Strongest pull
11-11-2009, 07:48 PM
#27
The problem is that most people seem to think of torque as the ONLY variable that matters, but in reality it's the COMBINATION of torque and RPM that gives you acceleration. If either one increases, your rate of acceleration will increase.
So in that theoretical engine, if you maintain constant torque, but increase RPM, your rate of acceleration will increase throughout the RPM range. At the same time, if you somehow increase torque while maintaining constant RPM your acceleration will increase. Both are important in figuring out how fast a car really is.
So in that theoretical engine, if you maintain constant torque, but increase RPM, your rate of acceleration will increase throughout the RPM range. At the same time, if you somehow increase torque while maintaining constant RPM your acceleration will increase. Both are important in figuring out how fast a car really is.
Second, horsepower increases as RPM increases using the following mechanics. We have already stated that:
F = MA
F/M = A
F * 1/M = A
Torque is turned into force through a bunch of constants:
T*K * 1/M = A
Consolidate constants:
T*K = A
So in a steady gear ratio, acceleration follows ONLY the torque curve.
Now, power is derived from the change in kinetic energy
(.5*M*V2²-.5*M*V1²)/t=P
.5*M(V2²-V1²)/T=P
So power is based on the squares of speed. Accelerating at a rate X from a stop and the same acceleration at 100 mph are vastly different in power outputs. This is why the car pulls more in first than 6th at the same RPM.
Torque comparisons, however, are only relevant if you are talking about a fixed gear ratio.
So:
1. acceleration is directly proportional to torque using a fixed gear. Constant torque = constant acceleration.
2. Horsepower raises with speed. A fixed acceleration at a higher speed is a higher horsepower.
3. Given multiple gear ratios, selecting the one which will produce the highest horsepower will always result in the highest acceleration. This is due to the greatly increased gearing advantage you will be using to overcome the lower torque.
4. The combination of torque and rpm is power, not acceleration. Power proportional to the difference in squares of speed. Acceleration is the difference in speed (no squaring).
11-11-2009, 08:00 PM
#29
Registered
Join Date: Jan 2005
Location: Palmdale, CA
Posts: 210
Likes: 0
Received 0 Likes
on
0 Posts
maxx, you are absolutely right. I purposefully oversimplified to make it easily understandable that torque alone does not make a car fast. The fact is that this is a commonly misunderstood concept, and to explain strict rules of physics would confuse many people.
11-12-2009, 11:08 AM
#33
mod edit
Thread Starter
Join Date: Jan 2009
Location: Eugene, Oregon
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
I still have a hard time believing the rx8 pulls as hard at 4000 as it does at 8000, which it would according to the idea that it would follow the torque curve.
On a side note, it doesn't matter what gear you're in, the wheel horsepower curve, both in size and shape, is exactly the same. This is because, as torque at the wheels decreases as each higher gear is engaged, wheel rotation speed (rpm) increases to perfectly balance it out, keeping the wheel bhp identical. Imagine how weak the torque force is at the wheels in 6th when compared to 1st; but then think about how much faster the wheels are spinning at 7000 rpm in 6th, vs 7000 in 1st. When you do the math they both offer the exact same bhp at whatever rpm you compare them at.
On a side note, it doesn't matter what gear you're in, the wheel horsepower curve, both in size and shape, is exactly the same. This is because, as torque at the wheels decreases as each higher gear is engaged, wheel rotation speed (rpm) increases to perfectly balance it out, keeping the wheel bhp identical. Imagine how weak the torque force is at the wheels in 6th when compared to 1st; but then think about how much faster the wheels are spinning at 7000 rpm in 6th, vs 7000 in 1st. When you do the math they both offer the exact same bhp at whatever rpm you compare them at.
11-12-2009, 03:26 PM
#35
U-Stink-But-I-♥-U
iTrader: (1)
Join Date: Mar 2005
Location: 12 o'clock on the Beltway.
Posts: 2,004
Likes: 0
Received 1 Like
on
1 Post
The above conversation is all over the map and way to complicated. There was one post that summed it up.
It is all very easy.
Torque can be simplifed to imply the quantity of force imparted to the car by the action of the wheels. Given an identical mass, more force gives more acceleration. It doesnt get any simpler. In a single gear, the car will accelerate the greatest at the torque peak. In fact, on a drum dyno THAT IS WHAT IS MEASURED!!! (accelleration of the drum) Your butt may not believe it, but yer butt is dumb.
HP is power. Power is work over time. More work per unit time, more power. Work is simply force applied over a distance. If you want to go fast (as opposed to quick), you are going to have to produce more force over a given distance in a shorter time, to overcome drag.
In the real world, chasing single numbers is usless. Unless you are a 1100hp dyno queen, and we all know that will never happen with the RX8.
It is all very easy.
Torque can be simplifed to imply the quantity of force imparted to the car by the action of the wheels. Given an identical mass, more force gives more acceleration. It doesnt get any simpler. In a single gear, the car will accelerate the greatest at the torque peak. In fact, on a drum dyno THAT IS WHAT IS MEASURED!!! (accelleration of the drum) Your butt may not believe it, but yer butt is dumb.
HP is power. Power is work over time. More work per unit time, more power. Work is simply force applied over a distance. If you want to go fast (as opposed to quick), you are going to have to produce more force over a given distance in a shorter time, to overcome drag.
In the real world, chasing single numbers is usless. Unless you are a 1100hp dyno queen, and we all know that will never happen with the RX8.
Thread
Thread Starter
Forum
Replies
Last Post
1.3_LittersOfFurry
Series I Trouble Shooting
9
09-22-2015 01:54 AM
