Does a lighter car go faster? (TOP SPEED)

[olithebad]

I started to wonder, will a heavier car go faster or slower? Since the dodge viper weighs around 1200kg and it goes fast, would it go slower if it weighed the original weight? Will a car have a better topspeed when it's heavier? Since the Veyron is heavy, but goes really fast.

 

[porthillking]

I am pretty sure that a lighter car will be faster than a hevier car, and i think the cornering is better in a lighter car, hence super light F1 cars.

 

[Techy]

The Veyron was able to reach its iconic speeds since it's an 4WD, and so is the GT-R. 4WD vehicles tend to perfect in launch and acceleration.

Lightness is a vital factor in developing a faster and a more reliable car, as more mass can impair the speed of the object. But if the object was able to hone a force greater than the mass, then the difference is small. Although a lighter object will promote the speed even further.

 

[Lizard]

The Veyron was able to reach its iconic speeds since it's an 4WD, and so is the GT-R. 4WD vehicles tend to perfect in launch and acceleration.

No. It helps but the reason is the 1000bhp engine.

 

[mattythedog]

Lighter is generally faster, and that will probably apply to top speed. Having a heavier car won't help matters at all...

 

[alonsof1fan91]

Well it depends on a lot of things.

For example:
Reduce the weight of the Enzo, IIRC it weigts roughly 1040kg and has some 800hp. Sounds nice, doesnt it? At first glance, yes, but after checking its weight balance (+ considering its very understeering behaviour because of its rear tires which are 355mm width IIRC) not really.
At Suzuka, Im 1-2 seconds faster with adding 160kg to the rear of the car.

It really depends on the car/driver. The MP4-12c has a 43/57 weight distribution after reducing its weight, so this car should be neutral to most drivers.

 

[olithebad]

Well, a lighter car has a better power to weight ratio witch makes it easier to ''move'' with the engine, so i guess lighter is better, but in a downhill more mass equals higher speed due to the 9.81 m/s acceleration in gravity...i think... or if anyone understands physics just tell :-)

 

[Techy]

No. It helps but the reason is the 1000bhp engine.

Yes, I know. I guess you haven't notice my ninja edit

Well it depends on a lot of things.

For example:
Reduce the weight of the Enzo, IIRC it weigts roughly 1040kg and has some 800hp. Sounds nice, doesnt it? At first glance, yes, but after checking its weight balance (+ considering its very understeering behaviour because of its rear tires which are 355mm width IIRC) not really.
At Suzuka, Im 1-2 seconds faster with adding 160kg to the rear of the car.

It really depends on the car/driver. The MP4-12c has a 43/57 weight distribution after reducing its weight, so this car should be neutral to most drivers.

You have a point as well.

Well, a lighter car has a better power to weight ratio witch makes it easier to ''move'' with the engine, so i guess lighter is better, but in a downhill more mass equals higher speed due to the 9.81 m/s acceleration in gravity...i think... or if anyone understands physics just tell :-)

Many car companies do not worry about elevation changes when developing their vehicles (depends on the car's purpose). The important aspect is achieving a small car mass, as it produces a more reliable engineering.

 

[Smuttysy]

If you're talking pure top speed runs, the answer is a yes and no.

For example, the LMP cars tend to go faster if you add the full 200kg of ballast to the nose of the car after you raise the nose to it's highest position and raise the rear, and full aero at the back only. For some other cars though this method doesn't work, it's a real trial and error affair in that respect. It also doesn't help you online, as the physics difference is too great to make this work properly.

As for the Viper, I can't be certain off the top of my head, but I think this is probably slower at it's original weight.

 

[Bottoz]

OP. Do a top speed run on Route X in your Viper. Then, add 200kg of ballast. Answer acquired!

In some forms of racing, there is a weight penalty for placing first. It helps in evening the field.

 

[DeadEnd]

Ballast might help with the cornering, but acceleration and the top speed will be negatively effected by adding weight to the car.

 

[McClarenDesign]

Weight effects acceleration up to terminal velocity, not the velocity itself. For that, you need either more power or better aerodynamics.

 

[ROYALEFATALE]

lightness will get you to that top speed faster, once you're over say 200MPH weight doesn't play a big factor and horsepower is what counts

 

[crcn11]

The Veyron was able to reach its iconic speeds since it's an 4WD, and so is the GT-R. 4WD vehicles tend to perfect in launch and acceleration.

