the 15/16 rim debate??

Josh Rampling · Dec 28, 2017

hi...just seen some pretty cheap bg goodrich m/t tyres on 15 inch steel rims, they are 33 inch..

I'm running 265/75/16 31 inch and want more diff clearance for off road use..

my friend tells me my diff will be lower as the rim is 15 inch... but this doesn't make sense to me, surely i would just have more tyre wall on show?

so say for example 285/75/16 is more or less the same as 285/80/15

please can someone clear that up for me ha, head is pickled.

brian47 · Dec 28, 2017

Work it out for yourself.
The first number is the width of the tyre in millimetres.
The second number is the aspect ratio as a percentage of the width Which calculates out as the sidewall height
The third number is the diameter of the rim in inches.

So the maths for a 205/55R16 tyre would look like:-

Multiply a tyre’s width by the aspect ratio to get aspect height (205 x 0.55 = 112.75)
Convert into inches (112.75 / 25.4 = 4.44)
Double the aspect height (4.44 x 2 = 8.88)
Add inside diameter of tyre (8.88 + 16 = 24.88)

Data taken from the Black Circles website. https://www.blackcircles.com/general/tyre-size-calculator
The ground clearance for the diff is generally a function of the total wheel radius.

Josh Rampling · Dec 28, 2017

brian47 said:
Work it out for yourself.
The first number is the width of the tyre in millimetres.
The second number is the aspect ratio as a percentage of the width Which calculates out as the sidewall height
The third number is the diameter of the rim in inches.

So the maths for a 205/55R16 tyre would look like:-

Multiply a tyre’s width by the aspect ratio to get aspect height (205 x 0.55 = 112.75)

Convert into inches (112.75 / 25.4 = 4.44)

Double the aspect height (4.44 x 2 = 8.88)

Add inside diameter of tyre (8.88 + 16 = 24.88)

Data taken from the Black Circles website. https://www.blackcircles.com/general/tyre-size-calculator
The ground clearance for the diff is generally a function of the total wheel radius.

i know how to work out the sizes haha. but he is says my diff will be lower with 15s but surely that can't be right as 33 inch tyre with 15inch rim has more tyre wall than 33inch tyre on a 16inch rim. therefor keeping the diff the same height?

brian47 · Dec 29, 2017

If you're currently running on 31 inch diameter tyres and then fit 33 inch diameter tyres, I would say that the difference in diameter is 2 inches, consequently the difference in the radius is 1 inch. Therefore the diff case will be an additional one inch above the ground.

Josh Rampling · Dec 29, 2017

thats what i was thinking but the fact my mate said 15s will put your diff lower threw me. i think he worked it out wrong... if the rim is smaller the aspect ratio of the side wall will increase if running the same size tyre as a 16.
thanks

JC Def 90 · Dec 29, 2017

Click the link Josh, hope it helps.

https://tiresize.com/tyre-size-calculator/

dieseldog69 · Dec 31, 2017

Josh Rampling said:
thats what i was thinking but the fact my mate said 15s will put your diff lower threw me. i think he worked it out wrong... if the rim is smaller the aspect ratio of the side wall will increase if running the same size tyre as a 16.
thanks

Your mate is wrong, the rim might be smaller but the tyre height will be the same, 33 is 33 regardless of internal rim size, rims are rims regardless of size, moving over to metric is what throws a lot of people out as they then have to calculate aspect ratios to get the same tyre height.

Josh Rampling · Jan 3, 2018

i thought so. cheers fellas

the 15/16 rim debate??

Josh Rampling

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Josh Rampling

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Josh Rampling

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