I searched now for hours everywhere, called Firmfeel, nobody knows what they are buying and selling. Nobody knows what swaybar roll ratings they sell or have.
How can that be? Many care about the Tbars and leafsprings ratings but not the swaybar.
Since I am calculating my whole suspension I need the roll ratings from a few swaybars to compair. I got some deflection lbs/degree numbers in a book but that sounds to me like lots of geometric measurement on the car, that should be possible easier.
Maybe someone got old Mopar books with this infos?

Thank you

What kind of numbers do you want? The lbs./deg. sounds correct to me. Are you saying that the sway bar dealers don't have that? That's sad.

I got a list of super old swaybars with diameter and lbs/deg. This DOES work but I will have to measure the arm length of the swaybar, the arm length where it attaches to the LCA and try to calculate the roll rate / spring rate at the wheel and this I wanted to avoid.
And no, nobody could tell me yet what roll rate their swaybar have. Weird, I would think if you produce something like that you at least calculate it once...
I will try then today to measure the geometry and let's see if I can find out the average roll rate of a 1 1/4" swaybar.
I need this for my suspension calculations...

Interesting discovery, nobody has defintive numbers/ratings. However a possible reason, is that there are unilimited ratings, mainly because as you touched on regarding mounting points/locations, but mainly wheel offsets and/or rim widths, which effect real world ratings. Therefore for simplicity I guess everyone just states Bar Diameter, which would only be good for comparsion on using different bars on the exact same suspension and tire rim/offest, if exact rates where important. I am starting to wonder if Sway bar Diameter has that much of a direct/precise input on handling, since there is so little empirical data advertised anyway. On TB's I feel Diameters are very noticeable in handling/ride, but they also have the same real world rating issues. Maybe just do it the hot rodder way, put the biggest one you can find on and tell all your buddies it rocks

wow. you know a lot about suspensions!

that being said, are most "stock" sway bars dialed in just right, or are they too soft?

I was just about to post about Hotchkis suspension parts for Dakotas, and their thick sway bars that everyone loves and raves about how they make their Dakota handle like a Z06.

then I remembered that the whole system includes new springs that are stiffer and lower the CG of the truck 2" or so, and shocks tuned to match the spring rates of the new springs...the total system costs about $1200.

There can be a big difference between how a car feels and how it handles. My freind had an '89 Firebird Formula with WS6 suspension. That thing responded to steering input very quickly and stayed pretty flat in the turns, he said that it "handles great". At that same time I had a '69 Dart with polyurethane bushings and 245 tires. I could pull away from him on any exit ramp. The Formula understeered terribly when you really pushed it.
My wife use to say that her Grand Am "handled great", trust me it responded great, but it handled like FWD GM production vehicle.

[quote

Spring rates are far more important to handling than sway bars, and a sway bar that's too big can easily negatively effect handling.

Basically, a sway bar is a small part of the suspension that should be used as a tuning device, not a cure all. A good handling car will have a well matched suspension, and I'd bet most people would be surprised how soft the sway bars are on real race cars.

---

Well, sorta, but you've got it kinda backwards. I think a lot of people would be suprised at how soft the spring rates are on a lot of competition cars because the sway bar is indeed a very big part of suspension tuning. But your right that matching componenets is the key to making it all work. A big part of this is because softer spring rates reduce wear on the tires, but combined with the bigger sway bar rates allow you to have comparable roll couple percentage to high spring rates without tearing up tires.

The reason for this is the WHEEL rate is the most important number you are trying to acheive. The wheel rate is achieved through a combination of spring rates, sway bar rates, shock rates, and even tire rates, as well as weight distribution, roll couple, location of CG height, size of the moment lever arm and the roll axis location.

Building a suspension is like building an engine. There are lots of little parts that can have a big impact on how well it works. Throwing the best parts at a bad combo won't produce a good handling car any more than it will produce a high powered engine.

Most companies 6040 is talking to are just producing basics parts that most guys are just bolting together on basically stock suspensions where pick up points and geometry are typically unaltered. So long as the parts are bigger than stock, much like a cam shaft, most guys assume they are better. If you start talking to people who specialize in this stuff, they know what you are after. These are companies like Afco, Landrum, Howe, Flexi-Flyer, Speedway, as well as companies that supply parts to Nextel and Busch teams. However, adapting these types parts to a stock suspension system is going to be a very difficult approach because most of them are designed for modified suspension systems and are not bolt on deals.