At least add "I think" before trying making a statement... 👎

 

[ROYALEFATALE]

it MUST be fast, it's a 4WD LOL

 

[mjm_98]

So is there terminal velocity with any force on earth in any direction

As the air being displaced (air resistance ) and other forces acting against the car (friction gravity) is equal to the force applied by the engine?
And isn't the density of the size of object and is cross sectional surface area has more of an impact on the displacement of air ?

Sorry it's basic as I don't have much knowledge of physics (d-c at gcse at year 9)

 

[ghsnu]

Speed is based mostly on aerodynamics, power, and torque (though a lighter car will benefit acceleration times and would require less power and torque): the more you have, the faster you go - hence the Veyron, SSC, etc. (and especially the old 1000hp+ F1 cars ). The less drag the car creates (note the Veyron's super-slick, super-clean design versus something crazy like the Revonten (sp?)), the better chance you have at reaching a higher speed since - as top gear puts it - trying to go 250mph is like hitting a brick wall. And as said before, AWD has nothing to do with it ether - all that does is benefit acceration and handling. Heck, I believe some guy (Chris Rado I believe - from Shift 2) is working on the fastest FWD drag car - 800+HP to the wrong wheels .

Going fast around the track is based off of weight balance, center of gravity, and weight of the car (excluding tuning, tires, downforce etc.): The lower the center of gravity, the faster you can go around a corner (and thus set a faster time) without risk of flipping or losing traction - cue the F1, LMP/Class-C (?) cars - and which is why you don't see a 700hp GT3 Land Rover competing (which I now want to see xD). The better the weight balance, the better weight transition is (I believe - don't know much about this). And obviously, the lighter the car, the more nimble it will be - cue Lotus' and F1 cars (again).

To the wisemen: please note if I'm wrong - I'm no physics professor or racer.

 

[McClarenDesign]

The veyron reached those speeds thanks to active aero and 1000 hp. 4wd has no effect on top speed limits.

ghsnu, you are correct.

 

[symustafa1996]

I feel like I'm in science class.

Well, it really depends on where the weight is shifting towards when it comes to cornering.
Imagine you place a brick in a Ferrari and drive it around Suzuka. It's probably going to destroy some interior bits. Now replace it with a, let's say, a tissue box. You can barely feel the effects.

It will not affect top speed as much as it will affect acceleration.
Basically,
power moves the weight of the a car. Say 1000hp moves 1800kg
now lighten the car, 1000hp moves 1500kg. Same power, but less to move. It will accelerate faster, because there's less to move from a halt to the top speed. The top speed will be around the same, because eventually, the engine will be delivering full power to the wheels.

 

[georgiebest]

Top speed will not be affected what so ever by the mass of the car. Unless you drive the car over the edge of the cliff, but I don't think that is quite what you meant by terminal velocity.

The only thing that influences top speed is aerodynamics. Theoretically, if you designed a car with virtually no drag coefficient it could achieve speeds of 1,000 mph with just a 1 brake horse power engine.

That is theoretical of course, and it would be impossible to achieve a car with so low drag. So in reality, engine power is a major influence in top speed, as drag can only be reduced so much, and in practical applications, drag is sometimes needed as that is how downforce is created which allows you to attain greater cornering speed.

Just think of it this way, there are to forces acting on a car that influence its top speed. The engine output, which gives the forward force, and aerodynamics which give the opposite drag force. As you increase speed, drag increases until it is equal to engine output, at which point you will not accelerate and will keep constant speed.

Hope this clears things up for you.

 

[mjm_98]

Top speed will not be affected what so ever by the mass of the car. Unless you drive the car over the edge of the cliff, but I don't think that is quite what you meant by terminal velocity.

The only thing that influences top speed is aerodynamics. Theoretically, if you designed a car with virtually no drag coefficient it could achieve speeds of 1,000 mph with just a 1 brake horse power engine.

That is theoretical of course, and it would be impossible to achieve a car with so low drag. So in reality, engine power is a major influence in top speed, as drag can only be reduced so much, and in practical applications, drag is sometimes needed as that is how downforce is created which allows you to attain greater cornering speed.

Just think of it this way, there are to forces acting on a car that influence its top speed. The engine output, which gives the forward force, and aerodynamics which give the opposite drag force. As you increase speed, drag increases until it is equal to engine output, at which point you will not accelerate and will keep constant speed.

Hope this clears things up for you.

Yeah so when The drag equals that is terminal velocity (I know it's normally applied when gravity is in play)

And weight also wouldn't matter when off a cliff if it's high enough as long as it doesn't alter the portions and aerodynamic properties as it wouldn't affect air displaced meaning forces would equal if given enough time and distance

Am I correct?

