Floorman279

iTrader: (11)

Posted here since you racers may know.....

So something ive been curious about lately, and figured id ask even tho its a very broad question with many factors....

So in a z06 vs fbody thread i was checking out, everyone was saying after about 130-140 z06 starts to catch an fbody quick due to weight......understandable

Example.....

A veyron weighs like 4200, 1000 hp, probably decent aerodynamics, i think tops out at 230-240.

C6 z06, 1000 pounds lighter, half the hp and tq, 205 ish top speed....again well above average aero...., but only 30 mph less top speed, despite a 500 power difference

My question is at what speed does weight really start to make your heavy quick car not so quick anymore? When do those heavy high hp cars really just start to lose their thunder generally......130, 140, 150?

ps, feel free to add in how weight effects cornering as well.....when can the best suspension and tire setup just not be able to make that boat turn hard....

MACHXLR8

LOL...Physics problem but where do you want to begin. This could get boring.

It is not a matter of speed but more of a matter of torque and acceleration, where acceleration is the derivative of velocity meaning the change of velocity over time or

a=DeltaV / DeltaT (Change in Velocity over time)

Unfortunately, it is not that easy since many things come into play such as:

*max torque @ ????rpm
*trans gearing (mechanical advantage)
*rear differential gearing (mechanical advantage)
*traction
*weight of car since Force =m(a) - (mass * acceleration)
* drag coefficient

There is no general answer to this since there are many factors that can change the result. You would have to take a particular car and calculate each factor individually depending on how accurate you want to get. You could even get to a point where you can calculate the friction factor of tires using a friction constant for rubber.

Then again you could always wing it by just getting in your car and running them. lol

RedFuryZ28

Weight isn't as much of a factor anymore at high speeds. At 120mph+ It mainly comes down to aero, gearing and horsepower. And 30 mph top speed difference is HUGE. Very huge. And when you're talking 180mph+ It takes A LOT of power to keep pulling hard at those speeds. Because there is so much more wind resistance pushing against your car.

Atomic

iTrader: (37)

What MACH said, but keep in mind weight only matters when you are accelerating. The car that weighs less, assuming equal aero and traction, will always accelerate faster from a given speed. Top speed or at high speeds the aerodynamics of the car dominate everything. Drag goes up with the velocity squared, meaning at 25mph if your drag is 2 units, at 50mph it is 8 units, at 100mph it is 16 units, at 150mph it is 36 units, etc.

Not familiar with that thread you got this from, but if car A is in the lead and pulling away in the beginning but then gets passed by car B at some higher speed and we assume neither spun, we can safely assume car A has the better power to weight ratio and car B has the better aerodynamics to power ratio.

Another example, with my truck 0-100 on street tires just about nothing short of a gutted race car on slicks would be close, but after that a simple bolt on vette would easily pass me by 160mph. Truck has huge traction and power advantage but the aero of a garage door compared to the vette.

Floorman279

iTrader: (11)

I figured this is where it would go right away. Ur 100% right but wasnt sure if there was a certain speed where avg high hp street cars start to feel heavy.........let me just look for a more simple answer cause im sitting here bored and just thinkng way too hard.

So we know the basics involved in moving a car

Power
Gearing from trans and rear
Weight
Aero

So its not an even 25% involved there. Lets assume the car has magical tires that hook in any condition and never spin...... To accelrate from 20-40 mph, aero is almost irrelevant and maybe has 5% contribution, with weight being a facto but not as important as power or gearing. Lets say 5% aero, 15% weight and lets say 40-40 for power and gear to equal 100.

Now lets try 100-120 mph, now aero becomes much more important.... Lets just say its now 25% the equation......what are the other 3s perentage of importance? But technically if you have lower gearing u can run higher weight to achieve the same goal with equal power level etc etc.......

Idk but i expect this thread to be looked at by others as pointless, but basically just thinking out loud.

Floorman279

iTrader: (11)

So u can basicallysay my question has no answer, because you can conquer one by increasing or decreasing another......

You top out at 150, but increase power and you top out at 155
Or
You top out at 150, but decrease weight and now get 155.

