Center of gravity
 

Does anyone know the center of gravity height of a Stock height s2k? All this talk about the FT-86 having the lowest center of gravity of any production car. I'm curious what the S2k's is and I figured the R&C guys would know the answer to my question.



To keep it on topic is lowering the ride height directly related to lowering the center of gravity? For example if the center of gravity happens to be 18.5" would dropping the car 2" lower the center of gravity 2" or is it more complicated then that?

Subaru is claiming a 460mm center of gravity height for the BRZ. Thats 18.1". How is it that our S2000's have a center of gravity 8" higher then this car coming out? The pictures of the BRZ make it look it a 4x4 and it needs a 3" drop.

Rob can you chime in and tell me the relation between lowering ride height and center of gravity height? is it directly related?

link it info..
http://wot.motortrend.com/subaru-rel...ut-139927.html
http://www.fr-sforum.com/forums/fr-s...formation.html





Edit I'm finding sources saying the CoG of the S2000 is 18.7" Which would make alot more sense. Any idea why Robs websites numbers are so far off?

Gotta compare apples to apples. I think you can only compare numbers for cars using that same data sheet if you are talking about this site
http://robrobinette.com/cg_height_calc.htm


top down and lowered 1", I bet the S2000 has a lower Center of Gravity. But then again, lower the Subaru 2" and it will probably be back ahead of the S2000. I don't really think persons that don't have knowledge of what each part on the car weighs can really calculate the CG. You can only go by the designer's info and then figure if you lower the car 1", the CG was probably lowered a little less than 1".

We should probably be more concerned about changing the roll center too drastically when lowering.

They're closely but not directly related, because lowering the car does not lower its unsprung mass. There's around 200 - 250 pounds (guesstimate) of wheel, tire, and suspension weight which is unaffected by lowering the car -- about 15% of the car's mass.

You don't actually have to have any knowledge of what any individual components of the car weigh. You can weigh the car flat and at a couple different angles. After that it's simply geometry.

you probably could, but it wont be as acurate as doing it with knowing exactly where all the weight is. I have a hard time beliving it is that simple by corner weighting and moving a few things around. I would think the manufacturer knows exactly where the weight is and everything is calculated with their custom computer programs. If they lighten the top of the car by 20 lbs right in the center, they have an easy way to plug a number into their program and see what the new CG is. I would think that Subaru played with their programs over and over again to make sure they achieved this super low CG so they could boast about it. I haven't seen it done but I know of software that should be able to get it done. Solid works, Pro E and more.. .

I don't have any degree in any related field but figure that the lower figure is related a lot to the Subies flat motor? Keeps mass low and centered between the wheels right?

The engine would likely be one major difference. The other would likely be the structural design needed to keep an open top car rigid. If you open both doors, and look through from one side to the other, an S2000 is really not that "thick" vertically. I assume there is some significant structural design to keep the car's chassis from flexing.

The CG numbers on my website CG Height Calculator are purely fictional--I just made up numbers to plug in and verify the calculations were correct. I have never actually raised an end of the car 10+ inches and re-weighed it.

I used to have a note stating the sample numbers were fictional but I just looked at the calculator and the note is gone. I'll add the note back to the web page. Sorry if the fictional numbers created confusion.

Rob Robinette

Neither I have, but I expect at some point curiosity will get the best of me...