I have commonly read that new pads should be broken in on seasoned rotors, and that new rotors should be broken in with used/bedded pads (ie, don't run brand new pads on brand new rotors). However, I'm not sure if freshly turned rotors count as new. I'll be bedding in a set of new pads next weekend and I'm trying to figure out if I need to dig up some old rotors for the job. I have already resurfaced the sets that I have. Thanks!

 

Well-the debate can continue I think. However-I went to Pocono last August with brand new rotors and pads and ran just fine. Cost me a session to bed them in but there were no adverse reactions. Our Prelude street rotors were turned once and the pads have been changed 2 times (my choice) without any problems. If you are changing compounds then you might want to take a different approach, but I doubt harm will come if you run either new or machined.

 

I've gone around and around on this point and this hasn't ever made much sense to me. I've seen plenty of out-of-the-box racing cars - real ones - start life with new pads and new rotors. Not to mention 9 bazillion street cars in the world.

What causal mechanism is it that we are supposed to be avoiding with this advice? Particularly since I have also been told that some compounds will react badly when used on rotors that have been bedded in with different compound pads...

Kirk

(who has new pads and rotors, front and rear, on the race car 20 feet from him)

 

I prescribed to this for years on my 944 and started the same way w/ the CRX. Then by circumstance (e.g. cracked rotor and only new pads around) it wasn't always possible and lo and behold, nothing bad ever happened (yet ), no delams, no bolts of lightening. If there is some truth to it (which is quite possible) then I would suspect its on the small scale of wear. I have lost count how many times I have started a race on out of the box new pads and they are fine too (as in no bedding). Just have to remember that at some point in the first few big brake zones they could or should fade but most times either a) its not that significant or b) I can get them stinky in the pace laps. Then again, this could be pad specific - I think some manufacturers feel the pads need the bedding/cooldown to perform well.

 

I've started out with new rotors and new pad and never had a problem. Now, I do spend most of my warmup lap riding and them stomping on the brakes. Usually by the green flag, the brakes are just right.

 

Well, I have always taken it on faith and have tried to follow that advice. I guess I don't have any real evidence either way. The only time I know for sure that I had a problem was when I changed pad compound on the same rotor and I transferred a lot of material on the first day.

I guess I'll bed the new pads in with the turned rotors and you'll here from me if all hell breaks/brakes loose. Thanks for the help.

 

" I'm not sure if freshly turned rotors count as new"

Yes they would count as new, they have no wear marks/ grooves.
the only thing is they are going to be a bit thinner.

 

Accepted - but what difference does that make where new pads are concerned?

K

 

The theory I had heard regarding this is that the grooves of a used rotor/pad allow for more contact area between pad and rotor (once the pads bed in so they aren't just contacting at high points).. thus theoretically better performance. That argument seemed a bit weak to me, since soon enough the new pads and rotors will work into each other according to their own hard and soft bits..

Then again, I'm pretty ignorant, so maybe it's really based on something else...

edit: clarification

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knestis &raquo;</TD></TR><TR><TD CLASS="quote">I've gone around and around on this point and this hasn't ever made much sense to me.</TD></TR></TABLE>

Yup. Same here. I allways use new rotors with new pads and never had any problems. On top of that, i change rotors at the same time as pads. Rotors being cheaper than most race or dual duty pads, why take the chance?

 

Read Carroll Smith's (R.I.P.) "Tune to Win". It is geared more towards open-wheel, formula racing, but has some really good points on general, all around race car set-up. And yes, it goes into great detail explaining that bedding pads and seasoning rotors is more of a chemical process (pads), and metallic crystalline matrix restructuring process (rotors), than just a wear/surface contact area process (which definitely is important, though, also).

In fact, reading all of his books, even for an amature racer, can be quite useful in understanding just what's going on with the car, as well as the driver.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by FormulaIntegra &raquo;</TD></TR><TR><TD CLASS="quote"> and metallic crystalline matrix restructuring process (rotors), than just a wear/surface contact area process (which definitely is important, though, also).</TD></TR></TABLE>

This would indicate to me that resurfacing rotors does not make them "new" as far as compatability with new pads. This "metallic crystalline matrix restructuring process" has already taken place if the rotors have been well used and would not be effected by resurfacing.

 

Except that resurfacing rotors creates heat, which changes the internal properties of the material (like heat treating in a machine shop). This heat created in resurfacing may induce the correct amount of molecular restructuring we need in our rotors, but then again, it may not. I don't exactly know, since there are so many different types of heat treating. That would be a good question for your local machine shop. If the heat generated from turning rotors is, in fact, just what we need, perhaps instead of seasoning our brand new rotors, we should take them out of the box and have them resurfaced before installing them. It may actually prolong the life of the rotor. Then again, I'm theorizing based on what little I know of basic metallurgy (another good book by Carroll Smith: "Engineer to Win" A study of the metallurgy involved in race car design) which I learned from the aforementioned book.
Anyone out there with more knowledge or experience care to chime in?

 

you dont just heat up some metal at whatever temperature and call it "heat treated". heat treating metal needs to be done at specific temperatures and cooled a specific rate to get the proper annealing and carbon/oxygen ratio to obtain optimum hardness or whatever specific property youre desiring. i tihnk you need to read some of the more technical stuff Carroll writes about in the first few chapters.

sending brand news rotors to be heat treated or cryo'd for better performance is definately commonly done, but not what we're really talking about here.

 

I have read the whole book, and that's why I brought it up in the first place. I wasn't trying to teach the class, just briefly explain that there's more to bedding/seasoning than surface texture.