I've got hold of 2 caterham antiroll bars and i'm about to fit them to my tiger, do you lads think i'm right to try the heavyest rollbar first(18mm) or should i fit the light one(13mm).
I'm fitting them on the front of the car first to see the differnce and then i'll fit the other one to the rear at a later date
any advice please

Try the lighter one first if they are interchangable. Or if you're feeling really swish, try blade adjusters to vary the effective spring rate of the bar.

Mmmmm ok i'm thick what are blade ajusters

The link that normally goes from the drop bar/link to the anti-roll bar is normally solid/fixed bar. If it's blade shaped/ a bit like sheet steel it can be adjusted to give a variable stiffness. IE with the blades vertical you get full stiffness, horizontal you get minimum stiffness. It can be done on one side or both to give more variation.

looks like this if that help explain things.

Thanks DIY Si, think i'll stick to rose joints and threaded bar for now but will bare that advice in mind for future upgrades, incase you haven't worked it out yet this whole suspension thing is doing my head in at the moment so i'll stick to what i know for now
Thanks

This is a non adjustable version, but gives you the idea I think. The blades on this one are fixed, but the overall idea is about what I was trying to explain.

Don't worry, I'm only just starting to learn about this stuff to! Roll centers and the like where all foreign to me a few weeks/months ago!

what happends if you don't have an anti-roll bar?

Not at a lot really. It can help with the suspension set up though. Some people use them, some feel them unnessecary.

I was under the impression that they are only really usefull on a heavier car or a car that is having its nuts thrashed off...

My antique 1995 polo has one...god knows why!

It depends on how you like to drive through corners.
Antiroll bars help keep the unloaded wheels in contact with the road (to a point) and therefore give better control.
The opposite is true in wet conditions as they make your car less stable in corners.
Most racers adjust them to very soft or disconnect them in the wet.
I have adjustable front and rear bars on my car but I keep the front one disconnected (rear engine).
This is because that the uk potholes give my front suspension a hammering and have a habit of forcing my adjuster collets off.
I would reconnect them for track use only.
The rears do feel better with the antiroll bar but I do not know how well they will do in the wet.

so would it be advisable to put one on a awd car that i plan to thrash the nuts off. its the reason i'm building it to do so!

is theres no real need for one on the rear i take it

With a lightweight car on stiff springs with a low CoG antiroll bars are gilding the lily a bit...
I would have said wait till you've thrashed it a bit & if you feel it understeers put one on the back, if it oversteers more than you like put one on the front. You could work it all out theoretically with roll stiffness front & rear, but theory doesn't always relate exactly to practise!
I believe it is usual practise to tune handling traits thus with antiroll bars - hence the "blade" adjustable variety. Incidentally, my understanding was that with those the blade itself bent, forming the spring of the antiroll bar - clearly it's much stiffer edge on!
cheers
Bob

Yup, the blade forms part of the spring, or it wouldn't really work when turned horizontal. Can't remember for sure, but I think they need to be made from spring steel.

Remember that with almost any Locost / Super7 that I have ever seen that did not have a full cage is so flexable that the front and rear suspensions are working totaly independently. This means that a sway bar has the ability to control sway only on that end of the car. It does not have the ability to move weight across corners as the books assume. This is why adding a rear bar may give the effect of less overstear. This is also the reason that adjusting the bump rebound on the shocks to full hard appears to only make these cars ride bad.

It is worth bearing in mind that the more you stiffen the front, the more you will promote understeer. Similarly, stiifening the rear increases oversteer.

John

This might be a question with out an answer, but would you be able to put a minimum figure on stiffness to make roll bars work "properly"? I appreciate most 7's aren't the stiffest of chassis, but what type of thing would be? ie would most monocoque's be up to it?

can't have enough oversteer, its the whole fun of these cars unless shes incontrolable

quote:

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Originally posted by DIY Si
This is a non adjustable version, but gives you the idea I think. The blades on this one are fixed, but the overall idea is about what I was trying to explain.

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Take the weight of the car with driver in lbs and multiply by 3 to get the ft lbs / deg where the swaybars and springs realy start to behave per the books. At 1 times nothing appears to work as the books claim. My new Locost that we started to build this weekend is close to 9500 ft - lb / deg but it does have a full cage. It is possible.
AW

quote:

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Originally posted by nitram38
Antiroll bars help keep the unloaded wheels in contact with the road (to a point) and therefore give better control.

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Let me try to explain whats going on with anti sway bars. Lets assume we have a car with identical front and rear suspensions. Also assume that the car has a 2000 lb weight with 50-50 weight dist. and is coasting around a corner. The front of the car weighs 1000 but weight transfer makes the outside tire hold up 750 lbs and the inside tire holds up 250 lbs both front and rear.

