anti roll bar settings

[khooni]

Full front soft and full rear hard for oversteer or full front hard and full rear soft to curb oversteer? Am I the only one that thinks the MC comes with too much understeer from the factory?

I'm getting mine fitted today and would like much expereinces or comments regarding settings. For some strange reason, I think the US guys recommend full front hard and full soft rear....

[exdos]

khooni,

At the moment, I've got mine set on full soft both at front and rear and I think that the car handling is pretty much neutral, but that's with adjustable suspension.

I like the front of the car to be pretty stiff in comparison to the rear so I would think that setting your front ARB on the stiffest setting and the rear ARB on the softest would give the sort of handling that I like. If there's any adjustability in anything that you fit, if you're like me, you'll never be happy until you've tried all the permutations. :wink:

[c_w]

I wouldn't say the coupe has a lot of understeer, although it probably will understeer as most cars do unless its power oversteered. I found the turn-in was really keen even on standard suspension.

Exdos; I assume even on softest settings the ARBs are still a fair bit stiffer than the original bars?

[exdos]

Exdos; I assume even on softest settings the ARBs are still a fair bit stiffer than the original bars?


They certainly are. The H&R ARBs have approx. 33% increase in thickness to the OEM and IIRC the stiffness is proportional to the square of the diameter, therefore the stiffness of the H&R ARBs is nearly a 50% increase on the OEM at lowest setting.

[khooni]

That's what I thought. You get much better turn in with full front hard. I am just thinking to myself that it would cause major understeer. But, at least it would make the car accelerate better as it will more likely squat in corners and rocket off.

[c_w]

I'm not sure I follow what you've written Khooni, I'd imagine full hardest on front with softer at the back usually makes turn in less aggressive and potentially more understeery?

[exdos]

You can theorise about this all you like, and the only definitive answer lies in the practical effect that it has on the handling of your MC.

I didn't remember correctly about the stiffness, in fact the torsional rigidity is a function of the diameter to the fourth power of the diameter of the bar and not the square (second power] as I stated above. This means that a 33% increase in diameter of the H&R ARBs over the OEM has a massive increase in torsional rigidity.

Khooni, the front ARBs, both OEM and aftermarket versions, come much thicker (hence stiffer) than the rear ARBs, therefore the effect these will have upon the handling of your car is naturally "factored in" provided you stick with the same setting (either softest or hardest settings) at both ends of the car.

Stiffening the front more than the back will increase understeer, therefore if I were you, I'd keep both front and rear ARBs set on the same settings (be it softest or firmest) unless you have an airfield where you can experiment with different front to back settings and if you find that you create dangerous levels of under or oversteer, you'll come out of it all safely.

In any case, I think you'll find the uprated ARBs on their weakest settings are more than enough for the streets of London :wink:

[Lee]

I have mine on the lowest settings and I dont think you would want them any firmer for London roads

[khooni]

I'm gonna try. BTW US roads are not better by any measure. So let's see if it's really bad.

[exdos]

I've got used to the handling of the new H&R ARBs on the softest setting so I set about changing to the stiffest settings yesterday. When I changed the rear ARB to stiffest, I found that the ARB makes contact with both drive-shafts to the rear wheels so it is impossible to adjust the rear ARB to any setting other than softest. The answer to this problem would be to use a longer stabiliser links than the OEM ones. Does anyone know if there is a BMW version for a different car or is there an aftermarket alternative?

[khooni]

turn in is sharper than I remember at stock and I have full front stiff. Don't know about links though. If I may suggest, why don't you try stiffening the front to see what you get instead of adjusting for oversteer at the rear.

Let me know what you think

[exdos]

turn in is sharper than I remember at stock and I have full front stiff. Don't know about links though. If I may suggest, why don't you try stiffening the front to see what you get instead of adjusting for oversteer at the rear.

Let me know what you think

khooni,

I don't think of adjusting the ARBs in the way that you seem to be thinking in the terms of getting understeer or oversteer, I'm thinking in terms of general "balance" of the car. As I see it, in any car I drive, I get understeer if I drive into corners carrying too much speed and I get oversteer if I'm too heavy with the throttle when the car isn't straight enough and I have to learn to handle each and every car that I drive by assessing its "quirkiness" ASAP.

