can anyone tell me thetop speed?
- Thread starter nemitz
- Start date
I just finished reading AZ's last post and I am simply stunned.
If increasing or decreasing horsepower will affect top speed then how can adding or lowering the weight of the vehicle NOT affect top speed?
Are you saying that if it were possible to take 1000 lbs off of a Focus that the cars top speed would not increase?
If increasing or decreasing horsepower will affect top speed then how can adding or lowering the weight of the vehicle NOT affect top speed?
Are you saying that if it were possible to take 1000 lbs off of a Focus that the cars top speed would not increase?
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Power-to-weight ratio is a measure commonly used when comparing various vehicles, including automobiles, motorcycles and aircraft (usually aircraft engines). It is, simply, the power the engine develops, divided by the vehicle's weight. It is used mainly to describle the expected acceleration performance of a vehicle.
Vehicle weights have relatively little impact on top speed, which is mostly dependant on aerodynamic drag, which is proportional to the square of the vehicle speed.
Drag (D) = Cd * A * .5 * r * V^2
Also, CLICK HERE for a good page detailing the calculation for hp required to overcome air resistance at a certain speed. The guy is using "perfect air," but its pretty close. It gives good insight to the answer of the question that started this post.
Vehicle weights have relatively little impact on top speed, which is mostly dependant on aerodynamic drag, which is proportional to the square of the vehicle speed.
Drag (D) = Cd * A * .5 * r * V^2
Also, CLICK HERE for a good page detailing the calculation for hp required to overcome air resistance at a certain speed. The guy is using "perfect air," but its pretty close. It gives good insight to the answer of the question that started this post.
I like my SVTF....it's fun 
O.K. if the car weighs 2900 lbs and has 170 hp and has a wind reisistance limited top speed of about 135 mph in 5th gear leaving all of sixth gear for simply cruising.
That means that this car at this weight has only enough horespower to move this much weight through the atmosphere at this speed.
If you could remove 1000 lbs from the car without changing anything else you would see a very noticable increase in top speed simply because the 170 hp is now being directed more effectively towards overcoming wind resistance rather than being used to drag all that weight up to speed as well.
Weight equals horsepower-horsepower equals speed.
The less weight you move with a given amount of horespower will equate to better acceleration and yes a higher top speed.
Therefore regardless of atmospheric variables if you greatly increase the weight of a given automoblie without increasing the power output you will without question lose acceleration and you will certainly lose top speed because that 170 hp can only pull so much weight given even varied atmospheric conditions.
170 hp is 170 hp- 2900 lbs is 2900 lbs and 170 hp is simply not going to pull 3900 lbs up to the same speed that it can pull 2900 lbs.
This is assuming a driver of about 200 lbs and squeezing four 200 lb passengers into the car, It would be a tight fit but could be done.
I do not think I can be any more clear about this, you can talk about contact patches, temperatures, humidity and equations all you want but you simply can not get around the fact that it takes all of this cars 170 hp just to get its aerodynamic profile and weight up to its top speed of 135 and if you will admit that by losing weight the car would have the ability to reach a higher top speed by freeing up usable hp then you must also admit that by increasing weight you are reducing usable hp which must result in a loss of top speed.
That means that this car at this weight has only enough horespower to move this much weight through the atmosphere at this speed.
If you could remove 1000 lbs from the car without changing anything else you would see a very noticable increase in top speed simply because the 170 hp is now being directed more effectively towards overcoming wind resistance rather than being used to drag all that weight up to speed as well.
Weight equals horsepower-horsepower equals speed.
The less weight you move with a given amount of horespower will equate to better acceleration and yes a higher top speed.
Therefore regardless of atmospheric variables if you greatly increase the weight of a given automoblie without increasing the power output you will without question lose acceleration and you will certainly lose top speed because that 170 hp can only pull so much weight given even varied atmospheric conditions.
170 hp is 170 hp- 2900 lbs is 2900 lbs and 170 hp is simply not going to pull 3900 lbs up to the same speed that it can pull 2900 lbs.
This is assuming a driver of about 200 lbs and squeezing four 200 lb passengers into the car, It would be a tight fit but could be done.
I do not think I can be any more clear about this, you can talk about contact patches, temperatures, humidity and equations all you want but you simply can not get around the fact that it takes all of this cars 170 hp just to get its aerodynamic profile and weight up to its top speed of 135 and if you will admit that by losing weight the car would have the ability to reach a higher top speed by freeing up usable hp then you must also admit that by increasing weight you are reducing usable hp which must result in a loss of top speed.
damn you guys will be me in my car....i'm scared to go 150+ cuz the damn hood looks like it's gonna fly off...
