what's better about higher priced rotors?

Tolerances, material, and where they are made.

My guess is the $19 rotors are made-in-china with questionable grade steel and wider tolerances.

Actually, that is somewhere between completely wrong and partially wrong. None of the discs are likely to be made of steel. If they were they would cost more and steel performs poorly at the temperatures that brake disc normally need to perform compared to iron. The difference between the $19 dollar discs and $48 may be similar to the difference between low sodium and regular foods at the super market where they charge double for not adding salt. They charge what they calculate people are willing to pay. The $48 ones are billed as "noise dampening iron" which pretty much guarantees that they are less wear resistant than the $19 dollar ones. I would expect that if asked the wholesale supplier would reveal that they sell mostly the $19 ones and mostly what you are getting with the more expensive brands is the extra cost of sitting on the shelf longer.

-jim

I always go for the cheapest ones I can get and never have issues with them like the warping the expensive ones seem to have happen all the time. I only need to replace them if I messed up and missed changing a brake pad soon enough or I break something off road.

I have been going this route since the 70's....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 (More Off Road album links at bottom of the view page)

Yes, I brain farted and typed the wrong word. However the meaning is obvious, the material from china is of questionable quality. Of course this being rec.autos.tech.....

Anyway, a questionable grade of grey cast iron. (not just iron, as iron is an element) There are different grades and it does matter. Processing and percentage of various other elements in addition to iron change hardness and other properties.

Cost is proportional to labor, the process controls on the material, the casting process, and the machining process.

With a supplier in china the major challenges are keeping processing constant and avoiding unauthorized material substitutions and contamination. Sure, it's less important if the Si content of the brake rotor material is off vs. having something in the pet food that kills your dog, but from a manufacturing POV it's the same sort of issue.

BTW, this being rec.autos.tech, there are grades of steel that can hold up to the temperature (as we are talking what, less than 600 degrees C?), but there are other issues like cost.

It depends on the rotor. Some of the cheap ones are just fine. Others are made from questionable iron mixes and will have hard and soft spots across the surface depending on the mix. Hard to see just looking at them.

The better ones are usually from places that actually test the iron and alloy it to the correct specs and then make the parts. They are usually much more uniform in quality between batches of parts as a result.

The unidirectional types are cast from good iron AND the vent ribs are cast in a curved pattern that makes them more effective when rotated the correct direction. The lower end ones have straight ribs which will work but just like most parts they can be improved.

For my cars, rotors not made in China are at least four times as expensive as those that are. Harder than hell to find, too. Only manufacturers I can identify are Bendix and BG.

Joel Spolsky wrote a nice little article about this. It's not about brake rotors but about software pricing. But the principles apply anyway:

In a nutshell, you make more money if you offer the same product at different prices. If you only offer it at one price, you miss out on making a greater profit from those who are willing to pay more, and don't sell at all to those who are only willing to pay less.

If all you have to offer are $48 rotors, the guy who won't pay a cent over $19 will go somewhere else, and the guy who would otherwise shell out more than a hundred bucks will just give you $48 (or maybe even go somewhere else also, if he's convinced he must pay more than 100 bucks for rotors!)

The market, quite simply, not only demands a product, but demands a pricing variety in that product. To meet that demand, you have to create pricing variety even where there isn't any underlying comparable variety in value.

I think the issue here isn't the fact it's the same product at multiple prices, but there are multiple products and multiple prices for the same application.

We don't know if the $19 rotors are half cast iron, half ground up rocks... or are the $99 rotors in a different box. The $110 rotors are the best quality, or maybe $50 rotors with a crazy markup.

It's also hard to evaluate a brake rotor in a parts store.

Frankly, for my cars, I'll usually buy either the cheap parts and acknowledge the fact that it won't last as long, or if I need heavy duty or good quality parts I stick with certain brand names and don't worry about the price.

