Rotors.... for 4.8is with hawk Pads??

[JCL]

Originally Posted by X5rolls

One thing I'm certain of at this point is I don't want to lose peformance. Not sure since I've not researched this at all but I'm under the impression that drilled rotors will increase the stopping performance under the most streneous circumstances.

I believe I read that there is a better release of gas or that it doesn't have a place to build up. Regardless of these claims, I can't imagine that normal or even very spirited street driving will benefit much from cross drilled or slotted. Going to the track I'm assuming one could benefit greatly with more agressive pads, higher performance fluid and stainless lines.

My goals are to not lose street performance and have a great look.

Thanks for the advice, I'll be digging into the research a bit more as time progresses. I enjoy reading technical information (not on everything) to learn the fundamentals of cars/vehicles.

Rotors are designed to dissipate heat. Airflow improves cooling. However, the most important thing to improve airflow is the vane design, and it is the first thing that gets compromised in a cheaper rotor. Straight vanes are cheaper to make, and you will see them on a lot of cheap rotors (and some expensive ones). The drilled holes don't help much in cooling, compared to the vanes and any ducts bringing cool air to the brakes. When you think of a steady state (hot) brake, it has heat being added by friction, and heat being dissipated by cooling. However, brakes don't often function in a steady state condition, they cycle up and down. That is why you can overheat just about any brakes on the track, because brakes can absorb more hp (do more braking) than they can dissipate as heat. On the track they don't have cool-down time, they are in use much more constantly. What becomes more important, given the heating/cooling cycles, is how long it takes for brakes to get heated up to the point where they fade (or you boil the brake fluid). That cycle time is impacted by the thermal mass of the rotor assembly. A heavier rotor has more mass to be heated up. Drilling a rotor reduces that mass, so you will overheat the rotor, and approach the fade point, more quickly. Sure, if there is more cooling from airflow, you could perhaps handle more constant braking hp, but since no brake is working in a constant mode, it doesn't matter much.

The above is why both Centric and Stillen (among many other reputable manufacturers) don't recommend using drilled rotors on the track. The reduced time to overheat them is that much shorter on the track, and the thermal cycles are more likely to crack the rotors from any stress risers. The same would apply on long downhill mountain grades, particularly when towing. Yes, drilled rotors can look cool, but drilling a rotor designed to have a plain friction surface is just reducing the performance of it. There are claims that you can improve initial pad bite, but you can do that effectively with changing pad composition. There are also claims that the gases can better escape, but since we don't use any pads that outgas any more, that is a bit silly IMO. The pad compositions used in the '60s did outgas, and that is why drilled rotors helped then.

Many manufacturers offering drilled rotors have moved to slotted rotors, to get the wiping action without compromising the structural integrity of the rotor as much.

If the goal is simply to get a better look, I would paint the rotor hats silver, and paint the calipers any colour you like. Both those improve looks without compromising braking performance.

[JCL]

Originally Posted by X5rolls

Thanks guys, the Stillen's look great - $800 bucks isn't as much as I was thinking they would be.

They seem pretty expensive for what they are. 2005 4.8i, rotors only:

Stillen Sport: $788
Centric Premium: $492
Centric Stoptech Drilled & Slotted: $552
OE BMW (Web price): $514

The Stillen look comparable to the Centric drilled rotors, if you want drilled, but for 40% more $. What you will need to check out is the vane design. The Centric rotors use the factory vane design, instead of cheaper straight vanes that don't provide the same cooling. Stillen's web site notes that they use curved vanes on their more expensive rotors, but not on the Sport. Might just be that they forgot to mention it, but the web page makes it sound like it is a straight vane.

Given the price comparison above, that is why I have stayed with OE rotors, and just found a good price for them.

[X5rolls]

Originally Posted by JCL

They seem pretty expensive for what they are. 2005 4.8i, rotors only:

Stillen Sport: $788
Centric Premium: $492
Centric Stoptech Drilled & Slotted: $552
OE BMW (Web price): $514

The Stillen look comparable to the Centric drilled rotors, if you want drilled, but for 40% more $. What you will need to check out is the vane design. The Centric rotors use the factory vane design, instead of cheaper straight vanes that don't provide the same cooling. Stillen's web site notes that they use curved vanes on their more expensive rotors, but not on the Sport. Might just be that they forgot to mention it, but the web page makes it sound like it is a straight vane.

Given the price comparison above, that is why I have stayed with OE rotors, and just found a good price for them.

Good point on the vanes - I'll add this to my list of things to look for and to compare. Thanks for that and the pricing info.

[X5rolls]

Originally Posted by X5rolls

Thanks guys, the Stillen's look great - $800 bucks isn't as much as I was thinking they would be. These go on my list to research when I need to get brakes, I still have a fair amount of pad left at 44k miles. I'd guess I'll get 50k out of them. I have some other projects going on or I'd probably pull that schedule forward and pop for them (assuming all checks out ok with them) and pads now. Trying to keep the vehicle projects and cash outlay on a serial path, I've done things in parallel a few times and the mechanical work gets stacked up.

