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Sway Bar Spring Rate Comparison - table (not just the standard Pfadt one)
Here I go again with one of my tables...
I put this together a while back to help me decide on which aftermarket sway bars to get. Maybe some others will also find it useful.
It shows the relative rates of the front and rear bars, and the ratio of the two. Values for all the sway bars were drawn from the popular PFADT comparison figure (http://www.pfadtracing.com/photos/da...Comparison.jpg), except the Hotchkis, which was determined from manufacturer's claims. The rear C5Z bar is the baseline for comparison since it's the lightest; everything else is given relative to it (so for example, the T1 front bar is 3.3 times stiffer than the C5Z rear).
The Rear/Front ratio is useful in determining the balance of the setup. Larger values are balanced more toward oversteer (rear tires breaking loose first), and smaller values are balanced more toward understeer (front tires breaking loose first). For instance, you can see the C6Z bars are balanced toward oversteer to make up for those big, beefy tires out back.
The T1 bars are the de facto standard in the racing world. The PFADT Johnny O'Connell bars mimic the T1's, but are a little lighter. The Hotchkis are similar to the JO'C but are balanced more toward oversteer.
*Not shown here are the LG G1 sways, but LG claims that they're interchangeable with the T1's.
You need to be very careful with some of the Pfadt numbers. They showed their racing bars as being much softer than they really are. Those particular bars had very bad attachment angles and the linkage ratio was not at all what they thought it was. I don't know what they did or didn't do for the Johnny "O" bars or between the stock and the T1 bars, but linkage ratios are a very important part of the equation. Before you go too far you should look at linkage ratios too.
There is a lot more to trying to predict the changes you make between understeer and oversteer than just the relative rates of the bars at each end.
Total roll stiffness is a combination of the deflection of both the springs and the bars. There is a differential stiffness between the front and rear springs already built into the car. The more you increase the bar stiffness the less the influence of the springs will be. So while you might think that increasing the front and rear bar stiffness in proportion to each other will produce a given result, the fact that the springs are contributing less will make the changes to the bars amplified. You'll notice that the differential between front and rear bar stiffness changes as the bars get stiffer, and this is why.
Bottom line is that you aren't going to be able to predict it just based on the relative stiffness of the front and rear bars. It's going to be in the general direction, but you can end up tail happy or pushing like a pig and there really isn't any way to tell unless you have the computer simulation codes to do it right, and since you aren't GM, that isn't likely going to happen.
As I've noted in other posts, the days of just slapping a stiffer bars on the car and producing a huge improvement in handling are long gone. That is why it is better to pick an engineered package, (like the Johnny O bars) that all works together than just trying to mix and match to get something that works.
Dialing in a suspension for good handling is something that takes test time experience and patience. Frankly I can't tell you how many cars I've driven at drivers schools that were so screwed up that God couldn't have driven them very fast without swapping ends and collecting immovable objects. Most folks do don't have experience doing this will dial in way more oversteer than is fast or prudent, just because, to them, it "feels" fast.. They mistake rotation rate for cornering prowess and go way too far in that direction.
If you don't have the tools and don't want to go with a package and are bound and determined to try to do it yourself, make sure that you have some (or a lot) of adjustability in the bars at one end or the other. That way you can dial it in and get good handling without excessive understeer or oversteer.
Also note that sway bar bushing can actually have a very big influence on how a set of bars work. Sway bars are a springs and the bushings that mount them contribute to the overall spring rate. The Corvette uses big bars and the mounting stiffness of the bars is a very large portion of the overall stiffness. Every good suspension engineer has a box of different stiffness sway bar bushings and these are used to fine tune the overall balance. The difference between an oversteering wild ride and car that pushes like a pig can be changed just be changing the bushing stiffness and not even touching the bars. Make sure you have the right bushings for the bars you want to install and then make sure you have some of the same size that are harder and softer than the first ones you install. That way you can fine tune between bar settings with bushing stiffness and get the car dialed in.
Thanks for the chart. It tells me that on my '01 Z what the relative stiffness of the Hotchkiss bars I installed are and what a difference it has made. I went from a stock front 1.38 to 2.0, and stock rear 1 to now 2. The upgrade to Hotchkiss has been perfect for the street. Thanks again.
T1s on public roads and streets are way to stiff. Rocks may give a softer ride.
Plus you must use heim joints, to mount the T1s. Which are loud and clanky. Only way to over come that is with LTs and straight pipes.
T1s are really for road racing only.
