Wheel Fitment

I always hear people asking, "Will this wheel fit the GT-S? What offset should I get?" There are a few variables when determining whether or not a wheel will fit your particular car, such as:

• Are you still running on OEM (or like-sized) rear struts?
  Most aftermarket struts will be slightly bigger than the OEM units. You'll get clearance issues. To confirm that you indeed have the OEM rear struts, here are the part numbers:
  Right rear, 48530-12220/12221/12430,
  Left rear, 48540-12160/12161/12370.
• If the car is significantly dropped (more than 1.5"), are you running springs stiff enough to ensure that the car doesn't bottom out and eat the tires?
  The fenders have "lips" that will chew up your tires for breakfast if you don't watch out for it.
• Did you get some insanely expensive big brake kit or swap?
  Big brakes mean calipers get pushed outwards. Be sure to ask a salesperson to actually measure the *smallest* inside diameter of the wheel to make sure they'll fit.
• What tire size do you plan on running?
  Most tire manufacturers provide specs so you can see how wide and tall the overall tire is.
• What wheel width (to properly mount the tire size)?
  Aim for a wheel width approximately 80% as wide as the tire. Wheels that are 6.5" wide or less are super easy to fit. A 7-incher may start to get tight depending on whether or not you have the properly-sized strut housings. Unless you're running fender flares, an actual 8.5"-width wheel is the max you can fit.
• How much negative camber will you be running?
  The more camber you run, the closer the tire's 12-o'clock position (top) gets to the strut housing.

You have to take into account the entire suspension and wheel/tire package to make sure that your car performs well on and off the track. If you've read through my site (are your eyes bleeding, yet?!), you'll know that I'm not a big fan of large diameter wheels on the AE92 GT-S. Going with a bigger diameter wheel usually means more weight given the same wheel design. More weight at the wheels just saps what little torque the 4A-GE has. Of course, if you're rich and have the money to burn, you can always invest in a set of SSRs, Volks, or Racing Harts. But, the weight you'll have saved at the wheel will be negated by the extra heft from the tire. I'd have to say that 16-inchers would be pushing it on the local Bay Area roads. 15" seems to be a nice compromise between looks, performance, weight, cost, and ride comfort.

At the least, you'll want a 15"x6.5" wheel for a 195/50/15 tire; 15"x7" for a 205/50/15 tire. Try to shoot for a wheel width around 80-85% of the tire tread width. That way, you can be sure that the tire is being well supported to take the vertical and most importantly, lateral loads. For daily driving on the street, avoid running too wide a wheel for a given tire size, though. If you do, you may end up forcing the sidewalls to stiffen up which will defeat its design purpose--flexing.

Be extra careful when buying wide wheels (I'd consider 7.5"+ as wide for the AE92). I'm not certain if wheel manufacturers have a standardized method of measuring wheel width. I've found that some will give you the overall width, while others give you the bead surface width. My Enkeis correspond to the advertised and stamped width on the wheels. The Lenso "Tom Slick" VPD race wheels that I got are advertised as 7.5" wide, but the overall width is 8.5". If you're getting race wheels, I'd highly suggest sucking up and being nice to the salesperson that you're dealing with and kindly ask for them to pull out a wheel and measure the overall width, smallest inside diameter, and most importantly, the backspacing. With these data, you won't have any question as to whether or not they'll fit.

Now, we get to the most confusing aspect of choosing wheels... Offsets. Offset is measured f/ the wheel's centerline to the wheel's hub mounting surface. Positive offset goes f/ the centerline towards the outboard side (side of car) and is the most popular type for almost all FWD and even some late model RWD cars. It's so common that when people talk about offsets, they mean positive offsets 90% of the time. Negative offset goes f/ the wheel's centerline towards the inboard side (middle of car).

A better way of talking about the hub mounting surface's location in relation to the wheel width is backspacing. It's much less ambiguous. Here's why. You take the measurement f/ the inboard wheel lip to the wheel's hub mounting surface. Easy, right?

Choosing the correct backspace will determine whether or not the wheel (or tire, indirectly) will physically fit on the car. The problem is, wheel manufacturers don't make all of their wheels w/ the most ideal offsets. They have to find a compromise b/t a bunch of popular cars and OEM wheels. Most of the time, though, you'll find a wheel w/ an offset that will work on your car.

As you start going w/ wider and wider wheels, backspacing becomes much more critical, so be careful. You may find that you'll need some spacers (don't go more than 5 mm in any case!) to create more clearance.

I hastily made some ghetto digital art of wheels w/ popular offsets and widths. Look at 'em for a few seconds and you'll better understand the relationship between offset and backspacing. More backspace means the inboard lip gets closer to the strut housing. Less backspacing means the inboard lip gets farther away f/ the strut housing. Play around w/ it in your head and you'll see what I mean.