JDWalton

Hey all, I have been asking alot of tire questions lately and found something I am wondering about.
XXX / 45 - 18 front
XXX / 40 - 18 rear


Will this be any issue or is the difference too small to really matter? just wondering cause if I go this combination it will be drasticaly cheaper.

schapman

depends on what xxx is?
my tires are 255/35-20 so to figure it out ((255*35)*2)+20.
all you need to do is substitue the 35 and 20 in mine with (45 or 40) and 18.
as long as the back sidewall is larger is should look fine.

hmartine

+1, you must know the tire width to figure out the height. here is an example:

new 255/40/18 tire

255 / 25.4 = 10.04" wide tire
10.04 x 40% = 4.02" high side wall
4.02" x 2 (two side walls) = 8.03" total side wall height
8.03" + 18" (rim dia) = 26.03" total tire diameter

Nuke

Use this:

http://www.1010tires.com/tiresizecalculator.asp

Also, tirerack has tire specs for all the tires they sell. You can compare specs there.

JDWalton

ahhh... never new exactly how that was calculated.
255/45ZR18
and
285/40ZR18

The diamater looks very close to me, I just dont know how close is good enough.

grampa_stang

Those are the same size shoes the GT500 wear.

Norm Peterson

Within 3% is generally considered close enough even for fussy situations involving ABS operation. That's a little over 3/4" in the case of tires about 27" tall, or about 3/8" on the radius. Tread depth represents only a little less than this (commonly 10/32", or 5/16"), and nobody ever worries about new vs worn for tire diameter and fit purposes.


Keep in mind that the "visual sidewall height" will be somewhat less than those calculations give. Part of it is the rim flange height, since tire profile height is taken down at the bead rather than at the flange OD (all around). And part will be due to tire compression under load (obviously only at the bottom).


Norm

JDWalton

that said I am purchasing tommorow, anyone got the quick scoop on how I handle the sensors in the tires?

Stoenr

You can reuse your old sensors, just need the install kit for each wheel. I think American Muscle sells them.


Same size I am running, zero issues.


Norm, you are the man!

JDWalton

hmm... how expensive are replacement sensors? only reason I ask is I was getting rims too and didnt want to have to dissassemble all of my stockers if I dont have too.