Sorry but I'm interested in this kind of thing ?

 

[iamjajo]

The North American Eagle land speed record car is supposed to hit 800 MPH. It weighs 13,000 lbs. Maybe the 50,000 HP makes the weight irrelevant.

 

[georgiebest]

Yeah so when The drag equals that is terminal velocity (I know it's normally applied when gravity is in play)

And weight also wouldn't matter when off a cliff if it's high enough as long as it doesn't alter the portions and aerodynamic properties as it wouldn't affect air displaced meaning forces would equal if given enough time and distance

Am I correct?

Sorry but I'm interested in this kind of thing ?

No thats different.
With gravity, all objects accelerate at the same rate. This is because the force (weight) that gravity has on all things on mass increases with mass. So an object with a mass of 100g will have a force of 1N in earths gravitational field (approximately, really it would be 0.981N but we shall keep things simple)
An object that has a mass of 200g will have a force of 2N in the same gravitational field, which means it has twice the weight. This would make you think that the heavier object should accelerate twice as fast as the light object, as it has twice as much force pushing it.

However, the heavier an object is, the more force is required to make it accelerate. This comes into cars as a lighter car with the same engine as a heavier version will accelerate quicker. This is all summed up by newtons Force=Mass*Acceleration.

However, two objects the same shape but difference masses have the same drag coefficient, but different forces on them. So when dropped, they will accelerate at the exact same speed, but one will reach terminal velocity before* the the other, as it has less force pulling it down, but the same amount of drag. This is the equivalent of two cars with the same aerodynamics, but one with a more powerful engine.

I went into more detail that needed because you said you were interested, and I studied physics to a high level.

 

[stormbringer]

summary:

Heavy car is faster when going downhill

All other times lighter car is faster.

 

[GT55YW]

There is a lot of talk of gravity and aerodynamics.

Why is everyone ignoring friction? As in, tires on road.

 

[Ecchi-BANZAII!!]

The veyron reached those speeds thanks to active aero and 1000 hp. 4wd has no effect on top speed limits.

ghsnu, you are correct.

Actually it does since more power are used from the engine to make the other set of wheels spin.
It also makes it heavier.
But it's the torque that makes it that fast.

 

[Famine]

Top speed will not be affected what so ever by the mass of the car.

If the car is not coming up against a gearing limit, yes it will. Not very much of one though.

But it's the torque that makes it that fast.

Nope. It's power. Since power is the rate of conversion of torque (force) to work - 1 horsepower being 550lbft per second - actual torque ratings are irrelevant to speed.

Top speed is governed by two things. These are friction and the ability to overcome friction . For a car these things are surface friction (rolling resistance), aerodynamic friction (air resistance) and power.

Surface friction is governed by just one thing - the car's weight. This is calculated using the car's mass and local gravity. Generally speaking, the rolling resistance is equivalent to around 1.35% of the car's mass regardless of speed - though be aware that both downforce and lift can alter this:

Rolling Resistance (lbf) = Vehicle Mass (lb) x 0.0135

If this didn't exist, pushing a car would be child's play...

Aerodynamic friction is governed by a whole host of things, but essentially describes the effort required for the car to push air out of the way ahead of it. This depends on local air density, on the cross section of the car (the shape it presents to the air in front of it), the speed it's going and the coefficient of drag (how efficently air moves over it):

Air Resistance (lbf) = Vehicle Speed (mph) x Vehicle Speed (mph) x Coefficient of Drag x Frontal Area (Square Feet) x 0.00256

Cd x Frontal Area in square feet is also known as CdA so if you don't have the individual values, the CdA can be substituted.

Add the two values to get total resistance:

Total resistance (lbf) = Rolling Resistance + Air Resistance

The amount of power required to overcome this resistance is, simply, the total resistance multiplied by the speed in mph, divided by 375:

Power (hp) required at speed (mph) = Total Resistance x Speed (mph) / 375

But remember that this is the power at the wheels. Power at wheels is what actually moves you places and so it's what's required to overcome the resistance. Crank power is just a headline figure and the resistance of powertrain and drivetrain components will reduce it by up to 25% for a particularly sluggish and dull four wheel drive system, or as little as 12% for a very efficient drivetrain with the powered wheels nailed directly onto the differential (FWD, some MR), maybe even less.


So, if we take the 253mph and 4150lb Bugatti Veyron with a CdA of 8.02 square feet...

