Drilled disks

[Ian Kellar]

I was reading the excellent guide to options on the V11UFO page, and something caught my eye. I thought the idea behind drilling disks was to reduce unsprung weight, as opposed to grooves, which clean the surface, if I've understood correctly. Here is the section which caught my eye:

 

Uprated Front Brakes

 

Larger diameter discs, 4 pot calipers and bigger master cylinder. James Whiting (see above) does an Alcon brake kit slightly cheaper than the £580 that Caterham will charge you as an upgrade. The 7 does not really need these on the road. If you buy them, though, you are rewarded with awesome stopping power and they feel better than the standard ones hauling a Superlight down from 125mph! James Whiting makes the point that the uprated brakes are unnecessary on the Fireblade 7 because it is so light! He uses, instead, 2 pot alloy ones which are physically less heavy than Caterham’s 4 pot upgrade.

 

The racing price list shows clearly that they do a set of rear uprated brakes. Even the R500 doesn’t have these so we are not sure exactly what they are……Anyone know?

 

An interesting point was raised recently. He stated that he had done an experiment a while back where he cross drilled the brake disc on one side only of a car. He said that the car pulled to the drilled disc side under braking. This must indicate that drilled discs are more efficient than solid ones! The 7’s discs are not drilled even on the uprated rotors so I reckon this might be an extra little “tweak”! Looks good, too.

---

 

I am a psychologist who failed his A-level physics, so this is based on a very rudimentary understanding.

As I see it, the ability of the disk to dissipate heat away from the pad is the primary indicator of it's efficacy. Given that the material for the disk is going to conduct heat better than air, wouldn't any drilling be counterproductive. If the ability of the disk material and air to dissipate heat was close, I could see that small holes might increase the surface area of the disk, and if they weren't in the path that the pad makes, that might produce gains. Other than that, I am at a loss to how drilling can help the efficiency of brakes. Can someone lend me a clue?

[Delberts Wallet]

Ian,

 

My understanding of cross drilled discs is that the holes help prevent the buildup of gasses that are produced when the pads get hot. I understand that this is what causes brake fade, so having the disks drilled will help to prevent this.

 

Can't be too sure though

 

Gareth

 

 

 

Who Dares Twins bum.gif bum.gif

[Peter Carmichael]

Holes are generally there because the heat from braking causes certain constituents of the brake pad to vaporise. The holes allow the vapour to escape from the braking surface, rather than the pad floating on a layer of vapour. This varies with brake pad material.

 

Peterid=teal>

253 BHP K-seriesteeth.gif, no gearboxbum.gifid=red>

[Delberts Wallet]

I must understand right then smile.gif

 

Who Dares Twins bum.gif bum.gif

[Ian Kellar]

Is that an important factor? A quick search on google threw up a couple of things, including a thread on an Nissan board that linked to the following, that makes the point that it's no longer an issue.

 

from http://www.teamscr.com/rotors.htm

Crossdrilling

 

Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, not a whole lot. Rotors were first ‘drilled’ because early brake pad materials gave off gasses when heated to racing temperatures – a process known as ‘gassing out’. These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.

 

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing the rotor to crack sooner, and make a mess of brake pads – sort of like a cheese grater rubbing against them at every stop. (Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it.)

 

The one glaring exception here is in the rare situation where the rotors are so oversized (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs.

 

 

The guy who linked to it said "I challenge you to get a Hawk Blue, or Porterfield R4 brake pad or other dedicated racing pad to fade. Ever. Simply, crossdrilled rotors fix a problem that no longer exists".

 

Is it that crossdrilling allows you to use non-race pads harder, thus allowing you to avoid the effects of using race pads under normal driving conditions?

 

Edited by - Ian Kellar on 19 Jun 2002 11:52:32

[oilyhands]

As Peter says the holes are there primarily to allow gases generated by the pad to escape, but they also have a secondary role in deglazing the pads...

 

Oily

[sjwb]

And they look so damm coolcool.gif.

 

Steve B

[Peter Carmichael]

Sevens are generally fitted as standard with very ordinary pad materials. Most people start upgrading their brakes because they perceive some sort of a problem. Most of the upgrades fix many issues in one go, but it is very easy to get out of balance.

 

Going back to the original V11UFO web page link:

 

We don't know what pads were used in the "pulls to one side" test. We don't know if it was braking from cold. We don't know if repeated braking carried on the effect.

 

In answer to the uprated rear brakes point:

 

The standard rears have the integral handbrake mechanism and are a single piston "claw" design caliper. By using a two piston caliper you eliminate all the nasty caliper flex and uneven clamping you get with a "claw" caliper. There have been two variants, dating from the Vauxhall race cars and the 2001 Superlight racers.

