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Thread: Ultimate Tire Size and Offset Guide

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    Ultimate Tire Size and Offset Guide

    *All credit for this guide goes to Xenonk on lgt.com*

    I finally compiled the most completed info I can come up with for wheel and tire fitment questions that everyone has. I mapped this entire post out so that you can pick a rim size you want and the rest will follow, including tire size.. I worked out this post so that you guys can decide on a tire size and it will point to you of what rim specs you need to fit onto the car.. as for brands and types of wheels and tires, well, that's a totally different thread on its own.

    -GT's bolt pattern is 5x100mm, NOT 5x114.3. Only the 2005+ Impreza WRX STi is currently running 5x114.3mm. Stock GT wheel is 17"x7" +53mm, as stamped on the back of the spokes of your stock rim.

    -OBXT bolt pattern is 5x100mm with +48mm offset (weighing around 20.5 lbs per rim). OBXT wheel is 17"x7".

    -2.5i and 3.0R models will need confirmation on stock rim sizes.

    -Center bore must have to be 56mm or larger (if the bore is larger than 56mm, use hub centric rings to fit properly to your wheel's center bore, but not always necessary if you have wheels with conical lugnut seating, the wheel will eventually center itself, but that's your call of how you want to go about that).

    -SpecB, OBXT, and 3.0Rs can use shorter tire sizes from the GT. But be sure to check and compare the load capacity of the tires. Try to use the same tire load capacities if you can within +/- 100 lbs. You can certainly always go over, but not under (as this requires for you to run higher tire pressures and this could cause more of an issue for tire wear).

    -Lug nuts threading are 12mmx1.25mm. Open or Closed End lugs will depend on the mounting thickness of your rim, usually, closed ends (like the stock ones) are fine.

    *All credit for this guide goes to Xenonk on lgt.com*

    -Here we go, here are your choices for rim widths (regardless of it being 17", 18", 19" or 20" rims):

    {offset in BOLD are the closest possible offset to OEM's scrub radius, you'll notice that once you go past 8" wide rims, you will run out of room on the inboard side to put/stuff any more of the wheel/tire to maintain the OEM scrub radius.. 8" and up will increase positive scrub radius}

    6.5" (+34mm to +60mm offset, +55) *for 2.5i only
    7.0" (+37mm to +57mm offset, +55)
    7.5" (+40mm to +54mm offset, +55)
    8.0" (+43mm to +51mm offset, +53)
    8.5" (+45mm to +48mm offset, +45) *will need to roll the fenders if tires are wider than 255
    9.0" (+43mm to +45mm offset, +43) *will need to roll the fenders if tires are wider than 255
    9.5" (+38mm to +40mm offset, +38) *will need to roll the fenders if tires are wider than 255

    and it also depends on what kind and size of tire you want to run as well (and that can get messy). But to be on the safe side, here is the tire widths you can put on each rim:

    195mm = 6.5", 7" and 7.5"
    205mm = 6.5", 7" and 7.5"
    215mm = 6.5", 7", 7.5" and 8"
    225mm = 7", 7.5", and 8"
    235mm = 8", 8.5", and 9"
    245mm = 8", 8.5", and 9"
    255mm = 8.5", 9", and 9.5"
    265mm = 8.5", 9", and 9.5"
    275mm = 9" and 9.5"
    285mm = 9" and 9.5"

    Once you decide on the rim size, the tire width you want to run, here are your final tire choices. Note that not all tires are built the same way, so sometimes you'll find two different tire models with the same size (225/45/17), but one can fit on a 7" rim, while the other one will need a 7.5". You'll have to look around the manufacturers' specs on sectional width of the tire.. normally you want your rim width be no more than 1.5" less than the tire's sectional width. For example, if you have a 8" wide rim, your tire's sectional width shouldn't be more than 9.5" or you'll have to deal with the flex on the tire sidewalls. Most performance driving set ups are 1" difference (ie. a 8" wide rim with 9" wide tire). Below I listed for you by rim diameter of which I recommend running with some notes on each tire with notes to go along with them as well:

    16 in. rims (for 2.5i, 2005-on) only:

    195/60/16 (great for snow rally or snow use)
    205/55/16 (OEM sizing which is also good for some non-tarmac surfaces)
    215/55/16 (oversized for the rim protection, but very sloppy sidewall handling)
    215/50/16 (wider footprint used for more daily driving without harsh gas consumption)
    225/50/16 (great for autocrossing, still usable for daily driving all year round)


    17 in. rims (for GTs 2005-on):

    205/40/17 (only for SUPER FAST acceleration and torque; for autocrossing only, do not use for daily driving)
    205/45/17 (only for FAST acceleration and torque; for autocrossing only , do not use for daily driving)
    205/50/17 (good for snow rally)
    215/45/17 (stock)
    225/45/17 (good autocross performance tire size for gearing, more mph per gear)
    235/40/17 (good autocross performance tire size for torque, more acceleration)
    235/45/17 (tallest tire you could use under the GT due to possible suspension clearance issues, best used with an 8" wide wheel)
    245/40/17 (good autocross performance tire size for traction, will need to have a flatter alignment to make use of the grip)
    255/40/17 (maximum grip, good for track days, will need a 9" rim to make use of the contact patch and a good alignment as well).