The info 6o4o is after had been published in the Mopar Oval Track modification book. I'll see if I can dig it up and post it for you. Since his is a stock type suspension with minimal adjustments, he is after the simple rates for the bars that mount and attach to the stock locations. This info has been out there for 30 years and has not changed.

6o4o, have you had your car on a set of scales yet?

Great infos here!
I also read in Mike Martin's book that many races (back then at least) use smaller tbars but larger swaybars as you wrote.
Since I decided now to take composite leafsprings I really need to know what spring rate I should order to get this car not to oversteer or understeer like crazy.

Yesterday I did get the car on a truck scale in my near! In Mike Martin's book they do it without person in the car, but I think that's an important point since that's how the car will be driven, so I removed the bench seat (I measured it today, it's 99lbs!!!! I will get a light single race seat in there for racing) and put my girlfriend in there on the floor that is just about 20lbs lighter than me. Moved my battery to the trunk passenger side and the tank was pretty empty.
The total weight of this car was 2 years ago bone stock with 1/3 full tank 4010lbs. Now it was (without girlfriends weight) 3630lbs!!! That without bench seat, with edelbrock heads, intake & waterpump. Unbelievable... the truck scale is +/- 10lbs I was told.
I will loose another 20-30lbs with the fiberglass leafsprings on the rear.
The car was with girlfriend 3770lbs. Front weight was 2116lbs, rear weight 1653lbs. So I got a 56.1%front weight bias. So looking at Mike Martings book I need 75% or more front roll couple to get a car that is neutral or understeers. (don't really want an oversteering car)

Center of gravity is (115" wheelbase) 50.2" behind front wheels and 64.8" front of rear wheels.
I did measure the center gravity height but the scale wasn't accurate enough and I just lifted the car 11" up so I got a CGH of 4"-6.85" and that seems to low to me, altough the car is very low (on the front almost touching the LCA bumpers and rear the leafspring is totally worn down)

Anyway, I did some measurements today on the swaybars! My rear swaybar I didn't measure, it's a totaly different system than the one firmfeel has (AAR type) so it doesn't make sense to measure mine. But I did average the length of the lever looking at the firmfeel pictures and I would say their swaybar lever length is about 11.8" +/- 2". So I will go from there. it attaches right behind the perch so I can take the motion ratio I used for the leafsprings. (57.8" perch-perch / 62.13" track = 0.9303)

On the front it was more interesting. I removed the swaybar link and lifted the car on a lift. I put my scale on the floor, took a straight piece of wood and put it between scale on floor and swaybar end. I then measured the distance between swaybar and LCA. I then lowered the lift, did 2 measurements (weight & distance difference) and I got a swaybar static rate of 275 and 270lb/inch AT the endlink. I would think that's with the lever length already included. If I would make it shorter the static rate would increase quick. The lever length is about 7.7" +/-1".
Also, should I have blocked the other wheel so it can't move up since the swaybar probably pushed it up?
The swaybar is mounted about 6.1" after the pivot point of the LCA (tbar) and if I undertand it right (now I am not sure anymore...):

motion ratio: attaching point or spring centerline / LCA (I'll take now the length from the pivot point to the wheel centerline instead just the LCA length) length = 6.1"/16.3" = 0.3747

Roll rate = static rate * motion ratio = 270lbs/in * 0.3747 = 101 lbs/inch

wheel rate = static rate * motionration^2 = 38lb/inch.

Now, what I am not sure also: in Mike Martin's book it's written confusing. Do I need to add all roll rates together OR wheel rates to get the roll couple distribution? I first thought roll rates because of this roll rate names but somewhere he writes about to get the wheel rate for the leafsprings. So I probably need to get the wheel rates for all and that will give me the roll couple distribution right?

(by the way, a Tbar would perfectly fit where the swaybar is, the only thing that would have to be done are some nice hex-brakets that fit on the end of the swaybar and voila, a tbar swaybar would have been done!)

What also confuses me:

On Tbars I found out that you get the diameter^4 and divided by the rating you will always get the same constant. Don't know why ^4 and not ^2 (since it's an area) but it works. I can now tell by the diameter of the Tbar what rating it will have, although the ratings of the Tbars is always shown.
BUT on the swaybars this doens't work, the diameter^4 divided trough the deflection lb/degree is not proportional to the next value. Why is that? Are the stock swaybars empty inside, because there is a formula for that: OD^4-ID^4?