 

The Vauxhall race cars had solid rear disks - variants on the standard cheap disks. WIth four piston calipers at the front and with the heavier Vauxhall engine, these cars achieved a slight rear brake bias, which is the ideal starting point for a race car brake setup. By fitting a proportioning valve in the rear circuit, it was possible to adjust the bias for optimum wet and dry use. You can also get this brake upgrade kit for road use with a rather pathetic design of separate handbrake caliper. The 2 pot calipers work rather well in a k-series track day car without any proportioning valve - the brake bias is safely set to the front and the pedal feel and brake bite is much improved over standard.

 

With the Superlight racers, the more lightly loaded front end meant that the same brake caliper setup gave a front bias. Up until 2001, the racers ran with a proportioning valve in the *front* circuit, which is a horrible bodge. In 2001, the Superlight racers upgraded to a larger vented disk setup at the rear and a more modern AP twin pot caliper design. This shifted the brake bias correctly to the rear of the car and required a proportioning valve in the rear circuit.

 

Peterid=teal>

253 BHP K-seriesteeth.gif, no gearboxbum.gifid=red>

[Bricol]

If you're into classic trialling, the cross-drilling gives all the water and mud somewhere to go - allowing the brake to work a bit longer.

 

Bri

[Bangers quotNquot Mas1697456953]

Don't forget unsprung weight!

 

If you drill through the ventilation ribs, a fair amount of weight will be removed smile.gif

 

Andy Marks

andy@metrol.com

[edmandsd]

I've just fitted AP hillclimb rotors to my car. They're lighter than a standard ventilated disc being solid and have slots not holes.

I appreciate that holes will let any vapours out that may compromise braking although slots will also do this albeit to a lesser extent.

Solid rotors will also heat up more quickly than a standard ventilated disc which would suit a hillclimb application although maybe not so much a circuit car.

Crossdrilled rotors can have a tendancy to crack between the holes with use. They will also have less surface area than a plain or slotted disc which would in theory reduce braking capacity.

 

Edited by - edmandsd on 19 Jun 2002 17:39:48

[Julian Thompson]

I've re-read my section on the V11UFO website and realised that I didn't say who "HE" was that did the experiment! Weird! Anyway - it was someone on Blatchat - and as Peter said, he didn't give any details at all about pad spec, temperature or anything else - hence my comment:

 

"I reckon it MIGHT be an extra tweak!"

 

I'm glad I didn't go overboard with the "lets all get the drills out!!"

 

Cheers

 

Jue

[StewartG]

I'm running an AP big brake kit on the front with the discs grooved and spotted as per EBC turbo groove design. I'm using Pagid RS14 pads. I was advised not to have the discs drilled right through because of the possibility of cracking. The discs are obviously lighter but not by much, they do look better IMHO.

I can confirm that stopping power is improved and the pads are showing no discernable increase in wear (there's no more brake dust than usual). Cost of having the grooved done was £20 plus VAT per disc and I have a spare set of discs should anybody be interested in having them done.

[elie boone]

IMHO holes are pretty useless, they crack very easely and get blocked by brake dust, in that regard grooves are better also for deglazing but for optimum cooling you need rotors witch are handed because the are working like ventilators.

Also you can not compare motorbike brake rotors against those from a car because a motorbike rotor is only +/-5mm in thikness

 

Edited by - elie boone on 19 Jun 2002 20:08:56

[Westfield]

There was a thread on this a while ago where I commented that I ran drilled stock discs on my Lancia. Have a look here.

 

http://www.blatchat.com/Topic.asp?topic_id=10803&forum_id=8&Topic_Title=Drilling+stock+brake+discs%2E&forum_title=TechTalk

[Phil]

The advantage of a race team is that after each race they inspect everything inclueding the disks and if ther drilled disks are cracked they are replaced, they are through away items, with a road car or road/track car they are not checked on a regualr basis and this is were the problems arise, this is why vented, grooved and dimpled diskes are the best options as they remove gases, deglaze pads and remove heat while on the move.

EBC list grooved disks for the Caterham and these complement there Green road pads making for a good cheap upgrade for the road, the disks on my 1990 1700ss DD are the same front and back using ford granada/sierra rear calipers and the std front cortina/triumph set up.

 

 

[Morls]

These wobbly looking things half way down the page here:

 

http://www.go-faster.com/acatalog/Honda_Braking_Accessories.html

 

Are all the rage for the supermoto fraternity, (and will be going on my XR650 as soon as I have an XR650).

 

The advantages are supposed to be the constant cleaning of the pad surface, by the scaping action of the leading disc edge, the dissipation of vapourised pad material and the reduction is unsprung mass (and correspunding gyro forces on a bike).

 

But most important of all, they look as trick as possible and can be used to pare off slices of home cured ham smile.gif

 

Although these facets might not be quite as important when hidden by a car wheel.

 

 

 

Mark

[elie boone]

Just to make clear that drilled discs only end up in the dust bin when the crack goes from hole to hole, but you got to check them regularly.