With my adjustable suspension I have managed to make my MC into a car which is extremely well balanced and handles precisely to my taste and my style of driving. I can't see the point of having the front ARB setting proportionately stiffer than the rear because I think I would be upsettting the general longitudinal balance of the car. As it is, I already have the dampers at the front set stiffer than the rear ones, which for me gives balance to the car.

[c_w]

Antiroll bars are used a lot to alter the balance of a car, stiffer on rear usually equals better turn-in, stiffer front (propertional to the rear) usually equals less turn in and can sometime introduce understeer.

I personally wouldn't go for full stiff at the front as that sounds like a huge increase on stock, I'd go with front and back at a similar increase.

[exdos]

Antiroll bars are used a lot to alter the balance of a car, stiffer on rear usually equals better turn-in, stiffer front (propertional to the rear) usually equals less turn in and can sometime introduce understeer.

I personally wouldn't go for full stiff at the front as that sounds like a huge increase on stock, I'd go with front and back at a similar increase.

I won't be happy until I've tried the ARBs at their stiffest settings but I want to retain proportionality between front and rear. I already get more turn-in than stock from my front flippers and from negative camber, and my only reason for wanting to increase the ARB settings would be to see if the car can remain even "flatter" around bends than it already does now. I can already create understeer and oversteer, at will, by driving technique in any car.

[khooni]

conversely to what you have suggested regarding turn in, the US guys and tuners have suggested stiffening the front for better turn in and in fact some have gone to the extent of disconnecting the rear altogether. I know this is normally the other way round and balance is generally better for stiffer at the rear vs the front but then again, most cars (I think) come stock rear bars stiffer than the front or at least the same. with the mC, the stock front is much larger than the rear. (can't remember the dimensions, but i think it was 23mm font and 19 mm rear).

might be wrong on the dimensions!

[c_w]

Having it like this as standard, I would have thought, is to make the car "safer", less prone to oversteer and to increase traction.

Most cars will have a stiffer front anti roll bar than the rear for these reasons. Some often used to have no rear bar at all.

[exdos]

conversely to what you have suggested regarding turn in, the US guys and tuners have suggested stiffening the front for better turn in and in fact some have gone to the extent of disconnecting the rear altogether. I know this is normally the other way round and balance is generally better for stiffer at the rear vs the front but then again, most cars (I think) come stock rear bars stiffer than the front or at least the same. with the mC, the stock front is much larger than the rear. (can't remember the dimensions, but i think it was 23mm font and 19 mm rear).

might be wrong on the dimensions!

Most cars are manufactured with a tendency to understeer because it's generally thought safer for the general motoring public who have no interest or understanding of car dynamics or driving control beyond the basics to pass the driving test. Joe Public will "lose his bottle" when he feels that the car isn't turning as much as he thinks he is steering, therefore he will keep the car within its safety "envelope".

As I've written before, I've set my car up with it's KW V3 dampers to stiffer settings at the front than at the rear and for me, the car handles better this way. Likewise, I have improved turn-in from fitting ACS flippers and by putting negative camber on the front wheels. The car is very balanced and handles beautifully set this way. When I fitted uprated ARBs, my purpose was to reduce the rate of lateral load transfer during cornering, especially since the turn-in that I already had was pin-sharp, and the general balance of the car was already very good. Fitting the H&R ARBs on their lowest settings improved the handling of the car in exactly the way that I hoped they would: the lateral load transfer was considerably reduced during cornering, but the general balance of the car was preserved. I have felt it unnecessary to make any adjustments to my suspension settings to take account of the new ARBs, therefore I feel the general balance of the car has been preserved. In wanting to try the ARBs at their highest setting, I want the rate of lateral load transfer to be proportionately controlled at both front and rear, in order to preserve the balance of the car. I believe that my car is at the point where further stiffening the front proportionately more than the rear will be counter-productive.

