Wheels and Tires Fitment Guide

98-05 GS300/400/430
01-05 IS300
02+ SC430

Author: rominl

Creation Date: 3/2/2004

Modify Date: 10/26/2005 (SC430 information)

Introduction

After modifying my 1998 GS400 over the past 19 months, I have learned a great deal of information about the car and aftermarket parts.  It's amazing just how many stuff you can find out there for the 2^nd generation GS.  If you are willing to spend the time and effort you can easily build up a GS that's not only special but unique.

Among all the parts I have put on my car, wheels are definitely one area that requires tons of study and research in order to get a setup that's perfect for your taste and style.  Make one mistake and you can be stuck with wheels that don't fit well, rub, or even hit your brakes.  It's very different from getting other parts for the car, where you just decide on the model and that's it.  With wheels, you have to decide on the diameter, width, offset, and disk type.  On top of that for the tires you also run into the same problems on tires as well.

I have had countless of people coming to me and ask about the fitments for their cars, so I have decided to compose this guide, which hopefully can give some pictures on how you should choose a fitment for your car.  Please note that I am just speaking from my experience so sometimes I could be wrong or the setup isn't perfect.

Definitions

First of all I want to go over some definitions, some of them are official and some of them are just my terms.  But I think they are very helpful.

First of all is offset.  If you have no idea what wheel offset is, please read the link from TireRack below.  It's extremely helpful:

TireRack Offset Description

Offset is definitely the most important area when it comes to choosing your wheels, and it goes side by side with the widths of the wheels.

Another thing to keep in mind is the disk type.  This is very crucial when you plan to have big brakes on your car.  Keep in mind, if you want to see whether big brakes (Brembo, AP Racing, Stoptech, Endless) will fit under the wheel, the disk type of the wheel is the more important.  Offset might have something to do with it but disk type is the most important.  You need high disk setup in order to clear the huge brake calipers.  With medium or low disk setup you will probably get more lips on the wheels but most likely you won't be able to fit any big brakes.

Most people with wheels they lower their cars as well.  There are a lot of way to measure how much a car is lowered, but when it comes to lowering and wheels fitment, I think the "finger gap" theory works pretty good (mainly because overall diameter of the wheel with tires could be different from a setup to another, and the wheel gap (the gap between the top of the tire and the fender) is what determines whether you might rub or not.

I would measure the wheel gap by finding out how many finger(s) you can stick in the wheel gap by placing your finger(s) horizontally.  This is important, horizontal, not tilted or angled.  Usually each finger is about ½ inch from my experience (of course each person's fingers are different, but this is a good ballpark).  So say you have 1 finger gap that means you have about ½ inch gap, if you have 2 then it's about 1 inch gap.

Last definitions would be fender rolling and trimming/shaving.  Often times when you want to put on aggressive setup on the car, you are required to work on the fender a little bit in order to avoid rubbing (when the wheels get way too close to the fender).  On the GS and the IS, I strongly suggest trimming or shaving the fender rather than rolling.  Rolling fenders on the GS and IS could be very risky since you might easily crack the paint, while shaving you can get the same result but it would be very easy to control and it is harder to crack the paint.  There will be another article about fender trimming and shaving on the GS and IS.

GS wheels fitment

The stock GS 17" wheels, as far as I know, are 17x8 with 235/45/17.  I have owned two sets of aftermarket wheels for the car, 19" VolkRacing AV3 19x8.5 +38 front and 19x9.5 +38 rear, and now I have the 20" HRE 540R 20x8.5 +32 front and 20x10 +43 rear.  I would classify my 19" setup as a conservative setup as it doesn't flush totally with the fender but have zero rubbing issue, whereas with the HRE, the setup is very aggressive and is flush perfect with the fender, but has slightly rubbing which was fixed relatively easy.

The following are the wheel sizes that I would suggest for the GS (if you don't want to have a staggered setup, just put whatever for the front in the back).  When I say the setup is conservative, it means you don't have to do any fender modification.  When I say aggressive, that means you probably have to do the rolling or shaving.  And in the case of professional, then some major suspension changes would have to be made in order to fit the wheel, and should be left to professionals hence I won't go over how here.

** on 20" wheels for the GS, keep in mind that the wheels are out of spec so the overall diameter is off by about 6%.  Your speedometer would be off, meaning that when the speedometer says 80mph, you are actually going at around 85mph already.  Plus, because of the 1" larger diameter overall compared to 18" or 19" (with tires), you have to be careful with your lowering.  From my experience, if you lower your car to 2 fingers, provided that you have the correct offset, you shouldn't rub (or very slightly) the top of the wheel well.  If you go 1½ finger gap or less, when going over uneven road or dips, you will most likely rub the top part of the wheel well.  Over time you will see part of the rubber wheel well flap got rubbed away.  Moreover, with 20", you will rub when you put your steering wheel at full lock (either left or right) and mostly when backing up.  This is due to the bigger diameter and when you turn, you rub the front and back of the wheel well (this is one reason why 20" are the biggest rims you can put on the GS with reasonable widths).

