Mahjik

iTrader: (1)

You are comparing the price of a 10 year old car to cars that are MUCH newer?

Think about what the FD cost back in 1993 and then use inflation to see what that price would be today. The FD was nearing what the price of a new Vette is today, however 10 years ago!

You can't compare a modded car to a non-modded car as that's not really apples to apples. Just take a look at the AutoX guys trying to chase down Z06's.

As for the Z06's being manufactured poorly, that has to do more with US manufacturing than overall. Sadly, it's a known fact that people should check the manufacturing dates of their US made cars and never get one completed on a Monday or Friday. Hell, I live in the town with a Ford plant and they say the same thing.

As for the Z06's falling apart, I haven't seen it. My father has one (2003):

http://mahjik.homestead.com/files/FD...2-MVC-007F.JPG

It's been at the track several times in the last year without a single failure. Unfortunately, when buying American, you never know the quality of the manufacturing you are going to get as it depends on the worker's mood that day.

However, when I purchased my FD, the engine was already done at 40,000 miles. I doubt my father's Z06 is going to need a new engine by then.

However, I was mainly referring to the C5 being the best bang for the buck. It doesn't have the Z06 power but can easily be enhanced with $1000 exhaust replacement and some better tires than the runflat junk they come with. The tire sizes and torque make those cars really tough on a road course unless you have a very modified FD.

DamonB

Some studying is needed. People who do not understand inertia, angular velocity and angular momentum are not going to understand a spinning wheel other than the fact it goes round and round.

As for the idea of the road supporting some of the weight of the wheel and therefore the suspension doesn't have to, that's extremely misguided (as in: it's terribly wrong). The road supports the weight of the whole danged car. The wheel is connected to the spindle which is connected to the upright which is connected to the suspension arms which is connected to the chassis which is connected to everything else. Just because the wheel happens to touch the ground doesn't mean some of its weight has no effect on the car because it's supported by the road. The whole car is supported by the road and all the car's parts are interconnected. The wheel gets no free ride, the idea that it does is completely false.

Let's go back and look at an engine's flywheel. Let's say a stock flywheel weighs 25 pounds and a lightweight flywheel 12 pounds. We remove the stock flywheel and and install the 12 pounder, saving 13 pounds in weight. After doing so we see greatly improved ability for the engine to change speed, both in acceleration and in deceleration. Is that ability due to the fact that the entire car is now 13 pounds lighter and the engine has less weight inside the car to drag around? Absolutely not. The 12 pound flywheel has a tremendously smaller amount of inertia that must be overcome in order for the engine to change speed. The lightweight flywheel presents large inertial gains but the weight savings is only about the same as having 2 less gallons of gas in the tank.

Just like the flywheel the wheels represent an inertial force that must be overcome to change the speed of the car. Notice I didn't say just the drive wheels; ALL the wheels on the car represent the same inertia. Just because the engine only drives the rear wheels doesn't mean the front wheels don't count. The inertia of the front wheels must still be overcome in order to change the speed of the car and the engine must do that. It doesn't matter that the engine is not directly connected to the front wheels.

DamonB

I don't have time for a long winded reply and to tell the truth the contact patch thread taught me that people would rather not change their minds so I will leave it at this for now: This statement is flat wrong

Everyone understands the wheels are also bolted to the flywheel, right? And they understand that the ground doesn't just support the weight of the wheel, it supports the entire car since it's all bolted together, right? The wheel doesn't get a free ride because it touches the ground. If it did so would the entire car, because the rest of the car is bolted to the wheels.

To find out why you must undestand rotational inertia, angular momentum and angular velocity. I spent a few semesters understanding them

Mahjik

iTrader: (1)

Same here, 2+ years worth of Calculus and Physics classes in college. I would have had a degree in Computer Engineering with a double minor in math and physics had I actually finished, but I quit in my last year. All I had left were electives and it sucked being in classes with freshmen at the time. Granted, it's been over 10 years since I've been in school, but I still remember most of the basic principals.

Whoa.. Don't put words in my mouth. I wasn't even talking about the suspension, but the mechanism that turns the wheel:

To make your analogy work better, just hold the bicycle front up in the air, spin the wheel and then turn the handle bars. How much harder does it get as the wheel is heavier, spins faster, etc.. However, how much harder is it to turn when the wheel is touching the street? Now, does it get any tougher as the wheel gets wider? Sure it does as the ground is not a frictionless surface.

Damon, I'm not saying that weight has absolutely no difference what so ever on performance (as race car tech proves... but as I said before, those guys are trying to shave off tenths of seconds off their lap times which is something people won't notice on the street). I'm saying that in most cases, the difference in everyday "street driving" with heavier rims (adding an additional 4-5lbs per corner which is what the original question was asked), the difference will not be noticeable all other things being equal (as long as you aren't talking 100lbs wheels at all 4 corners). However, with other variables added in such as, offsets, tire differences, width differences, etc, will all add into a different handling experience.

