Brake upgrades (Page 1/3)
pHoOl MAR 11, 02:07 PM
I've been doing some reading on here about brake upgrades, and I'm assuming this has been thought of already, but why wouldn't a 5x100 large rotor work vs doing a C4 corvette rotor and having to get it drilled?

Something like this for Subaru?
https://www.rockauto.com/en...8&cc=1428791&jsn=385
pHoOl MAR 11, 02:11 PM
Might have answered my own question... looks like the C4 rotors are half the price.
fieroguru MAR 11, 06:57 PM
The main reason is that the bolt pattern is one of the easiest things to change and other more critical dimensions can't be changed.


Say you were looking for a rotor to be used on an 88 Fiero and want to retain the stock calipers. The rotor you selected won't work for a few reasons.

Rotor thickness - must stay below 20mm to retain use of the 88 Fiero calipers (or use the C4 Vette caliper) - rotor in the link is nearly 30mm thick. So unless you want to start swapping calipers, that rotor is an immediate no-go.

Rotor Hat ID (back side that the wheel flange slides into) - again with the 88 Fiero, the front wheel flange on the hub is oversized - sized to allow a 5 x 4 3/4" pattern. Issue is when mfgs use a smaller wheel pattern, they normally reduce the ID of the rotor hat... This means that the vast majority of the rotors with a 5x100 and even 5x115 pattern will not clear the enlarged wheel flange on the 88... so that makes them an immediate no-go as well. I can tell just by looking at the link, that rotor will not clear the 88 front hub.

Rotor Depth - To move the calipers, you need room for caliper adapter brackets, unless you want a very complicated and more costly caliper bracket design). This means that you want the rotor to be deeper than stock, but you can go too deep or the rotor and/or the caliper will interfere with the a-arms.

Hub Pilot ID - Needs to be large enough to slide on the Fiero hub. Some of the rotors with 5x100 have a smaller pilot ID than the Fiero, so now you have to enlarge it with precision.

Cost - this only comes into play if you have the option to choose between two that otherwise fit the same. Using rotors from mass market applications will help keep costs down as well as ensure rotor availability for years to come.

Weight - again only comes into play if you have the option to choose between two. Lighter is better, unless it costs 3X as much.


Finding a large diameter rotor that fits, works with existing calipers, and doesn't require other cutting and grinding of other components for installation and proper clearance, is not easy. The list of larger rotors that fit well is very, very small. I have reviewed dimensions on well over 1000 applications and have a list of possible contenders at various size points that is over 140. However, the list of ones that fit all constrains is single digits... Options are very, very limited.
LornesGT MAR 11, 08:55 PM
Is that list only for 88’s?
fieroguru MAR 11, 09:44 PM

quote
Originally posted by LornesGT:

Is that list only for 88’s?



The primary focus for when I started making it was for the 88s, but I didn't restrict the fitment to just what fits the 88. If it was in the ballpark I added it to the list. The 84-87 rear rotor can't be as deep as the 88s, and the front can be deeper with the primary source of interference being the caliper to the shock.

pHoOl MAR 12, 08:40 PM
Fiero Guru,

If I have an 86GT, and was looking to start gathering parts, would you suggest getting 88 calipers or c4/c5?
fieroguru MAR 13, 12:38 AM

quote
Originally posted by pHoOl:

Fiero Guru,

If I have an 86GT, and was looking to start gathering parts, would you suggest getting 88 calipers or c4/c5?



Neither...

The 88 Fiero calipers will require you to install them upside down in order for the parking brake to work with the 84-87 cable setup.
C4/C5 calipers really mess with the bias and require several other parts and owner adjustment to get the bias back to anything close to stock... and you have other challenges with getting the rear parking brake setup to work.
pHoOl MAR 15, 05:49 PM
Oh ok I thought there were some options for upgrades on the 84-87s
michfiero1 MAY 12, 05:00 PM
pHoOl - you come up with a direction for your 84-87?
SCCA FIERO MAY 12, 06:36 PM
I was looking into a cheap upgrade for my 87 GT in addition to the Tuff Stuff booster for sticky tires, and for a better look. I'm pretty busy right now building a house and work, then going back to my second job after the house is done.

But I think I found a 13" rotor that seems like it would work with the stock calipers with adapters. I think I might get into it soon. We have a machine shop we have do work for us at one of my jobs that should give me a good deal on adapters.

I should probably just pass the info to Guru since I've been trying for a couple years to get on it...

[This message has been edited by SCCA FIERO (edited 05-12-2019).]