I hope you can find those values in that book.. I will try to order that soon, I totally forgot about that you told me to get it!

thank you

Dang! You've been busy! It is going to take me a while to get through all your info as I only get a few times a day that I can get on here and post. Here is a brief stab at your numbers;

You actually would want a car that would tend to be more towards oversteer than understeer. From the factory these cars understeer substantially and you want to loosen them up some to get a better "feel" to them. To steal a line from the movies, loose is fast and on the edge of control. These cars tend to work best on that edge.

Obviously there are a number of ways to achieve 75% roll couple. The MP book list a combo of 1.0 t-bar with a .85 sway bar and 230# leaf springs as 74.31 roll couple. There is another 1.0 t-bar, 1.0 sway bar and 275# leaf spring as a 76.8 roll couple. So you can vary how you reach your percentage based on the parts available. The speed and track at which you are racing at would determine if you want to go higher or lower with springs rates. Flatter tracks or street driving could use lower spring and higher sway bar rates. Higher banking or autobahn use would require higher spring rates and lower sway bar rates. Keep in mind that those numbers were from competition ready cars driving on super speedways and front to rear bais that was 50/50 or more to the rear, so don't take the as a firm recommendation of spring rates but rather an example of different way to acheive the same percentages.

6.85 Cg height does seem low. You might have to refigure that one. I would guess it to be 12-15" plus or minus a couple inches based on you lowered ride height.

yes, your roll couple of the sum of you wheel rates from torsion bars and sway bars and springs all combined.

In the mean time, here is some data straight from mother mopar;

torsion bars and wheel rate *old nascar sizes*
.92 - 137.5
.96 - 163.5
1.0 - 191.5
1.10 - 263
1.14 - 325
1.18 - 349
1.22 - 425
1.46 - 875 *
1.66 - 1455 *

sway bars and rates *these are from kit car data, which is a bit higher than stock sway bars as they used a splined shaft with bolt on arms.
.90 - 295
1.0 - 450
1.062 - 572
1.125 - 721

leaf springs, spring rate and roll rate
96# spring 70 roll
120# spring 87 roll
180# spring 130 roll
275# spring 200 roll
400# spring 290 roll
526# spring 380 roll

Thank you Tony for all the infos!

My friend did upgrade his 72 Roadrunner 440 with the XHD leafsprings, 1.16Tbars, big swaybars front and rear and 17" wheels. That car handles great, but he/I don't know if it understeers or oversteers. With other words: it's not really calculated, he just installed stuff on it. But the car is very stiff, specially on the rear, those XHD leafsprings seem to be pretty stiff, but he seems to be very happy with it!

Our roads here are very good, heck, there is no 50miles of freeway here without a road construction because they renew the freeway every few years although it was in PERFECT shape! (politics: there is 1$ tax on each qrt of gaz that goes to road construction. Now you can make the math how much money they MUST spend every year to use the budget!!)
There are hardly big bumps on any road and nowhere a hole, so I can go from a car that won’t see bad bumpy roads.

Now, to the other points:

Tbars, your numbers are interesting. Firmfeels b-body numbers are the following:

diameter rate lbs/inch
.840 89
.920 128
.960 152
1.00 179
1.12 281
1.16 324
1.22 396

They have a different rating than yours, maybe because yours aren't for a b-body. Different length, different rating right? I would think that the rating changes with the LCA length, although the motion ratio is always 1.

But anyway, the Tbars are the smallest problem of all, the motion ratio = 1 so the wheel rate is the same as the advertised Tbar rating. That much I did understand

If I ignore/remove for once the swaybars and take once the 1.12" Tbar with 281lbs/inch. That gives me a total front wheel rate of 562lb/inch.
On the rear I measured the motion ratio of 0.9303. So the wheel rate is 0.9303^2*leafspring rate.
To get a 75% rate I need a rear wheel rate of 94lbs/inch PER side.
This means I need a leafspring static rate of 108lbs/inch! That's pretty low, isn't it?

The roll rate numbers you posted, I did calculate the motion ratio for those numbers and it's 0.853, I got 0.9303, that's much higher.

So just to make it easy, if I take a 120lbs/inch rear spring (higher than I should!) I can make it up by making the front swaybar bigger than the rear and that's usually the case.

But the most important: your swaybar numbers make me happy again! I can't use the numbers since it has a different arm length BUT they are all proportional when you ^4 them and divide them by the rate! The lbs/degree number I had wheren't!
That means: I will redo the swaybar test today again but this time with the other wheel blocked so it can't move up.
Then I will have the rating for a b-body front swaybar with it's specific arm length and 1" diameter. Then I could calculate/average the rating for the firmfeel 1 1/4" or 1 1/8" swaybar IF it's not a tube, what I don't expect.

