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      07-13-2015, 08:23 AM   #1
nickhelou
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Most effective way to combat body roll?

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Hey guys,

I've visited my BMW parts store today to ask for the pricing for the M Adaptive Suspension for my 435i X-Drive (F32). I was told it can't be done. So now I am considering a aftermarket setup to combat my body roll. I want to conservatively drop my car to lower the center of gravity, and I want to stiffen it up. What suspensions do you recommend? I was thinking of going with some coil-overs + shocks and front + rear sway bars. But since I'm very new to modding, I need your help to determine what is actually good both on paper and in the real world for my car. Any suggestions are deeply appreciated.
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      07-13-2015, 09:14 AM   #2
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If roll is your main concern I would normally say just look at RSB. But its not a simple install. For the money, a lot of folks love the combination of Bilstein B8's and H&R sports. Lots of discussions in the suspension sub forum. Would recommend searching around....btw, coilovers ARE struts.
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      07-13-2015, 11:10 AM   #3
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Quote:
Originally Posted by Tomahawk View Post
If roll is your main concern I would normally say just look at RSB. But its not a simple install. For the money, a lot of folks love the combination of Bilstein B8's and H&R sports. Lots of discussions in the suspension sub forum. Would recommend searching around....btw, coilovers ARE struts.
I'm on the fence on H&R (No real life experience with them) due to some finding them amazing and others finding them too bouncy. I was thinking of getting KW V1's all around and H&R front + back sway bars. Do you think an M4's Sway bars would work too?
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      07-25-2015, 10:27 AM   #4
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Sway bars are the most effective way to counter body roll, bar none. There are now even"active" systems that push the car even further "into" the turn, dropping the inside wheel down, but the whole concept of a sway bar is that the more weight that transfers to the outside wheels, the more the sway-bar pushes on that side of the suspension like a spring, to resist the centrifugal force. Anything else you do may reduce it, but it won't have nearly the same effect. The sway bars are in effect massively increasing the spring rate of the outside wheels (which are under an extremely increased load, so they need it) in a turn.
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      07-26-2015, 07:07 PM   #5
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Quote:
Originally Posted by JamesNoBrakes View Post
Sway bars are the most effective way to counter body roll, bar none. There are now even"active" systems that push the car even further "into" the turn, dropping the inside wheel down, but the whole concept of a sway bar is that the more weight that transfers to the outside wheels, the more the sway-bar pushes on that side of the suspension like a spring, to resist the centrifugal force. Anything else you do may reduce it, but it won't have nearly the same effect. The sway bars are in effect massively increasing the spring rate of the outside wheels (which are under an extremely increased load, so they need it) in a turn.
+1. Sway bars. Coilover/shock,springs are more beneficial to nose dive.
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      07-27-2015, 03:04 PM   #6
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From my experience I find it's much better to first sort out the springs and dampers before sway bars.
Sway bars are a fine tuning item. They should not be used to compensate for poory sorted/tuned springs and dampers.

First identify what it is you are trying to fix in the handling and then get what is needed.
The adaptive M dampers show that sway/lean is directly dependent on the dampers primarily and secondarily on the sway bars.
With the M adaptive dampers there is still too much sway/lean in the base suspension.

This shows that the adaptive dampers still don't have enough control over the springs as they respond to weight transfer. As a turn happens the cars weight transfer to the outside, that compresses the springs, called 'compression'. The dampers have to respond by absorbing that spring energy by way of the damper fluid flow internally.
If the flow rate is too much/easy that will allow the weight transfer to compress the outside springs to a greater extent, and if the fluid flows too easily that lean will be more than wanted.

If you increase the spring rate, then for the spring to compress it will require more weight transfer in order to compress the springs. That's why a higher/firmer rate spring can help control weight transfer. A higher rate spring requires more energy/weight in order to compress it. With a higher rate spring you also need a damper that can then control the energy.

In a transition, left/right, as the car turns the other way the springs let up/rebound and the other side compresses. The dampers have to control both motions compression and rebound. If a damper does not control the springs rebound effectively, then the spring can return too quickly causing a "bounce" like quality. This can be felt more easily on turns that have bumps causing the spring to bound and rebound quickly.
If the damper doesn't respond with enough fluid control the car will feel bouncy, with more lean/sway, and feel less in control.

The question is whether the springs rate is too much and the damper doesn't control them enough, or the springs are too light and the damper is overly aggressive in controlling the springs motions.
Or, are the springs rates ok and it's the damper that doesn't have enough rebound and/or compression damping?

In my 335i Msport I can feel that the adaptive dampers don't have enough rebound damping. At the same time it feels as if the spring rates were chosen for added comfort in mind and thus allow more lean/sway during a turn and weight transfer.

This is how BMW achieved a suspension that allows "comfort" mode to give a more plush compliant ride over bumps, and then uses the active/adaptive dampers to provide more aggressive damping when set to sport. IOW, the dampers are artificially compensating for a lighter spring rate.
It's a compromise that BMW chose in order to achieve this dual role.
It works for the general public, but those of us who want and are used to a firmer and more controlled suspension find that there is something missing.

If you simply use thicker sway bars you may achieve a bit less lean/sway. However, you're compensating for a the primary suspension parts not being what they should be if you are trying to achieve a higher performance level from the suspension.

I suggest looking into firmer rate springs for both the front and rear, and then choose dampers that are designed to work with those spring rates.
You'll notice an improvement in handling all around with less lean, even with the same sway bars.
After that, you can decide if you need to adjust/fine tune the sway bars to get flatter cornering.

