What are your plans for the car?

The size of the bar is but one aspect of how the bar works. What kind of material is it made of? Solid or hollow? What kind of bushings will you run? I had poly in the front and rubber in the rear.

On the early cars, a rear sway bar is almost never needed. I ran one for many years, but also had custom front and rear springs, Koni shocks, solid front 1” bar, Arning drop, boxed lower arms, export brace, Monte Carlo bar and under ride traction masters bars. Since I don’t run SCCA any more, I took the rear bar off.

If you are just making a street car, I would say skip the rear bar and put in a 1” front bar and some good shocks.

 

IMHO, the best size in the front is 13/16" and the best size in the rear is zero.

 

1" is as big as you want to go. Bigger creates problems. Export brace is a major improvement, MC bar only gets in the way, needs extra holes drilled and the export brace does everything you'll need. Unless you're racing, rear sway bar is what Woodchuck said!

 

1965 didn't come with a factory export brace? I was unaware.

 

1" for front and no rear bar

 

There is a reason they didn't come with a rear sway bar in 1965. As far as the front bar, that depends on the engine...or rather the engine weight. Honestly, unless you have a good reason to do so I wouldn't change from what it came with stock.

 

1” front & no rear as others said for a street car. Good quality export brace with the deep ribs and thick steel should suffice for street and I’d skip the Monte Carlo bar and add ZRay’s crossmember to stiffen the lower chassis and lower control arms.

 

I believe the front sway bar that came on my mustang when I bought it was a 1 1/8" diameter and then it also had a 3/4" rear sway bar. I ended up taking the rear bar off and like how it drives now much more than how it drove before. I don't think the 1 1/8" front sway bar is needed, especially on a street car, and you could definitely get by with a 1" bar but I've been too lazy/cheap to swap it out. The export brace imo is a fantastic thing to add in order to stiffen up the front suspension, and I don't see how a good Monte Carlo bar would hurt either. Other things like a competition crossmember help out quite a bit as well.

 

I'm going to throw out there that I've got a 1" front bar, arning drop, 620 springs, 4.5 leaf reverse eye rear springs, yadda yadda yadda. The best handling upgrade I've done was subframe connectors. It's incredible how it made the car feel so much stiffer.

 

1” front and no rear bar. What a lot of folks don’t realize is unlike rear coil springs, leaf springs provide a natural anti roll properties. When the body rolls in a turn, the axle no longer parallel to the body, it twists the leaf springs front to back. This acts much like a torsion bar trying to return the axle to be parallel to the body. Coil springs have zero stability and why you have control arms to locate the axle.

This is why you see a leaf spring axle with little or no rear bar while as coil rear axle will have a good size rear bar. IMO body roll isn’t necessarily a bad thing. As you increase roll properties you increase the load on the outer tires making them work harder while the inner tires work less.

 

Your last two sentences are completely contradictory. The major downside to body roll is that you transfer most of the cornering load to two tires instead of all four. If cornering performance is your goal, then body roll is absolutely a problem and must be reduced as much as possible.

The OP's question is unanswerable without much more info about his intentions with the car, and especially without more info about what suspension modifications his car has, if any. Sway bar size and stiffness will depend greatly on what else he has changed and what he plans to do with the car.

I do agree generally though that a rear sway bar is rarely beneficial on an early Mustang, and is usually counterproductive. This holds true from bone stock to heavily modified, in most cases.

 

Yes the X brace and M/C bar do make a huge difference.
Put a torque strap on the engine if you need all the other go fast stuff.
The more power you make the harder you have to nail it down.

 

Good Lord Almighty in Heaven above, that^ is a glorious sight

 

I have a 1 inch front and 3/4 rear. I do not use poly bushings. I have had to change the height of my end links on the front and the rear. I think it was because I have lowered my car front and back. You want the ends of the bars on the last part that bolts to the end links to be parallel to the ground.

 

Another vote for no rear swaybar. Almost always they will degrade the handling of a vintage Mustang.