Now we add a rear sway bar that at this cornering load will add 100 lbs to the outside rear tire as the new rear bar tries to hold the chassis more level than the springs alone can do. The rear tire is now pushing down 750 + 100 or 850 lbs. The rear of the car still weighs 1000 lbs so the inside rear tire is holding up 1000 - 850 = 150 lbs. The weight that gets twisted into the chassis has to get transfered forword thru the chassis and ends up on the inside front tire or 250 + 100 = 350 lbs. Last the outside front tire holds up 1000 - 350 = 650 lbs. The right rear tire is more overloaded of the inside front tire is less overloaded so the car feels more lively. This all assumes the chassis is capable of transfering this sort of torque from the outside rear, forword to the inside front tire.

Reading the Staniforth book will help clear some of this up. The link below is based on his book.

see http://www.ncs-stl.com/Files/ChassisCalcsPublic.xls

Hope this helps

AW

[Edited on 13/11/06 by whittlebeast]

quote:

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Originally posted by gazza285

quote:

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Originally posted by nitram38
Antiroll bars help keep the unloaded wheels in contact with the road (to a point) and therefore give better control.

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You had better explain this one to me as I was under the impression that an anti roll bar worked in the opposite way, the loaded wheel pulled the inside wheel with it, therefore reducing roll. It's pulling the inside wheel away from the road, not helping to keep it in contact.

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It's more like a dog standing on four feet with you pushing on the body of the dog. Rover can still pick either on of his feet on your side. frond or rear. Pick any one. Push harder and Rover can pick up two. Push even harder and rover falls over. That simple.

If the chassis is floppy enough and the roll bars are hugh enough, then the chassis starts behaving like a race kart. An entire new set of math. With the 1000 lb and 3000 ft - lb / deg car at the left I did manage to put too large of bars. The car would not accelerate straight. It has a $2500 formula 3 torque sensing dif and the weight transfer accross corners at 1 gee acceleration was a fright coming off bumpy corners. The power would hunt from the left rear tire to the right rear tire and back. That seup only lasted one event and was removed as a lesson learned.

[Edited on 13/11/06 by whittlebeast]

I would think on most cars the swaybar's effects have less to do with weight transfer and more to do with increased roll stiffness. Weight is always going to transfer to the ouside wheel no matter what you do with the roll stiffness. In a super stiff racecar chassis you may see decrease in weight transfer as whittlebeast is describing, but in most cases I doubt it.

Roll stiffness is what we are trying to increase by adding swaybars. Why do we want more roll stiffness? Because body roll changes the geometry of the suspension and causes things like positive camber on inside tire and jacking effects among other things. All of which make the car slower and/or less predictable.

The outside tire is being pushed DOWN by the swaybar and the inside is being LIFTED by the swaybar. Simplest way to view this is draw a solid link from swaybar frame brackets to the swaybar control arm brackets and then add some bodyroll. The outer link is trying to get shorter, and the inside link is trying to get longer. The swaybars stiffness is what controls this.

If your swaybars stiffness adds 200lbs/inch to your roll stiffness you have just added 200lbs/inch to your outer spring and this is where the reduced roll comes from.

Hope Ive said that right. I rushed a bit.
Cheers.

The reason that a floppy car handles better with sway bars has NOTHING to do with weight transfer. Lareral weight transfer is only a function of cg height and g forces. The real reason they feel better is the less time that it takes for the chassis to reach full roll and take a set is reduced with the increase in overall roll stiffness. The other thing that is a big factor is camber change that is roll induced. If both ends of the car feel better by adding bars the real reason that it "handles" better is the outside tires are closer to vertical when fully loaded. Still without chassis stiffness the two ends of the car will work independently from eack other. Also remember that the shocks also have similar issues. If you realy want the car to handle you need a stiff chassis, stiff springs, good shocks and medium swaybars. 2 cycles per sec wheel rates, .75 degrees /g roll rates and 106% front tire loads.

AW

[Edited on 14/11/06 by whittlebeast]

That's enough pedantism, now what about monoshock systems? Any thoughts for a Locost application?

I would imagine it would be really tough to hook all 4 wheels to one shock. So I assume you are talking about the R1/R6 style coilover shock used on a LC.

No, the monoshock systems used on some single seaters, with both front or rear wheels using one shock shared between them.

Monoshock is a fine option. There is two problems that I know of. Lack of well documented calculations that you can figure out. And roll is totally undamped. You could add a second shock for roll damping only but to get the damping trully linier when rolling left and right may be tough and you just ended up with the same number of shocks. The added weight of the larger sway bar may wash with the saved weight. It would look cool

AW

[Edited on 14/11/06 by whittlebeast]