::.. How are these Rotors?

[Qube]

Assuming these can be procured cheaply (read: less than $200 for front and rear), how are they? Any comments? They would be exactly these with no doubt.

http://cgi.ebay.ca/BMW-E34-CROSS-DRILLED-REAR-ROTORS-PAIR-NOT-540i-OR-M5_W0QQitemZ8000428594QQcategoryZ33564QQcmdZViewIt em

http://cgi.ebay.ca/BMW-E34-ZIMMERMAN-CROSS-DRILLED-F-ROTORS-525-530-535_W0QQitemZ8000383777QQcategoryZ33564QQcmdZViewI tem

http://i5.ebayimg.com/04/i/04/5f/bf/7a_1_b.JPG

[Bill R.]

.
Assuming these can be procured cheaply (read: less than $200 for front and rear), how are they? Any comments? They would be exactly these with no doubt.

http://cgi.ebay.ca/BMW-E34-CROSS-DRILLED-REAR-ROTORS-PAIR-NOT-540i-OR-M5_W0QQitemZ8000428594QQcategoryZ33564QQcmdZViewIt em

http://cgi.ebay.ca/BMW-E34-ZIMMERMAN-CROSS-DRILLED-F-ROTORS-525-530-535_W0QQitemZ8000383777QQcategoryZ33564QQcmdZViewI tem

http://i5.ebayimg.com/04/i/04/5f/bf/7a_1_b.JPG

[sKilled]

Slap me if I'm wrong, but arent holes bad - ridges good? I'm almost dead certain that it's posted here somewhere...

[genphreak]

Ridges and holes do well in the wet.

Holes do better in extreme heat.

All (esp. holes) cause more pad wear and deplete braking by however much material is missing in relation to the remaining surface that is in friction with the pad. And are harder to re-surface when they get worn.

I use stock to avoid these pitfalls, I reckon they work a little bit better.

[DanDombrowski]

I have them, I made a post awhile back about how they look, even has some pictures in it. I really should follow that up, I said I would....

So far, I don't notice any more dust than usual. I usually wash my wheels about once a week (car too :) ), and they seem to have about the same amount of dust on them after a week as before, mabye slightly more.

For the additional price over plain rotors, its definitely worth it for the bling factor if you have open wheels.

I'll admit that there is no performance increase, at least in normal braking. They're supposed to prevent brake fade, but honestly, the only time I've ever felt brake fade in the E34 was when I went from 70-0 over and over again to find out how much braking it took to induce brake fade. Took 3 or 4 times. I've autocrossed with stock rotors and didn't have any fade there either. Then again, I wasn't the fastest guy on the track.

Oh yeah, don't notice any more noise either.

That help?

[Kobe Diesel]

The prev owner of my car had x-drilled installed in rear about 3k miles before he sold car to me. When I inspected the brakes the pad thickness and rotors were in spec with good wear pattern (zimmermann and pagid). Last week, I noticed that the pads are much thinner, and this is after about 5k miles of ownership. Before last week when I did rear brake maint., the rears were slightly squealing. I did the front brakes the day I got the car, Brembo OEM rotors and Raybestos pads and they have held up terrific since (very little dust).

Keep in mind that braking power is distributed about 85-90% front, the remainder to the rear. And I have this much wear occuring with rear only b/c of X-drilled feature. My opinion - they eat up pads.

I thought of doing x-drilled/slots for the front next go around, but might reconsider this. If I really want bling factor, I'll just paint the calipers.

I have searched ebay for rotors and am curious - are the ebay stores selling original Brembo/Zimmermann/ATE rotors or are they selling built-under-license to spec rotors?

[Qube]

Well I have the Privat Kraftwerk wheels so I'm thinking full calipers AND x-drilled rotors... but if I'm going to be spending a fortune in pads ;) I'll decide in about half an hour.

[Bill R.]

that outgasses under extreme conditions built up a layer of hot gases between the pad and rotor and that the drilled holes allowed a place for these gases to escape. But the reality, or at least my version of it is that any time you drill holes in rotors you lose thermal mass which is needed to absorb heat generated by braking, the more thermal mass the less chance of boiling the brake fluid and having brake fade... Thats why i can't understand these people that put the bigger rotor with the most thermal mass and then drilling it full of holes....



I have them, I made a post awhile back about how they look, even has some pictures in it. I really should follow that up, I said I would....