As I see it, if you stiffen the front ARB proportionately more than the rear ARB, or even remove the rear ARB altogether, as you suggest, then you are going to get longitudinal flexion of the chassis so that you considerably reduce lateral load transfer at the front but considerably increase it at the rear. Since the theoretical purpose of the ARBs is to help to confine the Polar Moment of Inertia (PMI) in order to reduce lateral load transfer to keep the inside wheels loaded almost as much as the outside wheels during cornering, which in turn increases both grip and traction, then by removing the rear ARB you will produce an unbalanced car. Further, you would be using body flexion as part of the suspension and this goes against the general intention to make the chassis as stiff as possible so that the relationship between the sprung and unsprung masses can be properly controlled and tuned by equipment which is designed to act as the suspension, per se.

My sole objective in doing any mods is to drive around corners faster. I have found that with my car set-up with exactly the same KW V3 settings but with H&R ARBs at their lowest setting, it is possible to apply more throttle during cornering without the back end coming out, than with OEM ARBs. This has increased cornering speed and improved considerably wet road traction and grip. I attribute this to the fact that the inside wheels make much better contact with the road, because lateral load transfer has been considerably reduced, therefore both rear wheels are almost equally loaded thus preventing diff slip. I am hoping and predicting that setting the H&R ARBs to the highest setting both front and rear will reduce the lateral load transfer that little bit more but still give enough "driver feedback" for me to detect any tendency of the car to break away, plus still give a decent ride.

I do 90% of my driving on "the twisties", on roads which are similar to those we use on the Welsh Weekend or Cotswold meetings. My comments are made solely on first hand experience and after trial-and-error experimentation with the suspension modifications and adjustments on my MC.

[c_w]

conversely to what you have suggested regarding turn in, the US guys and tuners have suggested stiffening the front for better turn in and in fact some have gone to the extent of disconnecting the rear altogether. I know this is normally the other way round and balance is generally better for stiffer at the rear vs the front but then again, most cars (I think) come stock rear bars stiffer than the front or at least the same. with the mC, the stock front is much larger than the rear. (can't remember the dimensions, but i think it was 23mm font and 19 mm rear).

might be wrong on the dimensions!

As I've written before, I've set my car up with it's KW V3 dampers to stiffer settings at the front than at the rear and for me, the car handles better this way. Likewise, I have improved turn-in from fitting ACS flippers and by putting negative camber on the front wheels. The car is very balanced and handles beautifully set this way. When I fitted uprated ARBs, my purpose was to reduce the rate of lateral load transfer during cornering, especially since the turn-in that I already had was pin-sharp, and the general balance of the car was already very good. Fitting the H&R ARBs on their lowest settings improved the handling of the car in exactly the way that I hoped they would: the lateral load transfer was considerably reduced during cornering, but the general balance of the car was preserved. I have felt it unnecessary to make any adjustments to my suspension settings to take account of the new ARBs, therefore I feel the general balance of the car has been preserved. In wanting to try the ARBs at their highest setting, I want the rate of lateral load transfer to be proportionately controlled at both front and rear, in order to preserve the balance of the car. I believe that my car is at the point where further stiffening the front proportionately more than the rear will be counter-productive.

As I see it, if you stiffen the front ARB proportionately more than the rear ARB, or even remove the rear ARB altogether, as you suggest, then you are going to get longitudinal flexion of the chassis so that you considerably reduce lateral load transfer at the front but considerably increase it at the rear. Since the theoretical purpose of the ARBs is to help to confine the Polar Moment of Inertia (PMI) in order to reduce lateral load transfer to keep the inside wheels loaded almost as much as the outside wheels during cornering, which in turn increases both grip and traction, then by removing the rear ARB you will produce an unbalanced car. Further, you would be using body flexion as part of the suspension and this goes against the general intention to make the chassis as stiff as possible so that the relationship between the sprung and unsprung masses can be properly controlled and tuned by equipment which is designed to act as the suspension, per se.

My sole objective in doing any mods is to drive around corners faster. I have found that with my car set-up with exactly the same KW V3 settings but with H&R ARBs at their lowest setting, it is possible to apply more throttle during cornering without the back end coming out, than with OEM ARBs. This has increased cornering speed and improved considerably wet road traction and grip. I attribute this to the fact that the inside wheels make much better contact with the road, because lateral load transfer has been considerably reduced, therefore both rear wheels are almost equally loaded thus preventing diff slip. I am hoping and predicting that setting the H&R ARBs to the highest setting both front and rear will reduce the lateral load transfer that little bit more but still give enough "driver feedback" for me to detect any tendency of the car to break away, plus still give a decent ride.



