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Premium Member
2004 Forester XT MT
Joined
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1,433 Posts
Discussion Starter #1
Have you ever wondered how much torque you are losing/gaining by changing the tire and wheel size? This spreadsheet will give you a pretty good idea by allowing you compare to sets of wheel/tire combinations.

I can't remember where I got this but it's pretty useful. If you know the author tell me so I can give credit where it is due.

View attachment wheel_inertia.zip
 

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Sydney Dinner Organiser
MY05 XT luxury
Joined
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1,694 Posts
What the f is a slug?
Damn you people - why cant you work in SI (metric) units!

And I was rather hoping this would actually have some example wheels where the rotational inertia was measured.
 

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Premium Member
2004 Forester XT MT
Joined
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1,433 Posts
Discussion Starter #3
dicknose said:
What the f is a slug?
Damn you people - why cant you work in SI (metric) units!

And I was rather hoping this would actually have some example wheels where the rotational inertia was measured.
LOL slugs drive me nuts, too. Nope just 3 different models for approximating wheel inertia. You can do one for the stock FXT wheels and post it for us.;)
That's what make this spreadsheet nice; it frees up more time for us to drive rather than crunching numbers.
 

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Premium Member
'09 STI
Joined
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4,129 Posts
So you're trying to imply that my 22" triple chromed dubs with spinners aren't high performance? I paid enough for them!
 

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Premium Member
2004 Forester XT MT
Joined
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1,433 Posts
Discussion Starter #6
dicknose said:
Wouldnt the best answer be to just measure it?
measure? isn't the whole world of engineering about approximations? :razz:

i agree with you. it's much simpler to bust out a device with which to measure. but isn't it great to know that you can derive formulas to come up with a fairly accurate answer?
 

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Sydney Dinner Organiser
MY05 XT luxury
Joined
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1,694 Posts
Its nice to estimate, but it will only give a rough answer.
Which is nice if the question is "whats the rough estimate of the rotational inertia of my wheel".
But its pretty well useless if the question is "how does that compare between these 2 wheels" - and the wheels are difference size and weight.
Changing from a 16 to 17 but the 17 is lighter. Or comaring two 17s that have about the same mass but have very different styles.

The problem is that this guys assumptions are very wild and dont seem to be based on actual wheels. Now comparing his results to some actual measured results would be interesting. But saying "its a disc" is only good for a very rough approximation.
 
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