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Discussion Starter #1 (Edited)
Hi,

I am looking for one of our tire experts to review this spreadsheet that I have been working on to compare different tire combination to so I can understand the difference in tire height and profile size between different size tires front and back. This is in MS Excel format, you can either view it or download it and test it. Looking for some feedback.

https://www.dropbox.com/s/1x2vcj328sli46j/Tire combo compairison chart.xlsx?dl=0

Thanks,

Joe
 

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One thing I noticed right off the bat was that you have kept the same aspect ratio even as you increase wheel diameter. Typically you decrease it each time you go up in wheel diameter to keep the overall diameter close to the same...

235/60/15 = 26.1"
235/50/16 = 26.1" or 235/55/16 = 25.3"
235/45/17 = 25.4"
235/40/18 = 25.4"

Also, many people drop the aspect ratio again for the rears if they are significantly wider than the front in order to keep the sidewall height similar front/rear. (I did not)

Front - 235/40/18 = 25.4"
Rear - 275/40/18 = 26.7" or 275/35/18 = 25.6"
 

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^^^
Aspect ratio is the second number in the tire sequence. It is a percentage of the width of the tread expressed in millimeters.

So a 235/50/16 is 235mm wide, the height of the sidewall is 50% of the width (50 is the aspect ratio). So the sidewall height from the ground to the bottom of the wheel is 117.5mm. And it fits on a 16" wheel.

If you increase the tire width and keep the aspect ratio the same, you end up with more sidewall and a taller tire.
 

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Discussion Starter #5
^^^
Aspect ratio is the second number in the tire sequence. It is a percentage of the width of the tread expressed in millimeters.

So a 235/50/16 is 235mm wide, the height of the sidewall is 50% of the width (50 is the aspect ratio). So the sidewall height from the ground to the bottom of the wheel is 117.5mm. And it fits on a 16" wheel.

If you increase the tire width and keep the aspect ratio the same, you end up with more sidewall and a taller tire.

So if I use the formula of (tire width x tire profile) /100 this is the correct way to calculate the tire aspect ratio?

Thanks,

Joe
 

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Discussion Starter #6
67Rally

So I should just divide the tire size (235) by the aspect ratio (50) to get the sidewall height or do I need to divide the sum by 2?
Rim size does not come into play on this or does it?

Just trying to get the math right on this.

Thanks,

Joe
 

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Discussion Starter #8

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Discussion Starter #9

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67Rally

So I should just divide the tire size (235) by the aspect ratio (50) to get the sidewall height or do I need to divide the sum by 2?
Rim size does not come into play on this or does it?

Just trying to get the math right on this.

Thanks,

Joe
Sorry, I didn't see this post.

Tire size (235) x aspect ratio (.50) x 2 = total sidewall height in mm.

Divide that number by 25.4 to find the height in inches. (25.4mm = 1")

Add that number to your wheel (rim) height to get your total height.

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Just to clarify, the aspect ratio is a percentage of the width. If you have a 60 series tire, the sidewall is 60% as tall as the tire is wide. You double that number when calcualting overall height since you have a sidewall below the wheel, plus the height of the wheel, then another sidewall above the wheel. Hope that makes sense.

***********************
 

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FWIW, I checked out the spreadsheet and I'm not really sure what your goal is here.

You have some strange sizes listed in there. I don't even know if they make some of those sizes. A 235/40/15?

Also, when plus sizing, most people run the same series front and rear, or even drop the rear down a series as mentioned before. Not up.

i.e. 40 series front and rear, or 40's up front/35's in the rear. I don't think I've ever seen 40's up front and 45's in the rear.
 
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