so I'm looking to get new wheels for my SOHC Del Sol in spring, and I'm torn between a few sets of 15's and 16's. The main deciding factor is how much of a difference would there be between a set of 15" wheels that weight about 11 lbs, to a set of 16" wheels that weigh about 16.5 lbs? I know that more weight = less power, and for example a 14" wheel that weighs 19lbs, will be much more performance friendly than a 20" wheel that weighs 19lbs, due to the majority of the mass being further out on the rotating diamete. I know all this, but my question is if anyone knows approximately how much of an effect or difference there would be between the 15's I'm looking at and the 16's. anyone that may have experience with this sort of wheel change, I would appreciate any information and advice you could give me.
thanks
-Pat


Modified by xprm311x at 8:22 PM 1/13/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xprm311x &raquo;</TD></TR><TR><TD CLASS="quote"> ...I know that more weight = less power...</TD></TR></TABLE>

actually, not to be a nit-picking ******* but more weight = less acceleration. Power will remain the same, as will torque.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xprm311x &raquo;</TD></TR><TR><TD CLASS="quote"> and for example a 14" wheel that weighs 19lbs, will be much more performance friendly than a 20" wheel that weighs 19lbs, due to the majority of the mass being further out on the rotating diamete.</TD></TR></TABLE>


very good.

Now onto your question about 16"@16.5lbs vs 15"@11lbs


I am neglecting drag cause I am lazy.

Let:


T: torque at the wheels
I: total moment of inertia of the rotating parts
u: angular acceleration of the rotating parts
M: total mass of the vehicle
r: external radius of the tires
a: linear acceleration

T = Iu + Mra (1)
u = a/r (2)

(2) into (1)

T = I(a/r) + Mra
a = T[I/r + Mr)

Let R1 be inner radius of ring
R2 be outer radius of ring
m be the mass of the wheel.
I of a ring = 0.5m(R1^2 + R2^2)
I of cylinder = 0.5mR^2

So without knowing the actually weight distribution of the wheel wieght it is hard to give an exact % difference. But either way it seems you will see more effect from driving with a half tank of gas rather than a full tank.

it says here http://www.audiworld.com/tech/wheel13.shtml that adding about 10lbs of mass to your wheels is the same as adding 20lbs in your back seat.

There is also one last thing you need to consider "unsprung weight" that is how much your suspension weights, this determines how nice of a ride you will have as your suspension will be able to react quicker cause it has less mass to move/accelerate up and down. You can probably search that out or ask and I will try to find out for you. But right now I have to cut this short cause I am going to miss my GF's hockey game and that means that I just won't get laid tonight...lol

Cheers, hope that helps.

Edit: ****, forgot the findings, limitations, and recommendations.

Finding: wheel wieght doesn't have that much effect as I originally thought. Go with what you like.
Recommendations: Research "unsprung weight" and see how much it will effect you, or ask me later!
Limitations: all of this is theoretical, none of this has been backed up with emperical evidence.




Modified by old man neri at 7:11 AM 1/14/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by old man neri &raquo;</TD></TR><TR><TD CLASS="quote">you will see more effect from driving with a half tank of gas rather than a full tank.

it says here http://www.audiworld.com/tech/wheel13.shtml that adding about 10lbs of mass to your wheels is the same as adding 20lbs in your back seat. </TD></TR></TABLE>

Yup.

Gasoline weighs about 6 pounds per gallon, so...

 

lol yeah, I meant less power to the ground, because the motor has to push the wheel. sorry I'm not an engineer :-P but thanks, you have been extremely helpful