Cross drilled rear rotors Options

[Harpo]

Is anyone using cross drilled rotors on the rear?

Thanks

David

[IronHillRestorations]

Only if they are vented rotors. You don't cross drill solid rotors.

[nsr-jamie]

The Automotion catalog sells or sold stock 914 solid (non vented) rear discs. I believe they were made by Zimmerman but need to double check that and my catalog may be a couple of seasons out of date.

You should talk with Eric Shea at PMB for all your needs.

I am not sure, but I hear from my friends here in Japan that cross drilled discs look great but wear out your pads much much quicker. Never attempt to drill your own rotors.

[underthetire]

And they like too crack between the holes. Grooved rotors are supposed to be a better option.

[SLITS]

Unless you are into serious racing, you are wasting your money on grooved or cross-drilled rotors.

They fall into the category of "Bling" for street use.

[Elliot Cannon]

I've had cross drilled solid rotors on my car for over 8 years. I use them for the same reason I painted the calipers red. And it's got nothing to do with stopping power. (IMG:style_emoticons/default/laugh.gif)

[sean_v8_914]

they deliver on the street cool scene. yellow calipers are much faster than red

[dlestep]

Drilling started with the 550 and 356 GT drums and went through the 908 and 917 as a weight savings move, nothing more.
If you are going to run cross-drilled rotors, the entries and exits have to be countersunk or "break edges at 30 thousands."
The holes should not be any closer than three diameters in a line or arc.
Slotting in my eyes, is worse because it has two surfaces. The floor of the slot removes too much material. If the vertical wall is not radiused it will create
stress risers as well and will exhibit a higher temperature than the upper pad contact surface, and temperatures will not be uniformly distributed.

[Harpo]

Thanks for the advise. I will save my money

David

[Drums66]

.....I used them for a long while myself (IMG:style_emoticons/default/idea.gif)
(IMG:style_emoticons/default/shades.gif) (blue caliper's)
(IMG:style_emoticons/default/bye1.gif) (IMG:style_emoticons/default/smoke.gif)

[Chris Hamilton]

On my 4-lug car they look like this

(IMG:http://www.914world.com/bbs2/uploads_offsite/thextremeresources.com-5687-1326856453.1.jpg)


30k miles later, and 3 seasons of autocross on race tires, still look exactly like they did when I put them on.

[Eric_Shea]

as a weight savings move, nothing more

Three reasons... none of which is really weight. (IMG:style_emoticons/default/wink.gif)

1. Heat. When the brake pad grabs the rotor, it creates friction, which creates heat. If that heat can't escape, it leads to brake fade, which reduces the brakes' stopping power. How well that works on a solid rotor without venting and cooling vanes? I doubt if it hurts. (IMG:style_emoticons/default/confused24.gif)

2. Gas. This actually isn't much of a problem any more; however, materials used in some older pads caused gas to build up between the rotors and pads limiting stopping power. That was the main reason cited for drilling rotors on sports purpose vehicles.

3. Water. If a car drives through a puddle, or a rainstorm, the brake rotors can get wet. A wet brake rotor can be slippery for the pads to grab. Having drilled holes makes it easy for heat, gas and water to be quickly moved away from the rotor surface. Not sure I've ever noticed this (the water thing) on a non-drilled rotor but, that's what they say.

The obvious downside of using drilled rotors (as mentioned many times) is that all of those holes tend to weaken the rotors. After repeated stressful driving, the rotors can crack. Some don't as you can see here... rear brakes don't get as much of a workout as the fronts probably saving them from the stress crack scenario.

Chris, have you set your venting clearance lately? Those rotors don't look like they're getting "blued" which, with your driving style described, they should be.

[NORD]

On my 4-lug car they look like this

(IMG:http://www.914world.com/bbs2/uploads_offsite/thextremeresources.com-5687-1326856453.1.jpg)


30k miles later, and 3 seasons of autocross on race tires, still look exactly like they did when I put them on.

I've never seen the spool part of a brake disc drilled out like that.

That save much unsprung weight? (IMG:style_emoticons/default/driving.gif)

[stugray]

After repeated stressful driving, the rotors can crack.

This exactly why they will not allow drilled rotors in vintage racing.

They allow factory vented rotors however.

Stu