ARB contribution to wheel rate?
ARB contribution to wheel rate?
(OP)
Hi guys,
Long time reader, first time poster.
I understand you need the spring rate and motion ratio of the roll bar, but mathematically, how do you include this value into your overall wheel rate?
This has been bugging me for a while now.
Thanks
Long time reader, first time poster.
I understand you need the spring rate and motion ratio of the roll bar, but mathematically, how do you include this value into your overall wheel rate?
This has been bugging me for a while now.
Thanks





RE: ARB contribution to wheel rate?
That said, we can now calculate torsion spring force on ordinary way, and then wheel-rate through Mr ^ 2.
When the car roll, thus we can say that swaybar remains stationary in its absolute center because the inner wheel springs out as much as the outer wheel springs in. We should therefore use half the spring force per suspension side.
There are a lot ideas around concerning swaybar function, like "lifting the inner wheel" and the like. It can create false ideas about what is happening, but it requires as much strength to lift up one side of the car as it takes to pressing it down on the other side.
I've heard ideas that the car's ordinary springs helps to lift the car on the inside wheels, but it is so that the lifting force of these springs decreases by as much per mm as the car is lifted. So it is all about that the swaybar is getting twisted in proportion to the roll of the car.
Goran
RE: ARB contribution to wheel rate?
RE: ARB contribution to wheel rate?
The swaybar will only add to wheelrate in ROLL, with as much as the bar is twisted. (Times the Mr).
Goran
RE: ARB contribution to wheel rate?
The single wheel bump rate is roughly half way between the roll rate and the bounce rate.
If you have grippy D blocks then they affect the bounce rate
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: ARB contribution to wheel rate?
The link below is a ARB spring rate calculator. I have not confirmed the accuracy but offer it as a visual aid for those interested.
http:/
RE: ARB contribution to wheel rate?
Norm
RE: ARB contribution to wheel rate?
I recall that adding a moderately stiff sta-bar to the front of a car that was not originally fitted with any bars at all gave the distinct impression of holding the front end up in a turn, relative to its earlier behavior (this being in addition to keeping it more level). Some of that may have been due to parallax or other illusion, but I don't think it all was.
Norm
RE: ARB contribution to wheel rate?
RE: ARB contribution to wheel rate?
It consists of two parts ...
A, a number of different swaybars that have different angled arms. The first is at 90 degrees and it gets a deflection of 120 mm at the load 185kg. The figures come from practical full-scale experiments I have made. Problem solution is to resolve how much the deflection will become with the other described angles of arms.
http://www.hemipanter.se/Kr%E4ngningsfj%E4der.jpg
B, the second problem is to solve the spring constant of two springs working against each other, which is linked to swaybars against the usual feathers.
http://www.hemipanter.se/Springs.jpg
Perhaps no direct marvels but about what we are discussing here. I will show the answer within a coupple days if anyone like to try to come up with some figures.
Goran
RE: ARB contribution to wheel rate?
Norm
RE: ARB contribution to wheel rate?
Goran
RE: ARB contribution to wheel rate?
"Grippy D blocks"---Well, you try to not do that.
Wheel rate, I just factor in the max of the bar rate per wheel and let it go at that. No matter what the paperwork says, it never works out perfectly at the track.
Much like setting up the dampers, ARB's, Panhard bars, require a LOT of track testing and adjustment to achieve a proper setup. I suspect that this is also done on the production side as well...It's just not publicized since, how would that look to John Q. if he knew that "science" was not all it takes to make his Toyahonda?
Rod
RE: ARB contribution to wheel rate?
If I may allow myself to be a bit philosophical.
I think the great value of engineering knowledge is to acquire the right understanding of the events so that you can work more rationally on the track. This swaybar problem is actually also an experiment I did in real life to get just a practical evidence to show why different types of swaybars produce different effects on the cars. I have seen several formulas for swaybars not taking everything into account, which easily creates distrust of computations. It is therefore important to understand "both sides of the coin".
In many discussions with amateur racing team, I come across another kind of problem, you have a knowledge of the nature of a design but wrong idea of how important it is. It makes you prioritize errors both in the building of a car and pit stop.
Goran
RE: ARB contribution to wheel rate?
I have a B8 A4, and B8 S4. These cars have the same motion ratio front and rear. I have a susp. setup on the A4, and am trying to achieve the same chassis frequency F/R on the S4 I have on the A4.
I have a roll bar of known stiffness and motion ratio. I have a spring of known stiffness and motion ratio of rear suspension.
I know how to find the wheel rate JUST using the spring, how do I mathematically include the ARB?
RE: ARB contribution to wheel rate?
In the first 90dgr example we had D of 120mm.
If we had another arm,like the last figure,
there will be D of 60 mm each arm,
Number two 67,5 dgr have a D of 140mm.
Number tree 45 dgr have a D of 160mm.
Number four 22 dgr have a D of 430mm.
Here is the answer for the other problem (hope I can explain it properly).
In example A1-A2 the spring rate will include one single spring when moving the plate C for a rate of 1kg/mm.
