GT350 Rotor Measurements

[DocWalt]

No gain in running 18” wheels unless you are concerned with price of the wheels and tires.

You can't get wider than a 305 in 200TW 19" tires. You can get 335 wide 18" tires.

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[zzj]

I think there must be a reason that both GT4 and fp350s use the 18 inch wheels? I don’t think the cost is a major concern for a car cost 200k+ and 100k+

 

[xt6wagon]

I think there must be a reason that both GT4 and fp350s use the 18 inch wheels? I don’t think the cost is a major concern for a car cost 200k+ and 100k+

GS mandated 18", haven't checked gt4 rules. Regardless, they are much lighter cars with smaller braking systems, making 18" wheels possible.

You might be able to run 18 on the stock brakes if you used a rally style rim that maximises caliper clearance, but I fail to see the point as the tradeoffs woukkd suck with heavy rims and minimal air volume in the tire.

 

[Norton961]

I think there must be a reason that both GT4 and fp350s use the 18 inch wheels? I don’t think the cost is a major concern for a car cost 200k+ and 100k+

The rules make them use a 18” wheel.
In non ruled classes or track rats, there is no benefit of a 18” wheel. My friend has a GT4 build and we both have Forgeline GA1R and GS1R wheels. The difference is his are 11x18 on 305/685R18 slicks and mine are 11x19 Pilot sport cup 2 305/30ZR19.
His weigh 45.5 pounds each
Mine weigh 47 pounds each.

I have AP brakes front and rear and I can run a 18” wheel and probably will buy a second set of forgeline GS1R wheels. Only because I can get slightly used slicks for dirt cheap.

 

[rocket71]

Epiphany - Thanks! What do you do for a living? That is almost the information I needed.

Here is a paste from the Wilwood email. It has a link which explain the hat offset, which is the rear face of the hat to the mounting spot of the rotor. (that is so hard to verbally explain)

It sounds like you’re trying to keep all other dimensions equal but just reduce the rotor diameter. If this is the case, you’ll need to measure the thickness of your existing rotors as well as your existing hat offset. For example:

Hat diagram
http://www.wilwood.com/Images/HATS/Hat_Drawings-Large/170-13926-lg-dwg.jpg

Rotor diagram
http://www.wilwood.com/Images/Rotors/Rotor_Drawings-Large/GT-60-Curved-Vane-Rotor-dw-lg.jpg

 

[DocWalt]

The rules make them use a 18” wheel.
In non ruled classes or track rats, there is no benefit of a 18” wheel. My friend has a GT4 build and we both have Forgeline GA1R and GS1R wheels. The difference is his are 11x18 on 305/685R18 slicks and mine are 11x19 Pilot sport cup 2 305/30ZR19.
His weigh 45.5 pounds each
Mine weigh 47 pounds each.

I have AP brakes front and rear and I can run a 18” wheel and probably will buy a second set of forgeline GS1R wheels. Only because I can get slightly used slicks for dirt cheap.

I just said why there's a benefit to 18" wheels. This is for autocross use in a class that limits you to 200 treadwear tires. Very specific use case.

 

[Epiphany]

Epiphany - Thanks! What do you do for a living? That is almost the information I needed.

Here is a paste from the Wilwood email. It has a link which explain the hat offset, which is the rear face of the hat to the mounting spot of the rotor. (that is so hard to verbally explain)

It sounds like you’re trying to keep all other dimensions equal but just reduce the rotor diameter. If this is the case, you’ll need to measure the thickness of your existing rotors as well as your existing hat offset. For example:

Hat diagram
http://www.wilwood.com/Images/HATS/Hat_Drawings-Large/170-13926-lg-dwg.jpg

Rotor diagram
http://www.wilwood.com/Images/Rotors/Rotor_Drawings-Large/GT-60-Curved-Vane-Rotor-dw-lg.jpg

Retired philanthropist and ballroom dancer extraordinaire. At least that's how I answer online inquiries since the OPM handed over all my personal data when they got hacked by the Chinese in the 2015 data breach.

I like to always verify cad data by physically measuring to compare so I pulled a few parts off the shelf to check them. I also wanted to see how much impact a 5/8" reduction in caliper boss height would look on a GT350 knuckle.

I started by mounting a factory GT350 Brembo front caliper onto an OEM knuckle. Caliper is mounted backwards for a clearer line of sight when photographed and has no impact on dimensions that I obtained. The pencil lines on each boss illustrate the 5/8" worth of material that would be removed in the mod you are considering.

Next, I wanted to take a quick look at factory bolt depth or embedment into the knuckle so I measured a service bolt and added another line that shows where the end of the bolt is when installed and no material removed.

I added a brief dash or short 3rd line to show where the factory bolt would be if you remove the 5/8" on each boss. You would end up with a threaded through hole on the left side.

Of note, you could also remove ~3/16" from each of the two bosses on each caliper. This would reduce (however slightly) the amount you would be removing from each knuckle boss.

Another area to check for clearance is the strut body-to-caliper clearance. I don't have my GT350 on hand anymore to check but it should be ruled out as a concern. Clearance can probably be minimal since it should remain static under most conditions. Closest portion would probably be where the kink is on the transfer tube.

Lastly, I checked a new factory rotor to verify the factory cad data. It was probably 25* out or so when I measured which can have an effect on any tolerance comparison to that of something measured under much warmer circumstances.

I laid a straight edge atop the hat that cantilevered over the rotor face and got a dimension of ~.869" which is probably within the engineered spec as the cad previously shown had it at .866" (a few thousandths is definitely within reason). If you subtract the hat thickness of .314" (cad showed .315") you get the offset that Wilwood shows in their chart. Measured offset would be .555" (cad would be .551").

 

[Austinj427]

Damn you are always a wealth of knowledge and specs.

 

[Trackaholic]

Where can one get the cad files of the components? Or how does one go about getting permission to get them? Seems like aftermarket companies must have some kind of agreement in order to do their designs?

-T

 

[TheDeadCow]

Where can one get the cad files of the components? Or how does one go about getting permission to get them? Seems like aftermarket companies must have some kind of agreement in order to do their designs?

-T

I was wondering the same.

I can tell the models aren't native to solidworks because I can see in the feature tree the "imported" geometry.

 

[Epiphany]

Where can one get the cad files of the components? Or how does one go about getting permission to get them? Seems like aftermarket companies must have some kind of agreement in order to do their designs?

-T

Short of a friend with a CMM/handheld scanner, it isn't easy. GM and Chrysler (for example) will share certain data to the aftermarket. Ford shares only the boring stuff - anything SVT, Cobra, or Shelby is hands off. Data isn't shared so that items can be copied (unless the proper legal agreements are in place) but rather to aid in developing new products where access to OEM data ensures correct fitment, etc.

I can tell the models aren't native to solidworks because I can see in the feature tree the "imported" geometry.

The OEM's are way beyond programs like Solidworks but thankfully file formats can be converted such that "lesser" software can read them.

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