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GT350 Brakes with 18" Wheels

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Has anyone used or know of anyone that has used the below Racing Brakes rotors with modified stock calipers? I'm trying to find a solution to enable the use of 18" wheels for the track use w/o spending $3K+. I have access to the mill so not worried about machining down the mounting pads on the stock calipers. Mostly curious how the pads sit on the 380mm rotor (any overhang) and does an 18" wheel (like Apex EC-7) actually fit?

https://www.racingbrake.com/RB-2pc-Rotor-380x36mm-Downsizing-from-OE-s-394x3-p/2611.htm
 
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Might be best to call RB and ask them. They have a number of clients with various combinations of OEM and custom calipers and rotors, so they should be able to tell you what works and what doesn't.
 
Agree.....did contact them and didn't get a straight answer about 18" wheel fitment even their website states, "Fits under 18" wheels which is more favorable to track racer in choice and cost for wheel and tire."
 
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Agree.....did contact them and didn't get a straight answer about 18" wheel fitment even their website states, "Fits under 18" wheels which is more favorable to track racer in choice and cost for wheel and tire."
My understanding is that their custom calipers and 380mm rotors together fit under Apex wheels. The question is, does the factory caliper clear when the knuckle is machined so it fits on the 380mm rotor or not?

I don't have that information, but it wouldn't surprise me that even after the OEM caliper is moved in by 7mm to match the smaller rotor, that the caliper body is still too tall to fit under an 18" rim where the inside of the barrel is 13mm closer in than a 19" rim.
 
My understanding is that their custom calipers and 380mm rotors together fit under Apex wheels. The question is, does the factory caliper clear when the knuckle is machined so it fits on the 380mm rotor or not?

I don't have that information, but it wouldn't surprise me that even after the OEM caliper is moved in by 7mm to match the smaller rotor, that the caliper body is still too tall to fit under an 18" rim where the inside of the barrel is 13mm closer in than a 19" rim.
Yep many 19” wheels won’t clear the calipers so 7mm may not be enough. The AP racing caliper setup like @Black Boss uses does fit under 18” wheels.
 

Fair

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That's pretty smart - downsize the GT350/R rotors to 380mm, relocate the caliper, to be able to use 18" wheels.

B61G1903-L.jpg

When the S550 was being announced some wheel makers knew early that the 380 mm / 6 piston caliper was coming in this and several other cars. Some of these wheel makers adjusted their 18" wheels to fit...

B61G1910-L.jpg

This was the new "dropped" barrel for the Forgestar CF5 in 18x10", made to clear these PP1 brakes. I am point to the change in the image above.

DSC_9878-L.jpg

The older F14 wheel barrels were more tapered (see above), and frankly a little easier to mount tires to. But these did not clear this 380mm 6 piston package...

DSCN0120-L.jpg

That tapered barrel was phased out and all Forgestar made since 2016 have this stepped barrel, to have more brake clearance.

B61G1937-L.jpg

The caliper clearance is far better than the stock 19x9's on this PP1, but it is closer radially at the caliper...

B61G1933-L.jpg

Not too terribly close with the updated wheel barrel, but its close enough to look.

P9271305-L.jpg

I run a 380mm 2-piece 6 piston Powerbrake caliper and it cleared all of the Forgestar/MOMO 18" wheels on our S550.

IMG_1543-L.jpg

I ran an 18x11" Momo under those brakes with plenty of room. Should be similar to the RB rotor/GT350 caliper. Send me your caliper and rotor data and we can check with Forgestar/MOMO for wheel fitments.

Cheers,
 

boardkat

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Apologies if I missed something elsewhere, but is everybody not already aware that you can fit 18s over the stock GT350 brakes? A friend I compete with accomplished it on his R back in 2018 with a bit of machining on his spindle to fit 18x12/335 on CF5s. Here’s a screen cap from his book of faces vid showing the work in progress and the final result:

1d10df7cf8bfb2c5003df222ef48110c.jpg

ac961579378adfacb95edda38f57562d.jpg
 

Fair

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Apologies if I missed something elsewhere, but is everybody not already aware that you can fit 18s over the stock GT350 brakes?

Did not know that! What is he doing? Machining the caliper bosses and moving the caliper inboard radially? Is that rotor a stock GT350 rotor - not machined down radially as well?

24740113_10155672802876223_303405605_o-L.jpg

18x12" Forgestar CF5 wheels are bigger than you can get from any "standard" set of Mustang aftermarket wheels... Can you share the pics of the flares on that car?

Thanks,
 
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It's entirely possible that Ford, in their wisdom, actually made the rotor offset the same between the GT350 and the PPx versions. Rotor offset is the distance from the center line of the rotor to the inner face of the mounting flange. If that was the case, then a 380x34 replacement rotor made for a PPx car would fit the GT350, except that the pad would misaligned and the rotor would be 2mm thinner. Milling down the stands would fix the pad alignment and the 2mm thinner rotor wouldn't matter so long as you change your pads early and don't get close to the backing plate. Using a thinner rotor than OEM opens up the possibility that the caliper pistons could get pushed too far out of the caliper. They probably wouldn't fall out, but they might get jammed or stuck. Or they might be fine - no way to know.

In any case, the RB replacement 380mm rotor for the GT350 is 380x36 - the correct thickness - so to go back to the OP's original question, it's likely that at least some 18" rims will fit over it if the mounting bosses on the knuckle are milled down.
 

boardkat

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That's not a stock GT350 rotor.
Yeah, I didn’t have my coffee before I wrote my post and misinterpreted what the OP was asking slightly. Thought he was just interested in seeing the GT350 caliper w/ 18” wheel solution. When I get info back on what rotor my friend is using I’ll post it up - and have him confirm that it was for weight reasons (not because the stock rotor wouldn’t work - or not). Stay tuned!
 

boardkat

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OK, confirmed - it's a custom 15" 2pc rotor from Wilwood that has similar thickness to the GT350 stock 15.5" piece. He didn't confirm if the stock rotor would work but did say he was more concerned with weight loss (which is why he went the direction he did).
 
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Did you mind getting more details from him?

How much did take off the knuckles to move the brake caliper inward?

Does he have a part# for the wilwood rotor that normal peeps can buy?
 

boardkat

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Lake Oswego, OR
Did you mind getting more details from him?

How much did take off the knuckles to move the brake caliper inward?

Does he have a part# for the wilwood rotor that normal peeps can buy?

He took 3/8” off the knuckles

No part number he could provide since it was a custom order awhile back, and it looks like the only 15” option they have listed on their website is 31.8mm thick. Might need to call it in, describe what you’re trying to do and see if they’ll do another run. I’ll try and get you a contact at Wilwood to start a conversation.
 

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