 can use the same rear sway bars, so finding and swapping a heaver bar is relatively easy to do and is one of the first things a owner desiring to improve road handling in their 96-99 SHO may undertake.

From SHO-Times:

Common Stock Stabilizer Bar Diameters

Model

Front

Rear

'89, '90, '91

24mm

26mm

'92, '93 5-speed

24mm

23mm

'93 auto

23mm

23mm

Most '94-'95 5-speed

??

23mm

At least one early '94 auto

23mm

19mm

Most '94-'95 SHO auto, some '94-'95 SHO 5-speeds

20.6mm

21mm

So if we only change the rear bar, what choices do we have? Factory the 96+ come with the small 19 mm, then we can step up to 21, 23 or 26 mm.

How do we translate diameter to stiffness?

Again relying on Puhn pp150

This solves for spring rate, or the pounds required for one inch deflection.

Dia mm

Dia inches

A

B

C

K

Change

19

0.748

8

40

8.5

127.7

100%

21

0.827

8

40

8.5

190.6

149%

23

0.906

8

40

8.5

274.3

215%

26

1.024

8

40

8.5

447.9

351%

So a 21 mm bar is 150% stiffer than stock, 23 mm is little more twice as stiff and the killer 26 mm is three and a half times stiffer. I put the 26mm bar on from the SHO Shop which is a Ford part. It keeps the tail dead flat even when I hook a 90 degree turn into Stake & Shake at speed. It also transmits a fair amount of "road information" over every expansion joint especially with 17" rims. One might wonder if the 21 or 23 mm bars might get most of the effect and yet retain a higher "Spouse Acceptance Factor"? The arms of the sway bar are short and a solid 26 mm bar looks like bridge support next to a flimsy 19 mm bar and I wonder if I have not converted my IRS to a solid rear axle sometimes?

Cost

The SHO Shop sells the brand new 26 mm for $199 including hardware. They say it is 30% stiffer than the OE 21 mm. Did some 96s come with 21 mm? My 97 came with 19 mm.

Bone yards often can find a used 26 mm for $50. Then you have to call Summit for some Performance Suspension sway bar mounting brackets and links.

Installation

I recommend a lift, getting the OE bar out is not too bad a job, it has some give. Getting the new bar in is a pill. We had to drop the passenger side rear tire to snake it in from that side.

Once in we saw that the new bar was in upside down so it had to come out and go back in again. With all that it still only took an hour, two grown men and a fair amount of bad language to intimidate the new bar into place, twice.

I also would recommend drilling the C brackets that mount the bar to the chassis for a zerk (grease) fitting. The bar will need grease about every 6 months and fittings make the job very easy. Get tiny fittings because you are weakening the bracket with a hole so make it a small one. If you forget to grease the fittings you will get an "audible" reminder.

If you lack calipers one easy way to measure sway bar diameter is to wrap a paper around the bar and mark two lines across the paper with a pen. Unwrapping the paper the distance between the lines is a circumference. Divide by 3.14 to get diameter.

Finding the correct size for you.

The 96 + SHO unibody is much stiffer the then 89-95 SHO which can require braces to stiffen their chassis. For this reason the same size bar in a 96+ will be more effective than it was in 89-95 SHOs. Combine the stiff chassis with the over size bar and firmer bushings and the bar far more effective than in the original application. If the 26 mm bar is plenty and the 19 mm bar optimized for family comfort, what is the best size? Both Fred Puhn and Don Alexander (Performance Handling) recommend that an anti-roll ball be large enough to limit tire camber change due to body roll to 2 to 3 degrees.

An excessive bar stiffness can cause the inside wheel to lift from the road surface during cornering. This causes wheel spin when the bar is too stiff at the drive wheels. Corner exit speed is hurt, especially in low speed turns. Alexander, pp 85

Since we are only tuning with the rear bar, we need not worry about wheel spin at the drive wheels. Photos of Solo II race cars at work can show an inside tire with air underneath. But does it follow that a 26 mm rear bar may be too stiff for the 96+ SHO?

