Quote:
Originally Posted by Pretzel
Thank you @Max Well for putting this together. If I’m reading this correctly, it takes an additional 135hp to shave 0.5 seconds off the 0-60 time?
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At least based on this rough approximation it does, which shouldn't be taken as Gospel for what the actual will be. The early phases of the curve are an estimation because of the complexities of take-off and the host of variables that come into play during that phase of acceleration (tires, road friction, drivetrain efficiency, ...).
As background - back in 2014 when I was researching how to calculate acceleration for different vehicles, it became readily apparent that I wasn't going to be able to model real-life curves the way professional software can (not only because I don't have any knowledge of this field but because of the complex equations needed which I couldn't ever clearly find, and the ones I did find I didn't understand!). But I wanted at least a layman's way of understanding this, so this Sim was produced.
The main issue it has to figure out during early acceleration is the maximal amount of power which can be put down and used to accelerate the vehicle. Too much and the wheels just spin without producing forward motion of the vehicle. So the sim takes the vehicle weight, uses rough coefficients for road surface friction and that of the tires, and a constant placed here and there along with the efficiency of the engine to transfer the power to the wheels to come up with a maximal amount of power such a vehicle can apply before the wheels spin and lose grip with the road. It then uses this power until a speed is reached where the tires shouldn't spin and the power available to the vehicle then becomes fully useful. In other words, if one had two identical X3 M40i G01s next to each other on a track, one might argue that even stock the 355 HP would cause the tires to spin early on. So whether one could modify one to have 555 HP, if the tires and everything else is equal, if the 355 is going to spin the tires then so will the 555 HP, so nothing is gained by having that additional power. That is until the road surface and tire friction coefficients allow grip when that extra HP can be utilized.
So in this sim, oftentimes the first 3 seconds or so are identical even if I change the HP, because that is the time needed for the coefficients of friction I am using to allow a vehicle's aerodynamics and HP variables to become relevant when the tires and road surface have 'full grip' if you will.
As such, I've not focused too much on this first three seconds of acceleration in the sim, but I've been pleasantly surprised at how close it approximates some of the real world data at the higher speeds which Forum Members have shared (FSociety and others). If I were more knowledgeable of the calculations and science I could probably massage the parameters if we had a lot of data series, but that is way over my head and would require the addition of detailed tire and rubber info, track surface data, atmospheric variables, ... - so most definitely over my head and not something I'm ever going to pursue!
For 0-60mph times, it seems that wt/HP vs 0-60 mph chart I had shared some months ago might provide another idea, esp if you look at BMWs only, as it seems different Mnfrs have varying degrees of efficiency in that regards.