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I have a set of 15" 99-00 Si wheels that weigh 16lbs each. Then I have 17" wheels that weigh 19lbs each. I don't know about you all, but do you guys/gals notice a difference in track times (et's)& off the line speed?

Do you think the little weight difference of 3lbs and rotational weight makes a big decrease in acceleration?

There is no question about the performance difference i.e. corner, traction,

Any comments on the subject?

BTW: both sets of wheels match on the tire calculator
205/45/17
195/60/15

 
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I think si wheels are a bit heavier than 16lbs....

 
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Yeah, your going to feel the difference even if your 17" rims is the same weight of your 15s because it takes more force to spin something with more outer weight.

 
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^^agreed, but, with our cars---adding or reducing a little bit of weight will not change the performance wise---there will be a very minut difference.

 
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17" tires weigh more than 15" tires as well. Remember its not only 3lbs. Its 3lbs each corner plus the added weight of all 4 tires, and the addition force needed to spin the 17's.

Yes you can feel the difference, and yes it would affect your track times.

 
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totally agree

 
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Thanks for the clear answer...As for HondaKorn yes the Si wheels weigh
16lbs without the tire

 
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what those it matter anyways are cars are slow

 
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i say for daily driving you won't really notice your off the line speed with 17's. I got 17's, but i didn't really notice a decrease in acceleration, however the car seems to corner better since i have the wider tires now. If you asking for DD purpose's, you won't notice. If you want to track the car just switch back to the 15's. A couple of pounds won't make a already slow car that much slower.

 
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i run better with my 17's on, i tried useing 14's with 17lbs in the tires and ran a worst time, less wheel spin, more go with the 17's, but i would recomend 16 for track, still a nice size for cornering too

 
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its not only about weight... with 15s you get off the line quicker, its been proven over and over again that bigger wheels effect a 1/4 mile time.

 
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There may only be a 3 lb weight differentce... but rotational Inertia is influenced greater by the diamiter of the wheel in question then the actual weight...

Simple formula for rotational Inertia is I = M*R^2

So for your 15" wheel of 16 LBS will have a rotational inertia of some where around 263467n and the 17"wheel at 19 LBS would have a rotational inertia of about 401802 about a 52% difference in Inertia... meaning inorder to accelerate the 17" wheel at the same rate as the 15" wheel, you'd need to apply about 52% more power.


I personally have a set of 15's for autocross and open track and a set of 17's that came with the car when I bought it for the street. Frankly I cry when I swap from the 15's to the 17's and cheer when I do the opposite.

As far as Cornering... that depends greatly on the tires you run. If you are running a soft walled tire on a 15 and the same tire on a 17, the 17 is going to give you the better steering responce. However, if you are running tires designed for compitition that have reinforced sidewalls then side wall flex becomes less of an issue. at this point with running Falken Azenis RT-615's on my 15's and allseason tires on my 17's... the 17's stll feel "mushier" then the 15's.

Acceleration traction, once again, is more dependant on your tire compounds then wheel size.

 
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wow... that was beautiful Zzyzx.... honestly haha

 
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In the formula I=M*R^2

does M represent Mass
and what's the value of R?

I want to calculate the difference for a new set of wheels I'm thinking about purchasing compared to the ones I have now.

 
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I= Inertia
M= Mass
R = Radius

Square the radious, and remember to convert evey thing to metric first...

 
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Actually, that is incorrect. You can use the fps (foot pound second) system, just remember that the unit for mass is slug. To get slug, devide the weight in lbs by 32.2.

 
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Also, i'm sure the 15s weigh much less than the 17s, so each 1 lb. of centrifical weight loss equates to 6 lbs. If 17s weigh 20 lbs and your 15s weigh 5lbs a wheel lighter, its like taking off 120lbs.

 
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wow ... this became a math class .. thats dope to see that we actually have smart people here tho

 
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i'm a retired rocket scientist

 
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true true,, both are right...