Total weight needed?

[hotrod]

Does that sound right? Everyone told me I'd need a heavy car, but that heavy?

There are quite a few cars that are north of 4000# out there from what I have heard. Many cars have hundreds of pounds of ballast in them, but you would have to talk to the roadster guys to get a feel for what the stable/fast ones typically weigh. Required weight to get your power to the ground depends very much on two things. How much power you are making and how much drag you are fighting. The roadsters as a class have the toughest nut to crack regarding drag and they are also inherently unstable at high speed due to the bluff front end. That makes them inclined to swap ends at the slightest upset.

The only way to battle that problem is to get enough weight in the car that you can keep it planted when it is at top speed and looking for an excuse to swap ends.

Ask around and I think that weight is not out of line if you have enough engine to require that much weight on the rear wheels.

Larry

[Bville701]

For 180 MPH a good 3000# sounds good to me, but every car is different...

We have a modified roadster that weighs just over 3200 lbs, and we have gone over 200 MPH. Some cars weigh less, some cars weigh more.

Good luck with your build. I look forward to seeing a build diary on this site.   

[Stan Back]

"It's the only car that I knew of like mine I could referance."

And he's never gone that fast.

[panic]

As the stability, it looks like the highest directional inertia helps.
This means that, for the same amount of ballast and the same CG, it should be split into halves and each half moved as close to the front or rear as possible (and ahead/behind the axles). This creates a "dumbell" effect, which is strongly resistance to yaw and pitch compared to a centralized mass of equal weight. You can also increase roll resistance by mounting it in the F/R roll axis, but that's probably much higher than you want) and difficult to do.
Unfortunately, this also makes steering corrections more difficult, since in addition to the tire adhesion and chassis mass you have to rotate both weights around an axis as long as 1/2 the wheelbase (whereas a centralized mass at the CG has a much lower moment of inertia, and simply pivots on its own center).

[38flattie]

Good luck with your build. I look forward to seeing a build diary on this site.   

I have one: http://www.landracing.com/forum/index.php/topic,8271.0.html

I think I'll just build the car, try it, and worry about it then!