    18 in. rims (for GT 2005-on):

    215/35/18 (only good for autocrossing use, do not use for daily driving)
    225/35/18 (only good for autocrossing use, do not use for daily driving)
    215/40/18 (uncommon tire size, close to OEM overall tire diameter, good for daily driving)
    225/40/18 (typical sizing, most popular size, GREAT for daily driving)
    235/40/18 (very large, but great for pot-hole city driving, may need fender rolling)
    235/35/18 (rare size, but closest to OE tire sizing to keep the spedometer reading correctly)
    245/35/18 (common autocross, performance size, very good for daily driving)
    255/35/18 (very good daily driving size, even better on the track)
    265/35/18 (very good daily driving use, but the car wont be able to use all 265mm of tread for the track)
    275/30/18 (tallest tire you can mount without fender clearing issues on a 2" lowered car if you get the right offset)
    285/30/18 (aka, the "STREETS OF DREAM" setup... the widest you can go.. this is the next tire size I am going for and a rim to match it)

    18 in. rims (for Spec B.2006-on, 3.0Rs 2008-on):

    225/40/18 (common tire to use and gives a better acceleration since it's 0.5" shorter)
    235/40/18 (rare size to find, but near stock height for proper gearing)
    245/40/18 (popular tire size for the larger cars)

    19 in. rims (for GT 2005-on):

    225/35/19 (common typical sizing for 19" for our cars)
    235/35/19 (tallest tire you can mount without fender clearing issues on a 2" lowered car if you get the right offset)
    245/30/19 (rare size, but also tallest tire you can mount without fender clearing issues on a 2" lowered car)

    Use these at your own risk, but to my knowledge on a lowered car with a small-spring perch type coilover, it should work and ride fine. The most you'll probably have to do to the fenders is to just roll the lip of it in to give yourself another 5mm of clearance. I hope this helps.
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    Re: Ultimate Tire Size and Offset Guide

    Here's a more comprehensive tire/wheel tool and calculator: Allows you to compare different wheel diameters, widths, offsets, and tire sizes.

    http://www.bigcustomwheels.com/info_specs.jsp
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    Re: Ultimate Tire Size and Offset Guide

    ^^ great link founf some nice rims and tires on there. about 200-300 higher then what i had looked at before but i think its the shiping and handling compaered to going to the local discount/americas tire by my house. but saved the link,I loved the whole fit calculater thing to tell you if it will fit a un-lowered stock body. i think there was a ting there to tell you if it would trow off your spedomiter aswell. thanks for the find.

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    Re: Ultimate Tire Size and Offset Guide

    Great info thanks
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    Re: Ultimate Tire Size and Offset Guide

    As almost none of the wheel / tire information applies to the Outback, got a question.
    '99 Outback Wagon that came stock with 15" wheels / 205/70-15 tires.
    I've got a set of 16" wheels from a '99 Legacy GT and would like to put 225/60-16 tires on.
    Anyone know for sure if they will fit?
    Thanks.
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    Re: Ultimate Tire Size and Offset Guide

    they will fit. go with 55 or 50's. less roll.
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    Re: Ultimate Tire Size and Offset Guide

    Bumping this thread, anyone had 17x8 with a 35 offset on a BD? Found a good deal on some I'm fine with rolling fenders just want to make sure tire isn't rubbing on the struts.

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    Re: Ultimate Tire Size and Offset Guide

    WOW! thanks for bumping this resource. Fantastic work - thank you very much. I'm getting rubbing under load and hard cornering, and need to make decisions. This will help significantly.
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    Re: Ultimate Tire Size and Offset Guide

    Well I got home after work and measured the gap between the rim/tires and struts, plenty of room in the front but just about no extra room in the rear. I have 17x7.5 et 48, with my clalculations the 17x8 et 35 is .7 inches farther in (I think these calc are right, if I am wrong someone let me know cause then the wheels would work) and might be able to slide a piece of paper between the gap but that would be it, I guess I'll keep looking.........

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    Re: Ultimate Tire Size and Offset Guide

    And if you want to know the offset of your stock tires and it isn't listed above.

    http://www.cars101.com/subaru/tiresandwheels.html
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    Re: Ultimate Tire Size and Offset Guide

    ive been trying to find out, will a 17" rim with a 40 offset work?, when the wheel was listed, it was mentioned to be a 5x100 ET40, i presume the ET40 is refering to the offset? would that be correct? and it should fit right?

    edit: it mentions above to GT models 05 and up..? its still a 5x100 bolt pattern tho

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    Re: Ultimate Tire Size and Offset Guide

    Quote Originally Posted by SilentRacer
    205/40/17 (only for SUPER FAST acceleration and torque; for autocrossing only, do not use for daily driving)

    what makes these bad for daily driving?

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    Re: Ultimate Tire Size and Offset Guide

    Quote Originally Posted by Bookem
    Well I got home after work and measured the gap between the rim/tires and struts, plenty of room in the front but just about no extra room in the rear. I have 17x7.5 et 48, with my clalculations the 17x8 et 35 is .7 inches farther in (I think these calc are right, if I am wrong someone let me know cause then the wheels would work) and might be able to slide a piece of paper between the gap but that would be it, I guess I'll keep looking.........
    When I use this calculator I get 7mm more clearance on the inside and 31mm more extension outward. I know I'm bumping and old thread but found some rims with the same specs and want to know if they'll fit a BG5... did you end up getting them?

    Anyone know if they'll fit with the stock 215 45 tyres?

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    Re: Ultimate Tire Size and Offset Guide

    Hi All,

    I am planning to run 17x9.5 Rota Grids with a +35 offset with some 255/40/17 on a 2005 LGT limited. I was planning on rolling the fenders, would there be anything else that needs to be done, i.e. spacers? fender pull? camber?

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    Re: Ultimate Tire Size and Offset Guide

    Try going here http://www.willtheyfit.com, I don't remember where I got this site from but it helps.
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