Slotted rotors - Worth it?

[TheLowRanger]

The brakes on the D1 are nearly due for replacement, and I have been told that the current rotors are undersized so they can't be machined. This being so, I may be up for a set of new rotors. My next set of tyres will be 235/85/16's, and I know from when I put these on my RRC that my braking characteristics were reduced. My question is, would slotted rotors overcome the lack of braking, or do they only enhance braking marginally?

[Signal1]

NJZ fitted slotted rotors on his '97 D1; best he give you an opinion on their effectiveness. He was also told recently that slotted rotors chew pads and that perhaps Defender discs could be used! Over to Nik...

[njz]

The DBA slotted rotors seem to work well and many people on this site swear by them. I was recently told the slotted rotors can chew up pads but I haven't had them on long enough to see any major wear. If you want a real upgrade you can easily swap to defender front calipers and vented rotors.

[walker]

I hope they work, I just bought a set for the Rangie. :eek:

[Cameron_Def]

Yeah I got a set for my defender when I warped the last set (normal first ones from LR)

I recon I have 20% more stopping power, but that could come from straight disks and new pads .. but they can lock the defender up 4 wheels when ever I want now ....

I feel much more confident with them .. but I do get more brake dust .. but thats a given.

[justinc]

I have them on the RR, fronts and soon rear also. Excellent braking, I haven't noticed any pad wear more than usual:twisted: and they don't seem to fade as much either. I'm happy.

JC

[JDNSW]

Slotted rotors will provide better cooling but should have no effect at all on the actual brake effectiveness or pedal pressure (until the discs heat up). Any apparent improvement in pedal pressure or effectiveness in normal use will be a reflection of the worn out brakes you replaced, and perhaps changes in the pads, plus the fact that you now have new fluid that won't boil a bit above blood temperature.

Where they WILL be an improvement, is where the brakes are used consistently in circumstances where they get hot enough to lose effectiveness (which with disc brakes is pretty hot unless the fluid has absorbed water and boils!). This would be if you operate at close to maximum weight, or live in very hilly country, or regularly tow an inadequately braked trailer - or usually drive like a lunatic.

John

[Dave110]

we run slotted discs all round on the Defender with braided brake lines, Bendix 4x4 pads and run 235/85/16 tyres and usually loaded up to close the max when touring and have great stopping power' far better than standard well worth the effort to upgrade.

[Slunnie]

I've run plain and slotted. This biggest difference I have found (depite all of the brake theory) is actually caused by using better brake pads.

[amtravic1]

I've run plain and slotted. This biggest difference I have found (depite all of the brake theory) is actually caused by using better brake pads.

I agree, noticed no difference in stopping power between slotted and plain. Disc pads do make a difference though.

Ian

[Blknight.aus]

the ONLY downside to slotted rotors and high friction pads is the additional wear rates on both the rotors and pads. everything else is gold... Im just waiting on the ones in big reds to go undersize and shes getting the upgrade.

[Slunnie]

Thats true. I'm more than happy to change pads every 20,000km, for high friction and high temperature pads anytime. Piece of mind and a whole body is good value.

[PAT303]

I'm with Slunnie,I have found that slotted disc's weren't the improvement,it was the pads that made the difference. Pat

[Blknight.aus]

slotted rotors run cooler so go longer before hitting brake fade and they self clean better so pick up brakes quicker after you hit the mud..

for the fade resistance vented cross drilled rotors work almost as well but without quite so much additional wear.

[HangOver]

I fitted dba slotted and new soft pads, (can't remember brand) but well worth it IMO.
They did chew through the pads in under 20k but I recently changed the pads to El'cheapo brand and didn't notice any difference in stopping power.
I'll have to wait and see how long the cheapo's last

[Slunnie]

Thats the theory behind it, though I don't think that the difference in rotor is significant in comparison to the differences in pads. The other thing the slots are meant to do is reduce the fade effects from outgassing of the pad.

Out of interest, I ran OE plain rotors with EBC 2000 series proper greenstuff pads and drove down through the pass towards Fitzroy Falls in NSW with a loaded tandem axle trailer that had failed brakes. The hotter my brakes got the better they worked and I was able to brake enough to hear the tyres squirm on the road on any/every corner - it was just sensational.

