does weight affect the top speed of a car?
03-06-2005, 04:08 PM
#11
Registered User
Join Date: Mar 2005
Location: █ SF, CA █
Posts: 16,702
Likes: 0
Received 0 Likes
on
0 Posts
Found this: http://www.nsxprime.com/FAQ/Miscella...queHPSpeed.htm
What Factors Affect Top Speed?
[AWN] Many factors affect top speed. Weight (except very indirectly) is not one of them. Think about WHY there's a top-speed limit at all (i.e. How come you can't just put a really tall 5th gear in a car and accelerate all the way up to 600 MPH or beyond?)
The reason is friction, of which there are three main sources: Aerodynamic drag, losses through the transmission, and tire friction. The loss from each of these sources increases geometrically with increased speed. Eventually, you reach a point where all the engine's power is being used to overcome these losses, so none is left over for acceleration.
Weight affects none of these drag sources except tire friction, and even then, its effect is almost COMPLETELY overwhelmed by aerodynamic losses. If you loaded up an NSX with a couple tons of lead, it'd only drop the top speed by maybe 10 MPH or so.
What Factors Affect Top Speed?
[AWN] Many factors affect top speed. Weight (except very indirectly) is not one of them. Think about WHY there's a top-speed limit at all (i.e. How come you can't just put a really tall 5th gear in a car and accelerate all the way up to 600 MPH or beyond?)
The reason is friction, of which there are three main sources: Aerodynamic drag, losses through the transmission, and tire friction. The loss from each of these sources increases geometrically with increased speed. Eventually, you reach a point where all the engine's power is being used to overcome these losses, so none is left over for acceleration.
Weight affects none of these drag sources except tire friction, and even then, its effect is almost COMPLETELY overwhelmed by aerodynamic losses. If you loaded up an NSX with a couple tons of lead, it'd only drop the top speed by maybe 10 MPH or so.
03-06-2005, 04:10 PM
#12
Registered User
Originally Posted by PilotKD,Mar 6 2005, 04:48 PM
Weight effects acceleration, not top speed. Top speed will either be drag limited or gear limited. Drag limited meaning that you don't have the hp to overcome drag. You could have a 5000lb car with .28 coefficient of drag (very good) with 200hp and it may take 5 minutes to get up to top speed, but it will eventually get there. If it were not gear limited, it'd top out wherever drag equaled hp available. If you could some how take 1000lb off the same car without changing anything else, it'd get to its top speed a lot quicker, but would still top out at the same speed.
this is what I was trying to explain (mostly) Nice way of saying it
03-06-2005, 04:25 PM
#13
Registered User
Thread Starter
Originally Posted by jasonw,Mar 6 2005, 07:08 PM
The reason is friction, of which there are three main sources: Aerodynamic drag, losses through the transmission, and tire friction. The loss from each of these sources increases geometrically with increased speed. Eventually, you reach a point where all the engine's power is being used to overcome these losses, so none is left over for acceleration.
since at the top speed all of the engine force is being used to combat the aerodynamic/tire friction resistance, there IS NO MORE force left over for acceleration.
great find!!!
03-06-2005, 05:02 PM
#14
Registered User
Join Date: Dec 2003
Location: South Jersey
Posts: 2,432
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Wisconsin S2k,Mar 6 2005, 06:52 PM
edit: i read KD's post.
now how about top speed up an incline.....
if you have 2 identical cars, then load one up with an extra 300 pounds, the one with more weight will accelerate more slowly up the hill. but again, does that affect top speed?
woohoo, i love continuing to confuse myself. muahaha.
now how about top speed up an incline.....
if you have 2 identical cars, then load one up with an extra 300 pounds, the one with more weight will accelerate more slowly up the hill. but again, does that affect top speed?
woohoo, i love continuing to confuse myself. muahaha.
03-06-2005, 05:05 PM
#15
If you look at it mathematically you'll see that F=ma or a=F/m.
What that means is the more the mass, the less the acceleration for a given force. But it's acceleration nonetheless. Other factors aside when any force acts on an object it just continues to accelerate.
The end result is that if you put a 200lb sack of potatos in the passenger seat you'll have the same top speed, it'll just take a while longer to get there.
What that means is the more the mass, the less the acceleration for a given force. But it's acceleration nonetheless. Other factors aside when any force acts on an object it just continues to accelerate.
The end result is that if you put a 200lb sack of potatos in the passenger seat you'll have the same top speed, it'll just take a while longer to get there.
03-06-2005, 06:40 PM
#17
Registered User
Join Date: Dec 2003
Location: Santa Clara
Posts: 87
Likes: 0
Received 0 Likes
on
0 Posts
[QUOTE=Wisconsin S2k,Mar 6 2005, 04:52 PM]
now how about top speed up an incline.....
if you have 2 identical cars, then load one up with an extra 300 pounds, the one with more weight will accelerate more slowly up the hill.
now how about top speed up an incline.....
if you have 2 identical cars, then load one up with an extra 300 pounds, the one with more weight will accelerate more slowly up the hill.
03-06-2005, 06:44 PM
#18
Registered User
Join Date: Aug 2003
Location: Irvine
Posts: 8,362
Likes: 0
Received 0 Likes
on
0 Posts
i think weight can only affect how fast it'll get to the top speed of a car.
top speed only matter on the motor. think of you put a integra type R motor on a civic hatch, is the top speed going to change? i don't think so. the motor can only produce so much dosn't matter which body you can put in.
top speed only matter on the motor. think of you put a integra type R motor on a civic hatch, is the top speed going to change? i don't think so. the motor can only produce so much dosn't matter which body you can put in.
03-06-2005, 06:51 PM
#19
I think you're missing the point. Top speed is a factor of power and wind resistance. For any given car body if you put a more powerful engine in it will have a higher top speed (gearing allowing for it).
Conversely, if you have the same engine in a Civic and Integra it is their different CdA (coefficient of drag x frontal area) that will affect top speed.
Conversely, if you have the same engine in a Civic and Integra it is their different CdA (coefficient of drag x frontal area) that will affect top speed.
03-06-2005, 07:13 PM
#20
Registered User
Join Date: Dec 2003
Location: Santa Clara
Posts: 87
Likes: 0
Received 0 Likes
on
0 Posts
One more try. Let
m = mass (units Kg)
a = acceleration (units m/s^2)
f = dissipative forces (aerodynamic, loss in transmission, etc..) (units Newtons)
theta = incline angle, if you are going up a hill
g = accelration due to gravity (units m/s^2)
F = Net force that the ground exerts on the wheels (units Newtons)
then
m a = F - f - mg sin(theta)
When you reach top speed, the accelation goes to zero, and the term on the left hand side vanishes. If you are level ground, theta=0 and the last term on the right hand side vanishes. Thus, on level ground, the mass does not affect top speed (F = f). The situation changes if you are going up an incline since the gravitational force mg sin(theta) depends on mass.
m = mass (units Kg)
a = acceleration (units m/s^2)
f = dissipative forces (aerodynamic, loss in transmission, etc..) (units Newtons)
theta = incline angle, if you are going up a hill
g = accelration due to gravity (units m/s^2)
F = Net force that the ground exerts on the wheels (units Newtons)
then
m a = F - f - mg sin(theta)
When you reach top speed, the accelation goes to zero, and the term on the left hand side vanishes. If you are level ground, theta=0 and the last term on the right hand side vanishes. Thus, on level ground, the mass does not affect top speed (F = f). The situation changes if you are going up an incline since the gravitational force mg sin(theta) depends on mass.