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Old 05-17-1999, 08:13 PM   #1
Brian
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Default Question about the middle number in a tire size (e.g., 50 v. 55)

In a tire size such as 225/50/16, the middle number is related to the "tallness" of the tire, no? So if I were to put 55s instead of 50s, the car would sit a little higher off the ground?<p>And if this is correct, what other effects does messing with this parameter effect? Speedometer accuracy would seem to be an obvious one. <p>I'm just wondering if I should opt for 55s when I replace my stock Contis with Dunlop 4000s.
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Old 05-17-1999, 08:48 PM   #2
LCP
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Default Middle number is aspect ratio (height %)...

205/55-16 means that the height of the sidewall of the tire is 55% of the width of the tire, or 55% of 205mm. Take this number times 2 and add the wheel size and you'll get the total wheel and tire height. This also means that 225/50-16 yields almost exactly the same height.
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Old 05-18-1999, 03:29 AM   #3
Brian
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Default Re: Middle number is aspect ratio (height %)...

Thanks!<p>Okay then - this means (using your examples) that a 225/55-16 would be almost an inch (22mm = .87") taller overall? Is that correct?<p>225 x 55 x 2 = 247.5mm<br>205 x 55 x 2 = 225.5mm<br>----------------------<br> = 22mm or .87"<p>That's a significant height change! <p>My real question then is, why don't people seem to use this factor when attempting to raise/lower their cars (I mean just change height -- not performance issues -- pure cosmetics)? It just seems like one could get even a small adjustment to height by using a small tire size change. For example, if I wanted to raise my car 10mm (I just put on H&R springs and Bilsteins), why couldn't I just replace my stock 205/55-16 tires with 215/55-16s? That would give a height difference of 11mm, if I'm calculating and understanding this concept correctly.<p>-Brian
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Old 05-18-1999, 06:13 AM   #4
Dave W
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Default Shouldn't change the overall diameter

The reason why people don't, or shouldn't use this method to change the ride height is because you are changing the overall diameter of the wheel/tire. If you add an inch to the outside diameter, the speedometer would be off. To keep the speedo correct, the overall diameter of the wheel/tire needs to remain constant. This is where the idea of + and - sizing comes from. You can "plus 1" size a 16" wheel by going to a 17" wheel, but the tire will have a shorter profile to keep the overall diameter the same.<p>Hope this helps<br>dave<p>17" wheels
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Old 05-18-1999, 11:04 AM   #5
LCP
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Default Also don't forget the car only gets 1/2 as higher/lower as the wheel/tire does

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Old 05-18-1999, 04:16 PM   #6
Brian
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Default Thanks everyone for the responses. Very helpful and interesting stuff.

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Old 05-18-1999, 04:16 PM
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