Changed to EBC slotted rotors and EBC 6000 series 4x4 pseudo greenstuff pads and did the same thing with a similar trailer + load but with fully functional brakes and I had to stop on the handbrake part way through the pass - not being able to stop on the foot brake. A very smokey episode.

BTW, I would never ever fit cross drilled rotors to any vehicle. Slotted is fine, dimpled is fine but cross drill concentrates the forces and every hole acts as a stress raiser. These rotors will crack, and even after a short period of time you will probably be able to visually see radiating fractures from the cross drilling. I had a chat to the fellas at Dba a few years ago, and even they said that the cross drilling is basically for the bling brigade on the street. None of their circuit rotors have it. At work, the fellas have managed to fracture cross drilled rotors on a lightweight Pug on a single trackday. The only time we use them is on a lightweight energy breakthrough car that we built, which has minimal braking time while on the circuit, it is lightweight and it is done to get weight out and reduce rotational inertia rather than increase performance.

[Blknight.aus]

Thats the theory behind it, though I don't think that the difference in rotor is significant in comparison to the differences in pads. The other thing the slots are meant to do is reduce the fade effects from outgassing of the pad.

Out of interest, I ran OE plain rotors with EBC 2000 series proper greenstuff pads and drove down through the pass towards Fitzroy Falls in NSW with a loaded tandem axle trailer that had failed brakes. The hotter my brakes got the better they worked and I was able to brake enough to hear the tyres squirm on the road on any/every corner - it was just sensational.

Changed to EBC slotted rotors and EBC 6000 series 4x4 pseudo greenstuff pads and did the same thing with a similar trailer + load but with fully functional brakes and I had to stop on the handbrake part way through the pass - not being able to stop on the foot brake. A very smokey episode.

BTW, I would never ever fit cross drilled rotors to any vehicle. Slotted is fine, dimpled is fine but cross drill concentrates the forces and every hole acts as a stress raiser. These rotors will crack, and even after a short period of time you will probably be able to visually see radiating fractures from the cross drilling. I had a chat to the fellas at Dba a few years ago, and even they said that the cross drilling is basically for the bling brigade on the street. None of their circuit rotors have it. At work, the fellas have managed to fracture cross drilled rotors on a lightweight Pug on a single trackday. The only time we use them is on a lightweight energy breakthrough car that we built, which has minimal braking time while on the circuit, it is lightweight and it is done to get weight out and reduce rotational inertia rather than increase performance.


I'll buy that... Ive had them but then my driving style is normally very easy on brakes... my original pads cleared 60 K Km without problems wear wise (50% useable compund remaing) but due to an oil leak I insisted they be replaced under warrenty as the leak was fixed under warrenty AND I want the originals back as spares.

[GrahamH]

I fitted the vented rotor conversion from Triumph Rover spares to my '88 Rangie after a severe brake fade episode and I was very impressed with their fade resistance, but I agree with everyone else that they made no difference to the effectiveness of the brakes under normal circumstances.

Logically, just fitting slotted rotors could make no change to brake effectiveness compared to solid rotors given equal rotor temperatures. Effectiveness can only be modified by changing the surface area of the pad or the composition of the pad, either of which will change the coefficient of friction.

At the same time as I fitted the vented rotors, Ian gave me a set of harder composition pads which took a bit of getting used to. They were quite ineffective when cold, but once they heated up to normal working temperature they were much better than the original pads. I just had to remember to work them a bit before I tried any emergency stops - in other words, drive carefully for a few Km when starting out for the day.

I'd thoroughly recommend the upgrade, not for more effective braking under normal circumstances but for peace of mind, especially if towing a trailer or doing a lot of hill work.

I'll be upgrading the front brakes on my Disco soon but as the latest price I got from Ian was $550 for the vented rotor conversion, I'm still working on the cost benefit analysis to submit with the capital expenditure request to the Office of War and Finance.

[CraigE]

I fitted slotted and cross drilled DBA gold rotors to my RR (now my Dads) and they are great. Was told the same about chewing out pads but found that to be not true. Pedal and braking were a bit better over standard items but not a drastic improvement.
Hope to do the same to the Fender soon.

[rick130]

Slotted rotors will provide better cooling but should have no effect at all on the actual brake effectiveness or pedal pressure (until the discs heat up). Any apparent improvement in pedal pressure or effectiveness in normal use will be a reflection of the worn out brakes you replaced, and perhaps changes in the pads, plus the fact that you now have new fluid that won't boil a bit above blood temperature.