Same I can do for the rear swaybar. I will call them and ask what arm length it has, from this I probably could calculate the 3/4" swaybar. I won't get accurate numbers but it should be enough I hope!

Interesting topic here, it's really fun to do more than just bolt on! Now it hopefully also works!

Ok, I did measure at lunch my Tbar and the swaybar again but this time the other side was blocked with a piece of wood. The Tbar I measured with the wheel on and swaybar off.

Tbar: 0.9" diameter, 160lbs/in measured with the weight on the whole tire (flat piece of wood under the tire). I wonder if they used different material or my measuring method is so wrong and on what LCA length they rate their bars since that surely changes the rate if you change LCA length?

On the swaybar I got 217lbs/inch. Yesterday I did the mistake that the swaybar got stuck on the LCA, I just saw that today. I can't move the swaybar more than 1" up otherwise it will start to rub on the LCA that hangs down. (only solution would be to remove the LCA)
But this swaybar rates you posted TonyC or the swaybar rate I measured now, they need to be multiplied by the attaching point motion ratio (in my case 0.3735^2) so you get the real wheel rate I can use for calculatons, don't they? Or what's wrong?
Your number 1.0" - 450lb/inch seems MUCH higher than my 1.0" 217lb/inch.
That would mean that my bar is a tube or that they use a 3.7" arm length instead of my 7.7"?
OR is the swaybar rating always meant for BOTH sides, that means 217x2 = 434lb/inch? That would get close to 450... is that maybe the problem?

The sway bar info will be somewhat different since it was calculated on the kit car chassis bars, which were a little different from the stock bars. I do have an original kit car catalog somehwere in the garage. I'll dig it up and post what specs it is showing for bar length and arm length. That will at least provide the detail that will allow you to see what percent of difference exists between the stock configuration and the kit car configuration. If you know the difference, then you can approximate where your stock bars are at based on the diameter, arm and effective lengths.

I'm not sure why the torsion bars are different. They don't vary by a substantial amount, but they do differ some. Mopar Grand National racing was exclusively B body cars, so all the specs from the book are for B bodies.

120# rear spring doesn't suprise me at all for handling applciations. It is only in drag racing that high rear spring loads are really needed. When I was racing oval track, we usually ran mono leaf or three leaf set ups and used sway bars to dial in how we wanted it to handle. Since we were required to use stock parts we experimented not only with sway bar size, but quantities as well. At one point we had two smaller sway bars stacked on top of each other to get the best percentage. Creative interpretation of the rules at its best.

If you and your friend want to see how dialed in your cars are without the potential of hurting it or waiting for a chance to run laps on a track, you can always do a skid pad test. All you need is a parking lot big enough to lay out a 50 foot radiused circle and then run your cars around it until it slides out of the circle. I think Martin covers skid pad testing in his book if I remember correctly. Doing this will highlight whether it under steers or oversteers so you know what changes you need to make. It also will allow you to calculate how many lateral G it can generate now as well as after you make your changes.

I emailed XV motorsports, MAYBE they consider to sell their swaybars and I am sure they have ratings for them.

Yes, I got the skid pad infos. I surely will do this test when the car is finished. Now I won't anymore, my rearend is loosing LOTS of oil and the temperature droped from yesterday 80 to 35 degrees!

By the way, that's the race I will go next May with the other guys.. as you see, most of them got pretty stock cars. They survived with stock brakes but all of them had BIG troubles.. so I wonder how my 11.75" will do

http://www.mopars.ch/discus/messages/29/6973.html?1149495001

Yes, I still am not sure on those sway bars, I tryed to find formulas this afternoon but didn't find what I was looking for. I mean, it's nothing else than a Tbars with an arm length. But I wonder if you need to calculate the motion ratio (on the attaching point of the swaybar) to get the real wheel rate? I didn't read anywhere about it, but it would dramaticly lower the rate of the swaybar! I doubt Mike Martin did it like that... so who is right?

First the positives, you obviously are a bright and well educated mopar guy, you are motivated in your desire to seek out the ideal/preferred calculated results, and you are asking on target questions.

But, based on past similiar questions on moparts, and those answers already given here, there are always two main schools of thought, big T bars, small sway bars, and soft t bars and big sway bars. Most do seem to agree when used, sway bars are for tuning mainly, and no one has any emperical data to support their conclusions, including the dealers/maunufactures. What you are trying to do on paper is a well beaten path that even for example, VX? still has to resort to 4 post testing and then continue to experiment, and I am sure they have all the same computation skills already discussed here.