If you have a very stiff roll bar it increases the load transfer rate to the outside wheel and technically can reduce overall grip (your reducing lateral ROLL however.). As it laods the outer wheel it actually reduces load on the inner wheel and this is why you are more likely to start lifting wheels on the inside especially on tighter corners. I personally can't see setting them stiffest will help at all on a wet road and I would have thought it would make the car quite skittish (if they're *too* stiff) as the load transfer on the outer wheel is much faster which may overcome snappily in the wet.

[exdos]

I personally can't see setting them stiffest will help at all on a wet road and I would have thought it would make the car quite skittish (if they're *too* stiff) as the load transfer on the outer wheel is much faster which may overcome snappily in the wet.

c_w,

I will accept there will come a point when an ARB becomes so stiff as to make the car behave in the way you describe. However, how can either you or I know whether setting the H&R ARBs on the stiffest setting available will push the handling of my MC one step too far, until I have tried the ARBs at their stiffest :?: I've previously invited you to see how my car performs with all its handling mods, including H&R ARBs, and I think you will view the function of ARBs a little differently after such an experience. I will be meeting up with Steve1 (has a very similar set-up to me) in a week or sos time for a blast, why don't you come and join us?

BTW, have you sorted out your suspension problem yet :?:

[c_w]

Yep I will have to try and attend a meet sometime!

I've settled on the rear at a touch over 250mm and happy with the rideheight with the back a bit higher than the front (and to take into account some drop with driver and passenger since the rear axle appears to drop more on the Z3 as you sit so far back. I was thinking of changing shocks etc but going to leave it as it is now and see how I get on with the slightly higher ride height.

[exdos]

Yep I will have to try and attend a meet sometime!

I've settled on the rear at a touch over 250mm and happy with the rideheight with the back a bit higher than the front (and to take into account some drop with driver and passenger since the rear axle appears to drop more on the Z3 as you sit so far back. I was thinking of changing shocks etc but going to leave it as it is now and see how I get on with the slightly higher ride height.

For the best aerodynamics (reduced tendency to lift) the rear of the car should always be higher than the front.

[c_w]

BTW, have you sorted out your suspension problem yet :?:

Not about the ARBs but about my rear "butt" strut; I drove the route which caused the worse grounding again last night and it grounded again fairly easily. However I feel that this might just be the road more than the suspension setup. If anybody is familiar with the A523 out of Macclesfield towards Leek (before the A54 junction) there is a big dip in the road (pretty dangerous really) where the road opens up and goes downhill then goes uphill very sharply, driving over that at high speed it grounds everytime for me.

[exdos]

c_w,

As I see it, the only way that your butt-strut can ground would be if the road was very severely cambered and you drive along the crown of the road and then get maximum compression of the springs. Such a road would be a single-track road and you'd be driving at inappropriate speeds if you then grounded. If you are grounding on a two lane road then there must be a huge amount of vertical play in your rear suspension for the underside of your car to make ground contact.

I've just measured my present ground clearance specially to answer this problem for you and I have a ground clearance of 95mm under my butt-strut when the car is unladen and there is approximately 10mm-12mm of free-space left in my rear springs, therefore the minimum ground clearance when my car is fully laden and with springs fully compressed would be 83mm. Let's call it 75mm allowing for some tyre deflection as well.

I do 90% of my driving on rural A and B roads and I'm not known for "hanging about" and I still haven't had any ground clearance issues with my butt-strut after some 12k miles of driving on all manner of badly surfaced roads at relatively high speeds. I just can't see how your car can descend another 75mm more (that's 3 inches :!: ) on its rear suspension than mine to cause grounding on any A road in the UK. I still think that it's your springs that are bottoming out rather than your butt-strut that's making ground contact. Can you show me a photo of your rear springs either on or off your car?

Have you tried my paint test yet to prove its your butt-strut that's grounding?