Where they WILL be an improvement, is where the brakes are used consistently in circumstances where they get hot enough to lose effectiveness (which with disc brakes is pretty hot unless the fluid has absorbed water and boils!). This would be if you operate at close to maximum weight, or live in very hilly country, or regularly tow an inadequately braked trailer - or usually drive like a lunatic.

John


slotted rotors run cooler so go longer before hitting brake fade and they self clean better so pick up brakes quicker after you hit the mud..

for the fade resistance vented cross drilled rotors work almost as well but without quite so much additional wear.


sorry fella's but slotting the rotor doesn't result in a substantially cooler running disc.

The slots main functions are.....

1. as the pad is clamped against the disc and progressively gets hotter, the pad de-gasses and a layer of this gas (called the firebrand) builds up between pad and rotor. The slots allow these gasses to dissipate effectively giving better pad/rotor bite.

2. the slots provide a minor de-glaze of the pad, giving better bite over the life of the pad.

holes actually do a better job on both counts and also reduce unsprung and rotational weight (only applicable to racing) but the downsides are as Slunnie addresses above. I would never use them again (and I have, on a race car) unless I had enough budget to replace every race meeting. IMO, unless the holes are cast, they are dangerous.
As to reduced pad life, I seem to get reasonable life out of the Ferodo pads I use, I'm guessing over 80,000 country km .

[CraigE]

Thats the theory behind it, though I don't think that the difference in rotor is significant in comparison to the differences in pads. The other thing the slots are meant to do is reduce the fade effects from outgassing of the pad.

Out of interest, I ran OE plain rotors with EBC 2000 series proper greenstuff pads and drove down through the pass towards Fitzroy Falls in NSW with a loaded tandem axle trailer that had failed brakes. The hotter my brakes got the better they worked and I was able to brake enough to hear the tyres squirm on the road on any/every corner - it was just sensational.

Changed to EBC slotted rotors and EBC 6000 series 4x4 pseudo greenstuff pads and did the same thing with a similar trailer + load but with fully functional brakes and I had to stop on the handbrake part way through the pass - not being able to stop on the foot brake. A very smokey episode.

BTW, I would never ever fit cross drilled rotors to any vehicle. Slotted is fine, dimpled is fine but cross drill concentrates the forces and every hole acts as a stress raiser. These rotors will crack, and even after a short period of time you will probably be able to visually see radiating fractures from the cross drilling. I had a chat to the fellas at Dba a few years ago, and even they said that the cross drilling is basically for the bling brigade on the street. None of their circuit rotors have it. At work, the fellas have managed to fracture cross drilled rotors on a lightweight Pug on a single trackday. The only time we use them is on a lightweight energy breakthrough car that we built, which has minimal braking time while on the circuit, it is lightweight and it is done to get weight out and reduce rotational inertia rather than increase performance.

Interesting,
The DBA website says quite different.:confused: The conversations I had with DBA were a little different. while they did acknowledge that minor fine cracks may appear around the cross drilled sections, they maintained it would not be enough to cause damage or make them unsafe.:question:
The slotted versions are supposed to dissipate gas build up and help brake fade. The cross drilled are supposed to dissipate gas and dust build up with some cooling properties and the vented dissipate heat better.
As I said I hae put them on my old RRC with Bendix 4x4 pads. It has now done 30,000kms (my Dad now has it) and the pads are only just over half worn, Discs are perfect, no cracking around cross drilled sections. No brake fade as there was with solid rotors.
If the rotors were going to crack I would have thought this would happen with hot brakes and water, but has not yet.

[Slunnie]

I just had a look at their website and it looks like dba are now doing cross drilled for race spec. Interesting, and admittedly it was 3 years ago that I sat down with them. I wonder if the kangaroo paw rotor construction now makes cross drilling acceptable where traditional ventilating design didn't. Thats some good development in that case.

This said, if there are cracks I still would not run them. It's a bit like the Cooper rep that told me it was ok to drive on tyres that are missing lugs... until I asked about them being liable in the event of an accident.

