Also, seeing as the pads drop in from the top on our calipers, there would be no way to make the pad wider, disproving the lower image I created. So we are left with either a taller pad or material differences

 

I'm totally stumped with how a fixed [single] positioned brake caliper can accommodate two different diameter rotors. Something that I have come to think is accurate must be wrong. The steering spindle knuckle would make the most sense where I'm wrong, with one pair (LH & RH) for 13.1 inch rotors and another pair (LH & RH) for 14.0 inch rotors - each different pair having different mounting points for the brake calipers. Next would be the brake calipers themselves, one size for 13.1 inch rotors and another size for 14.0 inch rotors. Beyond that I'm at a loss to solve the mystery.

 

Not to say you were wrong, but I do agree with that logic
Do we know for sure that the brakes on an F-Sport wear on the whole rotor surface? not just a patch? Thats my last guess before I throw away my engineering degree

 

I'm not even focusing on the effectiveness of the braking - I'm just trying to figure out how it (what I 'think' is accurate) is able to work at all...regardless of how well the brakes work.

I must be wrong about either the 'one size' steering spindle knuckles (LR & RH) or the one size brake caliper for 4GS RWD models...otherwise (the way I see it) you simply could not use two different rotor diameters with such a setup.

 

Not the whole rotor surface. There's part of the rotor near the hub that is not covered by the pad. With what I think is the same pad material dimensions (for both the 13.1 inch and 14.0 inch rotor) it should cover the same area. A larger caliper of course would be needed to handle a little larger brake pad....but 'I think' only the AWD models (for some reason) may have different calipers. It would make more sense (in my view) for there to be two different steering spindle knuckles. So, maybe that is where I'm wrong.

 

Is it possible that the pads are sized for the bigger rotor and overhang the smaller one?

 

No, because you would clearly see unscrubbed areas when you replace your pads.

It's more likely the outer edge of the larger disc makes no contact with the pad. This is not uncommon.

By the way, a larger pad doesn't increase stopping power. It just maintains the same level of performance longer as the pad material heats up beyond a certain point, and also lasts longer.

 

It's not uncommon to see a very small amount of the outer edge (~1/32"-1/8") of a vehicle's rotor surface that has no coverage from the brake pad.

 

That's what I'm saying - pad contact area smaller than rotor is common. Pad larger than the rotor is not common, it would create a weird lip on the brake pad - which never happens.

The larger rotor(even if no contact) has also benefit of serving as additional metal to dissipate heat(at the expense of higher unsprung weight which the 2-piece offsets).

 

According to Lexus parts website, I am finding the following information (Parts were found looking under 2013 GS 350 AWD)

PAD KIT, DISC BRAKE, FRONT Part Number: 0446530491 Supersession(s): 04465-30491; 0446530460; 0446530490; 446530491

From 201409 to 201410.
From 201409 to 201510.
From 201410 to 201510.
From 201510 on.
From 201510 to 201809.
0000003 0; H00000O 0; H000003 0; I000015 0; I000003 0; G000015 0; G000003 0; ARL10,GRL12; GWL10; GRL10; MARK TEXTAR T4146,THE CRAFTED LINE; MARK TEXTAR T4146,KOREA SPEC&F SPORT; MARK TEXTAR T4146,FRONT WHEEL BRAKE-18INCHES DISC(ORANGE PAINTED); MARK TEXTAR T4146,FRONT WHEEL BRAKE-18INCHES DISC; MARK TEXTAR T4146,F SPORT;
From 201510 on.
From 201409 to 201510.
A0000070003 0; 90000070003 0; Z000002 0002 0; M000002 0002 0; GSC10; ASC10,GSC10; MARK TEXTAR T4146,TIRE & DISC WHEEL-235/40R19+265/35R19(F-SPORT); MARK TEXTAR T4146,TIRE & DISC WHEEL-235/40R19 8.0J ALL SEAZON TIRE(F-SPORT); MARK TEXTAR T4146,FRONT WHEEL BRAKE-18INCHES DISC(ORANGE PAINTED); MARK TEXTAR T4146,FRONT WHEEL BRAKE-18INCHES DISC;

I interpret this as saying that the same brake pad is being used for all GS350 models
Also, this picture is the image i found online of the part number- perhaps we can find photos of F-Sport pads?

 

I have found that the parts application websites are not the best or the most accurate...and can be very confusing - which doesn't help with having full confidence in the results and may be where my understanding has gone awry. Even the vehicle body nomenclature (GRL10, GWL10, etc.) some of the parts websites provide can be confusing.

I think you are going to be better served looking first for parts specifically for RWD models (F-Sport RWD vs non-F-Sport RWD). Then, once you have determined what Steering Spindle Knuckles, Brake Calipers and Brake Pads are used for those two distinctly different models (one using the 14 inch rotor and the other using the 13.1 inch rotor), then do the same for the AWD models (F-Sport AWD vs non-F-Sport AWD). Then you'll have the three primary parts (Steering Spindle Knuckles, Brake Calipers and Brake Pads) we're focusing on for all versions of the 4GS except for the GS 450h which can be added later.

I searched for four specific 4GS models (F-Sport RWD, non-F-Sport RWD and F-Sport AWD & non-F-Sport AWD) that were either for sale or being auction or has been salvaged to get their VIN numbers so they could be used to search for parts specific to that particular model.

I would be curious what others come up with parts-wise for the different 4GS models. First the RWD models. In other words - How many different Brake Calipers are there for F-Sport RWD models, and what are the part number(s)? How many different Brake Calipers are there for non-F-Sport RWD models, and what are the part number(s)? How many different LH & RH Steering Spindle Knuckles are there for F-Sport RWD models, and what are the part number(s)? How many different LH & RH steering Spindle Knuckles are there for non-F-Sport RWD models, and what are the part number(s)? Same for Brake Pads. Then, the same for the F-Sport AWD models...and non-F-Sport AWD models... It's quite a task, especially if you don't have complete confidence with the parts website that are chosen, which means double-checking might be needed! Same for confidence in the VIN numbers used, etc., etc.

 

Ok guys... first of all, great analysis in this thread, but....

Would one of you with an F Sport go visit a non-F Sport owner and compare rotors and pads already? Take your wheels off and compare the brake components and pads to see if there are obvious differences?

 

If anyone in the NY/Northern NJ area wants to compare sizes come on over

 

The pads are the same exact size. Multiple sources confirm both the f-sport and non-fsport use the same part number.
The rotors we already know is about one inch wider.

I'm also fairly certain the caliper is exactly the same except for the mounting bracket position. Also I'm fairly certain the inner diameter of the f-sport rotor the parts the pads don't touch is larger on the f-sport.

WHAT I WANT TO KNOW IS WHY LEXUS IS LYING ABOUT THE NUMBER OF PISTONS ON THE NON F-SPORT!

 

Do you have any knowledge that the brake caliper mounting position (two bolt holes on the Steering Spindle Knuckle) is located differently for the F-Sport RWD versus the non-F-Sport RWD? If so, that would make perfect sense and explain how one brake caliper could be used with two different brake rotor diameters (13.1 inch and 14.0 inch) by having two different Steering Spindle Knuckles - one Steering Spindle Knuckle for the F-Sport RWD with brake caliper mounting holes to accommodate the 14 inch rotor, and another Steering Spindle Knuckle for the non-F-Sport RWD with brake caliper mounting holes to accommodate the 13.1 inch rotor.