Hello. It’s time for me to get tires, wondering if I can run a P285/40R18 on all four corners of my 05 GT? It has stock suspension.
Done many times already. BUT, to clear the oem 2 piston calipers on the front of my 2010, I had to use a small 3mm hubcentric spacer. (H+R brand). This effect was cuz the of deep dish chrome bullitt wheels I'm using. The rears don't require any spacer. All 4 x 18x10 wheels have a 45mm offset. By adding the small 3mm spacer on the fronts, the effective front offset is now 42mm. ( The lower the offset, the more the tire resides outboard...away from ther strut...and vice versa). Without the 3mm spacer, the inner sidewall bulge will just barely rub against the front strut assy. IF instead, a 275-40-18 tire is used on the same 18x10 wheel (with the same 45mm offset), the inner sidewall bulge is less, and clears the front strut assy...with no spacer required.
Inner side wall to outer side wall on a given brand of tire can vary from manufacturer to manufacturer. Sidewall to sidewall spec is also known as ..'section width'. And most 285-40-18 tires are typ 290+ mm...in 'section width'. The 285 designation is sorta generic. Actual 'tread width' spec on a 285-40-18 will also vary between tire manufacturer's...and will also vary depending on width of rim used. A 285-40-18 on a 18 x10 rim will typ have a tread width of just 10" (254 mm).
When I was playing around trying to measure various small clearances, I used the shank end of drill bits, since mine increment in 1/64" increments..... and simply stuffed the shank end between inner side wall bulge..and strut assy. ( I could barely get my arm over the front tires to stuff various sized shannks in there, until I found one that barely slid through). This works good... with the provisio that drill bits with round shanks are used....and NOT drill bits with triangular shaped shanks.
1mm = .039370". ( 25.4mm = 1 " ) (1mm / 25.4 = .039370")
3mm = .118" ( 3 x .039370").
1/8" (8/64) = .125"
7/64 = .109375"
I repeated the measuring experiment with tires pointed straight ahead, then fully CW..then fully CCW.
The last thing I wanted was to have to install Roush steering retainers..which reduce the turn radius.