Anybody know the kind of formula for rotational weight. For wheels. brakes, drivetrain etc....

Like if you make 365HP to the wheels with 25LB rims... what will you make with 15LB rims... etc

I have no clue... Raptor- You know this stuff?

It all has to do with this, ASK RAPTOR :P


It has to do with where the weight is placed in the design of the wheel (more weight at the center or hub of the wheel, or more to the outside of the wheel), the diameter of the wheel, the weight and diameter of the rotor, etc. Inertia, accelerating forces applied to the wheel and kenetic energy all play a factor. That's a tough answer to put together when you look at all the variables. It would be better to try different wheels or rotors while noting their weight properties and designs and make some data sheets to compile the effects between different designs.

When all else fails, ASK RAPTOR :lol:

I = 1/2m r^2 that is the equation to find inertia of a solid sphere. which is close enough to a rim

What ever dude :razz2: (in my best brain dead surfer dude voice)
:lol: :lol: :lol: :lol: :lol:

Ummm, moment of inertia of a solid sphere is (2mR^2)/5.
Moment of inertia for a solid cylinder is (mR^2)/2 which is what a rim + tire could be respectively considered.

i ment cylinder not sphere

so how many dooods on here have had to take physics/calc?

Ive taken physics in High school.. forgot all the formulas... Math sucks so Ill never see calc in my lifetime... GO Math for Liberal Arts!

Well about the formulas... I dont know how to apply that to HP or anything... I know that 100lbs is roughly .10 off 1/4... but what about rotational lbs.... It has to affect WAY more than non rotational lbs.

I think the most basic/simplified/non-mathamatical way to figure it is:

-10lbs = +1hp
Multiply by 4 for rotational weight.

I'm in my first of two physics classes right now. I had two semesters of calc last year and have to take differential equations this spring.

ive taken 2.5 years of physics if you count both highschool and college. im currently near failing calc right now.


as for you question, there is a way to relate it to horsepower but it is not easy. there are some other things you will
need to know.

a number for the change in rpm of the tire and the inertia of the tire.


now for some crazy math stuff. i do problems like this a lots so they are not too bad for me

1.take the change in rpm of the tire and change that into radians per sec. then divide by the
total time of the change. that will give you radians per sec^2. this is your rotational acceleration

2.then mutiply by the inertia which gives you an average torque during the time period

3.take the change in rpm and change it into radians per sec

4.mutiply by the torque in #2 which gives you foot pounds force per sec.

5 divide by (1hp/550 foot pounds force per sec) this gives your horsepower

that looks about right to me.

i'm in calc 271 right now, calc 2 i guess. it sucks huge ass, its so goddamn hard. what majors are all of you foolios going for?

i'm attempting Mech. Eng here, but i still have a long way to go

I'm in my second year in the power & machinery area of Iowa State's agricultural engineering program. It is damn close to mechanical engineering but agricultural based.

Business Finance major with a Psychology minor. This semester I am taking Calc I for the 2nd time and god damn I am failing it again! I just am not able to figure out this spatial shit...I get striaght A's in my other math courses (statistics for example), but this calculus junk just can not be related to real-life in a not pointless way. CVD: add calculus to your list.

don't worry dude, i took calc 1 three times at my shitty old community college before i got it right (kinda) its seriously ALL ABOUT THE TEACHER. they can make the material hell, or they can make it easy to digest, but either way way its fucking gay.

im in calc 1 for the second time and will probably be in it for a 3rd time

I totally agree with that, I was fortunate enough to get an awesome teacher for Calc I and Calc II.

Alrighty... well I want to go into a business major.. but work on computers... Have to decide this year..

But anyway back to those formulas.... I guess there are no easy ways.. besides what CVD said, so then with that example you can gain 20 horses by shedding 10 pounds off each wheel? Doesnt seem like much I guess... 10 pounds is alot though...

How much do stock 16" 1G wheels way?

How can you convert lost weight into gained hp? Horsepower is not a function of the weight of your wheels. If you're talking about lighter pistons or flywheel or something, then you can gain some power. But even if you had no wheels on your car at all, it would still have the same power at the crank as if you had 400 lb wheels on it.

Im not talking power at the crank... Im talking power at the wheels... Same applies to both pistons or flywheel compared to wheels becuase lighter wheels will be easier to spin therefor you gain horsepower becuase the engine can push harder and not loose power through transfer.

Lighter flywheel, wheels, crank pulley etc usually make more of a difference in the lower gears. The power gains tend to get less and less as the gears get higher. Fidanza had a good description of this on there web page with some charts showing the diminishing power gains as you went from 1st to 4th gear, but I haven't been able to find it recently. On the dyno, I haven't seen much of anything for gains out of lighter crank pulleys and flywheels. Putting more air in your tires can give better gains on the dyno than a lot of mods. :)

I would recommend a lighter SFI Spec 1.1 flywheel like the 12lb ACT just for safteys sake though, if your making some decent power. Seen too many flywheel explosion pics on DSMs the last few months.

I took Calc I twice and Calc II once. I was going for Mech. Eng. too, but have now decided on business management. Too many ME's just sit in an office all day. I have to get my hands a little dirty if I am designing stuff.

I did notice a little difference up through 3rd gear when I did my fidanza, nothing huge, but I would say 5 hp. Just enough to notice.