Brake upgrades (Page 1/3)
Daryl M FEB 18, 05:22 PM
When you all consider brake upgrades, how often is unsprung weight considered? It would seem that going from small, relatively light disks to 12 or 13 inch vented rotors would add a bunch of weight.
DimeMachine FEB 18, 06:09 PM
Unsprung goes up further if you go from the stock aluminum calipers to steel..
Daryl M FEB 18, 06:15 PM

quote
Originally posted by DimeMachine:

Unsprung goes up further if you go from the stock aluminum calipers to steel..



88s already have calipers that are half steel. Bigger diameter trims also weigh more than stock, not to mention bigger tires. All of that changes handling. Not sure how much though.
cvxjet FEB 18, 06:43 PM
I switched my 85 SE V6 to 88 brakes- In the rear I switched the subframe/suspension to 88 and the brakes came with that.....Up front I bought Sluppy123 adapters and ALUMINUM hubs, so although I had to go up to 12" Vette discs the weight overall stayed the same.

On the tire/wheel problem, I installed 16 x 7" wheels that only weigh 14 lbs each and General G-Max tires which are lighter than most other tires (By 2-4 lbs) in sizes 205/55 and 225/55 which were sizes very common on a number of cars back in the 80s and 90s so are available from a number of manufacturers.
thesameguy FEB 18, 07:12 PM
Roughly the same approach - added a little brake weight, took away a little wheel/tire weight.

If the choice comes down to reliable, repeatable stopping and a little extra weight, I'll take that deal every time. I found the stock brakes ... inadequate for how I like to use the car.
pmbrunelle FEB 18, 07:57 PM
If fade resistance is a metric you wish to improve with a brake modification, weight gain is intrinsic to the mod.

You need rotor mass to absorb heat, and you need rotor size to dissipate it.

My consideration for unsprung weight with regards to a brake modification is that yes, it will increase, do it anyway.
Frenchrafe FEB 19, 04:45 AM
My experience with this is that our cars are not highly lightened race cars!
We are not driving prototypes!

A little more unsprung weight is more than compensated by better heat dissipation and better brakes.
I race against Lotus and while I can never handle in the turns like they do, I can brake a little later and with my power I can accelerate out of the turns harder, so keeping up and even overtaking a better handling but lower powered Lotus.

As well, our brake upgrades use cost effective off the shelf parts. Try doing a big brake upgrade on something more exotic! Loads of money!

------------------
"Turbo Slug" - '87 Fiero GT. 3800 turbo. Sticky tyres. Driven hard!
https://www.youtube.com/cha...1wZvWQlkYxTjivW_0XNg

Blacktree FEB 19, 09:36 AM
As mentioned above, this is a case of "give and take". You want good brakes? That will usually involve more unsprung weight. You have to decide for yourself if being able to stop the car safely is worth the small impact on handling.

That said, you can do things to counteract some of the weight gained. Mentioned above was the lighter tire & wheel combo. That's especially effective, because it also reduces rotating mass. And I used Wilwood aluminum calipers (instead of iron) in my front brake upgrade, to minimize the added weight. Stiffer shocks will help to control the extra unsprung weight.
Will FEB 19, 11:41 AM
Two piece rotors with aluminum hats drop a little weight as well. They don't even have to be expensive... I'm looking at 12 3/16 x 1.25" units that are $85 each from Wilwood.
fieroguru FEB 19, 09:48 PM
It is all about balancing your goals with your pocket book and optimizing the benefits of your decisions.

Increasing rotor diameter improves the mechanical leverage the calipers have to stop the car. They also have more surface area for air to cool them to reduce brake fade.

Increasing rotor width helps with air flow and cooling (fade resistance), but normally adds even more weight than the same diameter rotor that is thinner.

With the 88s, the bang for the buck is larger rotor, but keeping the thickness close to the stock width. This keeps weight down, and also saves $$$ as the stock calipers can be retained.

When I developed my 13" brake kit, I was looking for the largest/lightest rotor with the proper offset and ended up with a rotor that is about 6.5 lbs heavier than stock per corner. The 13" rotor gives 33% more mechanical advantage with the stock 88 calipers, which is a very noticeable improvement.

The 12" C4 rotor is only about 3 lbs heavier than stock 88 and provides a 21% increase is mechanical advantage. This is a very good compromise of benefit vs. weight, but fitment and needed clearance work are the two main drawbacks and why after running it for 8 years I developed my own brake kit. Since this rotor is for a Vette, lighterweight 2 piece rotors are available and could keep the weight gain near zero, but it will cost about $1000 for the hats and rotors.

The rotor diameter change also impacts the wheels and tires you can run.
12" C4 rotor requires 16" wheels on an 88.
My 13" rotor kit requires a 17" wheel (but I have installed it in 16x7 35et wheels with some caliper and brake hose bolt clearance work)

Larger/wider wheels adds more weight, but you get stiffer sidewalls and wider tires which allows you to run softer/stickier compounds with good tire life - even with 200 or less treadwear.

Having ran a 205/245 stagger in a stock weight fiero with 3x the stock power and 33% more brake leverage, I found the front tires and rear tires lacking... 225/285 is what I wanted, but couldn't find both widths from the same mfg and model tire with 200 treadwear so I settled for 235/285.

The issue with wheel width is that it sometimes forces you to upsize the diameter as well.. to go much over 8.5" on an 88 requires an 18" rear wheel to clear the knuckle clamp flange on the strut. So I had to have an 18" rear to get to 9.5" width, but didn't want the extra weight of the 18" wheel up front, so I focused on a 17" wheel. Finding a 17/18 with 8"/9.5" widths in a 5x100 pattern is a challenge by itself, but keeping weight to a minimum and cost down... took quite a bit of research.

For comparison,
Stock 14" wheel with a 215/60/14 tire - it weights 32 lbs. Pretty light, but sloppy performance... light or not, I would never enjoy driving my car with this combo.
Stock 15" wheel with a 215/60/15 tire is ~ 40 lbs. This is really the benchmark of wheel/tire weight for performance.
16x7 35et Millie Miglia MII with 205/50/16 tire weights 41.2 lbs. Little heavier, but allows 12" brakes and stiffer side wall.
18x9.5 Enkei Kojin w/ 285/30/18 weighs 45.2. So about 5 lbs heavier but can fit 13"+ brakes and 285 wide tires.

So 33% better brakes and 285 sticky rear steamrollers for a 12 lb (less in front) weight penalty per wheel/tire... For a stock powered Fiero the car will accelerate slower, with 3x the stock power the added weight is is easily overcome.