OK Phillip - thanks for the clear explanation! Now, if I understand correctly, if my pickup has the required torque to pull the 4000 lb. trailer up Grapevine, and your lawn tractor doesn't, I'll be moving and you won't. So torque does matter, but more HP with the required torque means the work gets performed faster. Insufficient torque means no work is done.
If Curt wants to haul a load of gravel to camp, he'll need a minimum amount of torque to accomplish the job, regardless of how fast it gets done. Did I get it right? On Tue, Jul 29, 2014 at 7:34 PM, Fmiser via Mercedes <mercedes@okiebenz.com> wrote: > > OK wrote: > > > > IIRC, the V8 has more torque, which is what a truck needs. > > Well, no. Not really. But sort of. > > Nothing against you Don, but this is a very common > miss-perception. So I'm not picking on you - just using your > comment as motivation to respond. *smiles* > > Torque is rotational force. There can be torque with no movement. > Unless there is movement, no work is being done. > > If there is torque, and movement occurs - then work is being done. > With a stopwatch (or calendar?) you can measure how fast the work > is being done. This is horsepower [or watts]. > > If you have an engine with a fixed horsepower attached to a > transmission (presuming an infinite ratio and lossless - which > doesn't exist) the torque can be any value at all. For high > torque, it will be moving slow - but for low torque it will be > moving fast. > > If we don't change the diameter of the tire, the torque on the > axle necessary to pull a 4000 lb [1800 kg] trailer up > Grapevine out of Los Angeles is fixed. So if your your 400 hp > pickup and my 7 hp garden tractor have the same size tire, the > torque needed is the same. The difference is speed. Your > pickup will get to the top a lot faster than my tractor > because the axle can turn faster because your engine has more > horsepower. > > So far it's very clear - but then reality rears it's ugly > head. Transmissions have fixed ratios and losses. Engine > ratings are for _maximum_ horsepower - but the actual > horsepower and torque vary depending on speed. This makes it > almost impossible to actually do an apples-to-apples > comparison. > > Nevertheless, looking at the torque value is pretty > meaningless. If you look at the torque values for various > engine RPM, you can get a clue as to how usable the > power is. If there is little torque at low RPM, then high RPM > will be needed to get useable power. This makes it feel like > the driver has to work the engine harder to get the job done. > > So - to repeat. Just a torque value is nearly meaningless. > Torque at a particular RPM is useful - but that is by > definition horsepower! > > -- Philip > > _______________________________________ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > > All posts are the result of individual contributors and as such, those > individuals are responsible for the content of the post. The list owner > has no control over the content of the messages of each contributor. > -- OK Don NSA: The only branch of government that actually listens to US citizens! "There are three kinds of men: The ones that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." WILL ROGERS, *The Manly Wisdom of Will Rogers* 2013 F150, 18 mpg 2012 Passat TDI DSG, 44 mpg 1957 C182A, 12 mpg - but at 150 mph! _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com All posts are the result of individual contributors and as such, those individuals are responsible for the content of the post. The list owner has no control over the content of the messages of each contributor.
