What am I not getting

[tehschkott]

265/70/17 = 265mm wide, 70% aspect = 31 inches
305/70/17 = 305mm wide, 70% aspect = 33 inches
315/70/17 = 315mm wide, 70% aspect = 35 inches

How is the tread width (265/305/315) resulting in larger outer diameter wheels? Is that not entirely controlled by the aspect rating of 70?

I'm watching this and I guess I'm missing something. To get wheels with larger OD would you not need wheels with larger aspect 75, 80, 85?

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[jss81258]

265/70/17 = 265mm wide, 70% aspect = 31 inches
305/70/17 = 305mm wide, 70% aspect = 33 inches
315/70/17 = 315mm wide, 70% aspect = 35 inches

How is the tread width (265/305/315) resulting in larger outer diameter wheels? Is that not entirely controlled by the aspect rating of 70?

I'm watching this and I guess I'm missing something. To get wheels with larger OD would you not need wheels with larger aspect 75, 80, 85?

If I understand the question....

All 3 examples you have are all on 17" wheels. The wheel diameter doesn't change, in your example.

Aspect ratio is the ratio between the tire tread width and tire side wall height. So, the wider the tread (265, 305, 315), the taller the side wall assuming the aspect ratio remains the same, which it does in your example(70 for all three).

Taller side wall equals taller tire. So, as the tread width increases, so does tire height, assuming the aspect ratio remains the same.

Edit: Forgot that you can do the math. For 265, side wall = 185.5. Double it (top and bottom or opposite sides of the wheel/tire) = 371 mm = 14.61 + 17 (wheel diameter) = 31.61. Not exact but close enough, and manufacturers may not make the tire exact anyway.

 

[tentspast]

The previous poster beat me to it, but I presume you are talking about the tyres rather than the wheels, all the wheels are exactly the same diameter.
So the aspect ratio is the sidewall as a percentage of tyre width. In this case each tyre has a sidewall which is 70% of the width.
For example for the 35" tyre, 70% of 315mm width is 220mm. Multiplied by 2 for both sidewalls = 442mm, plus the 432mm of the wheel gives you a full diameter of the tyre of 34.4 inches (close enough to 35".)
If you apply the same to the 31's, 70% of 265 is 186mm. Multiplied by 2 = 372 plus the 432mm of the wheel makes a diameter of 31.6" (close enough to 31".)
Does that sort of make sense? I feel like I've probably made it even worse to understand lol

 

[tehschkott]

*blinks*

It's a percentage of tire width, not rim diameter? JFC. Great. Just great. That 100% answers my question. Just when I thought this stupid system sorta made sense, off it goes.

Thank you both. I'm tracking now.

 

[jss81258]

The previous poster beat me to it, but I presume you are talking about the tyres rather than the wheels, all the wheels are exactly the same diameter.
So the aspect ratio is the sidewall as a percentage of tyre width. In this case each tyre has a sidewall which is 70% of the width.
For example for the 35" tyre, 70% of 315mm width is 220mm. Multiplied by 2 for both sidewalls = 442mm, plus the 432mm of the wheel gives you a full diameter of the tyre of 34.4 inches (close enough to 35".)
If you apply the same to the 31's, 70% of 265 is 186mm. Multiplied by 2 = 372 plus the 432mm of the wheel makes a diameter of 31.6" (close enough to 31".)
Does that sort of make sense? I feel like I've probably made it even worse to understand lol

Dang! If I knew you were going to post with the math, I wouldn't have bothered editing my post!

What makes it even more confusing, especially for folks new to all this, is that they mix metric with imperial here in the US. So you have a tire with metric width that fits on an imperial wheel, and then show an imperial tire height. Makes perfect sense to me!

 

[Frenchy]

I can answer this question for everyone here. Yes the first number is the tire width or known as the section width. The second number known as the aspect ratio is actually a percentage. Example of a 265 70 17. 70 would represent 70% of the 265. In a 265 75 16 the 75 would represent 75% of the 265. Does that make sense?

 

[tehschkott]

Asked and answered already but thanks.

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