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View Poll Results: 2012 17" vs 18"
17" 16 47.06%
18" 18 52.94%
Voters: 34. You may not vote on this poll

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Old 02-13-2012, 02:26 PM   #11
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Quote:
Originally Posted by FordBass View Post
235/40/18 has the same air capacity as 215/50/17

What do you mean by capacity? Volume? Recommended inflations rates? Or recommended load capacities which could be the same but could be at differing PSI's to acheive that same rate?
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Old 02-13-2012, 02:42 PM   #12
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I have 18" but I would have been happy with 17". I just like the 18" rims that were offered better than the 17" and if you want the handling package you have to get the 18". I have 16" snows on it now.
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Old 02-13-2012, 08:19 PM   #13
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Quote:
Originally Posted by Geezer View Post
What do you mean by capacity? Volume? Recommended inflations rates? Or recommended load capacities which could be the same but could be at differing PSI's to acheive that same rate?
They hold the same volume of air.
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Old 02-13-2012, 08:48 PM   #14
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Ford Bass, Do you have a source for tire size volumes (cubic inches, whatever). I've never seen one and would like to do some research in this area. Thanks.
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Old 02-14-2012, 01:52 AM   #15
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Ford Bass, Do you have a source for tire size volumes (cubic inches, whatever). I've never seen one and would like to do some research in this area. Thanks.
Yea the source is geometry

I did some math and came up with the loss from the diameter increase was gained back with the 20mm width increase.

It's not 100% dead on but the volume is fairly close.
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Old 02-14-2012, 11:49 AM   #16
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Yea the source is geometry

I did some math and came up with the loss from the diameter increase was gained back with the 20mm width increase.

It's not 100% dead on but the volume is fairly close.

Well you're better at it than I am. I can't come up with formulas to accommodate for the elliptical shape (even if I could somehow measure it) that accommodates the various sizes, wall thicknesses, thread thicknesses etc. (most manufactures calcs are outside dimensions). Way too many variables for me. As you're aware a tire is not a simple round tubular shape like an inflated inner tube which does make calcs lots easier. Even tires with the same widths, aspect ratios and diameter are often not the same size (manufacturers play games and their actual measurements an often use differing wheels widths, etc. to establish the cross section width.

I was hoping you found some manufacturers calculations indicating volume (like fluid volume since it's an easy way to measure) of the tire. What got me started on this was reading an article on a European touring car race site and how the increased pressures they needed to run with the super low profile (30 and 35 aspect ratio ultra performance street tires vs dedicated race rubber) was screwing up handling and necessitating significant suspension modifications as a result.
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Old 02-14-2012, 09:10 PM   #17
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Im going with 17x7's only because I'm lowering it about 2.25" all around.
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Old 05-24-2013, 07:06 PM   #18
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Quote:
Originally Posted by Geezer View Post
Well you're better at it than I am. I can't come up with formulas to accommodate for the elliptical shape (even if I could somehow measure it) that accommodates the various sizes, wall thicknesses, thread thicknesses etc. (most manufactures calcs are outside dimensions). Way too many variables for me.
Geezer, you might find Chapter 5 to be of some interest...
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Old 05-25-2013, 08:13 PM   #19
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For me, I'd say what BBK's fit 17's vs 18's?
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Old 07-06-2013, 01:06 AM   #20
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Replaced my 18s with 17s and am much happier. Better ride, more tire choices, lower tire prices, no difference in handling. Purchased Enkei M52s in black.
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