You guys are stating weight as if it were all or nothing. It's not like that. It's about percentages. adding 500 lbs or taking away 500 lbs from a car that's going 150mph really won't loose / gain much.

BTW: This is not just "my opinion". I kinda... sorta... am an expert in the automotive field.

Rich

 

Sal:

Trust me on this one. It's another one of those things where it "seems like", but I'm right on this one. Mass doesn't come into play as far as top speed (terminal velocity) is concerned.

Here we go again.

Incidentally, unlike the last time (the "brick wall" thread), I'm done with this one. Nothing left to add.

Human nature is funny. Not only do people, in general, seem reluctant to learn, but actually resent being taught.

 

So are you saying that my example DOES hold true? If a 190mph Hiyabusa weighed 5000 lbs and the shape was not altered at all, it would still reach 190mph?

I am not reluctant to learn, and I do not resent being taught, but coming here and just saying it's one way and that's how it is, in far from teaching. If the majority here are not understanding it, then explain why and acutally "teach" it instead of just saying that's how it is.

 

I don't think it is a point of people not willing to learn-- You just made a blanket statement that is incorrect. I agree with you about a little bit of weight not affecting speed, but obviously there is a point at which weight directly affects top speed. If there was a lightning that weighs 20,000 lbs and one that weighs 5,000 -- Do they have the same top speed? I think not...

 

Not trying to be a smart a$$.......but if you increase weight it does add to the rolling resistance. The tires still have to roll across a hard surface and there is an interaction going on there, I.E. a squished tire doesn't roll as well as a non-squished tire.
It puts more stress on the given size wheel bearings and so on etc. It does create more drag......no?

 

Silver-Y2K-SVT is right,
A common misconception about attempting to go fast is that it's important to be light. If you have enough track to truly reach top speed, however, lightness becomes irrelevant. Light weight only helps acceleration. So basically if the room they have to do this in becomes a factor then the heavy weight will become a disadvantage.
Friction both on the ground (tires) and air (aerodynamics) play a larger role.

You can almost think of it this way. Drop a 5000 lbs car and a 200 lbs man from a building. Not taking into account wind resistance.. they will both accelerate at the same rate. (Think of it as gravity being the power of the motor)

AT least this is what I remember from Physics class

 

Aerodynamics is by far the biggest factor involved in the top speed of the SRT10. Horsepower and weight do factor into the equation with weight being the smallest factor. Weight will have some effect but it is a small percentage when talking about the difference between an L and the SRT10 where top speed is concerned. To say weight is absolutely no factor is incorrect in the real world.

Yes, I've had a few semesters of college physics but I've also delt with motorcycles for years in the real world. I can tell you for a fact that anything you learn in the real world is worth twice what you can get out of a book or on the internet for that matter.

A degree is a wonderful thing but experience is the best teacher. When you have both it's all the better.

 

Guys We are NOT talking about theory here.

This is NOT an unlimited - infinite length race track... The equations ONLY work in the rarefied world of science. In the real world the weight definately DOES affect the abilty to reach a certain speed.

The speed must be reached in a carefully described track. Even the salt flats have a carefully described run up and slow down area ...

Doug

 

Here guys.. this may help explain what we are talking about...

Got this from here..

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.

 

Yes that is what I was saying. The question becomes is it leight enough to reach that top speed in the distance it has to do it.

 

Agree with that to a degree.

But.......

Over here in the UK, we have a very popular car called the Astra GTE (Pontiac Lemans) its fitted with a 2.0l 16v engine producing 156bhp. The car weighs around 1100kg and has a top speed of 137mph.
The smaller brother of the Astra is the Nova which is basicly the smae car only smaller, still a 3 dr hatch but weighs around 850-900kg. The most popular mod at the moment is to tansnplant the engine from the Astra into the Nova, then you have the same 156bhp engine in a lighter car.

The top speed of the car is now around 144mph, i know because i used to have one, no mods just a stock engine.
Although its the same engine it has less weight to push through the air thus giving it a slightly higher top speed. This is where torque comes to play by having the force to push through the air.

Having said that the Dodge has the airodynamics of a brick.

Another example is the Lotus Carlton (pictured here)


The most controversal car ever released in the UK. Powered by a 3.6l Twin turbo V6 built by Lotus it had 377bhp and 419 lb/ft

Its official top speed was 176mph but this was drag limited.

If the redline was hit in 6th gear then the Carlton would travelling at 286mph.

There is no way it could ever hit that speed.

The same engine was out in a stripped out Carlton which weighed about 300kg less but it only managed 12mph more.

Aerodynamics play a huge part in top speed runs

 

Light weight at Bonneville typically hurts due to tire slip (wheelspin) at speed.

The ONLY place vehicle weight enters the equation is as a minor contributor to rolling friction (through wheel bearings and tires), and that contribution ITSELF is negligible compared to air resistance. Weight contributes ABSOLUTELY nothing to air resistance.

For example, for a typical vehicle, at 120 MPH, the air resistance force is in the vicinity of ten times the rolling resistance force. Furthermore, rolling resistance is for all practical purposes a constant, weight is a small contributor to rolling resistance, and the force of air resistance increases with the square of vehicle speed. So at 240 MPH, air resistance is around 40 times the rolling resistance.

The effect of wheelspin is, however, significant. Think of a Lightning running flat-out, WOT, at 149 MPH and 5000-ish RPM. You have a good 350 HP going to the ground, confounded by the inevitable aerodynamic lift (light azz-end) at speed. How much wheelspin do you think you're getting? A ton, at the cost of top speed. Put about 400 pounds of sand in the bed and your top speed will actually INCREASE, given an 8% longer run-up/shut-down area.

A lightly-modded 'Busa on the salt typically sees around 10-20 MPH of wheelspin (5-10% slip) at top speed (ca. 190 MPH).

Now give this a rest, look it up and convince yourself (REALLY look it up, not just some silly Google search, but a Dynamics/Mechanics textbook), and enjoy the Superbowl.

 

oww my brain hurts after reading all that

 

So you all are trying to convince me that the sam truck on the same track with the same run up distance will run the same top speed as another identical truck that weighs twice as much ?

BS. We are not comparing equations here ....

We are talking about Dodge trying to out do Ford on the SAME track under similar conditions.... It may be that the 120 hp is enough to overcome the 500 lb difference in weight. The real question is the 120 hp enough to over come the aero issues AND the weight. I agree the aero is the bigger issue BUT I wont agree that weight doesnt matter.

 

The record for the Lightning was set on a banked oval (infinite run-up distance), and no doubt the SRT will be run on one also (Chelsea, perhaps).

Weight will play no part in the success or failure of the record attempt.

Aero will count, but doubtless the Dodge will succeed. They wouldn't PUBLICLY try unless they had already tested and confirmed that it was possible.

You can believe what you wish. Fortunately for most of the rest of us, Mother Nature doesn't give a damn what you are willing to believe (or not). This is about as basic science (fluid mechanics) as it gets. Sometimes I just have to shake my head...

Oh well. Really, I'm done with this one. I just implore you to study up a bit instead of throwing the "BS" accusation.