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

[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.

[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.

[apetrov1x5]

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

[Airfrcd]

Originally Posted by X5rolls

Can anyone recommend a high quality drilled rotor for the X5?

Thanks!

Rotora/.

[X5rolls]

Originally Posted by JCL

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.

A good technical explanation - thank you. Interestingly enough, the Viper and Shelby's stock rotors are not drilled but the Carerra S's are.

[ekimv65]

Originally Posted by JCL

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.

What a detailed explanation! Thank you for the time you took to do this. In the other message on the board, I said I may use these on my race car. That was supposed to be sarcastic. I use nothing but two piece Coleman's for the track! I do like the idea of painting the calipers and rotor hats, that will give it a nice look.

I am going to order some Zimmerman's, is that a good rotor? A local indi made a statement that that is what he would use.....

Thanks again!

Mike

[JCL]

Originally Posted by X5rolls

A good technical explanation - thank you. Interestingly enough, the Viper and Shelby's stock rotors are not drilled but the Carerra S's are.

You're welcome. If you go up the hierarchy, right up to Formula 1, they don't use drilled rotors.

[JCL]

Originally Posted by ekimv65

What a detailed explanation! Thank you for the time you took to do this. In the other message on the board, I said I may use these on my race car. That was supposed to be sarcastic. I use nothing but two piece Coleman's for the track! I do like the idea of painting the calipers and rotor hats, that will give it a nice look.

I am going to order some Zimmerman's, is that a good rotor? A local indi made a statement that that is what he would use.....

Thanks again!

Mike

I don't know anything about the quality of the Zimmerman rotors, although I have heard the name. I saw one web site advertising plain Zimmerman rotors for $31 each, so that isn't too comforting.

What is the attraction for using an unproven rotor such as the Zimmerman when you know the stock rotors work well, and there are well-regarded alternatives such as the Centric Premium? Your mechanic makes $ if you buy rotors off him, and nothing if you buy them online and have him install them. If you trust your independent mechanic more than all the opinions on this board, then you should buy them. If not, go with something that many have had good results with, either OE or Centric Premium plain.

[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.

[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.