TURBO7379

On any tyre the figures given mean as follows -
e.g. a 225/45/16
225 is the overall width of the tyre in mm
45 is the aspect ratio or profile .
16 is the diameter of rim it will fit in inches


It is the aspect ratio which affects the diameter of a tyre . It is worked out by dividing the height of the sidewall by the tyre width and multiplying by 100 to give a percentage .

To get the tyre sidewall height you multiply the tyre width by the aspect ratio and divide by 100 .

So in your case -
205 x 45/100 = 92.25 x 2 = 184.5 + 406.4(16") = 590.0 mm = 23.26" tyre height

225 x 45/100 = 101.25 x 2 = 202.5 + 406.4 = 608.9 mm = 23.97" tyre height

To get the rolling circumference you multiply the tyre height by pi ( 3.142 ) .

23.26 x 3.142 = 72.97"
23.97 x 3.142 = 75.31"

So the difference in the rolling circumference of the 2 tyres is actually 2.34" .
Hope you understand all this and it helps .

Sieze

Why do 225/45/16 tyres have over an inch more circumferance than 205/45/16. All that is changing is the width of the tyre. How can that change the rolling circumferance?

Sieze

Thanks alot. I knew someone must know. Now I can arrange for my slicks!