SVTfocusdriver, you can not and will not get me to admit you are right when all you doing is throwing happenstance scenarios. Hell, I could prove that god is a pickle if I took the liberties you are.
read the article I posted a link to, and come back when you can provide some evidence for your claims.
Until then, this argument is getting old...
read the article I posted a link to, and come back when you can provide some evidence for your claims.
Until then, this argument is getting old...
What is so happenstance about getting five 200 lb. adults to sit in your car and see what happens?
In the interests of safety you could simply use weights to simulate people and go it alone.
I do not need to prove this to my self, I proved this to my self years ago.
From Websters Dictionary.
Horsepower: 1: the power that a horse exerts in pulling.
2: a unit of power equal in the U.S. to 746 watts and nearly equivalent to the English gravitational unit of the same name that equals 550 foot pounds of work per second.
Horsepower by definition is measured by the abiltity to move a given weight over a given distance in a given time.
From what you guys are telling me is that if a Focus SVT weighed 9000 lbs but had the same aerodynamic shape and contact patch and still the same 170 horsepower it would still reach 135 mph given enough room?
AZ is correct. Weight is a small factor in top speed relative to aerodynamics. In fact on ecould ADD about 100 lb of weight to a Focus and maybe gain 10 mph (I'm talking aero mods...not engine).
Race cars are built as light as possible to reduce the effects of INERTIA. Acceleration deceleration and cornering are all affected by the force that has to be reated to. This force increases with the car's mass. It's all physics.
Race cars are built as light as possible to reduce the effects of INERTIA. Acceleration deceleration and cornering are all affected by the force that has to be reated to. This force increases with the car's mass. It's all physics.
AZ is correct on this. At speed, weight has little effect on topping out. My focus ran almost exactly 133 even gutted. Same as full interior(200+lbs heavier). But when I addded power, then I started ripping to and through 140. If the car were lowered, the top speed might be increased, but that effects wind resistance. When the Lexus LS was governed to 155 in the late 90s, I was stunned. How could such a heavy car go so fast. It was then that a man much wiser than I explained that weight had little to do with top speed. It's all about aerodynamics, and power. E-
I never had physics, but I do remember hearing something about terminal velocity. I know that is a little off topic, but I think that it may convince people that weight shouldn't affect top speed.
Terminal Velocity is a certain speed that all objects could reach as they fall back to earth. It doesn't matter if it was a gallon of water or a gallon of lead, they would both eventually reach the same speed. SVT might be able to explain this better.
Terminal Velocity is a certain speed that all objects could reach as they fall back to earth. It doesn't matter if it was a gallon of water or a gallon of lead, they would both eventually reach the same speed. SVT might be able to explain this better.
The amount of friction is proportional to the amount of weight. Which means, the heavier a car is, the more friction there is between the road and the tires. Thus, you would need more power to overcome the increased friction.
The gallon of lead would reach a higher terminal velocity as it is more dense than the water so it is more able to overcome the air resistance. SHape and density become part of the equation when air resistance is involved. Aerodynamics once again play a part.
If there was no atmosphere they'd both continue to accelerate at 9.8 meters per second squared and reach the ground at the same time.
End of physics lesson from Boeing Flight Test.
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True, but the air resistance increases with the square of the velocity so once at speed (call it 130 or so) the friction added by weight plays an incredibly small part of the whole equation.
Ya Im with you man....Im a driving instuctor in the focus challenge...we have about 20 SVT Foci in the group most modified...we are seeing around 140 to 145 on the modified normally asperated cars...wow they can stop and turn though
Last post I promise.
After searching some european road tests I found some interesting stats.
ZX3 1.8 113 hp....118 mph tested top speed
ZX3 2.0 130 hp....125 mph tested top speed
SVT / ST170 170 hp....135 mph tested top speed
Focus RS 212 hp....144 mph tested top speed
These are all basically identical cars (yes they have differences,I know) the largest difference being engine output.
Yes the standard zx3 sits a little higher than the others but it also has the smallest contact patch, the RS and SVT are nearly physically identical except that the RS has a larger contact patch and wider frontal area (they have flared fenders to accomodate wider tires).
How do you explain the speed differential between these cars?
Nearly identical weight, size and shape but varied horsepower.
Weight equals horsepower.
If you alter either you WILL see a difference.
