Anyone ever post how to detirmine new tire size??

johnboneske · Post by **johnboneske** » 17 Jul 2014, 07:48

Here is how. I helped someone...

Do you know how to figure out what the size means? in your 225/50/17 vs your 225/45/17 they are 225MM wide which there are 25.4MM per inch so 8.85" wide, by 4.425 high, by 17" wheel. So if you want to figure out the height it is 4.425+17+4.425+25.85", and the circumference is x 3.14159= 81.210" around... the tires your looking at are same width, 3.98 sidewall height so it is 24.96" height and 78.41" around... there are 63,360" per mile...figure it out...how many revs per mile, your speedo will show faster than you are going though...

My personal car is a 2001 Volvo S80 and it had factory 16" wheel with 215/55/16... I am going to a 225/50/17. My speedo is off 3 to 5 MPH depending on speed(showing faster than I am going) so if you figure it out this will fix it...

Post by **shaker_chi** » 05 Aug 2014, 21:56

Reason your speedo is off you went too high on the sidewall. If you jump from a 16 to 17 inch rim, the 225/45R17 would have been more appropriate So the sidewall height is a percentage of the width:

225 = 225 mm wide (you are correct)
50 = Sidewall is 50% of 225 = 112.5mm = 4.43+4.43+17=25.86"

215 = 215 mm wide
55 = 55% of 215 = 118.25 = 4.65+4.65+16=25.2

mrwassman · Post by **mrwassman** » 25 Jan 2015, 16:27

I've used Tireracks' "revs per mile" to quickly distinguish how close tire sizes are.

Silvershield82 · Post by **Silvershield82** » 08 Mar 2017, 22:02

Has anyone tried using the sizes of old and new tires?
Old Tire Size / New Tire Size = Multiplier to scale with

I also found this formula for computing the size:
275/40-17 ((275*0.40)/25.4)*2+17 = 25.7"