But on a road race track, the T1s just allow the car to fly though corners without body roll with proper tires and an aggressive high neg camber alignment.
all anti-sway bars are hollow.
C5 Z51 black, T1 Blue ( old style)
T1 spring Upper, C5Z51 lower
Front
Rear
sorry for some of the crappy old cell phone pics
when the T1 full suspension, shocks, sways and springs are installed, the car will ride about 1" lower then stock ride height, which is about ideal.
I put this together a while back to help me decide on which aftermarket sway bars to get. Maybe some others will also find it useful.
It shows the relative rates of the front and rear bars, and the ratio of the two. Values for all the sway bars were drawn from the popular PFADT comparison figure (http://www.pfadtracing.com/photos/da...Comparison.jpg), except the Hotchkis, which was determined from manufacturer's claims. The rear C5Z bar is the baseline for comparison since it's the lightest; everything else is given relative to it (so for example, the T1 front bar is 3.3 times stiffer than the C5Z rear).
The Rear/Front ratio is useful in determining the balance of the setup. Larger values are balanced more toward oversteer (rear tires breaking loose first), and smaller values are balanced more toward understeer (front tires breaking loose first). For instance, you can see the C6Z bars are balanced toward oversteer to make up for those big, beefy tires out back.
I have just acquired an 01 Z06 with stock Sway bars. I'm looking to upgrade them to go with the Pfadt featherweight coliovers for HPDE use
I guess I'm confused. So the JO'C middle setting is a smaller number than stock C5Z, so it dials in MORE understeer??? I thought the car had understeer to begin with and we are trying to dial that out ???
Here is the Pfadt comparison. I estimated the numbers and did the rear/front ratio and came up with the same numbers as the above chart posted by Skyavonee.
So, again, it is my understanding that the Stock C5 Z06 is set up from the factory with slight understeer, Correct?
The greater the difference between the front and rear, the more you add understeer, Correct? (Assuming the front bar is always larger)
The closer the ration gets to 1, the more oversteer, Correct?
So if these assumptions are correct, the .75 stock ratio will have less under steer than the Johnny O' rear bar in the middle setting generating a .65 ratio.
This may all be academic as it seems a consensus that the Pfadt Johnny O' sway bars provide an improvement in handling. I just like to undstand.
You need to be very careful with some of the Pfadt numbers. They showed their racing bars as being much softer than they really are. Those particular bars had very bad attachment angles and the linkage ratio was not at all what they thought it was. I don't know what they did or didn't do for the Johnny "O" bars or between the stock and the T1 bars, but linkage ratios are a very important part of the equation. Before you go too far you should look at linkage ratios too.
There is a lot more to trying to predict the changes you make between understeer and oversteer than just the relative rates of the bars at each end.
Total roll stiffness is a combination of the deflection of both the springs and the bars. There is a differential stiffness between the front and rear springs already built into the car. The more you increase the bar stiffness the less the influence of the springs will be. So while you might think that increasing the front and rear bar stiffness in proportion to each other will produce a given result, the fact that the springs are contributing less will make the changes to the bars amplified. You'll notice that the differential between front and rear bar stiffness changes as the bars get stiffer, and this is why.
Bottom line is that you aren't going to be able to predict it just based on the relative stiffness of the front and rear bars. It's going to be in the general direction, but you can end up tail happy or pushing like a pig and there really isn't any way to tell unless you have the computer simulation codes to do it right, and since you aren't GM, that isn't likely going to happen.
As I've noted in other posts, the days of just slapping a stiffer bars on the car and producing a huge improvement in handling are long gone. That is why it is better to pick an engineered package, (like the Johnny O bars) that all works together than just trying to mix and match to get something that works.
Dialing in a suspension for good handling is something that takes test time experience and patience. Frankly I can't tell you how many cars I've driven at drivers schools that were so screwed up that God couldn't have driven them very fast without swapping ends and collecting immovable objects. Most folks do don't have experience doing this will dial in way more oversteer than is fast or prudent, just because, to them, it "feels" fast.. They mistake rotation rate for cornering prowess and go way too far in that direction.
If you don't have the tools and don't want to go with a package and are bound and determined to try to do it yourself, make sure that you have some (or a lot) of adjustability in the bars at one end or the other. That way you can dial it in and get good handling without excessive understeer or oversteer.