Well I wish I would have put money on needing brakes (lining warning just came on) at 50k miles. Time to decide what to do now. I might go with drilled (they really do look good) or OEM, still not sure.

Wondering if my stock bearings will fit non OEM rotors, any idea?

Maybe non OEM rotors come with new bearings anyway. I'll call to check if stock pads (which seem to be great) will work with one of the drilled rotor recommendations above. I'm really tempted to do the brakes myself (locate the right manual - not sure if I need any special tools) but my garage isn't heated and I guess I don't like working in the cold much, might break down and have an indy (who I'll have to find) or the dealer (who I've had ok luck with) do the work. Not sure yet.

[apetrov1x5]

anyone know how to identify OEM rotors from non-OEM?

[FSETH]

Rotors and bearing are two seperate items and changing rotors doesn't require any actions to the bearings. They are behind the rotors and stay attached to the car. They will not come off when you remove the rotors.

This is my last ditch effort to try to talk you out of drilled rotors...don't do it.

As far as I know, any pads will work with drilled rotors, but they will wear faster than if you used them with plain rotors.

I also suggest getting an indy to do the brake job if you are not comfortable. At minimum, I would find someone who has knowledge and experience doing brake jobs to help you if this is your first time.

Good luck.

[X5rolls]

Originally Posted by FSETH

Rotors and bearing are two seperate items and changing rotors doesn't require any actions to the bearings. They are behind the rotors and stay attached to the car. They will not come off when you remove the rotors.

This is my last ditch effort to try to talk you out of drilled rotors...don't do it.

As far as I know, any pads will work with drilled rotors, but they will wear faster than if you used them with plain rotors.

I also suggest getting an indy to do the brake job if you are not comfortable. At minimum, I would find someone who has knowledge and experience doing brake jobs to help you if this is your first time.

Good luck.

Thanks for the feedback - I'm leaning towards stock parts now, they are well designed and manufactured. Can these rotors be turned or are they like a few others that are not recommended for turning? They are original as are the brake pads currently on the X5.

As far as doing the brake job, I've done so many on other vehicles I've lost track just not on the X5. I looked at the brake installation notes in the articles section (thanks for those who contributed) and it's about as easy as it can get. Just hate doing work on vehicles in the cold. I should have installed the heater years ago, grrrr.

[FSETH]

Originally Posted by X5rolls

Thanks for the feedback - I'm leaning towards stock parts now, they are well designed and manufactured. Can these rotors be turned or are they like a few others that are not recommended for turning? They are original as are the brake pads currently on the X5.

As far as doing the brake job, I've done so many on other vehicles I've lost track just not on the X5. I looked at the brake installation notes in the articles section (thanks for those who contributed) and it's about as easy as it can get. Just hate doing work on vehicles in the cold. I should have installed the heater years ago, grrrr.

I wouldn't recommend turning the rotors. BMW rotors are notoriously thin to save weight in the first place. You would have to measure them to be sure it was even possible though. Even if they are OK to turn or reuse as is, they would most likely be below the minimum thickness before your new pads wear down. I would just change out the rotors with the pads, personally. You will want to change out the brake fluid as well.

[X5rolls]

Originally Posted by FSETH

I wouldn't recommend turning the rotors. BMW rotors are notoriously thin to save weight in the first place. You would have to measure them to be sure it was even possible though. Even if they are OK to turn or reuse as is, they would most likely be below the minimum thickness before your new pads wear down. I would just change out the rotors with the pads, personally. You will want to change out the brake fluid as well.

That's what I was concerned about - I don't really mind spending the $ to do the right thing (replacing rotors too) but if they were they type that could be turned it would save hundreds of dollars on a brake job I'd rather do myself anyway. Fluid change now makes sense too, had that done under normal maintenance when it was at the dealer around 35k miles.

[TowX]

Here's why you don't put drilled rotors on your car, when the rotors weren't designed to be drilled:

These rotors were OE Porsche Zimmerman rotors, drilled by a "reputable" Porsche specialist. They came with my 911 when I bought it 4 years ago so I thought I'd give them a try. I'd been on track at MidOhio, pulling 135 on the back straight every lap when I started to get a bad vibration under braking. So I slowed down and pitted in. Didn't even make it to my garage when it went BANG, loug enough that a couple of folks thought there'd been a wreck. And the right front tire locked up immediately. Had I not pulled in, it could have broken at speed on the track and would have caused a major spin at best, or even worse.

Now I run Porsche 996 Twin Turbo calipers and rotors on my 911, rotors that were drilled from the factory. I've put 2 years on those rotors, probably 30 or more track days, and no issues at all.

Oh, and drilled rotors will reduce your brake performance. Think about it- you remove about 20% of the friction surface. So not only do you need to increase your pedal pressure to stop, but you also can put extra heat into the brakes. Sounds crazy? If you need greater pressure, and need to be on the brakes longer, there's less cooling time between braking applications. When I went from the stock solid rotors to the drilled rotors that broke, my brake temps went up almost 100 degrees. Yes, I have a pyrometer that I use to check caliper and rotor temps. After the rotor broke, I put the old stock rotors back on and the temps went down. Oh, and my lap times went up close to half a second with the brake friction I got back.