DamonB

Your observations of the bicycle wheel analogy when mounted to a bicycle are correct but are not representative of a car. On a bicycle the axis of the handlebars is in line with the center of the wheel as well as the wheel's axis so the forces are balanced; cars are nothing like that. To make your bicycle example representative of a car you need to remove the bicycle wheel and weld an axle in place sticking from the side of the forks a few inches. Then place the wheel on the end of this axle so the wheel is no longer centered under the forks and the handlebars but is instead hanging off to the side of the bike. Spin the wheel and try turning the handlebars again. You'll find that with the wheel offset to the side of the pivot you will have large inertial forces that you must overcome in turning the handlebars that were not present when the wheel was centered inside the forks. Remove the wheel from the bike and hold it in your hands. Tilt it and move it around in different directions while it spins, you will understand right away.

The front wheels of a car do not pivot about the center of the contact patch, they pivot about the steering axis which is 3 dimensional. First you have scrub radius which is the distance from the center of the contact patch to where the steering axis intersects the ground and then you have caster angle as well. These two combine to make the wheel steer in 3 dimensions, not just 2, and they ensure that the axis of the wheel is never inline with any of the pivots so there are always intertial forces present when the wheel is turning.

Your observations of the bicycle wheel are correct but your example is wrong. Your example does not represent how the front spindle of a car is designed and thus does not represent the effects the weight of a wheel has on a car.

Mahjik

iTrader: (1)

Yes, it was a simplistic example just to prove a point about friction needing to be in the equation.

As I said before. While weight is a factor, I firmly believe (and have witness and felt first hand) that an extra 4-5lbs (as weight being the ONLY difference) on each corner is typically not noticed in everyday driving, especially on todays vehicles with PS.

Put it on the track and run some lap times and I'm sure that difference might appear.

DamonB

So you agree the bicycle example doesn't represent a car but still insist it applies? Friction is not involved at all in any of the examples. The tire friction has nothing to do with the intertial forces; all my examples assume the wheel is suspended in air and free spinning. No tire friction.


Key words in this statement are the use of "I" so I added emphasis there. You may not notice them yourself but that doesn't mean they don't occur or aren't noticed by others. Plenty of people have said their car feels peppier when they went to lighter wheels on the street. They probably don't notice the handling much but they certainly notice the acceleration. Again, it's very similar to adding a lightweight flywheel to the engine but not as pronounced since the rpm of the wheel is less.

Myself I don't notice that I tend to leave magazines all over the house but my gf does, she spots it every time and I don't even though we live in the same house and my eyesight is just as good as hers

Mahjik

iTrader: (1)

Nope, we are talking about apples and oranges on that subject.

And people also noticed getting well from taking placeboes.

The front strut bar is another good example of that. I'll be the first one to say that if you pulled mine off right now without me knowing about it, it's doubtful I would know the difference tooling around the street. As soon as I saw that it was gone, I would "suddenly" remember the car not handling as well (and I've seen someone do something like that in the past).

People can exaggerate and "make" themselves feel/see what they want. Doesn't mean it's always the case; as mind can be a trerrible thing to waste.

In this case, that doesn't mean the effect they are feeling/seeing is "strictly" from weight but possibly (and most likely) from some other change (or combination there) of the new wheels.

For most people who move to larger wheels, they are also adding a larger tire which is more weight. People sticking 18x9.5 or wider in the rear, sure they are going to notice a difference. However, with all things being equal, I serious doubt 4-5lbs on the corners is going to be that noticeable "on the street".

SleepR1

The steering feel is a bit duller with 255/40-17s with 9 x 17s all around vs stock 225/50-16s with 8 x 16s all around. This is especially noticeable when doing slalom courses. The 17-inch combo is 7 lbs heavier than stock per corner, which is ~18% more than stock per corner. Before I modded the engine, there was a slight acceleration difference (slightly slower with bigger wheels). On the street, ride comfort was about the same. Much more tramlining. Steady state cornering went way up. After modifying the engine, the acceleration hit is a non-issue, so the only hit thus far with larger wheels is the dulled steering feel.

moehler

iTrader: (12)

Alright... I have a bachelor's degree in physics, I'm one class away from a masters in physics and I work as an professional engineer, so I figure that I should cut in here.

The weight of a wheel will affect BOTH the "dead weight" of the car and the rotational velocity of the wheel itself. Hence a wheel that is 10lbs heavier is NOT the same as just throwing a 10 lbs bag of stones in your trunk; it would be like throwing a >10lbs bag of stones in your trunk. This result comes simply from the conservation of angular momentum (of the wheel) and the conservation of translational momentum (of the car).

