*Official Weight Reduction thread*

[Fearit22]

Yeah, even though the top is lighter the manufacturers put in extra reinforcements in addition to the weight of the mechanisms used to make the top move up and down. They are usually 50-100 lbs more.

[Smokinspeeds]

*new Idea*

At first thought you will call rice but there is weight reduction goodness in this

Ordered a pair of sidemirrors with the turn signal light on the side. (have yet to wire the light part on) My lx has power mirrors. The new mirrors are still power. I quickly realized the HUGE difference in weight. The stock mirrors feel about 5lbs ea. but the new ones I got are barely even 1lb each. For $21 tis not bad plus the look pretty good. Not a lot of weight off but still 10lbs is 10lbs plus there are carbon fiber versions (albeit you'll pay $30-$50 depending on power/non power) which might be even lighter. (got the lights on ebay btw, there are PLENTY on there in a number of designs)

Another (different) Idea I've had would be to hinge the trunk somehow (leave to each's own where/how) thus getting rid of the arms. Those are about 5-10lbs?

Yet another a bit more extreme that I've only seen ONE person on here do,
FUEL cell in the trunk and drop out the stock tank. JEgs has them for anywhere from 80-120 or so for a decent 8-12 gal that would fit nicely in the spare tire depression. IF anyone decides to do this I would definately say to make sure the speakers have electric tape around any connections (no batt in trunk either) so that you can't have sparks or anything that with fumes would = dissaster.

My .02

[deevergote]

A car with a removable hardtop and no convertible mechanism can be lighter... of course, without the top, aerodynamics can be compromised. Not to mention safety. If I blow a tire and fly off the track, I don't want to flip over in a convertible!

How about tire weights? I know some tires weigh less than others... rotating mass is fairly significant. Along the same lines, what size wheel is best? 15" or 16"? I know 17"+ is WAY too big, since it moves the weight of the tire to the outside... centralizing the rotating mass of a wheel is best, as far as I know (I'm no physics buff, but that much makes sense to me).

[aleks77]

how much better would a car with 25lbs a rim/tire be then a car with 40lbs a rim/tire handling wise? Just want to know if this would be a HUGE difference or something you probably wont even notice?

[deevergote]

Handling wise it's not that big a deal. It's the rotating mass that matters. The more weight a wheel/tire has, and the further from the center that weight is, the harder it is to spin. Therefore, it gets to speed slower. If you're autocrossing, you have to figure out where you can benefit more... sacrificing some acceleration for control with a larger, wider wheel... or losing some control by going with smaller wheels. I notice that many still opt for the smaller. Drag racing is where it's usually taken into consideration.

I've HEARD (not confirmed or researched in any way) that 1 pound of rotating mass is equal to about 3 pounds of non-rotating mass. So basically, a 15lb difference in wheel weight all around is like dropping 180lbs. Is it true? I dunno. If it is though, coupled with the other old addage (every 100lbs is .1 sec off your 1/4 time) then you're gaining almost .2 sec! That's a significant difference for changing your wheels... Which leads me to think perhaps it's not true

[HondaFan81]

my stock flywheel weighed 17 lbs.

[wed3k]

my stock flywheel weighed 17 lbs.

odd, when i shipped a flywheel out it weighed in @ 19lbs

im running a 13lb flywheel and the whole rotating mass thing is so true. i have more torque but i lose out in the hp...

i also took out a/c, lightweight battery and backseats out...should be around 90 lbs but i dont really feel much of a diff in the corners (i still need put my front strut bar back on though)

[deevergote]

Battery relocation to the trunk is also helpful for handling. NOT for drag, since you want as little weight in the rear as possible... but the even weight distribution will help for autocross, road racing, and general driving fun.

I know it's kind of off topic, but does anyone know the weight ratio for the Accord? You know, like how the Miata is 50/50... what's the CB7? 40/60?

[Fearit22]

You can consider a wheel to pretty much be a hoop which is also similar to a cylinder in a physical sense. The moment of intertia for them is I = 1/2 * m * r^2 ... So the weight isn't nearly as important as the radius of the wheel which like it was said affects where the weight is distributed. The mass linearly affects the wheel while the radius exponentially affects it which I will prove now.

I'll derive a relationship for the acceleration compared to mass and radius...

