Motorcycles typically do use SS. Car’s don’t because of cost but also performance. Stainless steel doesn’t transmit heat as well as grey cast iron to the air flowing over it. SS can be used as an insulator on brake pads.
Why not aluminum? The low transition point temperature, heat capacity and the lack of surface hardness are the biggest problems. The surface can be fixed with high amounts of silicon alloy and heat treat but the temperature is a problem. Brake rotors need to store heat as well as dissipate it and aluminum just can’t store as much as iron.
I can see that, perhaps, for replacement rotors, but surely a brake system could be designed from scratch to use SS rotors. Heat flow an be handled by many methods such as air passages, surface treating, etc. And there are many grades of SS…
Heat flow is already handled by air passages - that’s what the vents in the rim are for, and it’s what slots are for if so-equipped. Adding more air passages and slots wouldn’t really be possible (take a look edge-on at a vented rotor - it’s mostly air passage now).
It’s common around here to see the saying that anything is possible with a smart enough engineer and a big enough bank account, and that’s generally true, but re-inventing the wheel just because you can doesn’t make much economic sense.
When you buy rotors at an auto parts store, the clerk usually gives you 3 options - cheap, decent, and good. You spend more money to get a better product.
The average person is not going to go in there and spend $150 for an option that isn’t any better and is probably worse than the $50 option.
Consider how most cars are driven , virtually every day. That cleans off the surface of the rotor and all is well. So what is the incentive to make rotors out of SS? Really none.
Corvettes have carbon rotors that solves the problem but at a very high cost. Same for special Mustang models, Porsches ect. These are limited use cars, for the most part plus the carbon rotors are cool car jewelry!
I’ve lived with the problem on a few cars living in the rust belt that don’t drive very far. Rotors rust out before the pads wear out. Usually takes a few years. Not really a big issue.
I disagree with your statement that rust doesn’t increase wear. Yes, the rust is removed next time you drive, but that is removing the metal that formed the rust, and quickly. And in the salt belt and with some driving patterns, I suspect that most of the metal is removed via rust. See my previous post about holes in the rotor.
I don’t see a reason why SS rotor would be much more expensive. The cost difference in the metal itself has to be less than a dollar.
Reminds me of decades ago when mufflers where not SS and lasted 20-40k miles. Yeah, you could say, not a problem, they last a few years and then you replace them.
Botom line, for a few dollars more, you can have rotors that last much longer.
Stainless steel is iron+carbon+chromium (minimum 10.5%)+molybdenum.
Just the ingredients list shows you that SS is going to be more expensive than cast iron.
So, in addition to being more expensive, heat management is crappy which means braking performance suffers.
Bottom line, for a few dollars more you can have an inferior product that makes you more dangerous on the road.
I could maybe see making rotors for show/museum cars out of stainless so that you didn’t have to worry about surface rust on a vehicle that is literally never driven, although you’d do just as well making them out of aluminum, or coating the normal cast iron rotor in a corrosion inhibitor that won’t wear off because you never drive it.
I found a great write-up on cast iron vs cast steels, including stainless.
Clearly spells out the difficulty in casting steel (stainless or other) that would be required for vented rotors (motorcycles don’t use vented rotors) and then the difficulty in machining the raw casting. Iron is cheaper to cast into complicated shapes to cool the rotor and cheaper to machine into a finished product.
The rotor surface rusts overnight on my Corolla when it’s raining. I notice it the first stop of the next day, makes a sort of scraping sound. The first stop removes the thin rust coating apparently. The body of the caliper doesn’t seem to rust much for some reason. Maybe it is coated with a zinc treatment or something. Galvanized chain link fences don’t rust much, presumably b/c of a zinc treatment.
I suspect the zinc treatment is a zinc phosphate conversion coating that will prevent rusting before installation and may continue to work on the hat. It will be worn off by the pads, though.
I took a look at some calipers earlier today. Ones that I could see on cars with open style wheels as I strolled through some parking lots. None of the caliper bodies appeared rusted. The rotors, yeah, parts of them were rusted on all the cars. But none of the calipers.
Back when many Asian cars were manufactured in Japan and shipped to the U.S. the rotors were covered with a clear plastic hat to prevent rust.
Part of the pre-delivery inspection was removal of that hat. Some guys would ignore or forget about the hats and the cars were sold to the unsuspecting consumer.
Several days later they would be back with a complaint of smelly brakes due to the plastic hats melting while in use.
The 4 rotors and brake pad sets I just put on the Grand Prix yesterday, were purchased online and picked up at my “nearby” Advance Auto Parts.
The rotors are Car Quest Wearever Platinum and have painted/coated hats, edges, and cooling vents.
The pad sets are Car Quest Wearever Platinum Professional Ceramic.
With discount codes applied, tax, out-the-door, the whole ball off wax was 200 bucks.
Now I remember why they wanted to charge me another 200 bucks to install them at my local shop. It was tough on this old body, working that close to the ground! CSA
That post was written last Sunday. Here’s an update today, on the following Wednesday…
I just spent all day Monday and most of the day Tuesday (yesterday) on a 1,501 Road Test on I-75 South. The car ran like a champ, didn’t consume any fluids, and the brakes are EXCELLENT!
I don’t think I’ve ever had brakes that work that well. I’d buy those again in a second.
About the aging “backyard mechanic body,” I had to sneeze a couple times on the way down to Bradenton and it nearly killed me. My entire rib cage was sore from lifting tire/wheel assemblies, jacks etcetera, but mainly from pulling on ratchet handles and breaker bars!
What are they thinking when they “Lock-Tite” those caliper carrier bolts?! (Rhetorical question I guess. They, GM, must be thinking “lawsuit avoidance.”) I’d break the bolts loose by pulling on the breaker bar with all the strength I could put into an arm or two, but they didn’t exactly loosen. It still required nearly they same amount of pull to unscrew the bolts all the way out. It was like every bolt was cross-threaded (but none were, just thread locker).
I had the compulsory little cuts on both hands and Monday morning just before I departed at 4:50 a.m. I pulled a wire brush bristle out of one finger. No wonder it kept hurting. I did do an excellent job of cleaning up the hub surface where contact is made with the new rotors and the back sides of the wheels where they contact the other side of the new rotors. That’s where rotary and hand wire brushes were used.
I also used those “tubular” 3M Scotch-Brite “brushes” chucked into a drill. I can’t remember what they’re called, but they are excellent for cleaning up that hard to get area around the studs protruding from the hubs, the ones the lug nuts go on. Anybody else use those?
Anyhow, I drove the first day just over 1000 miles and got just past Atlanta (later than evening rush-hour, too) and stopped in a motel for a few hours. I wanted to get through it because traffic is crazy there ordinarily, and then there were 3 former U.S. Presidents in town for former GA Governor Zell Miller’s funeral and the news was about how traffic would be screwed up.
Yesterday was a cake walk with only 500 miles left. After leaving the frozen north it was a welcome sight and feeling taking I-275 through Tampa & St. Pete and getting on the Sunshine Skyway Bridge (in the sunshine!) and then seeing all the colorful windsurfers cutting back and forth in the water and all the pier fisherman (politically incorrect… I mean fisherpersons), as I was arriving in Bradenton.
I was up early this morning, at first light, and went out for a bike ride in Nike shorts and dri-fit tee-shirt! It was well worth the car maintenance and the drive! CSA