Examples -> tires.... either the cheapest possible, or BFG. balljoints - the cheap ones last about 4-5 years in a street car, or 4-5 races in my race car. I buy cheap ones for the street, nothing but Moog for the race car.

Ray

It is impossible to evaluate a rotor in a parts store. We would HOPE (but I wouldnt bet on it) that there are agencies which quality approve this sort of part to keep dangerous materials or processes from coming into our market.

I learned my lesson years ago on cheap tires. There might be cheap tires that are good, but the tires I am pretty sure are good all cost money. And I am willing to pay for quality in this arena.

Gray iron is generally not the best iron for rotors. It does have good properties for noise dampening. The $48 rotors are probably gray iron and the $19 are probably not. Unless you are mainly concerned with keeping your brakes from squeaking the cheaper ones are probably a better deal.

-jim

'grey cast iron' is a very generic description, it covers a wide range of grades. Certainly some are quite poor for a brake rotor while others can be quite good.

While there are likely brake rotors from other generic classes of 'cast iron', odds are most are probably one grade or another of 'grey cast iron'.

Quality comes from attention to detail. The odds of finding that in a bargin basement part from china, especially with a casting and machining operation are probably quite slim.

googling around it appears that noise dampening iron is a reference to a higher carbon content. How that relates to wear is hard to say without knowing the details of the processing.

Gray iron is not the best choice for rotors it is used for drum brakes. Back when asbestos was used in brakes it was almost never used for rotors. But the removal of asbestos often has resulted in brake noise (squeaks) and gray iron rotors are a remedy for that.

-Jim

It's obvious you're not getting it or just not reading it. terms like grey cast iron, white cast iron, etc are extremely generic terms. There are various grades of cast iron within each grouping. Not to mention special names used by various manufacturers. There is a wide degree of materials that are covered by each term.

The Bosch automotive handbook reads: "Gray cast iron brake disks with bilaterally acting calipers have proven to be the most satisfactory layout."

Now, since you disagree, what is 'better'?

well, i've certainly gotten an education from all of you that provided answers. some additional research i've done has provided me with the decision to go with a slightly higher priced rotor than the $20 unit.

not the fact that higher priced means anything. be that as it may, i went with a Wagner ($45) for this go-round. the car (z-28) has 150k, so i figure it was time to retire the original rotors.

one of my thoughts concerning this is that, with the option of purchasing a $20 rotor, i'd change the rotors out everytime i change pads - i would never expect to get 80/100/150 k miles out of a set of $20 rotors.

the Z is my daily driver and i dont "dog" the car. i drive as sane as the next "ordinary" driver. dont get me rwong, i do occasionally get her up to speed out on the back roads.

obviously, i want to match the proper components for this style of car, with "good value". i dont want to over-extend myself financially because i do not weekend-race this car and i dont push it to its absolute limit.

as a point of contrast, i have a 90 Trooper with which i did a complete brake overhaul. i replaced everything: rotors, pads, calipers, master cylinder ... i used the $20 rotors on this vehicle because i *rarely* use it. mostly only to pick up stuff at the hardware store. (i cant remember the last time i started it up:) so with this vehicle, i figured the $20 rotors will be sufficient.

but i have a concern on the Z28 because of its daily use. (the 64 Buick LeSabre convertible will not get the $20 drums :)

thanks for all the input - i appreciate it!

regards, michael

It'd be nice if rotors had stamped ratings much like tires. As it now stands, we pretty much have to trial and error to determine the good ones; means we have to guinea-pig our customers! I've found tire ratings are at least relative even tho' actual mileages might be exaggerated. In early '90's, cheap brake and tire stores sprung up around here. Used cars we sent to auctions would bring just as much with new cheap tires as with new better ones--unless maybe they were Michelins. Then, "Will they hold up for our nicer, retail cars"? Put a set on my pickup, one on wife's car. Partner did same with his car and his daughter's car. His daughter, sitting at a red light, tires with no more than a coupla thousand miles, & one blew out--on sidewall iirc(I always kinda thought she had hit sidewall on something Regardless, she immediately got new, better tires). His car needed new tires at approx. 8-10 k. He drove like a working fireman--accelerated and stopped fast. His car would wear flat spots "overnite". My vehicles would need new tires, tho' worn more evenly, after about 12-15K miles. Altho' tires were pretty they had ratings of like B,C,C. Size ~