Each of these cars gained approximately 40 hp and 10 mph on the car with the next lowest hp output, with the exception of the 1.8 which was closer to the 2.0 in both power and top speed.
After searching some european road tests I found some interesting stats.
ZX3 1.8 113 hp....118 mph tested top speed
ZX3 2.0 130 hp....125 mph tested top speed
SVT / ST170 170 hp....135 mph tested top speed
Focus RS 212 hp....144 mph tested top speed
These are all basically identical cars (yes they have differences,I know) the largest difference being engine output.
Yes the standard zx3 sits a little higher than the others but it also has the smallest contact patch, the RS and SVT are nearly physically identical except that the RS has a larger contact patch and wider frontal area (they have flared fenders to accomodate wider tires).
How do you explain the speed differential between these cars?
Nearly identical weight, size and shape but varied horsepower.
Weight equals horsepower.
If you alter either you WILL see a difference.
Each of these cars gained approximately 40 hp and 10 mph on the car with the next lowest hp output, with the exception of the 1.8 which was closer to the 2.0 in both power and top speed.
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No it does not.
No one said 52 more HP is not going to make a car have a higher top speed if there is still gearing left to use.
What was said is load up the the RS with 200 extra pounds and it will still hit 144 mph. As you stated HP is weight moved over TIME! No one is placing a time limit to achive the top speed in this post. So a car with X HP with X gearing with a weight of +/- 500 lbs. will have the same top speed.
This because wind resistance increases at the square of speed. So to make an SVTF reach, oh, say 170 mph in 6th gear you will need over 300 hp.
I did not say to load it with 200 lbs I was trying to make the point that increasing weight will effect top speed.
My suggestion was to load the car with five 200 lb adults and see if that would effect top speed.
The car seats five so this is not unrealistic.
How can you say that adding horsepower will increase top speed and decreasing horsepower will lower top speed but changing the weight of the vehicle will not change the top speed?
Weight directly effects the usable horsepower of a given vehicle, How is this so hard to understand?
It should be obvious from the varied speeds attained in the European tests that I found that the same car with widely varying hp ratings end up with widely varied top speeds with nearly identical weights and aerodynamic profiles.
So you say that given enough time an RS or SVT with a full load of adults, full fuel load and a fully packed luggage bay will still reach its known top speed of 144 or 135 respectively?
Maybe, possibly in the case of the RS because I do not know if it is running out of power or simply hitting its redline but an SVT runs out of steam in fifth gear.
You load that car to the max and it will NOT reach 135, it simply won't have the power to do it.
My suggestion was to load the car with five 200 lb adults and see if that would effect top speed.
The car seats five so this is not unrealistic.
How can you say that adding horsepower will increase top speed and decreasing horsepower will lower top speed but changing the weight of the vehicle will not change the top speed?
Weight directly effects the usable horsepower of a given vehicle, How is this so hard to understand?
It should be obvious from the varied speeds attained in the European tests that I found that the same car with widely varying hp ratings end up with widely varied top speeds with nearly identical weights and aerodynamic profiles.
So you say that given enough time an RS or SVT with a full load of adults, full fuel load and a fully packed luggage bay will still reach its known top speed of 144 or 135 respectively?
Maybe, possibly in the case of the RS because I do not know if it is running out of power or simply hitting its redline but an SVT runs out of steam in fifth gear.
You load that car to the max and it will NOT reach 135, it simply won't have the power to do it.
Maybe this will make you see...
http://www.rbracing-rsr.com/aerohpcalc.html
SVTF
Cd: .36
F Area: 23.66
Weight: 2750 (W/O driver)
Speed: 135
LOOK at the HP needed
Change the weight by 1000 lbs. either direction.
LOOK at the HP needed. This small change is easily with in the +/- of any dyno.
What this means is weight has no MAJOR factor on top speed. So sheding 1000 lbs from the SVTF will have almost no change on the top speed.
STILL DON'T BELIEVE CHANGE THE WEIGHT TO ONE LBS.
http://www.rbracing-rsr.com/aerohpcalc.html
SVTF
Cd: .36
F Area: 23.66
Weight: 2750 (W/O driver)
Speed: 135
LOOK at the HP needed
Change the weight by 1000 lbs. either direction.
LOOK at the HP needed. This small change is easily with in the +/- of any dyno.
What this means is weight has no MAJOR factor on top speed. So sheding 1000 lbs from the SVTF will have almost no change on the top speed.
STILL DON'T BELIEVE CHANGE THE WEIGHT TO ONE LBS.
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