Z

 

Thank you for all your comments. I continue to be so impressed with responses from the forum members.
What a great resource.
I am going to go with a 1"sway bar in the front, export brace and no rear sway bar.

 

Many people don't understand the role (pun intended) of the sway bar. Yes, it is there to reduce the amount of body roll. How does body roll affect handling? That depends on a number of factors. First, one has to understand what occurs during body roll. Let's consider this from the point of view of a turn to the left... As the body rolls, the suspension on the right is compressed and the suspension on the right is extended. Because our front suspension is of the independent type with unequal length control arms, this induces changes in camber that reflect the suspensions camber curve throughout the range of movement. It also, typically, raises the center of gravity at the front of the vehicle as it is harder to compress the suspension than extend it so the movement is greater on the "unloaded" side. The amount of roll is also tempered by spring pressures, both front AND rear, and by weight on the suspension and how it is distributed.

With that in mind, a larger front or additional rear sway bar is NOT always a good thing. Some amount of body roll is needed to transfer more weight over the tire with the greater traction, the "inside" one. That's why you see road-race cars that actually lift the outside tire off the road surface in a hard turn. If you don't have the capability to maintain grip on the "inside" tire instead of turning you go straight (understeer). So, the choice of a sway bar is really subject to suspension geometry and inertial forces incurred during the turn. It may 'feel" better with less roll, especially when you are not reaching the limits of handling but, when it counts, it may actually make things worse.

 

Woodchuck, Are you mixing up inside and outside? i don't remember seeing a road race car lift an outside tire. Have seen them lift the inside plenty of times...

Rusty

 

Great topic here... What is good for one persons, car, abilities, check book, is not good for everyone. Largely dependent on what your expectations are and how you drive it. Same can be said for big inch engines, 9 inch rearends, 31 spline axles, 5 speeds, full chassis cars etc. I run HD shocks, HD springs, big brakes, metallic linings, 3.25 Trac Loc rear end, 1 inch front sway bar, 3/4 rear bar, I drive my cars fairly hard and find this combo just right for an inexpensive street set up. Sometimes a little experimentation goes a long way on what works for you!

 

I kinda like my 13/16” front bar with all poly bushings.
And no rear bar at all 🤷

 

That actually works the best for a mild upgrade.
Without changing a bunch of items, just merely removing a 5/8" front and replacing it with a 1" is a big increase...... toward increased understeer.

ex-Global West GM
1991-1995

 

Like @Tunnelwedge , my Monte Carlo bar is only "in the way" for about 30 seconds, then its out. Don't even think about a curved MC bar...

A 1" front bar works well. 13/16" bars were GT specific items that are not reproduced, thus they command some good $$$. I sold the one I had on my car, bought a 1" bar and put a Benjamin in my pocket. The car still handles well. No need for a rear bar in my experience.

 

If you follow any of the SHELBY playbook from over 55 years ago you will have a pretty nice street car. Modern Race car, chassis components will run circles around that vintage stuff. I have tried to make vintage stuff competitive over the years and thats why most sanctioning bodies will make specific classes for those oldies, because they just cant compete against these newer modern marvels.

 

If the vintage is allowed to run the updated "angles, lengths, and locations" that actually work....... it's a much closer comparison. Of course that is against the rule book.
We put a 16 year old in a '66 Global West car and he cleaned up down in the San Diego SCCA region. (1st in class, 2nd overall)

 

One more vole for 1in up front and none in the back. kip

 

1 to 1 1/8 inch in front, 3/4 to 7/8 inch in rear.

Yes and yes, both help to stiffen & stabilize the front end from flexing, particularly on curves, hard cornering/road racing courses.

Also consider sub-frame connectors, the weld on type. 😎

 

Sway bars do nothing to reduce chassis flex. All the sway bar does is transfer motion from one lower control arm to the opposite side. If you go around a right hand corner, where the left front control arm is forced upward from the shifting of weight to the left side, the sway bar forces the RIGHT control arm upward as well, to allow the right side to drop, reducing body roll. Remember that as this occurs you're effectively reducing weight on the right front corner and when it reaches a point where centrifugal force overcomes the friction coefficient between the tire and the road surface (lack of traction) the tire will begin to slide sideways. A properly sized sway bar will be a compromise that optimizes the grip of the "unloaded" tire to help turn the car.

