Development of our G87 M2 continues at high speed with new adjustable anti-roll bars (sway bars) from Eibach fitted ahead of track testing using advanced laser sensors.
Upgrading the anti-roll bars (otherwise known as sway bars) on a BMW M car is one of the most effective ways to sharpen chassis response, reduce body roll and fine-tune handling balance. As we have found with our M2 development car, BMW’s sports coupe is somewhat lacking in the cornering department out of the box. The good news is, an uprated G87 M2 anti-roll bar package can dramatically improve precision on the road and track.
Eibach UK recently invited us to test the company’s first G87 M2 anti-roll bar package for European market cars. We love finding new ways to measure the performance gains of suspension upgrades and our new laser sensors are a match made in heaven for Eibach’s latest kit.
For the first time, we can log ride height changes at each corner of the car around a lap – in real-time – via VBOX’s HD2 system. This means we can measure exactly what benefits aftermarket anti-roll bars bring to handling performance. Our new sensors can even assess the differences that, for example, the ARB’s full soft and full hard settings make to body control.
All combined, we are able to present a much clearer picture of how adjustable M2 anti-roll bars improve roll behaviour, chassis balance and grip.
What Does an Anti-Roll Bar Do?
A sway bar, or anti-roll bar, links the left and right sides of the suspension across an axle. Its job is to resist body roll through corners.
Without anti-roll bars, a car would lean excessively during cornering. In this situation, the outside suspension compresses heavily and overloads the tyre, while the inside moves into droop. You might think installing stiffer springs would cure this problem, however these create compromises elsewhere in the chassis.
Overly stiff springs can reduce traction under braking, acceleration and over bumps. The beauty of an anti-roll bar is that it primarily works when there is a difference in wheel movement across the axle. When the car is travelling in a straight line, both wheels move up and down together so the anti-roll bar has very little effect. Through a corner, however, it adds roll stiffness and helps keep the chassis flatter.
That makes an upgraded G87 M2 anti-roll bar a very powerful tool for suspension tuning. It allows us to increase cornering support without making the car unnecessarily harsh in a straight line.
Why Fit Adjustable Anti-Roll Bars to the G87 M2?
The red Eibach anti-roll bars fitted to our BMW G87 M2 are adjustable, which means each bar has multiple mounting holes on the lever arm. By moving the drop link (otherwise known as an end link) between these holes, we can change the effective stiffness of the bar.
The hole furthest from the bar gives the softest setting. The hole closest to the bar gives the stiffest setting. This is because a longer lever arm allows more flex, reducing the bar’s effective roll stiffness. A shorter lever arm increases the rate, making the bar respond more aggressively.
This type of adjustment is common in high-quality, aftermarket anti-roll bar kits because it fits neatly into the factory architecture. Unlike blade-adjustable anti-roll bars, which are more often found in motorsport applications, these Eibach bars can be installed in place of the factory bars while retaining a straightforward mechanical layout.
For a car like the G87 M2, that adjustability is extremely useful. It means we are not simply fitting a stiffer part and hoping for the best. We can tune the front and rear roll stiffness distribution to suit the tyres, dampers, spring rates, ride height, wheel alignment, circuit and even driver preference.
Why Adjustable Drop Links Matter
When fitting an M2 anti-roll bar upgrade, we recommend installing adjustable drop links too. The first reason is because they are stronger than the original parts. This is important as uprated anti-roll bars generate higher loads through the suspension system, particularly on track. A stronger drop link reduces flex and helps transfer the anti-roll force directly into the suspension.
The second reason why we recommend installing adjustable drop links is because they allow the anti-roll bar to be positioned correctly after a car has been lowered. Dropping the ride height is common for track use, but drivers often forget the knock-on effect this has on suspension geometry. Once the ride height is changed, the anti-roll bar may no longer sit in its intended operating position. By altering the drop link length, we can restore the bar angle and avoid clearance issues with the chassis, suspension arms and other components.
Even more importantly, adjustable drop links allow us to remove pre-load from the anti-roll bars after corner weighting. When a car is corner weighted, the ride heights are often slightly different from left to right. Even a few millimetres of difference can twist the anti-roll bar while the car is stationary. That means the bar is already loaded before the driver has even turned a corner. This can create inconsistent handling behaviour.
By adjusting the drop link lengths, we can avoid any pre-loading and allow the anti-roll bar to work evenly in both directions. For both fast road and track driving, this is a crucial detail.
How Anti-Roll Bars Affect Understeer and Oversteer
Anti-roll bars have the biggest impact in the middle of corners. At the apex of a turn, the car is in a more settled state than at corner entry or exit. At this point, the main influences on handling behaviour are the coil springs, tyres and the anti-roll bars.
If the car is understeering at the apex – meaning the front is washing wide mid-corner – we need to give the front axle more grip relative to the rear. You can usually achieve this by softening the front anti-roll bar or stiffening the rear anti-roll bar.
If the car is oversteering at the apex – meaning the rear is rotating too much – we need to give the rear axle more grip relative to the front. In this case, we can soften the rear anti-roll bar or stiffen the front anti-roll bar.
As a simple rule:
Understeer at the apex: soften the front bar or stiffen the rear bar.
Oversteer at the apex: soften the rear bar or stiffen the front bar.
The tricky part is knowing which change to make. If one bar is already at the end of its adjustment range, the answer may be obvious. However, if both bars are set in their middle position, it often makes sense to make one change at a time and then assess the car’s behaviour on the move.
On track, small changes in roll stiffness distribution can make a noticeable difference to driver confidence, chassis balance and lap time, so it’s well worth the effort to get right.
Measuring G87 M2 Chassis Roll with Laser Ride Height Sensors
For our G87 M2 anti-roll bar test, we are going significantly further than simply relying on driver feel and tyre temperature data, very good though they are for analysing upgrade performance. For the first time, we have installed advanced laser sensors on our BMW, which allow us to measure ride height changes at all our corners of the car on circuit.
These sensors scan the ground in real time and measure how the ride height changes as the car brakes, turns, rolls and accelerates. By logging that data, we can produce a clear picture of chassis movement throughout a lap.
This represents a major step forward in our assessment of suspension upgrades. These new sensors will not only allow us to state, with absolute confidence, that the anti-roll bars reduce body roll. We will also be able to measure the difference Eibach’s ARBs make to body roll – to the millimetre, and at each corner of the car.
For suspension development, this type of data is incredibly valuable. Teamed with feedback from professional drivers, it will give us an even clearer understanding of what the car is doing on track, and will guide the M2’s tuning process going forwards.
The Next Step: Track Testing at Anglesey Circuit
With the Eibach anti-roll bars fitted in our workshop, the Suspension Secrets adjustable drop links installed, and the new laser ride height sensors in place, the next stage is to return to Anglesey Circuit and compare handling performance.
We’ll be assessing chassis balance, roll control, steering response, traction and mid-corner behaviour, then compare the data from the laser sensors to the feedback from pro driver and coach Chris Dymond.
This is the point where the Eibach upgrade moves from theory to proof. We will see how much chassis roll is reduced, how the car responds to adjustment, and discover whether the new M2 anti-roll bar setup delivers the sharper, flatter and more confidence-inspiring handling we are aiming for.
In our next YouTube instalment, you will see these new G87 M2 Eibach anti-roll bars and laser sensors in action. Meanwhile, check out our G87 M2 anti-roll bar explainer below.
SHOP BMW G87 M2 SUSPENSION UPGRADES.