When it comes to tires for the GS, the following setup are preferred:

Keep in mind different brands of tires, even with the same profile, will be different too.  So for very marginal setup (read: aggressive), the tires might provide the 1 or 2mm that makes all the difference.  Tires like the Bridgestone SO3 and Dunlop P9000 are very rounded and "meaty".  The rounded corners will help to avoid rubbing.  On the other hand, from my experience, Nitto, Pirelli, Yokohama, etc... tires are very "square" so they might enhance the rubbing factor.

IS wheels fitment

I believe the IS stock wheels are 17x7 +50 with 215/45/17.  Because of the more compact design, getting wheels for the IS300 would be a lot more crucial in order to avoid any unnecessary rubbing.  I don't have any wheels on my IS300 at this point but I will do my best.  On the IS300, 19" is the biggest you can go.  Doing 20" on the IS300 would require tremendous amount of suspension work and in my opinion it's not worth it.
       

18"		Difficulty
18x7.5 +40	18x9 +50	conservative
18x8 +46	18x9 +50	conservative
18x8 +40	18x9 +50	aggressive
18x8 +40	18x9 +55	aggressive

19"		Difficulty
19x7.5 +40	19x9 +50	conservative
19x8 +46	19x9 +50	conservative
19x8 +40	19x9 +50	aggressive
19x8 +40	19x9 +45	aggressive

For tires on the IS300 it's even more important because of the tight wheel well setup.  The following are the tires I would suggest (and it highly depends on the tire choices too):

If you want extreme fitment, the max you can do would be 19x8.5 in the front with 235/35/19 and 19x9.5 rear with 275/30/19.  But I won't be disclosing any offset information here for certain reasons.

SC430 Wheels Fitment

Since November of 2004, I have become a proud owner of the SC430. One of the biggest complaints from most SC430 owners is the stock wheel design. The design from 2002 to 2004 (so called pie-plates) was just not pleasing at all. With the 2005 wheel cover changed to 5 spoke style, it looks a lot better. And in 2006 they once again changed the design and now it's a full alloy 18" setup, no more wheel covers.

Regardless, the stock wheel setup on the SC430 is even more conservative than that you can find on the GS, especially the real wheel where it's sitting very inboard. Visually this is not appealing at all. For sure getting better looking wheels at the correct size and offset becomes a highly discussed topic.

For the record, the stock SC430 wheels they are 18x8 +45, and they are wrapped with 245/40/18 tires. Keep in mind that most SC430 come with run-flat tires and also the tire pressure sensors. Run-flat tires have super thick sidewall for the support, that's why they ride very harsh. A lot of members have complained about the ride of the SC430, saying that it's very stiff and not comfortable. Little do they know that it's all about the tires, by changing the tires to normal all-season or high performance tires, the ride will drastically improved. Moreover, because of the tire pressure sensors, when shopping for aftermarket wheels, you want to make sure you can retain the sensors still. Please check with your wheel suppliers for more information. If you decide to run aftermarket wheels without tire pressure sensors, the warning light will come up on the dash.

Of all the information I have gathered, I have read that 19x9.5 +45 fits on the SC430 no problem, front and back. Granted this setup is extremely conservative and it's far from being flush with the fenders in the back, it's a very good baseline for calculations.

Currently I am running 20x9 +30 with 255/35/20 and 20x10.5 +29 with 285/30/20 on my SC430 without any fender modifications. It's pretty much as aggressive as you can go without modifications, and the SC430 is actually not very friendly in this manner, since both the front and rear fender lining are "integrated" with the fender lip, you can't just shave the lip and call it a day without spending time with the lining as well. I would suggest against this.

And for wheel size, I will only talk about 19" and 20" setup. 18" is the same as stock and personally I think 19" is the minimum.

There are several things I want to point out. First of all, besides the "weak" setup I mentioned, all other setups I put down aggressive as the minimum difficulty. The reason is with those sizes, tire choice plays an important role. Getting the right brand and sizes of tires is the key for no rubbing. If you want any conservative setup, you can just get the aggressive setup and add 6 to 10mm of offset for more room.

For 20", you actually run into the "typical" problem of rubbing the top of the front wheel well lining, just like what you face when putting 20" on the GS. However, on the SC430 it's actually worse since the lining is even stiffer, has more "knobs", and there are more places for rubbing. As long as your car is lower to around 2-finger gap, I can pretty much guarantee rubbing the top of the wheel well with 20" wheels. Mine does, but after a while the lining will be rubbed away, leaving a small hole there and everything will be back to normal.

In terms of tires, my suggestions would be as follows:

* Please keep in mind, if you want to run 11" wide rim in the back with 305 series tires, you want to add couple of mm to your wheel offset since the tires are wider. Otherwise you run into great risk of rubbing.

And again, different brand and model of tires have different shapes, curvatures, corners, thickness, etc… and all these contribute to how well the overall wheel package clears the fender. All setup here are aggressive, meaning that they are close to the fender walls. You definitely want to be careful and study enough to make sure you purchase the right combo.

Conclusion

Hopefully this is a good guide for everyone who is thinking about getting wheels and tires setup for your GS, IS, or SC430.  Getting a perfect set of wheels is very hard I have to say, it involves a lot of researching and patience.  Don't rush in finding your set of wheels.