All of this is predicated on what it is you are trying to achieve.
If you want a better performing suspension for better control and handling, then look to the primary parts first, then sway bars.

If you just want to "band aid" the suspension at a lower cost, then sure get some thicker bars, but you may still find that the stock springs and dampers allow too much body motions during transitional handling and when going over bumps and dips.
If you have excessive nose dive, then you have a clear indication that the springs and/or dampers are not correct for the type of driving you want.
Diving during hard braking and lift during acceleration shows a suspension that is not tuned for aggressive driving.

BTW, I'm not speaking just for track use, and you don't need to go with that firm of a setup. There are really good options out there for higher performance that still allow for a nice street ride.
If you have the adaptive M dampers, then you could try some firmer rate springs first and see how the dampers handle it.
If you have the static M sport suspension, same thing, try a firmer rate spring.

I'm sorry I can't give you specifics, but there are so many different ways to tune for what YOU want. Other BMW drivers with the same car as yours can tell you what they didn't like and what they did to correct it. That's a great place to start.
Also, call up tuner suspension dealers and tell them what you are feeling with your car and what you want.
Suspension tuning is a science and an art to get it to what you like, and there are plenty of options out there for every need.

Happy tuning.
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      07-27-2015, 03:09 PM   #7
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Quote:
Originally Posted by nickhelou View Post
I'm on the fence on H&R (No real life experience with them) due to some finding them amazing and others finding them too bouncy. I was thinking of getting KW V1's all around and H&R front + back sway bars. Do you think an M4's Sway bars would work too?
If they are too bouncy that is because most likely the spring rates are too heavy for the dampers, as those dampers were not designed to deal with the heavier rate. The "bounce" comes from compression and rebound as the dampers can't control the energy and motion, so they "bounce".

A "hard" hit over a minor bump indicates too much compression damping that does not allow the spring to compress enough.
If the car bounces off a bump that could indicate that the rebound damping is too light as the damper can't control the springs return.

Coil overs are great when they are designed properly for the weight of the vehicle they are used on. Higher end systems allow for adjusting ride height, compression and rebound damping.
But, you have to have a good understanding of what those things are, what they do, and how they interact so that you can tune it.
There are also very good systems that have less adjustment and are better suited for the sporty street driver.
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      07-27-2015, 03:24 PM   #8
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Good posts above.

Those were basically my thoughts. Springs/dampers, then sway bars.
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      07-27-2015, 04:41 PM   #9
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Quote:
Originally Posted by Polo08816 View Post
Good posts above.

Those were basically my thoughts. Springs/dampers, then sway bars.
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      07-27-2015, 09:42 PM   #10
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Problem is, increasing spring rate will reduce weight transfer/compression on the outside during a turn, but it will also effectively over-spring the inside significantly and result in less traction there, in addition to the worse ride everywhere with insufficient damping. Going to adjustable or higher damping rate coilovers will help, but result in a significantly stiffer/firmer ride everywhere. The reason to do this is usually to drop ride height and get a significantly better performing shock (compared to OEM), but the actual OEM setup can vary quite a bit and affect the options here. The swaybars have a greater ability to resist quick changes in direction that would unsettle the car and cause significant weight transfer, as resisting weight transfer and still being able to absorb bumps requires very complex valving in a shock that is not usually seen at a reasonable price point.

Maybe I just got lucky with the camaro+sway setup, just from my initial few-hours outing in my 428 with DHP I am thinking the suspension isn't nearly as good as what I had in the Camaro ss, which seemed to have a higher quality of damping, as you go faster it makes the road feel smoother over rough spots, vs the 428 which doesn't seem to get better with speed and feels rather under-damped and "hollow". Not taking about chassis flex, just bump absorption and traction.

With my wrx it felt like there was ample traction, but the body roll was off the chart (well, not as bad as a forester, but still not good). It needed stiffer sways for sure.

Last edited by JamesNoBrakes; 07-27-2015 at 09:47 PM.
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      07-28-2015, 11:54 AM   #11
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Quote:
Originally Posted by nickhelou View Post
Hey guys,

I've visited my BMW parts store today to ask for the pricing for the M Adaptive Suspension for my 435i X-Drive (F32). I was told it can't be done. So now I am considering a aftermarket setup to combat my body roll. I want to conservatively drop my car to lower the center of gravity, and I want to stiffen it up. What suspensions do you recommend? I was thinking of going with some coil-overs + shocks and front + rear sway bars. But since I'm very new to modding, I need your help to determine what is actually good both on paper and in the real world for my car. Any suggestions are deeply appreciated.
Unfortunately you probably have the worst suspension setup available from the factory: Non-DHP xDrive.

If you want to simply combat body roll, then I "guess" sway bars would be okay.

But if you want the whole package with the ability to lower and adjust, then coilovers are the way to go for the xDrive since the M Performance Suspension isn't an option for you.
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      07-28-2015, 12:58 PM   #12
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Quote:
Originally Posted by Polo08816 View Post
Unfortunately you probably have the worst suspension setup available from the factory: Non-DHP xDrive.

If you want to simply combat body roll, then I "guess" sway bars would be okay.

But if you want the whole package with the ability to lower and adjust, then coilovers are the way to go for the xDrive since the M Performance Suspension isn't an option for you.
Going to go with KW V1's once their dealer here sorts out the parts needed for my car.
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