It has come time to replace the stock brakes. I use the car for about half of the year May-Oct. and during this time I do about 15 slaloms, 2 lapping days and 3 time attack events, in addition to about 4000 miles of street driving.

I am looking for good pad/rotor combo for my driving style (I do not change pads for events). I am looking for opinions on BLANK rotors only (no drilled/slotted ones) and they have to fit stock calipers. Price is not a concern.

Thanks in advance.

 

I don't understand why you wouldn't want to upgrade to slotted rotors... They are much better than stock/blank rotors...

 

I like Centric Rotors (parent company of StopTech Brakes). Dave Zeckhausen (former FD owner) is the east coast distributor.
http://zeckhausen.com/Mazda/RX-7_Gen3.htm

 

+1

I would look into "rebuilding" the stock calipers and use with slotted rotors and good pads would be all you need

 

afraid Im going to have to go with the "angry mob" on this one and ask why wouldn't you want to upgrade to drilled or slotted rotors...especially if you're going to be doing events like that..

 

brembo cross drilled and slotted rotors are for sale on turboimport.com
front and rear with lines and pads for less than 500$

I know you said blanks, but why?

 

More pad to rotor surface contact area (I'm not increasing the rotor size so I can't compensate for lost area that way).
More metal to absorb the frictional heat so Less chance of cracking (and no focal defects that could propagate a crack).
Less wear on the pad.


Overall for my purposes I want a good blank rotor. Unless someone can convince me otherwise with something more than opinion.

 

I'm happy with blanks. Right now I'm using Napa blanks but any reputable vendor works. While a blank is not technically the highest performance option, it's very durable and one of the less important factors.

The autox and street requirements for brakes is similar, and you should not have any problem meeting both needs very well.

The track and street requirements are not an easy thing to balance. You'll have to choose between the cold stopping power of a street brake and deal with fade on the track, or get a higher temp brake that might not bite well cold and will eat your rotors when they're not hot.

Run a search in this forum and you'll find a lot of past discussions on dual purpose brake pads. Search for "street track pad" without quotes and you'll find great info.

There are also good threads in the Race Car Tech section:
https://www.rx7club.com/showthread.p...reet+track+pad
https://www.rx7club.com/showthread.p...reet+track+pad


I've had good success with Hawk HP+, but I have made them fade a little bit on the track. They dust a lot and the dust is pretty hard to clean. I've also used NTech street pads and NTech race pads. They are actually very versatile (the race pad is relatively streetable) but dusty and probably thinning out my rotors. I've also heard good things about Carbotech, etc.

Dave

 

i personally believe that a cool rotor will handle more abuse. the slotted/cross drilled rotors will not heat as much as the blanks

 

Many people in this board have been using the Cquence Rotors. Do a search on google for them.

 

Get Brembo blanks for Tire Rack if Napa ones are too plebeian. I really don't understand the slotted fetish, especially when you can usually get 2 sets of blanks for the price of slotted ones. Spend the money you save on better tires and smoke everyone with slotted rotors from 60-0.

HP+ (or similar) are probably your best option if you don't want to change pads for track days (don't you go under there to bleed them anyway?). I personally feel they bite too hard for effective use with street tires, but HPS's won't last on the track.

 

i've been on HP+'s since i built my car. 20k miles and 2 years later, they still have plenty of life left. I daily'd it for the first year, and have ran around 40 autocrosses, if not more. no experiance on track yet.
my only complaint is the dust. you have to clean the wheels often or they will get ruined. but i guess thats the price you pay for any good pad.

and drilled is a bunch of hype. stick with blanks (brand doesn't really matter. its the last part to fail in a properly working brake system), and GOOD fluid, like Motul 600.

 

Slotted Rotors with upgraded lines, good pads and brake fluid.

 

Fixed

Seriously, drilled and/or slotted rotors are a waste of money, they don't provide any real benefits if your system was working properly to start with.

Prove it (about the rotors running cooler), oh wait, you CAN'T, because it's not true! There won't be any extra airflow from slots and there shouldn't be any extra air flowing through the holes in a drilled rotor, and they've got less thermal capacity, so even if they cool slightly better, they'll reach a hotter temperature for any given amount of thermal energy you throw at them.


Something along the lines of HP+ might be sufficient for the track use, but there comes a time when two sets of pads are required because the car and driver gets too fast for anything streetable.

 

umm, it doesn't work that way.

while additional mass provides more thermal capacity it isn't a factor in propagating cracks. Stress risers (focal defects?) are where cracks start. In fact a hot material is less prone to crack propagation than a cold material. (hot and cold being relative terms and a function of the material involved)

Not following that one either.

