Does wheel weight REALLY matter?

[chubbychu]

Originally posted by bobdobbs
Hey, did you ever stop to think about what we consider solid material in an atom -- the nucleus -- is really very, very small compared to the size of the electron cloud, which is just a bunch of little electrical junk flying around? And it's collections of atoms that form molecules that make up materials that we touch and use in our every day lives? And when you start putting all these atoms together, their electron clouds interact, but their nuclei stay far apart. So, really, the stuff that we consider solid is really made up of some very small nuclear material (the nuclei) and a bunch of electrons flying around in much larger "clouds". And the fact that you can't, say, put your hand through a tree is because the electrical forces in the atoms in your hand being opposed by the atoms that make up the tree. So, really, matter -- the stuff around us -- is made up of mostly empty space. Weird, huh?

What were you saying, plainol? :D

showoff

[glw]

thought it was confusing before? try this on...

[quote]A 10 lb reduction of wheel/tire weight will result in a total overall apparent effect of reducing vehicle weight by about 65 lbs and at absolute maximum, 80 lbs.

The analysis follows:


Question: What is the effective additional mass of wheels/tires due to their rotation?

For the vehicle in motion, the kinetic energy is given by:

Ekinetic =

[bobdobbs]

That's excellent. He's shown how weight distribution affects the effective mass. If a 15" wheel has, say, an Reffective/Rtread of 80%, a larger wheel will have an Reffective/Rtread of maybe 90%. So, instead of Mwheel,effective being Mwheel*1.64, Mwheel,effective is Mwheel*1.81. Ouch.

[eurosteez]

Originally posted by bobdobbs
Hey, did you ever stop to think about what we consider solid material in an atom -- the nucleus -- is really very, very small compared to the size of the electron cloud, which is just a bunch of little electrical junk flying around? And it's collections of atoms that form molecules that make up materials that we touch and use in our every day lives? And when you start putting all these atoms together, their electron clouds interact, but their nuclei stay far apart. So, really, the stuff that we consider solid is really made up of some very small nuclear material (the nuclei) and a bunch of electrons flying around in much larger "clouds". And the fact that you can't, say, put your hand through a tree is because the electrical forces in the atoms in your hand being opposed by the atoms that make up the tree. So, really, matter -- the stuff around us -- is made up of mostly empty space. Weird, huh?

What were you saying, plainol? :D

So theroretically bodbo, we could condense this planet into oh...say a square inch? or even smaller? it could be condensed so much it went negative(blackhole)?
But what does this have to do with you posting alot?

[DownTheHatch]

There's a simple experiment you can do that will prove to all of you the difference of weight vs. diameter.

If you have an office chair that rotates, give yourself a good push with your legs all the way out. Now gradually bring them closer to your body (the center of the rotating axis) as you spin. The speed at which you are spinning will increase as you pull your legs in, there is less rotational mass.

Now, take something that weighs about 10 pounds and place it on your lap, infact, add as much weight as you want, getting yourself started will be increasingly tougher but once you're going, your legs will be determine how much freer you will spin.

Weight = Intertia (force holding an non-moving object in its place) You will notice this when you try to launch the car, say at the drag strip, with heavy wheels you will have a really hard time getting that car to go anywhere quickly, the same thing applies at highway speeds, when you goose the pedal you will not get as quick of a response if the wheels were lightweight. Kind of like the difference between throwing a bowling ball or throwing a basketball.

Diameter = Acceleration (rate at which an object gains speed)
If you've ever worked with gearing, the sizes always determine the speed at which the gear rotates, a smaller sprocket spins 2x or 3x quicker than the larger sprocket, there are less rotations per minute, this is the same way a transmission's gears work, 1st gear is small, 5th gear is large. If you break it down, the wheels are actually gears in line with the transmission, if these gears are larger what are you going to get? Lower gearing ratios, this also affects your speedometer since it's configured for a specific wheel size.

So if a 15" wheel with 45 series rubber is the same diameter as a 17" wheel with 40 series rubber, which one is going to be quicker? Well, the diameter is identical, so you would have to look at the weights, if they weight of these wheels are identical there would be no difference in performance other than the more rigid sidewall would affect handling in a good way around the apex. And you would feel those potholes alot more.

So to answer your question...Does wheel weight really matter? Yes. Its the most important aspect of a wheel if you care about vehicle performance.

The more weight you take away from a wheel, the less the diameter matters, you could have 26" wheels that weigh 1 pound each and you'd be smoking the competition, unfortunately thats not the way it works in the real world, bigger wheels = more weight.

There is another way to counter additional wheel weight...that is to generate more engine power :)

[bobdobbs]

Originally posted by eurosteez
So theroretically bodbo, we could condense this planet into oh...say a square inch? or even smaller? it could be condensed so much it went negative(blackhole)?

This planet? No. Too small.

But what does this have to do with you posting alot? [/B]

What do black holes have to do with wheel size?

[chunky]

Originally posted by DownTheHatch
There's a simple experiment you can do that will prove to all of you the difference of weight vs. diameter.

If you have an office chair that rotates, give yourself a good push with your legs all the way out. Now gradually bring them closer to your body (the center of the rotating axis) as you spin. The speed at which you are spinning will increase as you pull your legs in, there is less rotational mass.

You can't reduce rotational mass except by reducing the mass that is rotating. So saying there is less rotational mass by pulling your legs in is a misnomer. What you are in fact doing is re-arranging the parameters that constitute angular momentum. Conservation of Angular Momentum for rotational systems that can change shape will lead you to the following conclusions: Moving the mass outwards results in a lower speed, but higher torque. Moving the mass inwards results in a higher speed, but lower torque. But in both cases, angular momentum is idential and thus the law of Conservation of Angular Momentum holds true.