I can tell you this, a 26 mm rear sway bar substantially increases the cornering limits of the SHO, which is reported to be .8 G stock. It makes the front end hold much better and the rear stay flat even in abrupt turns. Wide tires are more sensitive to adverse camber settings and the large bar keeps all four tires flat on the ground in any reasonable diving situation. Maybe this summer when I put my gummy 17" tires on we might just have someone look at the car at speed to see if I am lifting an inside tire. - (Grins)

Until that day I leave you with the thought that the under-appreciated 23 mm rear bar may actually be the optimal compromise between ride and handling, at least for those with families who may not share the drivers enthusiasm, at least to the same extent.

Thanks to SHO Jim for this suggesting this last topic.


This was also a discussion I had with a few folks there. Throughout the earlier posts about putting a 26mm rear bar on the car, I refrained from comments after Don Mallinson gave a good response as to why he wasn't putting one on his car.

If you do a lot of autocross, the bigger bar looks like a good way to go, but for higher speed road driving and track use, I find the stock setup to be fine. I found it to be well-balanced at Road Atlanta, and going through turns like the Carousel at Hallett, I was able to get both ends of the car singing the tires. For my ability at the track, the bit of understeer is fine, and touching the brakes while laying into the throttle makes the rear end track very nicely through higher speed curves. I even got some wear on the outer edge of my RR tire.

Ron Porter
Lake Orion, MI
'99 black 33K


3/26/03

Well since we own one of those damn de-contented '99's I really wanted to freshen the handling aspects a bit. So I got a hold of a 26mm Rear sway bar, here is my install story.

I really didn't notice much of a difference in ride harshness except that when you hit a bump with one rear wheel you feel it more (as expected), while roadway expansion/pavement joints since they usually hit both wheels at the same time are no different. I must say that we have not had the car up to Toledo or Detroit where the potholes own the road since installing the bar, and my only testing has been on the fairly smooth roads around Columbus.

The install:

Removal of the old bar was pretty simple. I did find it easiest to take off both rear wheels and send the bar out through the drivers side as when I tried taking it out the passengers side like I had read the brake plumbing on the Drivers side was at risk of getting snagged by that end of the bar. The bar slipped quite nicely out the drivers side.

Installing the 26mm (from a '89 SHO) wasn't as much of a walk. I wrestled with the position of the bar and it's added thickness and the fact that it is shaped a little different than the one that came out complicated things extensively. I tried putting in it from either side with no real success. What I found made the job MUCH easier was to pop the three rubber hangers off of the duals (two on the drivers side muff and one of the passengers side). That gave extra space above the exhaust which was a big help, then I also loosened the one 8mm bolt that holds up the lines going up to the filler cap on the passenger side. With some slack there it went in pretty easily from the drivers side. I had purchased the end links for a 89 SHO at Advance auto parts (also DBA Checkers / Part's America). They were the proper length and everything fit up just dandy. The same mount bushings from an '89 will fit right up to our Gen III's using the factory mounting bracket. Before I cinched the bracket down I sprayed some lithium grease between the bar and the main bushings and tightened everything down.

The Test drive:

Remember this car is non-SARC (sucks doesn't it). I noticed that your neighborhood speed turns were MUCH flatter and you could tell that it was the back that was keeping all of the body roll out, it was almost as if the back end was holding the front mostly flat (which essentially it is). Ride did not seem harsh at all (car still has 16's). At lower speeds it was a great improvement. When I pushed the car (35 MPH curves at 70) it didn't seem to be making that much more of a difference, but this car does have RS-A's on it as well, so maybe the next batch of tires will help that out, I am certainly more than happy with the improvement in lower speed aggressive maneuvers.

All in all it was well worth the 70 bucks I got invested in it (and the hour and a half of removing / installing). At high speeds the car did not seem to have a great propensity for oversteer or understeer, it may be plowing a bit more than it used to but I did not think it was very significant. I am waiting to get my FSTB from Bob hopefully that will level things out a bit and reduce some of the understeer I am now seeing.

Scott Krietemeyer
99 TG
Sunbury, OH


Contact Information