Also note that sway bar bushing can actually have a very big influence on how a set of bars work. Sway bars are a springs and the bushings that mount them contribute to the overall spring rate. The Corvette uses big bars and the mounting stiffness of the bars is a very large portion of the overall stiffness. Every good suspension engineer has a box of different stiffness sway bar bushings and these are used to fine tune the overall balance. The difference between an oversteering wild ride and car that pushes like a pig can be changed just be changing the bushing stiffness and not even touching the bars. Make sure you have the right bushings for the bars you want to install and then make sure you have some of the same size that are harder and softer than the first ones you install. That way you can fine tune between bar settings with bushing stiffness and get the car dialed in.
You need to be very careful with some of the Pfadt numbers. They showed their racing bars as being much softer than they really are. Those particular bars had very bad attachment angles and the linkage ratio was not at all what they thought it was. I don't know what they did or didn't do for the Johnny "O" bars or between the stock and the T1 bars, but linkage ratios are a very important part of the equation. Before you go too far you should look at linkage ratios too.
There is a lot more to trying to predict the changes you make between understeer and oversteer than just the relative rates of the bars at each end.
Total roll stiffness is a combination of the deflection of both the springs and the bars. There is a differential stiffness between the front and rear springs already built into the car. The more you increase the bar stiffness the less the influence of the springs will be. So while you might think that increasing the front and rear bar stiffness in proportion to each other will produce a given result, the fact that the springs are contributing less will make the changes to the bars amplified. You'll notice that the differential between front and rear bar stiffness changes as the bars get stiffer, and this is why.
Bottom line is that you aren't going to be able to predict it just based on the relative stiffness of the front and rear bars. It's going to be in the general direction, but you can end up tail happy or pushing like a pig and there really isn't any way to tell unless you have the computer simulation codes to do it right, and since you aren't GM, that isn't likely going to happen.
As I've noted in other posts, the days of just slapping a stiffer bars on the car and producing a huge improvement in handling are long gone. That is why it is better to pick an engineered package, (like the Johnny O bars) that all works together than just trying to mix and match to get something that works.
Dialing in a suspension for good handling is something that takes test time experience and patience. Frankly I can't tell you how many cars I've driven at drivers schools that were so screwed up that God couldn't have driven them very fast without swapping ends and collecting immovable objects. Most folks do don't have experience doing this will dial in way more oversteer than is fast or prudent, just because, to them, it "feels" fast.. They mistake rotation rate for cornering prowess and go way too far in that direction.
If you don't have the tools and don't want to go with a package and are bound and determined to try to do it yourself, make sure that you have some (or a lot) of adjustability in the bars at one end or the other. That way you can dial it in and get good handling without excessive understeer or oversteer.
Also note that sway bar bushing can actually have a very big influence on how a set of bars work. Sway bars are a springs and the bushings that mount them contribute to the overall spring rate. The Corvette uses big bars and the mounting stiffness of the bars is a very large portion of the overall stiffness. Every good suspension engineer has a box of different stiffness sway bar bushings and these are used to fine tune the overall balance. The difference between an oversteering wild ride and car that pushes like a pig can be changed just be changing the bushing stiffness and not even touching the bars. Make sure you have the right bushings for the bars you want to install and then make sure you have some of the same size that are harder and softer than the first ones you install. That way you can fine tune between bar settings with bushing stiffness and get the car dialed in.
Hope this helps.
Solofast, thank you for your response, that is all very helpful. Your comments once again reinforce how complex suspension modification is. The situation I am in is that my recently acquired 2001 Z06 already has Pfadt Featherlight coliovers on and stock bars. So, at this point to make a "recommended package" I have to add bars that Pfadt recommends, or, go my own route.
You State "Dialing in a suspension for good handling is something that takes test time experience and patience." Well, I have none of these. I am hoping with the Vast C5 track Corvette community, others experience could help guide me, and with a purchase of proper bars with adjustability I can dial in a safe, fast ride. Your comments on bushing is helpful, I would not have thought of that as an adjustment factor. my assumption is that the choices are Rubber and Poly, Poly being stiffer than rubber.
Linkage ratios, Hmm . . . , well, a brief excursion into the cyber world of Linkage ratios leads me to believe I don't have a shot in hell making sense of all those calculations. Here again, I am hoping "the community" might be able to point me in the right direction based on the coilovers I already have.
although the combinations of suspension parts and their application to the C5Z may be infinite and their effects on handling wide ranging, in the practical world, i have a few options limited primarily by what I am willing to invest:
1) Run stock bars, adjust with Poly bushings.
2) install aftermarket bars, tune with bushings and adjustable mounting points'
The T1's and LG's are probably too stiff for my purpose.
The exotics are too expensive.