 

I have 1 inch on the front and tossed out the rear bar I had for a few months years ago. The rear gives a false sense of security so to speak. It felt a little better under slightly spirited driving but things became a different story when pushing the car hard in a turn and it was more prone to having the rear want to come around. This was what was supposed to be a matched set from Addco.

 

The rear bar is suppose to make the car loose. So it was working. You just reached the limit of the rubber.
I have had Addco bars in my Fastback for decades. Yup it's fast and loose. Just the way I like it.

 

a rear bar with a locker works great for tight 180 deg pivots around a cone on an autocross course. if you have a rear bar on the street and really push it all the way your rear end is gonna come around. also you need a little body lean to force the outside tires on the pavement for max traction just like you do on the rear tires of a drag car.

 

We could go back and forth on this with no conclusive answer. What works for one guy might not work for the other, thats why when one shows up at a racetrack you see or hear many different car set ups. So lets start at the beginning.... Do many motorsports classes run sway bars or anti sway bars- yes they do, did some of the fastest cars from back in the day, like say ah TRANS AM run very stout bars on front and back ... yes they did for good reason! Granted they were not taking the grandkids out for an ice cream in their 66 coupes but you can apply their understanding of what makes a car get around a race track without wallowing and leaning like a beached whale. Appears original poster just wanted a good street cruiser without building a race car so all the items built for a vintage mustang should be an improvement .

 

The topic starter asked in another thread what he should do with his all original car and the answers varied between leave it alone and modify it only a little bit. With that in mind, a front 1" bar or if he can find a GT 13/16" bar would be my recommendation.

Body roll can be reduced by stiffer springs or sway bars. The difference is that springs do not affect the weight transfer. It is the same regardless if the springs are weak extremely stiff (to the point of solid). It is only affected by the center of gravity and the weight of the car (apart from the center of gravity moving a little to one side with extreme lean). Sway bars on the other hand do affect the weight transfer, as the outer wheel tries to lift the inner wheel, which loads the outer wheel as much as it unloads the inner wheel. The result on handling is a compromise of on one hand better grip due to wheels being more perpendicular to the road and on the other hand a worse balance between inside and outside tire loading.

In 1970, some Mustangs got rear sway bars with a 15/16" front and 1/2" or 5/8" rear bar, depending on the engine. Rather thin and as you can see also a rather longer "arm". Some aftermarket ones are of a similar design, but with much shorter arm that connects behind the rear axle. That alone makes it ~50% stiffer.

 

this sounds crazy but i knew some draggers that would preload a rear sway bar to put upward pressure on the left tire and downward pressure on the right tire. all them were using spools. also they were not dressed in drag clothes, just a helmet.

 

Nope, nothin crazy about that 😉
But a four-corner scale does come in handy.

 

Well we took a detour from a simple question... What sway bars should I add to my plain jane going for ice cream daily driver 66 coupe- to full vintage and modern race car designed suspension systems. Another note here if anyone has a car that can launch the front wheels skyward he knows something that probably 99.3 percent of most on here, dont or cant do. Back to the question, the way cars were built for performance over 50 years ago are different from the ways they are built today. Each one of us has different goals and expectations.

 

The OP in fact never gave any clarification on how their car is set up or what their intentions are with it. Their question was completely vague.

The reason cars are built different today is as a result of all that we have learned. Of course not everyone needs or wants modern suspension. That's not what this discussion is about. It's about educating folks on many misconceptions about suspension, sway bars, etc.

And like I said.. straight line traction is a totally different animal than going around corners. Tunnelwedge apparently knows how to go fast in a straight line. That's good, but irrelevant to any discussion about going around corners, which is what people have in mind when they're talking about sway bars.