I'm just curious why my rotors are different here's pics of both sides of my front and rear
Front-front


Front-rear


Rear-front


Rear-rear
Why does this side have a cut-out area?

 

balancing (lightweighting)

and it has a slight geometry difference.

 

mazda balances every rotor, and since its a casting, the amount they take out varies

 

I figured the answer would be something along those lines, thanks for the replies

 

Balancing. There is also a letter stamped onto each rotor from A - D (or F?) denoting weight range. You don't want to be more then 2 letters off when mixing and matching rotors.

 

^I knew about letters stamped for weights and figured the diff cutout areas was for balancing and weight

 

Max is E

 

any documentation? i'm under the impression they are graded PER BATCH. makes sense too, an A weight rotor from 1986 is going to weigh the same as a rotor from 2010? even though the 2010 rotor has a little taken off the sides?

ive never seen any documentation from mazda either way though

 

A-E weights and you can interchange rotors of the same series and compression ratio assuming you're within 1 letter either direction. For example, you can use a B, C, or D weight rotor if you've got a C one already to work with.

And all the posters are correct; it's factory balancing. The factory motor is pretty well balanced to begin with.

B

 

Interesting, so your saying the rotors may be weighted and balanced for that year and there may or may not be variations by year.

So a C weight 89 turbo may or may not way the same as a C weight 94 rotor?

I think pineapple racing has a vid on rotor weights. Think I'll go watch it.

I had a D on the front a C on the rear. From what I've been told, you want the heavier of the rotors on the front.

 

but is A the lightest and E the heaviest? That is the question.

 

^ yes, lettered weights range from A-E

 

or is E the lightest and A the heaviest? That was the point of the question.

 

yes, like 1,2,3, it's A,B,C

 

So is it better to have a heavier rotor in front or is that just a guild line?

 

i'm saying its by batch, not really by year. it could be they cast a bunch of rotors, balance em, and weigh them and then either grade that batch A-E or put em all in an absolute A-E scale. it could be in a batch of 20 rotors, they are all C grade?

and then they pick a pair of rotors and match the counterweight/flywheel to em

outside of a 70's shop manual, ive never seen any actual FACTORY documentation.

rob golden is a nice guy, but he's not mazda, although he learned the letter thing from somewhere

in japan they don't seem to follow the rotor weight letter thing, they either keep the factory assembly, or replace both rotors with new from the same batch.

 

I'll chime in for the hell of it. The rotors from any year/series came from the same "mold". Due to variances of rotors through the casting process (it's not 100% consistent), each rotor had a slightly different weight, hence the letter code. Most (as far as I know for S4/s5) were code C; the middle. They are probably only off by an oz, if that, per weight code. It's not saying one is significantly heavier than the other.

I'm wondering if anyone can find a code A and E and weigh them? See what it really came down to.

 

like Beefhole said, most of the Rotors are "C"

Even when u buy a pair of brand new rotors from Mazda, 90% of the time you will get a "C" rotor.

Its all in Rotary Engine early documents.

 

There is a video of their rotor casting process somewhere on the interwebz, basically they made 3 (i think) rotors per mold. And they made them vertically, so gravity does its thing and the weights were a bit off. As beefhole mentioned, the codes don't mean they are multiple lbs off.

Nowadays I bet they have better casting control and so they target weight Cs as they work with any rotor.

Correct, S4 rotors are heavier then S5 rotors but have the same A-E weight classification...so you do the math.