Rolling Resistance = 4150 * 0.0135 = 56.025lb
Air Resistance = 253 * 253 * 8.02 * 0.00256 = 1314.182lb
Total Resistance = 56.025 + 1314.182 = 1370.206lb
Power (wheel) required = 1370.206 * 253/375 = 924.43hp

Assuming the Veyron powertrain to be made of £5m worth of space-age materials and only losing 15% of the power on the way down, that's a required engine power of about 1035hp. This doesn't account for the change in CdA brought about by "top speed mode", but for the purposes of this comparison it doesn't matter.


So, let's take 200lb of stuff out of the Veyron

Rolling Resistance = 3950 * 0.0135 = 53.325lb
Air Resistance = 253 * 253 * 8.02 * 0.00256 = 1314.182lb
Total Resistance = 53.325 + 1314.182 = 1367.506lb
Power (wheel) required = 1367.506 * 253/375 = 922.61hp

So losing 200lb of stuff has reduced the power required to overcome 253mph-worth of resistance by a whole nearly 2hp (don't all gasp at once). This means that at 253mph the car still has nearly 2hp to play with and can overcome more resistance - it can go faster! How much faster?

Well, resistance is a cube of speed, so the percentage "increase" in power results in a cube root of that percentage increase in speed:

924.43hp/922.61hp = 1.00197%
Cube root of 1.00197% = 1.00066%
253mph * 1.00066% = 253.17mph

Woo! 0.17mph!

 

[georgiebest]

There is a lot of talk of gravity and aerodynamics.

Why is everyone ignoring friction? As in, tires on road.

Friction is the reason that your engine can make the car move forward.
If you had tyres with 0 friction, your wheels would just spin on the spot and the car would remain stationary.

There is a slight backwards friction force on the wheels, but it is tiny compared to the friction force that drives the car forward, provided by the engine. Because of this, even an increase in mass which causes more friction, doesn't really affect things because it increases backwards friction force as much as it increases the forward force.

If the car is not coming up against a gearing limit, yes it will. Not very much of one though.

How so?
As far as I know, the only way mass would effect top speed is when the car begins to approach quantum speeds and relativistic effects begin to come into effect. For the purpose of this thread that is extremely irrelevant.

At Uni we done a study about Lunar rovers. There has been one developed that can travel at a max speed on the moon of 360 mph. The only reason it is limited to this is internal friction due to the gears. There is no air resistance. There are 6 wheels and the rover weighs 50kg, static wheel friction does not lower the speed what so ever, just the acceleration slightly. The rover could weigh 5 ton and the top speed would not be affected, according to my lecturer, the reason it is light is purely because it costs a lot to get things into space.

 

[Famine]

How so?
As far as I know, the only way mass would effect top speed is when the car begins to approach quantum speeds and relativistic effects begin to come into effect. For the purpose of this thread that is extremely irrelevant.

Read the post above?

 

[georgiebest]

Read the post above?

I have read it.

I don't understand how weight is the only thing that affects surface friction, what about the friction coefficient for the tyre?

I'll repeat what I said in my last post as I wasn't very clear about what I meant.

The force that drives a car forwards comes from the tyres, as they are the only thing in contact with the ground. The force that turns the tyres comes from the engine. So far simple enough.

If you had tyres with no friction, the most powerful engine in the world would be useless, as it couldn't put any of its power down to create a forward force. You would have wheels spinning on the spot.

When a wheel is rolling, as you have pointed out, there is a rolling resistance. Lets assume we keep a constant road surface and coefficient for the purpose of explanation.

This rolling resistance is equal to the coefficient * the normal force. The normal force is the exact same magnitude as the weight of the car, resultant from its mass. Again, everything to this point is pretty clear.

When you increase the mass of the car, this rolling resistance increases, because the normal force has increased. However you have forgotten how the force that drives the car forward is also dependent on friction.

An increase in mass increases the friction of the tyres. This means there is a proportional increase in rolling resistance friction, but also friction used to drive the car forward. This would cause the overall forward force from the tyres to remain the same.

This is just a rough example with no maths to explain the concept. Imagine a car with a coefficient of 0.1 for simplicity. It weights 100kg and puts down 1,000N of force at the tyres. Its rolling resistance is 100N. If you increase the weight of the car by 100kg, making it 200kg. Its forwards force friction at the tyres would increase by 100N, due to the normal force increasing, making 1,100N and its rolling resistance would increase to 200N. In both cars the net force would be 900N. Again this is just a simple example negating a few things to explain the concept.

However we are talking about GT5, where the physics are far from 100% real. It might be a good experiment for someone to take a car to SSX, measure top speed, and then do weight reduction alone and repeat the test to see if there is a noticeable change.