Originally posted by Chris
View Post
Take a look at the graph below; it's taken from data from my MC's ECU during acceleration in 3rd gear under WOT as recorded by my datalogger.
In this graph, I floored the accelerator at around 1900rpm with the DSC on, and as you can see the engine response is immediate and that the rate of engine acceleration is almost perfectly linear throughout the rev range, showing that I was getting the same level of traction of the rear tyres on the tarmac throughout the rev range with no/minimal slipping, even when the full power was first applied.
So, if traction can be maintained, the DSC doesn't intervene, and that means around corners as well as in straight lines. Since the S54 MC also has a 25% limited slip differential some difference in traction on the two rear wheels is also permitted by the DSC, as it is in the S50. Therefore, if you can drive in a style which maintains both balance and traction then the DSC has no reason to intervene. This happens both on track and on public roads, because the physics is the same in both environments.
The DSC acts by temporarily cutting the power and/or applying the brakes to individual and/or all the wheels to prevent an impending serious instability/loss of traction/grip. It's my experience of the DSC on the S54 that the factor which initiates the DSC the most is excessive yaw. From my participation on this forum for the past 5 years I notice that a number of S50 owners have found themselves pirouetting in their S50 MCs through 360 degrees when the yaw rate has become excessive, and this happens so quickly that it catches the driver out. From what has been posted on this forum, this has occurred on both public roads and on track, therefore some MC owners have unwittingly driven their MCs at above "100% of what the car is capable of performance-wise", otherwise they wouldn't have lost control. So why has this happened?
In the wet, it is obviously easier to lose traction than on dry tarmac, therefore to maintain traction in the wet, it is more imperative to maintain the balance of the car and to make weightshifting as smooth as possible under acceleration, braking and cornering, because once traction is lost in the wet it is harder to regain than in dry conditions. If you do this right then again, the DSC on a S54 MC has no need to intervene so you're in the same situation as the driver of a S50 MC under control.
For me, the greatest weakness in the OEM MC is the excessive bodyroll because the suspension set up is inadequate for the engine power. The excessive bodyroll can cause the car to become suddenly unbalanced and thus permit the MC to suddenly exceed "100% of what the car is capable of performance-wise" and the DSC can prevent some of the spins and pirouettes that would otherwise occur. However, if you considerably reduce bodyroll by suspension modification, then you prevent the bodyroll that causes the sudden weightshifts that can cause many of the losses of balance that would otherwise cause loss of control.
Over the past 3.5 years I have systematically and progressively modified the suspension on my MC so that it is now fully adjustable front and rear for height, camber, toe, caster, bump and rebound, and with bracing and stiffer bushing all round so that the car's dynamic geometry remains as close as possible to the static geometry to which it is set. Consequently, it is now easier for me to preserve the dynamic balance of the car because the weightshifting is much reduced, which in turn prevents loss of traction under power to the rear wheels and increases lateral grip during cornering, and as such, the DSC has even less reason to intervene than it would without these changes. Therefore my MC can go around a track with tyres screeching away without the DSC ever needing to intervene, partly due to the improved handling characteristics from my suspension/aerodynamic modifications and partly from my own driving style, which is probably somewhat different from yours because I've now driven some 300,000 or so miles on the twisties in all conditions over the past umpteen years.
For interest, I've produced the graph below which shows the lateral G-force at speed versus corner radius.
If you look at the green line, which is a plot for 1G, you will see that your car will be pulling 1G at 30mph around a corner with a radius of 18metres, 50mph around a corner with a radius of 50metres, 70mph around a corner with a radius of 100metres and 100mph around a corner with a radius of 200metres, and so on. Therefore, if you measure the radius of an arc of a corner that you measure in Google Earth and know the speed that you travel around that corner, you can fairly accurately estimate the lateral G-force that your car can achieve. It is therefore quite a simple task to look at the graph and see how, say, driving at 30mph around a rounadbout (in a private car park denoted by cones, of course) will translate to the speeds you can achieve around all other corners of known radius for (private) roads and on track. As you can see, there's about a 20% difference in speed around a corner between 0.9G and 1.1G, therefore if you can increase traction and grip in anyway (driving style and/or car mods) you'll increase your cornering speed significantly, which in turn will increase your (car's) performance.
Hope this helps.
Comment