The recent controversy regarding 19mm vs 22mm bars has me thinking:

Does anyone have a table of the effective rates of the aftermarket bars relative to the stock bar?

I can provide the lever arm lengths for both the stock and Rspeed (3 options) for any intrepid engineer out there, if such a table doesn't exist. I think it would be enlightening for those trying to decide between the 19mm and 22mm options.

 

As far as I know, H-Sport is the only company that advertises the effective rate..and only on their competition bar. They are +226%, 294%, 383%.

 

Mini-Madness 22mm bar

+228%, +297% +384%

Could be the same bar?

 

i think george at MM did say this wuz the same bar

 

They may have a similar rate, but are not the same bar. The H-Sport is 25.5mm and hollow, so it weighs half as much.

 

In my my recent posts under ++ another sway bar question ++ there's a pointer to an article in Grass Roots Racing magazine’s web site. It’s a fairly long article but worth reading by those pondering deeper sway bar questions. In there are the calculations for finding relative torsional rigidity (twist) of sway bars. The calculation is:

Twist = (2 times torque times length) (pi times the diameter to the 4th power times material modulus).

Luckily they show a shortcut to find relative twist given the following assumptions:
-[FONT=&quot] [/FONT]the mounting holes are in identical spots on each bar
-[FONT=&quot] [/FONT]each bar is made of the same material

Anyway the shortcut is a much more straightforward calculation (bar diameter in mm to the 4th power) and here is what I came up with:

Bar diameter twist
16mm 65,536
17mm 83,521
19mm 130,321
20mm 160.000
22mm 234,256

The 22mm bar appears, using the above assumptions, to have 2.8 times the torsional rigidity of the MCS 17mm bar (234,256 divided by 83,521 = 2.80). If we further assume the H-Sport comp bar’s middle hole is in basically in the same location as the MCS stock hole this seems to correlate closely with their advertised 294% increase (which I assume means times not plus 2.94). This puts my calculation of 2.80 at exactly 5% below theirs.

Using the same calculation for a solid 19mm bar (130,321 divided by 83,521 = 1.56) or 156% of the stock bar. I again might assume this might correlate with the middle hole of the Alta 19mm bar. If so then the inner hole would be stiffer – the outer hole would be softer.

Bottom line appears to be, all things being equal:

19mm solid bar is +56% (x156%) stiffer than a 17mm solid bar
22mm solid bar is +180% (x280%) stiffer than a 17mm solid bar

If somebody has the exact hole locations for each bar these numbers can be refined further.


Somebody who races and sets up chassis should have all these calculations at their fingertips. Please check my numbers – it’s late and I’m tired!

 

By the same calculations posted by Redshift, an 18mm bar is 104976

That means its 60% (X160%) stiffer than a 16mm bar on a SS suspension and 25.6% (X125.6%) stiffer than a 17mm bar on a SS+ Suspension.

A 19mm bar is 98.8% (X198.8%) stiffer than a 16mm bar on a SS suspension.

However, comparing the holes on my 18mm H&R bar to the stock bar, it seems like the adjustment holes are slightly infront and behind the stock one.

 

Measure the length from the center of the sway bar inlcuding the entire end link. Divide this by your new longer or shorter length to get an idea of how the increase in leverage works. The end link length must be figured into this equation since it adds to the length of the lever arm. Hint; you can play with end link length a little to really fine tune your sway bar...further, you can play with bushing materials. End link length is limited by the total amount of space available within the entire suspension stroke. Spring/damping rates and ride height will affect where the actual operational range of motion is.

Then, simply multiply any increased sway bar diameter to the forth power and divide this by a smaller sized bar multiplied to the forth power.

You will see that small increases in size have a large effect on sway bar stiffness. This added stiffness adds to wheel rate. And wheel rate affects among other things, traction at the contact patch. Huh you say? In simple terms, if you do not have enough tire under your ride, stiffer will only make you slide faster - a tire can only absorb a given amount of weight transfer. When it saturates, it begins to slide. Written another way, figure how much load a tire can handle and work backward to define spring and bar rates...dampers too, but these for the most part are determined by spring rates. Some cars are over-tired - not enought wheel rate and some cars are over suspended - not enough tire. You must match a tire's load characterisitics to your set up. The compromise? Tires with higher load ratings are usually heavier and create more aerodynamic resisitence at high speeds if they are wider as well. Depends upon where you drive in the end.

If you know your cross weights and tire's max load, you can get a feel for how much extra weight transfer each corner can absorbe before saturation...or, do without in the case of the back end since rotation facillitated by a larger rear bar does so at the expense of rear tire grip.

Modulus refers to the bending frequency of a given material. Not all materials bend, or twist, alike. This is beyond me.

 

For another number helix says "22.5mm Helix Adjustable Rear Sway Bar...The outboard mounting hole (closest to the bar end) is approximately 35% stiffer than the stock "S" rear bar." They don't give percentages for the other mounting holes, though.

 

Snid,

That doesn't sniff right...the hole farthest away from center is also the stiffest setting. It should calculate out to well over 300% stiffer using diameter alone.

 

Nope... furthest out hole is the softest.