Slotted rotors aren't slotted for more cooling, they're slotted to wipe the fire band off the rotor face. This isn't as big a problem as it once was as pad materials have evolved over the years.

Drilled rotors increase the surface area of the rotor for additional cooling but they also reduce the mass of the rotor which lowers thermal capacity so that one is a tradeoff. It also reduces rotational inertia if you are looking for that last .00001 sec/lap

Either method should not crack if the edges are chamfered and stress risers removed.

I'm not saying you should get drilled or slotted rotors, I'm just pointing out your reasons for not wanting them are not altogether factual.

 

You're totally wrong and a slave to advertising.

By chamfering the hole, you're not removing the stress riser (it'll help a tiny bit), the hole itself IS a stress riser.

It's also not the temperature itself that's the problem, it's the thermal shock from the RAPIDLY increasing and (less rapidly) decreasing temperatures causing the rotor to expand at different rates depending on the local temperature (the face heats up first and it cools from the center, plus the hub conducts heat away from the center).

Think about it, as the slots and/or holes are "cleaning" the pad, they're wearing away a bit of the surface of the pad, giving more wear, making the pads wear out faster.

Drilled rotors DON'T necessarily cool better than plain rotors, and if they do, it's not by much and will be at least partially offset by the reduced thermal capacity.

I've got an SAE paper on the subject, and they found mixed results, so they're not really any better necessarily, while they are more expensive and MUCH more prone to cracking with hard use. A lot of their issues that the cross drilling helped with were really due to overheating pads glazing the rotors, so unless you're trying to track stock pads, you'll probably find plain rotors to be better.


One last note, if you're concerned about cooling, why not just get some brake ducts, they'll cost you maybe a little more than the premium for drilled rotors, but your rotors will last longer from not having stress risers in them and they'll run a whole bunch cooler, allowing the use of more street friendly pads and will give everything longer life, which should also reduce pad wear. They'll pay for themselves in no time flat.

 

OK I don't want to get into a pissing contest here. Right up front know we are both mechanical engineers (if your profile is correct).

Not unless the diameter of the hole is so small that the stress concentration factor is high. That would be a pretty darned small hole radius. Most stress risers in drilled holes are tiny imperfections (notches) around the circumference of the hole. That's why chamfering the hole removes/reduces those stress risers. The drilled hole itself is NOT the stress riser.

Thermal shock is caused by nonuniform heating (or cooling) of a uniform material, or uniform heating (or cooling) of nonuniform materials. That's not the case here. At the rotational speed of a disc rotor the heating is uniform around the face of the rotor. At the performance level we're talking here most people would be running top hats so heat transfer through the hub is not a factor.

The function of the slots and/or holes is NOT "cleaning" the pad. Slots increase system efficiency and decrease operating temps AND pad wear. They do this in two ways: Slots are (supposed to be) designed to wipe the fireband (boundary layer) off the disc before it reaches the point of contact with the pad. A secondary benefit is to provide an exit path for the hot friction material worn off by the pads (aka brake dust) some place to go other than back into the space between the pad and rotor. This isn't dust built up on the pad that needs cleaning off, it's dust that is already worn off the pad (by the rotor face, not the slot) and removing it also removes the heat energy the dust contains.

Holes are supposed to do the same thing but they aren't as effective and, if not done correctly, make the disc/wheel/tire assembly difficult to balance.

Agree.

Agree. I think mny people fail to treat their brakes as a System. It's not just drilled/slotted/cryrogenic/younameit rotors, it's the rotor, caliper, pad, line pressure, F/R balance (bias), airflow, etc. You have to view the system as a whole, not a collection of independent parts.

Again, cooling is part of the whole braking system (I think we're in agreement here). Moreover, I think cooling ducts and drilled rotors are wasted on the street. People who want drilled rotors just so they can "look cool" aren't pushing their cars to the limits that would justify such mods.

FWIW I have the RB BBK with the "drilled slots" on my FD.

Carroll Smith has some excellent info in his books. Along with my ME background, his books were the 'bible' when I consider mods to my cars.

 

Any hole will be a source of localized increased stress. A bigger hole is better, but it also reduces the section further, which is worse. Maybe not a stress riser, depending on the exact definition being used, but it is a point of higher stress, a stress concentration. There's LOTS of people with first hand experience that'll confirm that drilled rotors crack and fail around the holes much sooner than a plain rotor would have failed.

I've seen testing that shows that the rotor most certainly doesn't heat uniformally, the outer edge will be the hottest because that's where the cooling air gets to last, when it's the hottest and it's the point furthest from the hub, so heat will not be conducted away nearly as fast. Yes running seperate hats might diminish this effect, but it doesn't eliminate it and it'll increase the disparity as the heat will be transfered away at the localised points where it's fastened together.

