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Discussion Starter · #1 ·
How is a tire rim measured? I have a diablo 180/55/zr17 rear tire and these are supposed to be too big for a 4.5" rim. I wonder if the rim was replaced with a bigger one at some point in time.

Across the inside edge (between the spokes) I measure about 6" wide.

And while we're on the topic of tires, what are the numbers in a tire size measuring?
 

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Not sure about your rim size. I think a 180 wouldn't fit a 4.5 rim? 180 is the width, 55 is the profile and 17 is the wheel circumference
 

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Discussion Starter · #3 ·
In the faq there's a tire section that says 170 is stretching it, 180 doesnt fit at all.


I wonder if the previous owner just crammed a bigger tire on...
 

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I guess anything is possible, but that tire would be so wide for that rim it should feel pretty sloppy in turns.
 

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The rim size is cast into one of the spokes.
 

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The rim width is measured between the 2 bead surfaces..
 

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Discussion Starter · #7 ·
ducpainter said:
The rim size is cast into one of the spokes.
Nice, it says 5.50, thanks.

So, would a 170 on a 5.5" rim feel like a 160 on a 4.5" rim?
 

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Aguacate said:
Nice, it says 5.50, thanks.

So, would a 170 on a 5.5" rim feel like a 160 on a 4.5" rim?
Not exactly, I don't think.
I like a 180 on a 5.5 inch rim. My 96 came stock with a 170 on a 5.5 rim. I switched to a 180 and liked it. I ran a 170 this year and like the 180 better.
 

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Rim size and tire size are two different things (just a disambiguation on title of article), and what tire size fits on your bike is almost more a matter of the motorcycle than the rim. your 5.50 rim can hold a 170, 180, or 190. the second number of profile height will affect the motorcycles handling *quick turning vs slow turning* and the third number is NOT circumference, it is rim diameter that the tire will fit on. Referring back to the tire width, what of those three options your bike will take depends upon the tire clearance to the swing arm, any cables or brake lines, and any thing else on the rear end of the bike.

Furthermore, getting appropriately sized tires for your bike is a matter of taste. If you're a very aggressive rider and are constantly on the sidewalls of your tires, looking for more tread you want a higher profile tire, like a diablo 190/55 or 180/60. These tires will make you feel like your bike is falling over to the sides faster as well. Higher profile height for the same width means the edges of the tire tread are closer to verticle than on a lower profile tire. *Imagine a tire that has no profile. It will be flat and won't lean at all*

So what it basically comes down to are two things. What is your bike, and how do you ride it?
it sounds like (since you're asking :) that you should stick with the standard tire sizes for your bike for a while (i.e. get used to what you have and then replace them with the same sizes.

Hope this was a helpful response. [thumbsup]
 

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Discussion Starter · #10 ·
yeah, I vaguely remember right before I went to bed thinking something like "did I just start a thread with the words 'tire rim' in the topic?"

Thanks for the post, good info.
 

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If you want to get technical about tire sizing...

Let's take an example 180/55ZR17

The width of the tire: 170, 180, 190, etc. is the measuremeant accrose the widest section of the tire in millimeters in it's standard state. Obviously putting a wide tire on a narrow rim will make it fatter, and vice versa, to some extent. In our example tire size the tire would be 180mm wide.

The next number in the size: 50, 55, 60, etc is the percentage of the width of the tire in hight. So our example tire would have a hight equal to 55% of the width so that's h = 180 x .55 so our tire would be 99mm tall.

Next we have a letter, in our case the letter is Z a Z rating indicates that the tire is rated for speeds in excess of 120 mph. This used to be the highest speed rating given to tires, but that's changed in the last few years, still nearly all sport bike tires will have a Z speed rating.

Next is an R which merely stands for radius, and it is followed by the radius of the wheel the tire is made for in inches. Our example size is for a 17in wheel.

Since there are 25.4mm per inch, our 180 tire would be 7.08 inches wide. This is the measurement and the widesest point, and with a motorcycle tires profile we can see this would fit well on a 5.5 or 6 inch wide rim. You can see that a 7 inch wide tire on a 4.5 inch wide rim would be awefully pinched. A pinched motorcycle tire ends up with very vertical sides, and in extreme cases can even ended up with a point in the middle. Neither of these situations are good for handling. Well there you go, probably more than you wanted to know about tire sizing, but it's late, and I can't sleep.

Justin
 
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