And I always get confused when I read something like "200% stiffer". Do they mean it has twice the stiffness, or three times the stiffness? To me "200% stiffer"="300% the stiffness of" or "three times the stiffness". Think about something that is equally as stiff... would it be "100% stiffer" or "0% stiffer"?

So "35% stiffer than stock" means 135% the stiffness of stock. I think.

 

You know, sometimes you just can't trust me, i'm old. The hole farthest from the center allows the most twist and therefore less roll. You are correct and now I need to go back and correct my previous statements. I goofed, sorry guys...gals. Shorter end links, not longer create less roll. you can still fine tune a sway bar by adjusting the end links.

100% stiffer is twice as stiff. Sway bar stiffness works in the forth power. Multiply a 16mm bar to the forth power. Do the same with a 22.5mm bar. Dived the cubed 22.5mm bar's number by the 16mm bar's cubed number and you'll see that the 22.5mm bar is it is about 390% stiffer. This is why I get all worked up over large bars. The can add tremendously to wheel rate.

...perhaps I should not drink wine whilst posting...

 

Meb, I think you goofed again. If I'm reading it right, the hole farthest from center (outer hole) allows for the least torque (from the swaybar to the chasis) and therefore more roll. The inner setting allows the swaybar to torque the chasis more and therefore, forces the car to roll less.

 

...Kapps...more torque allows more twist. It is the resistance to twist that creates weight transfer...only had one glass tonight; white, not terrible potent. (insert smile here, dunno where they are???)

Lever arms are fairly easy to figure out in simple form. Take a 10 foot piece of wood with a fulcrum in the middle. Place 10lbs on one end. It will take 10lbs of force on the opposite end to lift. If the fulcrum is placed 2.5' closer the the weighted end, it will only take 5lbs of downward force to lift the weight - hole farthest from center. If the fulcrum is placed 2.5' closer to the force end, it will now take 20lbs of force to lift the weighted end - short hole on the sway bar.

The longer distance from the center of the sway bar allows more torque and therefore more twist, but less resistance to roll and therefore less weight transfer...another glass of wine perhaps, I'm beginning to second guess myself. I once knew this stuff pretty damn well.

 

Thats right, the hole closest to the sway bar bushing is the "stiffest" hole. (shorter hole = stiffer sway bar setting)

 

Yeah meb, I understand what your saying. Statics is still somewhat fresh in my mind . I was figuring the torque on the MINI from the bar while you were figuring torque on the bar from the MINI.

...now I need a glass of wine

 

May I recommend a vintage?

Describing what's going on is difficult sometimes. It's like trying to keep all ten of your fingers on ten different elements and then making the connection. I cannot believe I actually went on a rant above and reversed the entire length of end link relationship. All I had to do was remember where the settings on my bars are. Absent minded I am.

 

There is 2 aspects to determining sway bar stiffness. 1. Bending of the sway bar arms (Yes, the arms do bend slightly) 2. Twisting of the center section of the sway bar (i.e. the long straight section) By shortening your lever arm (i.e. using the closests hole to the axis of rotation) your are affecting both of the previous aspects. 1. The sway bar arm is now shorter, so it's harder to bend. Think of it this way, If you had a long stick and a short stick and you clamped one end of each stick in vice. If you push down on the free end of the sticks, which stick is easier to bend? 2. The shorter sway bar arm will inflict more angle of twist to the center section of the tube causing more reaction force at the other end. Just remember, the more twist, the more resistance. Hope this make sense!

 

The stick is a great analogy Aron

 

formula for stiffness of a solid round steel anti-roll bar from Fred Puhn's book:
How to make your car handle (HP Books) page 150.
doesn't include flexing of rubber mounting parts, which lower stiffness
quite a bit until they fully compress.

K = 500,000 D ^ 4 / (0.4244 A^2 B + 0.2264 C^3)

-------------<---------------B-------------->--------

.......^..........xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx .......^..... (D is diameter)
........l.........x............................... ...............x.......\.
.......A......x................................... ...............x........C
........l....x.................................... ...................x......\
.......V.x........................................ ....................x.....V

(please excuse the crude diagram)

 

Hi all,
I have a question for you all!
Say if you could shorten the MCS stock 17mm. sway-bar arms by 30mm. How much more torsional rigidity would you have in percentage (%) ? If you go any shorter than 35mm, I think the End Link connection may hit the rear spring.
I read somewhere on the this web site that the H-Sport 19mm. sport bar is equivalent to a 17.5mm. solid bar. It's rated at 54% - 88% - 128%
Is there any help out there?

Thanks,

 

plugging in 47" for B and about 7" for A and C (5.8" when shortened 30 mm)
gives a stiffness of 95 for stock and 140 for shortened 30 mm.
or 147% the stiffness of the original.

 

Are we discussing the length of the bar as it relates to the tire's center line, or the endlink lengths?

 

I assumed the ends of the bar....if you shorten the endlinks, it won't
appreciably change the rate.

 

I beleive that the links do add some value to tuning, all else equal. They are an extension of the swaybar. Although they do not 'twist', their length can have an affect on how quickly a swaybar 'ramps' up. If this were not true, both endlinks could be vastly different lengths.