In example B1-B2 there are two springs involved since the springs are preloaded against each other. The result is that in now takes 2kg/mm to move plate C to the left. In other word the same rate per mm as if the springs where standing in parallel under the plate C.
The explanation is that in the starting position the left spring is preloaded to 10 kg. By pressing it further together by 10mm we must add another 10 kg of force for a total of 20kg for this spring. Since the right side spring now is loose it will provide no "help" any longer.
In stead of giving us assistance moving the plate C to the left it is actually LOOSING 1 kg mm of assistance for every mm the plate C is moving to the left. This might be worth thinking of in the case of the sway bar loading up against the ride spring during cornering. A situation looking a bit of the reverse since the bar starts out unloaded against the ride spring that is preloaded by the weight of the car.
Goran Malmberg
RE: ARB contribution to wheel rate?
I contacted an aftermarket mfg. who's company name would resemble the initials in a High Rate ARB, regarding the swaybar that I purchased from them, to see if they would provide either the ARB rates for the replacement ARB at the different link positions or the wheel rates for the different link positions. They refused to provide any info. which makes me wonder if they actually know the rates?
You've got to love good customer support - if you can find it any place. <LOL>
RE: ARB contribution to wheel rate?
Goran
RE: ARB contribution to wheel rate?
For anything more than approximation, I should think a simple scale and test rig should suffice. The actual determination of wheel rate is not rocket science. Still, the final "at track" setup CAN be a bit of the "black art", especially when you factor in all the other variables---.
Rod
RE: ARB contribution to wheel rate?
Yeah, I forgot this stuff was National Secrets... <LOL> As if the competition can't measure the rates if they wanted to. It's all so silly to me.
RE: ARB contribution to wheel rate?
2. If you don't have the bar, and the mfr is unwilling or unable to provide you with stiffness data, theory is all you've got.
With respect to item (2), I wish I could remember where I saw a picture of a front sta-bar that was experiencing a visible amount of bending as seen in front view along the central (mostly) torsional section. You know that one is going to be somewhat softer than Puhn's simplified formula suggests. Maybe a lot softer.
If chassis structure does not permit the D-blocks to be located close to the arms, the simplified formulas will again over-predict the stiffness.
It's not that more theory will get the bar designed or properly chosen in one shot. More like if it isn't as stiff as the quickie formulas suggest, you'll know why it's not (and have a better idea how to proceed).
Goran - when I ran problem A through my spreadsheet I was getting very large deflections for the 22.5° model as well, and I doubt that the small deflection thinking associated with standard beam formulas would still fully apply. Those results aren't on this computer (and I think there's a factor of 2 involved as well), but I'll post them later.
Norm
RE: ARB contribution to wheel rate?
The other way, 120, 129, 180, and 585 mm
Norm
RE: ARB contribution to wheel rate?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: ARB contribution to wheel rate?
The reason that my two sets of numbers above diverge as the angle tends from 90° toward zero is because it's a model of an entire bar rather than fixed at the midpoint of the torsional section as per Goran's sketches. Unlike torsion during pure roll, the bending in the central portion is antisymmetrical rather than symmetrical and the slope at midpoint will not be zero. The first set includes only center section torsion and arm bending (this essentially being Mr. Puhn's approach, except that I've held Young's modulus E out as a variable).
Norm
RE: ARB contribution to wheel rate?
A straight torsion bar with a good mountings, and 90 dgr separate solid arms hooked to a good A-arm connection link, is a good idea from many aspects.
Easier to count on and a more precise function.
Goran
RE: ARB contribution to wheel rate?
Goran, I would love that to be the way that my race cars could be setup. Wow, would that simplify everything, especially on the front of the Lotus Cortina my son races.
Rod
RE: ARB contribution to wheel rate?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: ARB contribution to wheel rate?
This configuration is the same as the OEM except with several changes for racing. I've kept it as it was in the 60's for the vintage racing clubs requirements.
Std. dia springs, but at 300 lb/in and fully adjustable Koni inserts. Suitable reinforcing at the spindles to help with the bending loads. A one inch bar/leading link with proper Al D blocks with suitable lubrication fittings and NAS bolts. The fully adjustable lower control arm mounting is via a Rose joint as is the ARB mounting. Upper strut mount is with the top mount from a BMW (Ford stuff no longer exists), again to maintain the originality per the time period when "camber plates" were not legal.
It actually "looks" pretty original, but performance is much better. The one inch Holman Moody bar is shorter allowing for more positive caster and a bit wider to allow for the three degree negative camber we use.
Even the rear axle housing is tweeked a bit to allow for a bit of negative camber. The full floating Quaife axles seem to tolerate it okay. The 7/8" rear bar is mounted in the boot on the roll cage extensions and project through the wheel wells to the outermost axle housing.
It seems to work. No more roll steer, no more funny wheels in the air...4 corners better than 3...;o)
Class legal weight is 1730 lbs.(we are a bit over that) and the engine output from the recent dyno run, is 197 hp at 8100 RPM...It's quick enough for vintage.
Rod