Floorman279

iTrader: (11)

I just thought that there would be an answer like 140 mph is where it becomes difficult for any car to accel regardless aero power weight

AWPer

I swear I remember some documentary about the Bugatti Veyron where the engineers were saying after 200 mph, it takes about an additional 100 horsepower to get each additional 5 or 10 mph afterwards.

Marc 85Z28

iTrader: (8)

The answer you seek isn't much of an answer at all because the problem is far more complicated than you realize, and thus explaining it to you will be pointless as you'll never understand.

This thread doesn't belong here.

Floorman279

iTrader: (11)

You could try explaining what you know. I do realize the problem is complicated, hence my awkwardly worded posts. Also i thought asking a question about high speeds was appropriate for a street racing section. not sure where else would have been appropriate.

V8EATR

Generally, the faster you go the less important weight becomes because the car is mainly fighting air at that point, not weight. As stated 30mph in top speed is huge.

Floorman279

iTrader: (11)

Yea i did notice most high end supercars top out anywhere from 205-225. Regardless if they have 600 or 1000 hp. So thats an answer i was kinda looking for.....weight plays a small part at high speeds, but not nearly as much as aero and that wall of air......

Atomic

iTrader: (37)

The math for it is:

D=1/2*rho*Velocity^2*Cd*A

D=Drag
rho=fluid density
Velocity=speed in this case
Cd= coefficient of drag
A= area the drag is acting over

Velocity squared gets to be a big number really fast.

For acceleration
A=F/M

A=acceleration
F=force
M=mass

Force is the total tractive effort through the tires to the ground. The real equation is the force is equal to the time rate of change of momentum but since mass is basically constant with everything but a rocket its usually just used as weight.

MACHXLR8

The force provided by the engine is trying to accelerate the car but it will only reach a certain force depending on the cars horsepower. The main force acting against this acceleration is mainly air resistance. The force or motor output goes up with the square of the speed.
When these two (2) forces are equal, the car will not go any faster or continue to accelerate. The mass of the car remains constant but it is actually the delta of the two forces acting against each other that is affecting the acceleration as the speed increases over time.
The weight of the car comes more into play while accelerating the car from a stop due to inertia.

willizm

iTrader: (10)

The nice thing about having some weight is that maintaining traction is a little easier. At least that is what I keep telling myself to keep from holesawing my car up.

LightningTeg

I think its more about weight in the right place. Im really curious though at what point less weight would hurt though. Think about an Aerial atom. Its small, light, and doesnt make much power, but would put a hurt on most things it ran into on the street.

Dimeomboost

Im with u on this idea only problem is my truck would have to front wheel drive to take advantage of the weight for traction. #s10lyfeproblems

HioSSilver

iTrader: (8)

The biggest place weight affects stuff is at 0 mph. Getting it moving is the hardest part.

As far as cornering goes weight can help if you improve on the balance of the car. There were times when the alms/scca put weight on our race cars as penalty for either being to dominant or rewards weight for winning. Sometimes it actually made the car faster......cause balance

Same can be done for drag cars. It's why foxes are so popular. They are light. So to meet weight in some classes you add ballast were you want it and lots of other cars will struggle to meet the same weight with no ballast.

Killemall

Weight is primarily down low.

It takes a lot more to moyivate a standing object to movement than a moving object.

A c6Z for example...

11.6 at 124 mph car with 440 rwhp and 3200 pound race weight. 0-60 in 3.8

440 rwhp is not a lot of power by todays standards.

The 2010 R8V10 also puts down 440 to its wheels, but weighs 500 pounds more at 3700 pounds. 0 to 60 also in 3.8 (due to awd) 11.9 at 121 mph car

So here we have two NA cars putting down the same power, but with a 500 pound weight advantage for the c6z06

You could watch 50 videos and read 20 magazine articles and you would find that the lighter z06 is almost always gonna be 3 tenths quicker and 3 mph faster than the Audi R8 V10.

The 500 pound advantage shows its face from a dead stop to say 100ish mph...

But you could watch 50 races of the same to vehicles doing 50-150 mph roll races and you would see that they are nearly identical in this range.

500 pounds is significant from a dead stop but means far less at rolling speeds.

Gearing and c.d. drag are the factors that matter once already moving at a good clip.

vwdave

iTrader: (3)

If youre talking top end speed, as others mentioned, at high speeds, every mph faster you go it takes exponentially more horsepower than it did previously.