- Torque = Inertia*Angular Acceleration
t = I*a

- Inertia for a hoop (wheel) = 1/2*mass*radius^2
I = 1/2*m*r^2

so ..
- t = 1/2*m*r^2*a

then
- a = (2*t)/(m*r^2)

So, the acceleration of the hoop (wheel) will be inversely proportional to both the mass and the radius, but it's inversely proportional to the sqaure of the radius. This just means that the radius of the wheel will have a lot more of an affect on the acceleration of the wheel than the mass itself. It is also affected by where the mass is located because if the mass was located more towards the center then you would decrease the radius which has already been shown to be the most powerful influence in this equation. Showing this would require more complex integrals that nobody probably wants to see so I'll just leave it at that. Just note that this includes positive and negative acceleration so it would affect your braking in the same way as your acceleration which can have twice the bad affect for auto X. I tried to make this as clear as possible, but I am a physicist so I'm not always too clear....anymore questions just ask.

[deevergote]

I'm a psychologist... so numbers scare me (took idiot calculus and passed with B+... which was really a 40! )

Anyway, from my feeble understanding of your equations and your explanations, I don't see you accounting for the fact that the overall radius doesn't change. Properly sized tires on a larger wheel keep the distance from the edge of the tire to the center of the wheel the same... the mass of the tire is just further from the center. Taking that into consideration, does the smaller wheel really spin more easily even when the overall wheel/tire size is the same? The weight of the tire is more evenly distributed and closer to the center, but other than that, the size of the unit remains the same.

[Fearit22]

Well for that you can just consider the radius to be more like for the center of mass for a hoop in a way... not like center of mass of a circle because well that would be the center of course lol. I was trying to say that changing the location of the mass in that equation would change the effective radius of the hoop(wheel). There are much more complicated equations to describe all of that I was just trying to show in a general sense how things are affected. That was for a very thin hoop, but for a thicker hoop the inertia, I = 1/2*m*(r1^2 + r2^2). Where r1 is the inner radius and r2 the outer radius... so moving the weight farther out on the wheel would increase r1 and the overall moment of inertita, but if you had r1 get smaller while the mass remained the same then the moment of inertia would decrease. So this shows that the more the mass is spread towards the center then the less the moment of inertia will be. Where is gets complicated is that the mass of most wheels is not even from the center to outside. So you would have to integrate from several different points and represent the tire with different hoops then take apart each part of the rim and tire and weigh them individually. This is why that's really the best it can be represented is in a general case just to show the effects of total mass, total radius, and where the mass is located.

I've taken up through Calc 3, then differential eq., theory of partial differential eq's... lots of *** math courses that they make really hard here. The integrals I talked about here would most likely be something from calculus 3 because I think they would have to be triple integrals.

[deevergote]

Man... math makes my head hurt!

In a nutshell, am I right about the smaller wheel and fatter tire being better for acceleration than the larger wheel and skinny tire? From my understanding of your equations and explanations, it sounds like that's the case... The more centralized the mass, the easier it is to turn... a fatter tire (same overall diameter as the skinny tire) spreads that weight out, bringing it towards the center... Or am I missing it?

[Fearit22]

In general, I think that would be true. Tires can be pretty heavy, but no matter what metal the wheels are made of they will always be lighter than aluminum, magnesium, or whatever... It makes sense too. Look at the dragsters ... they use really small rims like as small as they can possible get, and then they just compensate by using much larger tires because they will be lighter.

Math can be a pain which is why I don't like my Math classes. I enjoy Physics because it's the application of all the boring stuff you learn in Math. Psychology is really interesting too though. I have a few credit hours in it... I think it would have been my second choice next to Physics.

[92acclude]

I had my car on corner scales recently. 2975lbs.

Thats with no backseat or rear seat belts. All the stuff was still in the trunk [mat, spare, etc]. And a roll bar. And a full tank of gas.

Taking out the spare, and all the crap in my trunk reduced the weight to 2925.

She's a heavy one.

On the list to die: AC, Cruise, drivers seat, hood / trunk.

[93EXaesthetic]

I had my car on corner scales recently. 2975lbs.

Thats with no backseat or rear seat belts. All the stuff was still in the trunk [mat, spare, etc]. And a roll bar. And a full tank of gas.

Taking out the spare, and all the crap in my trunk reduced the weight to 2925.

She's a heavy one.

On the list to die: AC, Cruise, drivers seat, hood / trunk.

where did you get yours weighed @? one of those truck stop places on the state border?