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Login to post Forums » Grassroots Motorsports » Steel brake rotors?

March 25, 2010 8:02 p.m. ditchdigger Reader

I ordered the only 10" diameter solid rotors I could find from speedway motors.

http://www.speedwaymotors.com/US-Brake-Specialty-Drilled-and-Slotted-Rotors,40518....

When they got here I opened the box to find the word "DRAG" on the label so I looked into them some more. They are US Brakes version of this wilwood rotor

http://www.jegs.com/i/Wilwood/950/160-2182/10002/-1

They are steel rotors. Dimensionally they are perfect for what I need. What are the drawbacks of steel VS cast iron? Would they hold up to a 1400LB car on the street and an autocross event per month? Are they just bad news that I should return and forget about?

The only 2 piece rotors I can find under 11" are giant 1.25" thick vented units and that is overkill, plus my reason for going with 2 piece is to reduce weight.
March 25, 2010 8:30 p.m. tuna55 HalfDork

I haven't heard of a disadvantage, but I am not a super expert. As far as I know, steel is "better" than iron in almost every aspect. I've never worked with steel brake rotors, though, only varying degrees of cast iron.
March 25, 2010 8:46 p.m. 96DXCivic Dork

Cast iron esp. high carbon has much better in terms of thermal properties which is the reason pretty much every car uses cast iron. In Engineering to Win, Carroll Smith says that in the GT40 program they tryed about every material know to man at that point and ended up using cast iron. I know you can get custom cast iron rotors from HRP World for around $100 a pop.
March 25, 2010 8:52 p.m. Marty! HalfDork

While also not being a brake expert myself, my take is that these rotors would be to thin for street use. 1400 lbs isn't a whole lotta weight, but braking obviously isn't the place to cut corners. I understand your need to want to save weight but sometimes you need that extra mass to dissipate the heat, without it you'll just end up with warped rotors and brake fade.
March 25, 2010 9:35 p.m. jimbbski New Reader

There are many cars on the road with solid front brake rotors. Most on them are older subcompact cars but they are lighter then today's cars so solid rotors worked fine.
March 25, 2010 9:38 p.m. BobOfTheFuture Reader

big rotor+lathe=win?
March 25, 2010 9:40 p.m. 96DXCivic Dork

In reply to jimbbski:

However steel is inferior to cast iron. There is no reason solid rotors won't work for that purpose on a car that light. If it was my car after the research I have done on brakes for the Formula team, I would want cast iron.
March 26, 2010 3:16 a.m. Appleseed Dork

If I recall correct, Speedway's "Drag" rotors are just that, for stopping you once at the the end of a drag strip. I know they're not intended for the heat cycles of other kinds of things, like road racing, track days, daily driving, etc...But you might get away with it on a 1,400 lb. vehicle
March 26, 2010 7:21 a.m. Giant Purple Snorklewacker SuperDork

I wish there was some way to determine what size brakes were correct for an application. Perhaps some formula and a treatment of how to use them. Perhaps an article in a magazine written by someone from this very forum who was also a brake engineer. Too bad nothing like that exists for us to refer to whenever a special application question comes up.
March 26, 2010 9:29 a.m. Knurled New Reader

Marty! wrote:

While also not being a brake expert myself, my take is that these rotors would be to thin for street use. 1400 lbs isn't a whole lotta weight, but braking obviously isn't the place to cut corners. I understand your need to want to save weight but sometimes you need that extra mass to dissipate the heat, without it you'll just end up with warped rotors and brake fade.

One of my customers sunny day daily drives a 650hp 1st-gen Camaro with what look like motorcycle rotors.

No warping, fade, or other issues at all.

The rotor and caliper and hub together weigh less than one OEM single-piston caliper.
March 26, 2010 10:52 a.m. Keith SuperDork

About the steel - one of the Miata aftermarket shop sells (or used to sell) a set of big brakes that used a steel rear rotor. We tried a set, and they grooved mightily in short order. Very rapid wear. It wouldn't be my first choice of material.

