Ok im thouroughly confused as to what these numbers mean 245/45/18? and what the frack is offset? I know im an idiot but im trying to learn all this stuff!

 

www.google.com


try Discount Tire

 

http://www.discounttire.com/dtcs/infoHome.do

 

http://www.tirerack.com/tires/tiretech/tiretech.jsp

 

Stock wheel size: 235mm 55% 17"
235mm / 25.4 inches/mm = 9.252"
Diameter = 9.252" * 55% * 2 + 17" = 27.177"

Your "suggested" wheel size: 245mm 45% 18"
245mm / 25.4 inches/mm = 9.646"
Diameter = 9.646" * 45% * 2 + 18" = 26.681"

At 60 MPH indicated, true speed = 60 MPH * (26.681"/27.177") = 59 MPH

Offset is the distance from the bolt attachment point relative to the centerline of the wheel:
https://www.rsracing.com/tech-wheel.html

 

Here is an awesome calculator for you as well, which helps you figure out offset, speedo, revs, etc.

http://www.bigcustomwheels.com/rt_specs.jsp

 

245=TREAD WIDTH IN Milimeters

45=45% of the 245 is the side wall height from the edge of the rim to the top(outer edge) of the tire...which in this case is: 110.25mm

18=rim size.

OFFSET=has to do with the RIM(wheel) backspacing. With the proper backspacing tire won't stick out past the quarterpanel.

 

Just to add about offset.
It is hard to explain, but easy to understand with pics.
Look at the rear of the tire. Now, take the centerline. Offset is how far (in mm) from the centerline the wheel mounts to the hub. +40 means it is 40mm out from the centerline (more tire is inside the vehicle).

 

Thats a common misconception, the 245 is section width, not tread width.

 

I just put 255/45/18 BFG KDW2s on my car.... wish I had gone to 275s.. I wasn't sure how it would look on the wheel.... but in hind sight... I think I would have liked wider. They don't protect the rim even as much as the 255 KDWS tires did. ... If it's of any conulation. now.. a 255/45/18 is the upsize that won't change the outside diameter of your tire enough to throw off your speedo.

 

For those of you that want to know way more than you need to;

http://www.stangnet.com/Tech-Article...d-Rims-14.html

 

275/35R20's will safely fit on the car, but they are a bit taller than either 235/50R18's or 255/45R18's, unfortunately 275/40R18's are the best fitment in an 18" for the Mustang and they are about 3/10ths of an inch shorter than either a 235/50R18 or a 255/45R18 and require a minimum of a 9" wheel to safely mount the tires.

The load index is fine at 99 though.

 

Try The Wheel & Tyre Bible on carbibles.com.

More info there than you'll ever need.

Martin

 

www.bigcustomwheels, as noted by ADRENALIN, will give you visuals as well as written info!