It seems to me that reduces my choices to Hotchkis and the Johnny O'Connell bars. (Please feel free to add other choices that fit in this catigory)
The Hotchkis front bar is less stiff than the JO'C
The Hotchkis rear bar is slightly stiffer than the JO'C in all 3 of the respective mounting points.
If anyone out there is running the Pfadt Featherlight Coilovers with one of these 2 bars and is willing to weigh in, I would be grateful. If you've ran both . . . Awesome!!
Here is the Pfadt comparison. I estimated the numbers and did the rear/front ratio and came up with the same numbers as the above chart posted by Skyavonee.
So, again, it is my understanding that the Stock C5 Z06 is set up from the factory with slight understeer, Correct?
The greater the difference between the front and rear, the more you add understeer, Correct? (Assuming the front bar is always larger)
The closer the ration gets to 1, the more oversteer, Correct?
So if these assumptions are correct, the .75 stock ratio will have less under steer than the Johnny O' rear bar in the middle setting generating a .65 ratio.
This may all be academic as it seems a consensus that the Pfadt Johnny O' sway bars provide an improvement in handling. I just like to undstand.
I really see no need to immediately modify the cars suspension its DAMN good in stock form. I am on Pirelli take of 305/660/18 take off slicks with a track alignment....the car is damn fast and I have a ways to go to reach the limits in its current state.
The car from GM has under steer due to the smaller tires on the front, running a square setup makes the car neutral.
Last edited by FASTFATBOY; 10-09-2016 at 09:10 PM.
are there really no spring rates available for these bars?
I always wondered about how they can rate and compare different model bars....torsional stiffness, shape, overall length, etc would all mean different rates in my mind. I don't think you can just measure the diameter of a bar and claim a thicker bar will be stiffer without knowing the shape, bends, arm length, etc that you're comparing to.
Is there a standardized type test fixture you can put a bar into to get a true measurement of the spring rate so you can compare different bars from different manufacturers?
to compare solid bars, (diameter)^4 goes into the formula, divided by lenght of the straight section and divided by (lenghth of arm)^3. this is an approximation from memory, maybe google will come up with the formula.
to compare solid bars, (diameter)^4 goes into the formula, divided by lenght of the straight section and divided by (lenghth of arm)^3. this is an approximation from memory, maybe google will come up with the formula.
I am surprised the community has not availed themselves of this formula to calculate their bars and post the results. It wouldn't be long, we would have most bars documented. When I get my new bars, if it has not started, I will start a new thread to post the results of my bars as it applies to this formula above.
keep in mind, the formula is for the bar only. when its installed the angle of the arms to horizontal comes into play also, as well as the angle of the links. but i guess any bar for the same car will be pretty similar.
First you need to figure out what the car is doing now since you've changed the springs.
That means you need to figure out what the spring changes were relative to stock in both the front and rear, and what percentage change was made at each end.
If the front springs are say 50% stiffer and the rear springs are 30% stiffer you've increased the bias of the springs toward the front and you'll likely need more bar at the rear, just as an example.
Also, what are you going to use the car for and what is your goal? If you want super cornering grip that is really done more with tires than with bigger bars and springs. The stock setup is very good and can actually handle a lot more grip than you can get out of a typical street tire. There are some 200 treadwear tires that have fantastic grip on the street and have good tire life, but also be advised that if you change tire sizes you're going to have to retune the suspension, which leads us to the second question.
What wheels and tires are you going to use, and is this different from stock?
Thirdly, what does the car handle like in mid corner, steady state sweepers? Does it push or can you feel the back end have a bigger yaw angle?
Based on all this you can try to make a determination of what you want or need in terms of bars. But remember if you've stiffened the springs you may not need or want more bar on the car in the first place.
There are autocross test sessions all over the country and that is where you can take the car when you get it done and spend a day fine tuning it. Not only is it a lot of fun, you'll get to run as many runs as you want and by the time you're done you'll have handling that is a world better than you thought it could ever be. If you don't have the experience to do that, then ask around in your area and find someone who is running Corvettes in autocross at a national level and get them to help dial it in.
My stock (except for Stoptech BBK) 04 Z06 handles very well indeed with the 04 model Sachs shocks. However, under one particular loading, through the turn 16 thru 18 complex at CoTA, I run on the bump stops with Michelin PSS tires (or even stickier R-comp tires). Since I like the suspension, and this is the only turn complex where this problem manifests itself, I am going to do "nothing" because my car works fine everywhere else.
07-27-2012, 09:57 PM
Sway Bar Spring Rate Comparison - table (not just the standard Pfadt one)