I have standard 1.6 Miata brakes on my Locost. The front rotors are vented, but small. Never been able to overheat them and the car stops very well. The last versions of the classic Mini weighed around 1350-1400 lbs and had solid 8.4" front rotors.
March 26, 2010 11:03 a.m. slantvaliant HalfDork

Detroit Wonder Metal still has its place.
March 26, 2010 11:36 a.m. ditchdigger Reader

Just called speedway and returned them. I also pointed out the missing details on the description. Super great customer service by the way. Really impressed! They emailed me a prepaid return shipping label so I don't have to eat that cost.

My brakes actually perform quite well. The GSXR calipers on the Fiat 124 rotors stop the car like crazy but being little 8.4" rotors they do look pretty goofy behind my panasports. I figured if I could drop 4lbs of unsprung rotating mass, increase the leverage with a larger rotor and at the same time make it look badass it was all win on my end. Nothing is ever that easy though.

Now to find a car with cheap 10 to 10.5" solid rotors that can be machined to accept an aluminum hat!
March 26, 2010 11:45 a.m. ZOO Dork

A1 Rabbits (1975 to 1984) had really small, non-vented front rotors. I can't remember the size, however.
March 26, 2010 11:57 a.m. jimbbski New Reader

96DXCivic wrote:

In reply to jimbbski:

However steel is inferior to cast iron. There is no reason solid rotors won't work for that purpose on a car that light. If it was my car after the research I have done on brakes for the Formula team, I would want cast iron.

I wasn't commenting on the steel vrs iron issue but only on the fact of solid rotors vrs vented. Many cars came with solid "cast iron" rotors.
March 26, 2010 12:04 p.m. z31maniac Dork

ditchdigger wrote: Now to find a car with cheap 10 to 10.5" solid rotors that can be machined to accept an aluminum hat!

I'd be weary of doing that after seeing some cracked hats in the E30 M3 camp........
March 26, 2010 1:35 p.m. Keith SuperDork

10" iron solid rotors: rear 1994 Miata. You can get 'em for about $10 at NAPA.

I've been happy with Speedway as well. Plus I love their catalog, especially all the cheater parts
March 26, 2010 1:58 p.m. YaNi Reader

Cast iron is used in brake rotors because it has better thermal stability (aka lower thermal expansion) than steel, SS, Al, etc.

As far as vented vs solid - the vented rotor will obviously dissipate heat more quickly. You can probably just change the pad compound for track use, since they will be operating at a higher mean temperature. There's no reason they won't work, you just need to size them correctly for the application so you don't burn up pads.
March 26, 2010 7:43 p.m. 44Dwarf HalfDork

http://peterdmotorsports.com/parts-db/catalog/index.php?cPath=26_44
March 26, 2010 9:43 p.m. 96DXCivic Dork

z31maniac wrote:

ditchdigger wrote: Now to find a car with cheap 10 to 10.5" solid rotors that can be machined to accept an aluminum hat!

I'd be weary of doing that after seeing some cracked hats in the E30 M3 camp........

YOU NEED TO USE TO 2024 or 7075 for the rotor hat.
March 27, 2010 8:14 a.m. Knurled New Reader

Something reminded me of something else....

VW used solid 9.4" rotors on the front of some MkIII Golfs and Jettas. All 9.4" brake calipers are the same, they just have thinner pads for vented brakes.

Anyway.

Last week, a Jetta TDI came in for the annual intake manifold rodding-out, oh and could we look at the brakes? They feel weird.

The Jetta had the vented 10.1" front brakes. We recommended brakes the last time it was in. Well, somebody else did them. New pads and new 9.4" solid rotors! The pads were only 2/3rds contacting the rotor, and in the space of a year, they had worn to the point where the two pads were close to touching at the top!

I wouldn't have believed it if I hadn't seen it for myself.

BTW - That IS information to file away - you can put an 02A/02J transmission in a MkII/MkIII without going to Plus suspension by using '99 TDI axles.

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