There's that damn "i" word again.

 

You're welcome - though whether or not it is "irrelevant" is rather debatable. Please see previous comment dealing with assumptions, presumptions, and guessing.

 

Nuke did my dirty work. No guesswork involved here. Consider yourself educated now.

 

I wouldn't call it "dirty" work I just like having facts to back up my points.

 

LOL. My goodness, should you increase your hat size now?

Honestly, I have little interest in the topic at hand, but decided to respond to a comment I still believe to be inaccurate - despite my education, or lack their of.

 

So now you've been provided facts to back up a statement I made, and you still think it's inaccurate.

I believe the moon is indeed made of cheese. I don't care what facts you throw at me.

Your lack of interest in this topic is made clear by the number of replies you've made in this thread. Is it too much to ask to admit when you're wrong? Or does your hat size prevent that?

 

I believe your assertion that - and I quote: "Weight is irrelevant for top speed" - is inaccurate. It is, however, quite possible that it does not have as much effect as I assumed. I have admitted quite clearly that I am in no way an expert on such things, nor have I ever bothered to find out. Nor will I likely look into it anymore. It simply means very little to me.

Hey, now that helps!

LOL. Your assumption about what has inspired me to reply is quite incorrect.

Kindly see my last post (or was it two posts ago?), and my statement above.

7 1/4. Has been for many years. Likely will be for many more. But then again, I don't believe I've ever told your (or anyone else) that I have just given them an "education" on the internet. That's to say that I haven't been right from time to time when others or wrong, but when this does happen, I've found that there is never a need to pat myself on the back.

Know what I mean?

 

Assuming *reasonable* limits on weight increase, and not your silly hypothetical, weight is indeed irrelevant for top speed. You can believe whatever you wish to believe -- the facts say that your belief is misguided.

 

Ok. Define "reasonable." Or consider me silly and misguided. I have no issues either way.

 

As I've already said in a prevous post:
What's the aerodynamic force, ignoring rolling resistance, required to move a Vette through the air at 200 mph? About 450 lbs, while the rolling resistance for a car with DOUBLE the weight is only about a 40 lb difference in force required. Insignificant.
http://snipurl.com/cx23

So, concerning a 3000 Vette vs. a 6000 lb Vette, the difference in top speed is insignificant, therefore, a weight doubling is insignificant when discussing top speed and street cars.

A doubling of weight, as improbable as that may be, is reasonable. Asking if a 30,000 lb Vette would have the same top speed as a 3,000 lb Vette, other factors being equal, is not reasonable.

 

Ok. So help me out here. Everything else being equal (power, gearing, aerodynamics), what would be the top speed difference (in MPH, please) of a car weighing 3000 vs one weighing 3900 lbs. Pick whatever power and drag you wish.

Thanks.

 

Roll resistance power (approximate) = weight * 0.013 * mph / 375
Air drag resistance power (approximate) = fA * Cd * 0.003 * mph^3 / 375

Car A weighs 3000 lbs
Car B weighs 3900 lbs

3000 lbs * 0.013 * 200 mph / 375 = 20.8 lbs force to overcome roll resistance
20 sq ft * 0.30 * 0.003 * 200^3 / 375 = 384 lbs force to overcome air resistance
Or 404.8 lbs total force

3900 lbs * 0.013 * 200 mph / 375 = 27.04 lbs force to overcome roll resistance
20 sq ft * 0.30 * 0.003 * 200^3 /375 = 384 lbs force to overcome air resistance
Or 411.04 lbs total force

That's approximately 1% more power required for the 3900 lb car vs. the 3000 lb car, shown by 411/405=1.015. Since speed is proportional to the cube root of power, the cube root of 1 is 1. In other words, speed will decrease by about 1%, or 2 mph.

Bottom line is that the 3000 lb car will go 200 mph, the 3900 lb car will go 198 mph, all other factors being equal. You may disagree, but I call a 1% difference in top speed insiginificant.

BTW, I know you didn't ask for it, but comparing a 6000 lb car vs. a 3000 lb car...
6000 lbs * 0.013 * 200 mph / 375 = 41.6 lbs force to overcome roll resistance
20 sq ft * 0.30 * 0.003 * 200^3 / 375 = 384 lbs force to overcome air resistance
Or 425.6 lbs total force, or about 5% more power. Again using the speed vs. power proportion, speed will decrease about 1.7%, or 3.4 mph. In other words, a car that weighs twice as much as another car, if all other factors are equal (gearing, horsepower, wheels, etc.) the light car will do 200 mph and twice as heavy car will do 196.6 mph.

 

You are absolutely right. Don't worry about anybody that argues with you. They are wrong about this.

 

2 (or 3, or even 4) mph would certainly be fairly insignificant (I view irrelevant a bit differently - perhaps its my test director background?) in the eyes of most when talking about such a high top speed - mine included. So I suppose that my earlier statement - "if there is a difference, then that difference would apply to a much smaller extreme (ie..900 lbs), though how much would quite possibly be very minor" - was safe and correct.

Thanks.

 

But I thought you'd never pat yourself on the back?



And sure as ****, I'm still correct too.