So far, I don't notice any more dust than usual. I usually wash my wheels about once a week (car too :) ), and they seem to have about the same amount of dust on them after a week as before, mabye slightly more.

For the additional price over plain rotors, its definitely worth it for the bling factor if you have open wheels.

I'll admit that there is no performance increase, at least in normal braking. They're supposed to prevent brake fade, but honestly, the only time I've ever felt brake fade in the E34 was when I went from 70-0 over and over again to find out how much braking it took to induce brake fade. Took 3 or 4 times. I've autocrossed with stock rotors and didn't have any fade there either. Then again, I wasn't the fastest guy on the track.

Oh yeah, don't notice any more noise either.

That help?

[genphreak]

that outgasses under extreme conditions built up a layer of hot gases between the pad and rotor and that the drilled holes allowed a place for these gases to escape. But the reality, or at least my version of it is that any time you drill holes in rotors you lose thermal mass which is needed to absorb heat generated by braking, the more thermal mass the less chance of boiling the brake fluid and having brake fade... Thats why i can't understand these people that put the bigger rotor with the most thermal mass and then drilling it full of holes....Interesting viewpoint Bill. Surely the extra surface area would help to sink the heat back to the air swirling round the rotors though... tho not much during braking I guess- I suppose that's when the thermal mass counts most...

[Qube]

Okay so I'll get them. Any other hardware I should get at the same time? Nuts and bolts?

[Alexlind123]

My mother's dodge durango had a problem with cracking rotors, probably because the terrain is fairly mountainous for a bit with some steep grades to heat brakes up. Finally my dad ordered some crossdrilled rotors that are gold in color (powerstop comes to mind, but im not sure). The crossdrilled rotors are far, far better and have already payed for themselves twice over in the price of new factory rotors. Whether this is due to better rotor material or the actual crossdrilling, i do not know.

[DanDombrowski]

Bill,

You're right about the drilling to help relieve the layer of gas that develops, that was another reason for putting the holes through.

As far as the heat capacity of the material, yes, you lose some. However, I've done enough engineering analyses to know that the amount of material you lose by drilling is probably neglidgable.

I was referring to the increased convection of having the holes through the disc. How much more? I have no idea, but as I understood it, that was the reason for claiming less brake fade.

Ideally, you would want more of the energy in braking to go into the air through convection than into the rotor's heat capacity (becasue all of that energy will have to be either convected out anyway or conduct into the caliper and brake lines), but without heat capacity, the same energy results in higher temperatures of the disc and caliper, and you're right back where you started from.

A question a lot of people ask about these is "If they're no good, then why does Porsche put them on their cars?"

I think the reason is that Porsche has done the real engineering thermal analysis to show that the pros outweigh the cons, at least with the rotors that they put on their cars. Weather or not Zimmerman or any other company has done the same analysis or is just banking on the bling factor, I don't know, and probably won't ever be allowed to find out. But for the price difference and the fact that labor is free, I thought I would give them a try. So far they seem the same to me.

[Springfield1952]

Am I missing something here? Aside from the discussion on the merits of cross drilled vs. solid rotors, the eBay auction is for Zimmerman rotors at $150/pair Buy it Now price while BMA has Zimmerman's for $127.50/pair. Why spend the extra $22.50?

Curt.

[DanDombrowski]

Yeah, no reason. I got mine from BMA too, they were only slightly more expensive than blanks.

[granit_silber]

In a recent issue of Roundel Steve Dinan is quoted saying that they have tests that show slotted rotors work better (less stopping distance) than drilled or slotted and drilled rotors.

Besides craked rotors and worn pads, you lose a lot more braking area with holes vs. slots.

Drilled rotors work on race cars because they only have to last one race before being replaced. On street cars I think they're stupid. But hey, to each their own. For my car I'm going with the ATE rotors with the elliptical slots (more so for the wear indication than the bling)
-ashley

[Qube]

Am I missing something here? Aside from the discussion on the merits of cross drilled vs. solid rotors, the eBay auction is for Zimmerman rotors at $150/pair Buy it Now price while BMA has Zimmerman's for $127.50/pair. Why spend the extra $22.50?

Curt.

Yep. You are missing my point in the first post. I'm getting them legit for $200 front AND back.

[Visions]

Slotted rotors slice the brake pads each time so you are always driving on clean pads... Drilled does the same but less...

[sKilled]

Thanks for the info - I just switched to stock replacements. Brembo front and Bradi rears.