View Single Post
      04-22-2007, 06:57 AM   #25
NFS
Major General
 
NFS's Avatar
 
Drives: 335i m-sport LCI
Join Date: Jul 2006
Location: UK

Posts: 9,214
iTrader: (0)

Quote:
Originally Posted by leftcoastman View Post
While I agree that torque in and of itself isn't enough to determine how fast a car is, I wouldn't say it's so simple to say that torque multiplication is what makes low gear acceleration so rapid.

At low gearing, you are travelling at low speed. Air resistance increases as a square of speed. At higher gears, you're probably going at a high speed, therefore the power necessary to overcome that air resistance (which has been growing as a square) is much higher.
Frictional resistance (air and road) is obviously a factor and it's effect does increase (roughly) to the square of speed. However, a vehicle will accelerate most when wheel torque is greatest.

If you work out the torque at the wheels (multiplying by gear ratios and final drive ratio) then you will see that it is massively higher in 1st gear than 5th or 6th.

There are several small light vehicles which can accelerate to 60 mph very quickly. They are often powered by high revving engines with relatively low levels of torque.

To continue to accelerate as swiftly in the upper gears you need the ability to generate lots of torque at high revs.
__________________
NFS is offline   United Kingdom
0
Reply With Quote