View Single Post
      05-04-2011, 02:04 AM   #22
swamp2
Lieutenant General
swamp2's Avatar
United_States
534
Rep
10,408
Posts

Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

iTrader: (3)

Quote:
Originally Posted by e1000 View Post
The problem with this statement is that it is only true for 1st gear, and that's precisely why I added the part about acceleration being traction limited. If peak torque of the S65 truly comes at 3000rpm, it theoretically is the max instantaneous acceleration the M3 is possible of IF AND ONLY IF the tires don't break loose.... and we all know if traction control is off, they will most certainly be roasted to a pulp.
Hardly. It is not just true for 1st gear. Run the calculations in a spreadsheet if you can show otherwise.

The issue of traction is an obvious exception and one that brings enough variability to the problem that there becomes no real definitive answer. However, let's discuss just a bit. Though is does depend on temperature of the tires, surface and generally the maximum friction available in the surface. If you launch carelessly or in a show boating fashion sure in 1st you can have your tires spinning well through 3000 rpm and above. On the other hand it can also be quite the opposite with a good full hookup around that rpm. Also do note that the torque curve for the M3 is VERY flat - about 90% of peak torque available from 2500 rpm all the way to about 8000.

Quote:
Originally Posted by e1000 View Post
In all other gears, 3000rpm in that gear (for example 3rd) will be inferior to a higher rpm in a lower gear (2nd) simply due to the multiplication factor of the shorter gear (numerically higher) delivering a greater ammount of resultant torque to the wheels. The alternative is partial throttle acceleration, meaning the torque curve is artificially limited by the driver to match the thresholds of traction, thereby changing the point of peak power.
What will be inferior? Not counting the corrections for aero and tire losses the statement is true. Now those corrections can be larger than I thought (see a following post) however the approximation becomes worse in higher gears not lower gears. You MUST clearly state whether you are speaking about in a given gear or at a given speed and then whether you are talking about peak values at the crank or at the wheel. Lastly you must clearly specify instantaneous or overall (perhap including overall across gears).

Quote:
Originally Posted by e1000 View Post
In the end, we are saying the same thing. I just want to make things clear so others don't get the wrong idea.
I'm not at all convinced we are saying precisely the same thing. I have chosen my words carefully and precisely and stand by them as written.

Quote:
Originally Posted by e1000 View Post
Lots of people get the relationship between HP, torque and gearing all wrong. Remember folks, torque is multiplied through the gearbox, horsepower is not.
Here we agree!

Cheers.
__________________
E92 M3 | Space Gray on Fox Red | M-DCT | CF Roof | RAC RG63 Wheels | Brembo 380mm BBK |
| Vorsteiner Ti Exhaust | Matte Black Grilles/Side Gills/Rear Emblem/Mirrors |
| Alekshop Back up Camera | GP Thunders | BMW Aluminum Pedals | Elite Angels |
| XPEL Full Front Wrap | Hardwired V1 | Interior Xenon Light Kit |
Appreciate 0