Wheel and Tire Fitment - read here first.

Redneck_Racer said:

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.

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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.

At first I had considered running 285-40-18" tires on all 4 corners until reading the specs over on TireRack.com. According to their specs, section width for Continental extreme contact sport tires on a measured rim width of 10" is listed at 11.4" Same also applies for Goodyear Eagle F1 Supercar tires. Only exception were Pirelli P Zero Rosso tires with a section width of 11.2" on a measured rim width of 10" Anyhow, my main concern is not so much with the tread width, but rather it's the 11.4" section width that I'm concerned may cause the inner sidewall to rub against the front strut assy? Therefore my question is this, would running 285-40-18" tires paired on 18x9.5" rims with 45mm offset clear the front strut assy without requiring a hubcentric spacer or would running 275-40-18" tires provide more clearance instead

I'm thinking about new rims for the Bullitt and have fallen in love with the Shelbly CS-11s. I'd love to run a staggered setup but will a 20x11 with only 50mm offset fit in the rear? Current setup is 19x10 square with 285/35/19 and it's close in the rear.

bujeezus said:

I'm thinking about new rims for the Bullitt and have fallen in love with the Shelbly CS-11s. I'd love to run a staggered setup but will a 20x11 with only 50mm offset fit in the rear? Current setup is 19x10 square with 285/35/19 and it's close in the rear.

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It will poke out. You really need a 58-60mm ET.

I run 19x11 with 285 40 19 and +50mm offset. No rubbing

I think I'm gonna pop a wheel off tomorrow and do some measuring. Went to the Shelby site and they had a disclaimer about possibly needing a Watt's link in order to run the 11s!

Oh gosh, just in time, im considering rims and tires i bought a 2007 base convertible used 45k miles. Manual trans. It has 20 " ugly rims . I scraped them really really bad pretty quickly at my atm. The tires are 245 35 lr 20. Any thoughts as to what would have been done and would it be easy to undo to fit those big low tires?

There was likely nothing changed on the car to fit those 20s other than maybe some wheel spacers if the offset wasn't quite right. Should be as easy as finding a set of wheels you like and swapping them over.

AHaze said:

There was likely nothing changed on the car to fit those 20s other than maybe some wheel spacers if the offset wasn't quite right. Should be as easy as finding a set of wheels you like and swapping them over.

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Thank you so much!!

qq poll, can you have staggered set-up with square wheels?
current wheels are 19x8.5
looking to fit 275x40 in rear, 255/40 front
the OP suggest 275 does not fall within range of tyre sizes for 8.5 wheel but the tyre shopt says they can fit it

bourneagain said:

qq poll, can you have staggered set-up with square wheels?
current wheels are 19x8.5
looking to fit 275x40 in rear, 255/40 front
the OP suggest 275 does not fall within range of tyre sizes for 8.5 wheel but the tyre shop says they can fit it

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Tyre shops will say all sorts of daft stuff. The 275's should be on a 10" wide rim...and the 255's should be on a 9" wide rim.

MY .02, Really depends on the tire model and aspect ratio as far as fitment, FWIW - I run a 325/40/18 on a 10" rim, works well, would it be better on a 11" probably, but the manufacture approved it for 10" wide

bujeezus said:

I think I'm gonna pop a wheel off tomorrow and do some measuring. Went to the Shelby site and they had a disclaimer about possibly needing a Watt's link in order to run the 11s!

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Chatching up on this -- late, but did you switch to 11's?