I am working on a 13" brake upgrade designed by RCR here.

I am trying to use the 2004 STI rotors with the z28 calipers.
The issue arises as the rotor hat on the rotors is too small compared to the stock Fiero hub, as the pictures show below.

I have called the local machine/speed shops and none of them seem interested or capable of machining my hubs slightly smaller.


That said, if I grind down the hubs myself, should I be concerned at all about creating an imbalance in the hub itself by removing uneven amounts of material?
If I was working further away from the center of rotation then I would be concerned, but I feel like with the hub being relatively small in comparison to a wheel and tire, that the imbalance would have nominal, if any effect.

Any experts want to weigh in here?
Thanks

[This message has been edited by DKcustoms (edited 12-21-2015).]

How fast do you plan on your wheels turning? Do you have a lathe? How much imbalance are you willing to live with?
I would recommend having a machine shop do it, or not doing it at all. But I'm sure it can be done at home. It wouldn't be the first Fiero to drive like that shopping cart with one wonky wheel.

[This message has been edited by Formula88 (edited 12-21-2015).]

quote Originally posted by Formula88: How fast do you plan on your wheels turning? Do you have a lathe? How much imbalance are you willing to live with? I would recommend having a machine shop do it, or not doing it at all. But I'm sure it can be done at home. It wouldn't be the first Fiero to drive like that shopping cart with one wonky wheel.

Like I said above, none of the local shops claim to be capable of doing it.

Also, I won't be doing it if its going to lead to 'grocery cart syndrome'

The car will be used for drag racing and autocross, but I still don't expect super high speeds, I'll be surprised if its above 150 anytime soon.

Are the rotors installed backwards in the pictures? Reason I ask is that unless the hub flange has to slide inside the rotor hat (opposite of what is shown in the pics), there isn't any need to trim down the flange.

Measure the ID of the rotor hat and post the measurement. I am curious as to how much material will need to be removed and what the wall thickness will be between the stud and the edge of the modified flange.

Assuming there is sufficient wall thickness to safely do this mod, you will need to remove the wheel studs, then chuck up the hub using the OD of the wheel/rotor pilot surface. You might need to pop off the dust cap and use the center/support to stabilize the assembly. Then just turn down the OD of the flange.

quote Originally posted by fieroguru: Are the rotors installed backwards in the pictures? Reason I ask is that unless the hub flange has to slide inside the rotor hat (opposite of what is shown in the pics), there isn't any need to trim down the flange. Measure the ID of the rotor hat and post the measurement. I am curious as to how much material will need to be removed and what the wall thickness will be between the stud and the edge of the modified flange. Assuming there is sufficient wall thickness to safely do this mod, you will need to remove the wheel studs, then chuck up the hub using the OD of the wheel/rotor pilot surface. You might need to pop off the dust cap and use the center/support to stabilize the assembly. Then just turn down the OD of the flange.

Yes, the rotor is on backwards in the picture to show how much material needs to be removed.
I think I have some measuring calipers somewhere to get some precise inside measurements of the caliper.

The problem is that I don't have a lathe.
Perhaps I could unbolt the hub and mount it to a drill or anything to allow it to spin while I grind off material.

The rotor goes on just enough to prove that the bolt pattern is the same, but after that the rotor hat hits on the hub

[This message has been edited by DKcustoms (edited 12-21-2015).]

Your photo is deceiving. What you need to do is take actual measurements of the rotor's ID and the hub's OD before any info can properly be given.

As it stands right now, by your photo it appears as though you need to take a 1/4" off which is way too much and would make it unsafe.

quote Originally posted by fieroguru: ... I am curious as to how much material will need to be removed and what the wall thickness will be between the stud and the edge of the modified flange.

It shouldn't be too much, since the STI is also 5x100, straight from the factory. Unless the STI hub is much thicker, to make up for a lack of material on the edge of the flange. Then again, the diameter of the Fiero rear hub is significantly smaller than the front. I've only ever heard of one or two of them failing. And the one I have actually seen, the entire flange ripped off of the center, I believe.

[This message has been edited by Raydar (edited 12-21-2015).]

Any auto brake shop should be able to machine you hubs. I turned mine down on a brake lathe

Hi Kyle, I was wondering how it was going...

Guru and Thunderstruck have it right. But, based upon the fact you are staying with the 5x100 pattern, and based upon the hub being able to be drilled for 5x115 and 5x4.75", I'd think you'd be safe turning it down to fit in that rotor.

The issue I have is that you will be manually removing A LOT of material. To me, my effort would be spent elsewhere and just get the Cobra rotors.

Good luck either way. Let's see the pics.

Bob

quote Originally posted by RCR: Hi Kyle, I was wondering how it was going... Guru and Thunderstruck have it right. But, based upon the fact you are staying with the 5x100 pattern, and based upon the hub being able to be drilled for 5x115 and 5x4.75", I'd think you'd be safe turning it down to fit in that rotor. The issue I have is that you will be manually removing A LOT of material. To me, my effort would be spent elsewhere and just get the Cobra rotors. Good luck either way. Let's see the pics. Bob

I appreciate your words quite a bit.

However, this whole journey/project has been about me learning how to do stuff, and while I wait for progress on my motor, I have nothing but time, money, and energy to put towards getting this car exactly how I want it.
A new work week starts for me tomorrow, so the updates on this project may be slow, but I will make a decision sometime

you could see if you could get custom rotors too at https://www.adamsrotors.com/

[This message has been edited by Formula (edited 12-23-2015).]

quote Originally posted by Formula: you could see if you could get custom rotors too at https://www.adamsrotors.com/

I did some correspondence with the people at adams rotors, they seem to be very capable and knowledgeable, for they want more than $300 per pair for custom rotors, definitely not an option at this time.

But, I did get around to doing some measurements.

The stock 88 Fiero hub face is 145.8mm wide, or 5.7405 inches.
The 2004 sti rotor hat is 126.06mm wide, or 4.9630 inches.
In order to fit these rotors onto the Fiero hub, you would need to remove 3/4 of an inch, or 20mm, of material from the hub.

The following pictures show that with the calipers set at 10mm (removing half of the required material from each side) that it would not leave nearly enough material to have sage margins for strength.






I will have to go with the mustang cobra rotors and redrill them to fit out bolt pattern since they have a large enough rotor hat to fit our cars.