BMW M3 vs M5: Weight vs Power what's the best balance?

[velocitate]

I've been thinking about this recently. Especially, after spending some time at the Shift S3ctor 1/2 mile drag race event in Coalinga California. Wouldn't it make sense to follow the simple formula of more power equaling faster times? I would say yes of course! But wait! Let's the a look at the numbers: The M3 is about 3500LBS heavy and the M5 is about 4300LBS heavy. My M3 has about 520 hp and the M5 that I've been battling at the drag event has about 650 hp. (Yes, the actual hp numbers may be off) However, the M3 has a better power to weight ratio. In a 1/2 mile race the M3 won in terms of time but lost every time in trap speed. My trap speed was about 150 mph and the M5 came in at 158+ mph all the time. So if the run way would go on for a further 1/2 mile, the M5 would have passed me despite my better power to weight ratio. Does that mean that a lighter car gets off quicker but a more powerful car gets a higher trap speed? Should I forget about power to weight ratios? Your thoughts guys.

Video of drag race below.

[gblansten]

This will wind up in the M3/4 versus subforum.

http://f80.bimmerpost.com/forums/forumdisplay.php?f=526

[XT6Wagon]

as speed increases, it becomes power to drag over power to weight.

You can play with this in driving games that allow extensive tuning to a "performace point" limit. Open tracks with sweeping high speed corners will favor fat barges with huge engines, tiny short courses will favor things that are very light and have minimal power.

In your case the M5 has more frontal area, but its also got a whole lot more power. So (Power - Power lost to drag)/weight is going to favor him as speeds increase.

[Ian1973]

Right if you start at highway speeds up to near top speeds, you will have a harder time with the M5.

[velocitate]

Thanks, still trying to find the best place to categorize my threats. *Newbie move. lol

Originally Posted by gblansten

This will wind up in the M3/4 versus subforum.

http://f80.bimmerpost.com/forums/forumdisplay.php?f=526

[velocitate]

I never thought of power to drag as I kept thinking about how much weight is pulled by one horsepower. Strange how physics work. Thanks !

Originally Posted by XT6Wagon

as speed increases, it becomes power to drag over power to weight.

You can play with this in driving games that allow extensive tuning to a "performace point" limit. Open tracks with sweeping high speed corners will favor fat barges with huge engines, tiny short courses will favor things that are very light and have minimal power.

In your case the M5 has more frontal area, but its also got a whole lot more power. So (Power - Power lost to drag)/weight is going to favor him as speeds increase.

[CanAutM3]

The power needed to overcome aero drag increases with the cube of speed. So, it takes 8 times the power needed to overcome drag at 75mph to overcome it at 150mph .

In the end, it is still a power to weight thing, but I like to say it is about "available power" to weight; where "available power" is the power left for acceleration after power to overcome aero drag and rolling resistance have been removed.