If that is not the case and a hole isn't a stress riser, then why do the holes crack much sooner than plain rotors when used hard?

That sounds like pad off gassing, which really isn't an issue any more with modern pads (or at lest VASTLY improved). In that SAE paper they showed the holes all plugged up with dust, I'd think that'd happen with slots too, as the dust can't pass through to the venting on the inside and if it can build up in the hole, then why not in the slot?

Yes ducts and drilling aren't needed on the street, (although I don't believe drilled rotors are "needed" anywhere, as I don't feel that any slight benefits are worth the well documented downfalls and the steep price premium). I do believe that the place for drilled rotors is ONLY on the street, as they're SO much more prone to cracking that unless you take good care of your brakes and inspect them regularly over the course of the day, it could end up in catastrophic failure at the track, not good.

I've just read "Engineer to Win" and I've read the others years ago, but those were written quite a while ago, and technoilogy has kept progressing since then. I use it only as a guideline and ignore certain parts due to them being out of date (stuff like specifics on tires, brake pads, etc).

I use plain rotors on my car, street or track and they stand up just fine and a full replacement set (all 4) costs me maybe $100-$150.




To sum up, yes there may be some slight advantages to slots and/or holes, but IMHO the drawbacks of premature failure (holes, slots to a small extent) and price (both) outweigh them. Other people will have different oppinions because they weight the advantages and drawbacks differently, or are naive, ignorant or what not.

 

Also, don't forget that the outer portion of the rotor is moving faster than the inner (v=r*theta dot). This means that more friction and hence heat is being generated on the outside edge.
+1
also +1

 

I had thought of that, but there's also more mass further out for a given width radially (since the circumferance gets bigger), so I didn't really want to go there, since I'm not sure which is the more powerful part of that equation. It may be that the extra mass, in theory, more than offsets the extra friction.

 

Good call, I'd forgot about that.

I'm gonna take an educated guess and say that it largely evens out, else (at least racing) calipers would probably be designed with some sort of variable pressure across the face.

 

Ok sip,

Without all the engineering school talk, the rotors you can get from NAPA or any other source for $40-50 USD per rotor are just fine. IMO, they are better in the sense that you can purchase an extra set to take to the track with you for "just in case". If you are going to use the stock calipers; I would recommend you buy a used set of fronts, rebuild them and bring them with you to the track for "just in case" as well. You can usually buy a decent set for less than $150 (probably much less) and the rebuild kits are about $30 USD.

As for the pads, there really isn't a decent track and street pad. Mainly they are two different types of driving so they require different capabilities. You can use a street pad on the track *IF* you are able to drive within the means of the pad. i.e. if the pad starts fading you are able to notice and back down your efforts. Most people aren't able or willing to back down.

For Autocross, you want something that doesn't require a lot of heat to bite. It needs to bit cold. For the track, you want something that can take the heat. Those two combinations don't mix. You get either one or the other. Now it does depend on the track, your tires, etc.. You can get away with a less track duty pad on a track which is easy on the brakes and you are using a street tire. However, when you get to a grippy tire, you'll overrun the brakes very quickly.

You don't necessarily have to change out all the brakes pads. Running a decent upgraded pad on the rear and then putting a track pad up front is plenty for most of us normal track folk. A good combination would be to get Carbotech Bobcats for Autox and the street, then switch to their XP10 or X12 for in the front for the track. The good thing is that you'll stick with the same pad manufacture which makes dealing with the pad transfer layer on the rotor a non-issue. I'm currently using RX7.com's Bonez pads for the street and N-Tech Lapping Day pads for the front on track days. Great combination but I'm not sure how much longer Nick will be making pads for the RX7's.

Add in the SS brake lines and some decent brake fluid (I would recommend Super Blue/Gold ATE) and you'll be all set for any occasion.

 

Well, I do have some materials science background so the engineering talk doesn't bother me too much. That was the kind of info I was looking for. Some brand name and specific model recommendations for a pad that stood out as a better all around pad.

 

There have been a lot of tests/comments on pads in the FD new brake options thread - it's hella long but worth the read:

https://www.rx7club.com/suspension-wheels-tires-brakes-20/fd-new-brake-options-605463/

 

I liked Carbotech XP8 as a dual-purpose pad, if you're under about 300whp, and don't expect them to be very aggressive, but a good durable pad with reasonable dust. XP10 wore a little too crazy during street use, and the dust was ridiculous. I run PFC 01 now on the track, got lazy and have been running them on the street with no problems for months. They don't wear bad at all, even at cold temps.

I also like NTech competition pads, which I run for rear pads. Only problem is they don't have holes in the backing plates for spreader springs, so they drag and make a lot of noise and wear fast. I plan to drill the next set myself.