205-75-15 cost about $135, installed and balanced. Decent tires that would run about 35-40K for me cost about $180, installed & balanced, and had ratings ~A,B, B. That ended using el cheapos on cars we retailed: too much danger, not to mention poor mileage. Again, rotors desperately need reliable ratings. s

Yes you are right most people can't tell the difference between gray iron and ductile iron. White iron is not very machinable so it's unlikely you will ever see any of that in a brake rotor.

Given that many ( most? ) cars don't have that particular configuration we can assume that opinion isn't the definitive word on the subject.

Better in what way? Where I live corrosion from road salt is the main thing that shortens the life of brake rotors. If you want corrosion resistance then stainless steel is better. But it won't be better in price or in the ability to bring the vehicle to a stop. At any rate that wasn't the question. The biggest advantage of gray iron is its ability to dampen noise and vibration. So when you see one set of rotors advertised as being made of "noise dampening iron" you can be certain that one is gray iron. That property alone would seem to make it the perfect material for brakes. The problem is that it is not as tough or strong as steel or ductile iron. So there is a greater danger of catastrophic failure. I suspect that property is what is given the most consideration by manufacturers.

-jim

But it's not just those three, there are countless grades within each generic catagory. Given general practices in China, I would suspect that process controls and material substitutions would result in very poor parts. One could get a 'grey cast iron' rotor made of a low grade that is suspect of even meeting those requirements that performs poorly but that doesn't mean all grey cast iron is bad for brake rotors.

You were saying what was better, I just brought up another source that has a differing opinion.

You're the one making the claim... up to you.

There are various grades of each and there is considerable overlap in the ranges. The specific grade and manufacturing processes is what it all comes down to.

Noise dampening iron seems to refer to carbon content. For instance, Brembo uses a high carbon content for noise reduction.

Normally, there is no reason to change rotors with each pad change. The last rotors I changed on one of my cars were on an 89 Regal and the change happened ca 1996. These rotors were eaten up by road salt.

If the rotors are true, and you install them true, that is a good start. But you cant just have them machined, or take new ones out of a box, and install them, and be sure they will be "true".

Read the Babcox site if you are not sure what I mean.

NEVER, never, never let anyone use an impact wrench on your lugnuts. Even if they have torque stix and promise you it will be okay. I was burned on this twice at Discount Tire, and now I always torque my own lugnuts with my own torque wrench. No matter what anyone says, the use of an impact wrench CAN lead to distortion of the rotor.

The grades within the categories are based on the mechanical properties of the iron. It's relatively easy to determine the grades if you are willing to do destructive testing. After you have determined the grade of a batch of castings there are non-destructive tests that can be used to determine if the quality is maintained through out. The metal casting industry didn't just crawl out from under a cabbage leaf yesterday they have had this sort of stuff worked out for along time.

I don't know why process control would be any different for a Chinese foundry than an American. If any thing they may be more quality conscious. Considering the cost of shipping something so heavy from China if they get a batch of castings rejected they are going to be out a lot more than when it happens to an American foundry.

I merely said that the rotors you see in parts stores are most often not gray iron. I made the mistake of expanding on that and offering a possible reason. From that you conclude I have something against gray iron?

I didn't claim anything. I simply observed what it is the market place finds better and why.

Well, that may be how you and the marketing people at Brembo understand it. But if they are pushing noise reduction you can be sure it is gray iron. And if a company is not advertising a particular rotor is good for noise reduction then it probably isn't (unless their marketing people are just dimwits).

-jim