Bottom line, no matter what you determine, you will still be forced to either have some adjustability of your sway bar, which will require some design skills, or you will have to swap sway bars to see which fits your road conditions, tire combos, driving style, etc. I would agree that all your effort might give you peace of mind for a starting point, but you never know for sure if you made a correct choice, until you try a larger bar and then a smaller bar to gauge results. Unless you order a custom rear(?) bar, your choices are likely only to be a 3/4", 7/8", or maybe a 1" bar, anyway. For anybody in the states I would say, just buy all 3 and sell the other two on ebay after testing. I am not saying you are wasting your time, but I wonder how much improvement you are really getting when just swapping bars will give proven results for better, or worse?

On another Note, did you see the 1972? Le Mans road racing Charger in the the latest mopar mag? It might have had a couple of interesting solutions, but I think it is more Holman Moody Nascar based. One pic did show rear shocks mounted outboard of rear leaf springs, thought that was odd, but I am sure for some technical reason. Bet that would have been awesome to see run recently, only 400mile? drive for you

Almost forgot, the same road racing charger article states the LCA's are "boxed", something I have little regard for in any car not on a high banked oval running 1.25+" TB, but then I may be wrong




Anyway

ok, I found some stuff out!

First, I found an easy formula on a web page to calculate swaybar rates:

Rate = 793.5 * (Bar OD^4 - Bar ID^4) / (BarLength * LeverLength^2) = kg / mm

So, I take the numbers above from the kit car. I measured the bar length from end to end, not just the straight part but from hole to hole since I think that total length is important. Total length = 99.5cm = 39.17". Arm lengths I measured 20.5cm-21.5cm, it's not very accurate. That's 8.07"-8.46".
Now:

Rate = 793.5 * (0.9"*2.54*10 (to get mm))^4 / 995mm*205mm^2 = 5.18 kg/mm = 290 lbs/inch! Pretty close to the 295 number!

Same with 1.125" :

Rate = 12.65 kg/mm = 708.5 lbs/inch!

that's the Formula!
When I take it to measure my swaybar, but I take now 21.5cm, not 20.5cm (a little bit longer than the kit car) and the diameter I measured was 22.4mm (0.881"):

Rate = 4.34 kg/mm = 243 lbs/inch.

I measured with my woodblock on scale test about 210-260lbs/inch. It was every time a little bit different, not very accurate, but that's about what I calculate.

So the Firmfeel 1 1/4" front b-body swaybar will have a rating of about 982 lbs/inch!
The 11/8 about 644 lbs/inch, a little bit less than the kit car because of the slight longer arm length I took.

But what I still think that Mike Martin got wrong in his book:

You can't just add front swaybar rate and torsion bar wheel rates together on the front and same on the rear. The swaybar rate needs to be calculated with the motion ratio since it's attached some distance after the pivot point! In my opinion you need to calculate the real wheel rate of the swaybar and then add THIS to the Tbar and leafspring wheel rate.
The swaybar is attached 15.5cm (6.1") after the pivot, the LCA length is 41.5cm (16.3"). This gives a motion ratio of 0.373.
Wheel rate of swaybar: 0.373^2 * swaybar rate.

This would give for the 11/4" FF swaybar: 982 * 0.373^2 = 136 lbs/inch! A MUCH lower value!

Also it is really small compaired to the Tbar value since it's motion ratio is always 1!

Am I thinking right here or is it wrong?

By the way, I called FF, the rear b-body swaybar goes from perch to perch, they got the 44" ones and the 47.3" wide ones I would need (71-74 b-body).
It's 3/4" thick and the arm length he tld me is about 11" so the rate is about: 62 lbs/inch with the same motion ratio as the leafspring I got.

pre '71 is 44", Post '70 is 47"

Yes, there is a motion ratio that has to be calculated for the sway bars since they do not attach at the ball joint.

Just curious, have you done any recalculations for what rear wheel rate you would need if using the 1.22 torsion bar and 1.25 sway bar?

As an aside to anyone else following this, how would you build adjustability into a stock swaybar? Certainly changing the length of the lever arm would do it, but I don't know how easily that coud be accomplished since the lever arm is splayed outwards at its attaching point. Not to mention the interference you would have with the K frame. Do you change the length of the end links?

Only way I would think would be to somehow make the attachment point on the LCA moveable, and therefore change the motion ratio?