Wheel Guru's: Help me find a rim (specifics inside)

[Injected]

BTW Dave's talking about the effects of the lightened inertia being compounded thru the gearing. Do you really lack power in First and second?

First, regarding a previous post and inertia's relationship with gearing. F=M*L (L being the length of the lever-arm). The radius of the gear (also known relationally as the ratio) is an amplification process of the torque. Inertia is just the result of force, which is a result of the exeleration of mass.

The arguement about the effective weight of the wheels through the gearing is not right. Especially about the effective weight of the wheels being 18.4 times that of a lightened flywheel. In fact, it's the other way around. The reduction of the weight at the flywheel is amplified and has a far greater affect on accelleration and deceleration. Read this part of the earlier post:

150 lb.in2 sq. lightweight flywheel 275 lb.in2 . stock = difference 125 lb.in2 .

1300.5 lb.in2 . light weight wheel 1878.5 lb.in2 . stock = difference 578 lb.in2 per wheel
so for all 4 2312 lb.in2


18.4 times the difference for the wheels vs changing the flywheel. a lot more than 3 times the effect like you might believe from looking at just weight difference.

The truth is that one pound difference on the wheel is more like 6lbs difference on the car, not 2312lbs. If that where the case, the car would then accelerate like it only weighed 1000 lbs.

Back on topic. I do like the one's in the last post and will check them out. Right now I think I may go with the Speedy Lite-Fins.

 

[Attack Eagle]

umm I didn't say lbs... that's mass.
I specified the weights i was relating also previously, and it was a lot more than one pound!
8lbs difference per wheel and 10 lbs difference flywheel


I said also pounds inch squared... that's torque. not mass...

never mind anyway...

no one seems to get that saving 10 pounds at the engine flywheel (out of how flywheels in the driveline including the wheels!) is not the same or better than saving 32 pounds at the wheels... the wheels+tires are the biggest and heaviest flywheels in the entire driveline!
Except when the clutch is in, the flywheel is just another small part of the entire rotating assembly.

I have a 9 lb Fidanza flywheel and I can tell you it's good for rev matching, but I didn't notice any difference in acceleration (other than the difficulty in accelerating the rest of the drive line from rest with out bogging or stalling with such a light flywheel)... switching to lighter wheels however I certainly did.

IF your guesstimate is correct, then you would be the equivalent of about 200lbs lighter by switching to 8lb lighter wheels. Any one know what "rough weight difference" a pound on the flywheel is worth? I'm guessing maybe a factor of 3-4 max?

 

[Injected]

umm I didn't say lbs... that's mass.
I specified the weights i was relating also previously, and it was a lot more than one pound!
8lbs difference per wheel and 10 lbs difference flywheel


I said also pounds inch squared... that's torque. not mass...

never mind anyway...

no one seems to get that saving 10 pounds at the engine flywheel (out of how flywheels in the driveline including the wheels!) is not the same or better than saving 32 pounds at the wheels... the wheels+tires are the biggest and heaviest flywheels in the entire driveline!
Except when the clutch is in, the flywheel is just another small part of the entire rotating assembly.

I have a 9 lb Fidanza flywheel and I can tell you it's good for rev matching, but I didn't notice any difference in acceleration (other than the difficulty in accelerating the rest of the drive line from rest with out bogging or stalling with such a light flywheel)... switching to lighter wheels however I certainly did.

IF your guesstimate is correct, then you would be the equivalent of about 200lbs lighter by switching to 8lb lighter wheels. Any one know what "rough weight difference" a pound on the flywheel is worth? I'm guessing maybe a factor of 3-4 max?

Yes, I know what the effective mass of one pound of the flywheel is it's 1:20. Now that I understand that you were talking about torque (my bad) I'm not sure we are saying anything exactly different, but I think that there may be more to the debate so let's see if I can't clear up what I was saying a bit more:

In first gear, losing one pound make the car accelerate as if you took 20.83lbs off of the chassis, in second it's reduced to 6.22 in second and 2.72 in third. If you switch from a 7 bolt 19lb flywheel to a 9 lb flywheel, the car would accelerate as if you took 208.3lbs off of the chassis in addition to the 10 lbs actually lost, so 218.83 lbs in first, 72.15 lbs in second, 37.25 lbs in third. This is due to the gearing that the mass is amplified through. The wheels do not have as great an impact due to the direction of the force applied. The wheels are not amplified through the gears the same way that the flywheel is, is what my point is. As Coleman pointed out in that article I posted, a lb on the tread has as much kenetic energy as 2 on the chasis and as you move closer to the center, you will see less of a change until you reach the center (which is true of all spinning objects) and at the edge of the wheels it is closer to 1.5. YES lighter wheels will affect the acceleration of the car, but not nearly as much as a ligther flywheel. With the loss of 1 lb on each of the wheels, you will lose approximately 6lbs kenetic energy difference, plus the four for lbs for each wheel so the car will accelerate as if it where 10lbs. lighter. If you switch from 26lb to 16lb wheels, your car will see a difference in exceleration as if you removed 100 lbs from the car ((10lbs*4)*1.5+40)=100). If you are trying to reduce the effective mass of the entire system, you should do both and your car will accelerate as if you removed 318.3 lbs from the chasis when in all actuality you removed only 50lbs. Using the old addage that 100 lbs = .1 sec in the 1/4, you would loose about 1/3 off your ET. However the flywheel's 1:20lb effective mass equivelence and the wheel 1lb per wheel so 4:6lb equivelence demonstrates which is more efficient. Even considering the wheels a 1:6lb equivelence (which I do) the flywheel is more than 3 times more efficient. If I buy the Lite-Fin and it weight conservatively 6 lbs lighter than the stock per wheel, the car will accelerate as if the car where ((6*4)*1.5+24)=60lbs lighter.

If I follow your torque calculations correctly, I think we agree that the torque of the engine, amplified through the gears, must accelerate the weight of the wheels. That torque (F*L) must accelerate a certain mass. That change in weight's affect on acceleration due to the change in the amount of torque needed to rotate the difference in mass is what I am calling effective mass. So I think we may be saying the same thing, but not using the same terms to describe the effects of mass change.

Wow, I'm enjoying this conversation and I bet there is a lot of useful information presently in this thread. But, damn if I can't have a normal thread.

 

[Injected]

Okay, I just found out from a vendor that the Lite-Fin comes in both 17x7.5 (18lbs) and 18x7.5 (20 lbs) vs the stock wheel which is 17x6.5 and weighs 25 lbs (and bends like a mofo). Now I need to pick either 17 or 18. I'm leaning of 17's because of the fact that the spokes go all the way to the edge of the rim, which will make them look bigger than the stockers. 18's would be sexy though and since it is a 14 spoke, it wouldn't expose the brakes as 'too small' very well.

 

[Attack Eagle]

I'd pick 17's simply because of tire selection being wider and cheaper in the 17" sizing, as well as the obvious weight benefits, and the additional sidewall will better protect the rim from unavoidable potholes

 

[Injected]

I'd pick 17's simply because of tire selection being wider and cheaper in the 17" sizing, as well as the obvious weight benefits, and the additional sidewall will better protect the rim from unavoidable potholes

I completely agree.

 

[Attack Eagle]

post up some pics once you have those litefins on... I'm curious to see them in profile and at an an angle on the 2g.