Wheel Offset Calculator

RcrsWetDream · 05-02-2010, 12:53 PM

Just found this site, and I figure it's worthy of sharing for anybody looking to see how a different size wheel will work on their Suby.

As long as you know your stock wheel width and offset it spits out if you'll have more/less clearance from the strut and how much more it will push out (EXTEND) or suck in (RETRACT). It does not take into account wheel diameter, so if you're looking to go to a larger wheel diameter this may not give you 100% proof that they will fit.

Wheel Offset Calculator

mosc · 05-02-2010, 02:24 PM

Remember when using this that the stock wheel has extra clearance on both sides and the suspension designed for a specific offset. In other words even if you change wheel widths or tire size, you should in general keep the exact same offset.

I'm not saying that calculator is useless, just that without fully understanding what you put in there, it might do you more harm than good. What offset should you use? Stock.

RcrsWetDream · 05-02-2010, 04:22 PM

I'm starting to look at better rubber after my stock tires are used up and i'm trying to figure out what the best route is.. I know it's been beaten to death about suspension geometry and keeping the scrub radius the same, etc. I'm looking at stepping up to a 7.5" wide wheel with a +48 offset, running 235/40/17's, which pushes it out 1mm from the strut and 13mm further out towards the fender... Tire size would be off 2.3% at this point as well (24.4"). I would feel a lot better keeping it within 1%, but to do that I would need to run 245/40/17's, and probably an 8" wheel, which I don't want to do as I feel that would be going waaaay to far off on the offset and may even rub the fender.

I may just stick with a stock width rim, try to find a +55 offset option, and get some Direzza Sport Z1 Star Specs or RE-11's.

I obviously need to do more research

mosc · 05-02-2010, 10:25 PM

+48 is generally fine, it's relatively close to stock offset. 17x7.5" though cannot handle 235/40R17, you'll need a 17x8" wheel for that.

235/40R17 is a great size for the WRX. It's considerably shorter, like you said, which really helps shorten up your gearing.

Not sure about GR WRX wagon clearance though, the GD would have serious issues with 235 at +48.

RcrsWetDream · 05-02-2010, 10:55 PM

Pretty sure a 7.5 is the minimum wheel width for a 235... I mean the 7" wheels can hold a 225 so a 12.5mm wider wheel should be able to handle 10mm more rubber correct?

WReXd · 05-03-2010, 01:06 AM

I have 235/40/17's on my 7.5" wheels. Haven't had any problems in a year or so.

mosc · 05-03-2010, 09:30 AM

Quote:

Originally Posted by RcrsWetDream

Pretty sure a 7.5 is the minimum wheel width for a 235... I mean the 7" wheels can hold a 225 so a 12.5mm wider wheel should be able to handle 10mm more rubber correct?

You are incorrect

Quote:

Originally Posted by WReXd

I have 235/40/17's on my 7.5" wheels. Haven't had any problems in a year or so.

You are out of spec. If you are in an accident and your insurance company identifies the issue, they could find you liable. Also, you should fail inspection but that's another story as nobody is going to check your wheel width.

225/45R17 is 45 sidewall and handles tires about 30% wider than the wheel. 235/40R17 is 40 sidewall and handles tires only about 20% wider than the wheel. You have a "double whammy" effect where you are adding width and cutting sidewall. These jump you not 1 width size up, but 2. 17x8" is required for 235/40R17

Don't take my word for it, look up the tires for yourself. For example here's the specs for the RE-11:
Sizes and Specifications
235/40R17 widths: 17x8" to 17x9.5"

RcrsWetDream · 05-03-2010, 11:22 AM

Yeah you're right. I must have been looking at the 45 sidewall specs, and those fit the 7.5" wheel.

What do you think the best option would be. 7.5 wide wheels running 235/45/17's, or 8" wide wheels running 235/40/17's. It seems to be a trade off of running a slightly taller tire vs a wider wheel.

mosc · 05-03-2010, 03:25 PM

Correct, 235/45R17 is 45 sidewall and is fine for 17x7.5". However, you have a WRX 5-speed which has very tall gearing. You are much better off with a shorter than stock tire than you are with a taller than stock tire. I would recommend 24.5" to 25.0" tires. 235/40R17 is a great choice, it just requires a decent wheel width.

And there are a plethora of 17x8" +48 5x100 wheels on the market. You shouldn't have any issues finding what you want.