bigblockbob

this is an off topic question but i figure the people with road racing or racing experience woud know...Anyway I know drilled rottors are not better for brakes on cars but is it different on motorcycles?? I mean are the problems the same for them or is it a different ball game?? if i am in the wrong part of the forum please tell me and i will ask somehere else...

John Shiels

Not sure but I would guess they are cast in like Porsche and the brake to weight ratio is better. Also the brake on a bike get more air for better cooling. Just a guess.

bigblockbob

yeah but still slotted should be addequate for gas exchange corect ami wrong?? i just dont get the afixiation to drilled rottors.... am i wrong by saying that slotted is good enough... that drilling is over kill and it compromises the strength and durabillity of the rottor?? or is this wrong and if not is it different on bikes?? :confused: :confused:

mastiff

Just relaying what I've heard from people that seemed to know whats up. I heard that the so-called "gassing" problem is not that big of a problem with the new types of brake pad compounds being used. It is pretty much a consensu that crossdrilled rotors are for show- the smaller amount of metal mass makes them more likely to warp and the holes lead to cracks in all but cast rotors. The only reason porsche puts them on their cars is to satisfy customers who want them, but crossdrilled is unnecessary.

Today I read a journal of the 2001 One Lap of America contestant driving a 94 Supra. He had big crossdrilled rotors. 2/3 of the way through the race, they were badly warped and completely cracked. He vowed to put solid rotors on next time- he didn't expect to see a performance loss on road courses doing this.

Just my speculation, but maybe bikes can get away with their rotors because they are so light. A 600lb bike will have 5X less energy to dissipate as heat than a 3000lb car, and they have a very large surface area, so they are able to cool down quickly. Cars don't have this advantage

sffish

I think it might have to do with braking in the rain, although I'm not sure. The drilled rotors may improve braking in the rain, by letting the water have some place to go. I have heard that this is one reason that Porsche's have drilled rotors from the factory (along with the bling-bling factor).

han

Dylan Savage

The reason motorcycles use drilled rotors is because it ends up with a lighter rotor for a given diameter. You want a large diameter rotor for more stopping power, but don't want to pay the weight penalty. Generally heat is a non-issue on motorcycles since their brakes are HUGE for their weight.

bigblockbob

Thanks man that is good to know! :thumbs: I apreciate the help on this topic. And i just hate it when i see guys and they are like "Man these cross drilled rotors are awesome they help soooooo much they make me look like i have a race car i am so awesome because i have cross drilled rotors!" well anyway didn't mean to look dumb or likean an butt. but i apreciate the info on the bikes that answer is beliveable... :D

rbeckham

:iagree: Plus cooling ducts are not a problem with the bikes. They get a lot of airflow.

h rocks

I don't believe that bikes use cast rotors anyway. I think that some use SS or even titanium rotors. So drilling will not appreciably compromise a piece of rolled steel vs. a crummy cast piece.


[Modified by h rocks, 9:42 PM 5/29/2003]

Dylan Savage

When I raced motorcycles we never used anything but plain old cast iron rotors, and I never heard of anyone using anything but plain old cast iron rotors either. Braking really isn't an issue on motorcycles.. especially any sportbike made after like 1993. The brakes on bikes are generally about 10X overkill. Don't get me wrong, I'm not complaining :)

mastiff

I don't think the cracks have anything to do with the material, meaning that cast iron does not crack easier than SS or titanium. The cracks start from stress concentrations created by sharp edges. These edges occur when you drill a hole. Materials that are brittle would have a tendancy to have sharper edges and greater chance of stress concentrations. Of the three materials listed above, cast iron is the most ductile.

Jhodel

I have tried slotted and plain rotors on my 4 piston Alcon equipped Z28 and can't tell any difference at the track so I have concluded that drilled rotors won't improve braking either. The plain rotors stop as well, and don't fade any more then the slotted rotors so i just buy plain rotors and save some money. I am using PF 93 pads.

Jim

SFVetteman

Nowadays, most high performance motorcycles use steel rotors, which are usually stainless. Some of the more exotic stainless steel rotors are not just drilled but look more like a doily weighing less than 2 ½ lbs.

Cast iron more ductile than steel or titanium? According to the dictionary I’m holding in my tobacco stained fingers, ductile means: “Easily drawn into wire or hammered thin: ductile metals”. I don’t know of anybody that has accomplished this feat with cast iron, as it’s too brittle.

From what I have read, drilling cast iron impedes the ability of the cast iron to expand evenly when subjected to heat, which causes the cracking. That said, I’m using drilled and slotted Eradispeed rotors and have no problems so far. Part of the reason for this is the 14” rear rotors combined with a brake bias spring that shifts more braking to the rear. Most of the reason is probably because I’m not using racing pads and I tend to be easier on my brakes compared to a lot of folks.

LTC Z06

I'm pals with a Porsche engineer, even the Porsche rotors crack around the holes, he said marketing is the only reason they still use holes and if it were up to him (he's president of PCA auto-x and races too) they would have slotted rotors only.