Weight Reduction?

[BlackICE]

The 80 lbs number is hard to believe.

Amp 12.5
Subwoofer with enclosure 20 lbs est.
Difference in adding the different door speakers and tweeters 10 lbs est.
head unit difference 0 est

That is a max of 42.5 lbs. not counting the wiring changes. I doubt that the wiring is another 37.5 lbs.

Journalist often get the details wrong, or should I say embellish the facts?

BlackICE

 

[californiacuda]

The equasion for max speed at a particular hp number is.

Force = 1/2 Cx(drag coefficient) F(frontal area) D(air density) V(velocity) squared + rolling resistance

The rolling resistance is affected by weight, by not to a great extent. Rolling resistance is a little difficult to calculate. One book that I read said that at 180 mph rolling resistance was about 100 lbs . Acording an article in Motor Trend (referenced in another thread) at 200mph it took 874 lbs of force to push the GT.

As the speed increases the force exerted against to car by air friction is increased by square of the velocity.

Acceleration and handling are greatly affected by weight, but absolute top speed is just very slightly affected by weight.

 

[SLF360]

Cuda,
you are absolutely right. One more thing I forgot, of course prime target for weight reduction should always be first all unsuspended mass, as it affects ride and handling the worst.
Hence the lightweight BBS wheels should be a first for who is concerned, and make a difference more than ripping out beauty and comfort inside as a first. These things can become obsessive....

 

[Pipelion]

quote from Stepen;

1. Re Speed and acceleration perfomance it does not matter where you reduce.
2. Re handling, it is always better to reduce as much as high as possible, this reduces roll in curves if you manage to lower center of gravity, anything over the wheelhubs particularily, and as far front and as far back.
3. Keep an eye on front, back balance of reduction, as it will change oversteer/understeer tendencies. if you take weight away in the back, understeer will result and the back more controllable. Sometimes not desireable.

Also less weight means the car gets stiffer in the springs,as they are setup for the weight the car comes with.

I once setup a car with frontwheel drive so balanced, that depending where I moved the seatposition or lean back with my upperbody I would be able to get oversteer out of it. moving the seat more forward and move up closer to the wheel, the back would not swing out (like in rain and stuff not always a nice tendency).

If you like more oversteer tendency to eliminate understeer in tight corners, e.g. for trackwork or hill climb, consider to have a slight toe in on the back( 1-2degrees), as the car will come back easier once in oversteer mode with more pressure and grip getting on the outside wheel, as the inside lifts up. That way you get a very responsive but controllable feel. The slight rubb on a straight won't be much noticed. But for quartermile events, rubber straight of course...

hope that helps !

stefan,




Stefan


Nice overview,

You taught me some things, thanks.

Also, rotating weight has a premium over static weight ie,
any mass that has to be spun( wheels, clutches, cranks, pistons, flywheels, tires etc) and unspun(slowed down), are much more critical. The multiplication or magnitude depends on where the weight's positioned on the radius.

The factor over normal weight might exceed a factor of ten to one. One pound spun weight equals ten pounds static.

Static weight isn't accually static, since it's being accellerated during take off and slowed during breaking, both require work, through HP or breaking as well as turning. Which equals time and money.

A heavy hub isn't as important as a heavy rim. The hub sitting close to the center is easier to excellerate and decelerate. The rims weight is more critical.

But we have to remember we are discussing three types of speed effected by weight. Pure accelleration(1320 feet), excelleration/decelleration while turning(road & track). And all out top speed vs. wind resistance.

My two cents,

Allan

Also Cuda, intersting formulas. Bugatti was saying "as car approaches 250mph it takes 7HP per every 1 MPH increase".