Now, take something that weighs about 10 pounds and place it on your lap, infact, add as much weight as you want, getting yourself started will be increasingly tougher but once you're going, your legs will be determine how much freer you will spin.

Weight = Intertia (force holding an non-moving object in its place) You will notice this when you try to launch the car, say at the drag strip, with heavy wheels you will have a really hard time getting that car to go anywhere quickly, the same thing applies at highway speeds, when you goose the pedal you will not get as quick of a response if the wheels were lightweight. Kind of like the difference between throwing a bowling ball or throwing a basketball.

Diameter = Acceleration (rate at which an object gains speed)
If you've ever worked with gearing, the sizes always determine the speed at which the gear rotates, a smaller sprocket spins 2x or 3x quicker than the larger sprocket, there are less rotations per minute, this is the same way a transmission's gears work, 1st gear is small, 5th gear is large. If you break it down, the wheels are actually gears in line with the transmission, if these gears are larger what are you going to get? Lower gearing ratios, this also affects your speedometer since it's configured for a specific wheel size.

So if a 15" wheel with 45 series rubber is the same diameter as a 17" wheel with 40 series rubber, which one is going to be quicker? Well, the diameter is identical, so you would have to look at the weights, if they weight of these wheels are identical there would be no difference in performance other than the more rigid sidewall would affect handling in a good way around the apex. And you would feel those potholes alot more.

You still have to consider WHERE the weight is relative to the hub. If the weight is concentrated farther from the hub, you will need more torque to achieve the same angular speed. A 15" wheel will almost always have a center of mass that is closer to the hub.

So to answer your question...Does wheel weight really matter? Yes. Its the most important aspect of a wheel if you care about vehicle performance.

The more weight you take away from a wheel, the less the diameter matters, you could have 26" wheels that weigh 1 pound each and you'd be smoking the competition, unfortunately thats not the way it works in the real world, bigger wheels = more weight.

There is another way to counter additional wheel weight...that is to generate more engine power :)

More power makes up for a lot, but you still have to deal with forces that the suspension undergoes. The suspension has to work harder to control the motion of a heavier wheel. all the forces are linear, so the effect isn't as pronounced as the impact on acceleration, but the car will wander more over rough & uneven pavement with heavier wheels.

[bobdobbs]

Originally posted by chunky
You still have to consider WHERE the weight is relative to the hub. If the weight is concentrated farther from the hub, you will need more torque to achieve the same angular speed.

Not only that, but the addtional torque required is a function of the distance from the center SQUARED.

[glw]

IMO - the best tires weigh at least twice that of good wheels (15" to 17"). therefore, the diameter of the wheel (15" to 17") is probably not the most important part of the suspension picture - especially if you're still riding on the heavy stock struts and spinning the stock brake discs... the difference between fairly similar weighted 15" and 17" wheels will probably be indistinguishable.

for the average or beginning racer; get a light weight wheel that will allow you to fit the best tire for your purpose and you could compete with all but the most tricked out cars... your skill, tires, and other suspension components are more important than wheel diameter.

for the expert racer or person that can afford two sets of wheels and tires; of course a smaller and lighter wheel will be the best choice for absolute maximum performance. the rest of your car better be up to the task because your opponents few extra horsepower or a few other suspension mods might just make more of a difference than your smaller wheel diameter. and if your skills aren't up to the task, you will probably be beat by a more skilled driver on heavy larger equipment...


factoid
-------
although some say that larger wheels are better for appearance... 15" wheels are usually cheaper, lighter, and have better tire choices than 17" wheels.

[tony speed]

let us not forget that there are two main reasons for bigger rims:
1) looks
2) fitting of a bigger brake kit

[chunky]

Originally posted by tony speed
let us not forget that there are two main reasons for bigger rims:
1) looks
2) fitting of a bigger brake kit

#2 is mostly invalid. unless you're using 15" rotors on a civic, which is retarded in the first place considering the enzo uses 15" rotors. . .

[eurosteez]

So you guys are sayin if you take the stock 18's off a porshe and put 15's on it will perform better???????????????????

just tryin to understand all this physics....:o ....:banana:

[bobdobbs]

Originally posted by eurosteez
So you guys are sayin if you take the stock 18's off a porshe and put 15's on it will perform better???????????????????

The problem there is the GT3 has 295 tires in the back. Getting that width in 15" would be difficult.

[eurosteez]

Lets say you could get 15 by 295's on there?

I don't totally understand all that physics that glw was talking about....and I don't know if it answers this question......but lets assume both tires have the same width, would an 18' have more area(grip) on the ground than a 15' with the same width. I'm just thinkin larger diameter=more area touching the ground.

[bobdobbs]

Originally posted by eurosteez
Lets say you could get 15 by 295's on there?

I don't totally understand all that physics that glw was talking about....and I don't know if it answers this question......but lets assume both tires have the same width, would an 18' have more area(grip) on the ground than a 15' with the same width. I'm just thinkin larger diameter=more area touching the ground.

If they were the same width (295) and the 15" rims were the same width as the 18s, they would have the same amount of tread on the ground. If the 15" wheel is lighter, it will peform better, assuming no (performance) difference in tires.

Think of it this way: Your car is moving a weight around in a circle. The larger the circle (wheel/rim), the more work is required to move the weight, because the distance it travels is greater. If the circle thing throws you off, imagine pushing a heavy box down the street. With the larger wheel, you are essentially pushing the box FURTHER than you are with a smaller wheel. That requires more effort. That additional effort means your engine has to work harder.