Rotational momentum is directly proportional to the mass of the rotating object and is L = I*w (w is the angular velocity of the wheel). Hence as the I (the moment of inertia, proportional to the mass) increases, the angular velocity of the wheel itself must decrease to conserve L. So if your wheel was just spinning on an axle in free space (no contact with the ground or car), the wheel would slow down just due to the mass of itself. Now connect this wheel to a car ... the conservation of linear momentum (p = mass*vel) would tell you that more mass (the weight of the wheel) would result in a smaller velocity. These are essentially two different effects (the wheel slowing down and the car slowing down), so that the car will be "slowed" by more that just adding a 10lbs mass in the trunk. All of this assumes the same power output of the car BTW and ignoring friction.

So if I know this (or think I know this ) why did I ask the question? Because all this crap means little to me if I can't FEEL the difference. It seams, however that the effect is noticeable enough to feel it as some people have already pointed out...

DamonB

Everyone at work push away from your desk. Reach out your arms and legs and start yourself spinning. Then pull them in and watch yourself speed up. Reach them out again and you will slow down. When someone walks by and asks what in the hell you are doing tell them "Studying!"

Mahjik

iTrader: (1)

Yep, but how can you talk about wheels/tires and ignore friction?

Like I was mentioning before, it also depends on factors besides just weight (wheel size, offset, etc). All of those things can play a roll in the handling of your car as individual pieces or all together.

Does weight, in itself, make a difference? Absolutely. Will you actually feel the difference driving on the street? Only you will be able to answer that one.

Adding a wider wheel will definitely give you a different steering sensation.

moehler

iTrader: (12)

^^ The friction plays a very important role, and although it breaks down the conservation laws into more complicated bastards, the same effect should hold .

I should have also added that I assumed the same size wheels.

Mahjik

iTrader: (1)

On my old FC, and 300zx and 240sx cars, I changed the stock wheels out for aftermarket ones. Back in the early 90's late 80's, pretty much ALL aftermarket wheels were heavy not that I would have cared back then.

I use the same tires, just changed out the rims. They weren't substantially heavier than stock, but I would say about 3-4lbs heavier than the stock rims. I didn't notice a change in steering, braking, or acceleration.

DamonB

All it takes is weight. Inertia doesn't care how wide the wheel is. If you could accelerate the car to 60mph and then jack up the front end so the tires were no longer on the ground (therefore no tire friction) and spinning in the air you'd find the steering to still be heavier with the heavy wheels than the lighter ones, even if the heavy wheel is the same physical size and offset as the lighter one.

Look at the equations that moehler posted; size does not enter the picture.

Rotational Kinetic Energy

Moment of Inertia Concepts

I just found that site; lots of good stuff at Hyper Physics

Gyroscopic Effects

Mahjik

iTrader: (1)

His equations have nothing to do with how the car reacts to the road with friction.

DamonB

That's because road friction has absoltuely nothing to do with the interaction of a heavier wheel with the suspension compared to a lighter one!!!

Rubber friction is merely going to introduce scrub and this will be the same as long as we are talking about wheels only differing in weight; equal size and offset wheel with identical tires mounted. Take two identical wheel/tire combos and add weight to one. Only difference is weight, both will experience the same road frictional forces and so those do not apply to the comparison. As with any good experiment we are only allowing one variable to change: weight of the wheel.

Pattsy

iTrader: (1)

It takes more horsepower to rotate a heavier object, period. Rear wheel horsepower will be lower if you put heavier wheels / bigger brakes on your car. It was proven on one of speed channels car shows, "Horsepwer TV" i think. I don't remember exactly but i think they lost ~10hp with bigger brakes and wheels. It is up to you if you can "feel" 10hp on the street.

Pat

Mahjik

iTrader: (1)

Actually, mass is there (if you read). And determining the center of mass does change based on size.

moehler

iTrader: (12)

I only said that friction would "complicate the equations," the concepts remain the same...

moehler

iTrader: (12)

true... a wider wheel will most likely be more massive .

Mahjik

iTrader: (1)

lol.

DamonB

This would all seem strange if I hadn't seen it before Don't make the mistake of trying to prove your perceptions correct by observing only those facts that seem to fit your analysis.

Mahjik

iTrader: (1)

Damon, I think you have been ignoring the fact that I'm not disagreeing with you on anything. I am suggesting that there is more too it than just "weight". And while adding heavier wheels does make a difference, there are other changes that happen which also make a difference.

What I said was that the differences are probably not going to be noticeable with only a few pounds extra per corner (everything else being the same) in normal everyday driving (and in my cases, it was true). If you don't agree, that's fine. I'm not here to run for president or to start my own tire/wheel shop. I'll just wipe the tears off my keyboard and live with it.

DamonB

Crying no longer works for me. I bang my head on the desk