[CraigE]

I just had a look at their website and it looks like dba are now doing cross drilled for race spec. Interesting, and admittedly it was 3 years ago that I sat down with them. I wonder if the kangaroo paw rotor construction now makes cross drilling acceptable where traditional ventilating design didn't. Thats some good development in that case.

This said, if there are cracks I still would not run them. It's a bit like the Cooper rep that told me it was ok to drive on tyres that are missing lugs... until I asked about them being liable in the event of an accident.
Would be nice to get an unbiased professional evaluation of these, because I am thinking of replacing the Defender ones soon.

[Bushwanderer]

Obviously, it's a question of driving style & location, but I've found that the LR rotors & pads work well for me.

While it isn't under extreme conditions, I've even had the "pink slip" (NSW) (RWC) inspector be impressed by the braking on my Disco 1.

The way that I look at it is: the D1 rotors aren't really designed to be machined, therefore I don't want to go to harder pads, thereby promoting disc wear.

On the other hand, if I go to different disc rotors, the selection of appropriate pads becomes a lottery.

I'm happy with LR's selection on this one.

[Zute]

The idea of slotted rotors, is to help release gases that form between the pad and rotor under extreme heat. The gasses come from the resin that bonds the pads together. This is what causes Fade.
Cross drilled(holes) or slotted rotors would actually have less surface area than non drilled/ slotted rotors.
Some pads come with slots in the surface as well for the same reason.
You don't realize how much braking quality you loose over time.
Machining the disc surface of old rotors can have an amazing effect at returning the brakes to there former glory. The same as if new rotors are fitted.
To get better brakes they have to be Bigger, with more surface area between pad and rotor +clamping pressure.
Braking power = friction = more heat. Greater surface area allows heat to escape. ie vented rotors.
Slots and cross drilling are really only needed on racing cars. You have to be really flogging your brakes to make the pads fad. Better quality pads would be my first option in this case.

Brake Handbook by Fred Puhn (HP Books) is excellent reading for any one seeking better understanding.

[Dunnie]

If my Defender was a dog I would say that it was suffering from Hard Pad. The last lot of Bearmach pads are so hard that they will last forever but don't have any stopping power. What do you guys reckon are the optimum brand of pads for stopping power?

[Slunnie]

IF you can get them, the EBC 2000 series are absolutely brilliant - I think I got the last 2000's for the Disco2 when I bought. Avoid the EBC 6000 series like the plague.

[Dougal]

Out of interest, I ran OE plain rotors with EBC 2000 series proper greenstuff pads and drove down through the pass towards Fitzroy Falls in NSW with a loaded tandem axle trailer that had failed brakes. The hotter my brakes got the better they worked and I was able to brake enough to hear the tyres squirm on the road on any/every corner - it was just sensational.

It's interesting that almost all accounts of using EBC greens on 4 wheel cars are positive. Because I've ridden mountainbikes with EBC and they were terrible. Didn't stop well and faded easily.
I do think that mountainbike rotors run much hotter than your average 4wd though.

I fitted the defender front calipers to my rangie with vented rotors and I highly recommend it to all. 25% more clamping force might not sound like much, but it's the difference between having 5% braking power in reserve and 30%.

[rick130]

It's interesting that almost all accounts of using EBC greens on 4 wheel cars are positive. Because I've ridden mountainbikes with EBC and they were terrible. Didn't stop well and faded easily.
I do think that mountainbike rotors run much hotter than your average 4wd though.

<snip>


talking to one of DBA's engineers a few years back he really, really disliked EBC pads as they were so inconsistent batch to batch. DBA do a lot of testing, both on the brake dyno and track and this is what they had found. At the time, he felt Ferodo were more on top of the asbestos free game than anyone else.

[rick130]

I just had a look at their website and it looks like dba are now doing cross drilled for race spec. Interesting, and admittedly it was 3 years ago that I sat down with them. I wonder if the kangaroo paw rotor construction now makes cross drilling acceptable where traditional ventilating design didn't. Thats some good development in that case.

This said, if there are cracks I still would not run them. It's a bit like the Cooper rep that told me it was ok to drive on tyres that are missing lugs... until I asked about them being liable in the event of an accident.

In my experience, cross drilling cracks discs, either solid or vented rotors. As I said back on the first page, if the holes are cast the problem is reduced although
you could be right and the 'kangaroo paw' casting of the rotors reduces/evens out the expansion of the rotor reducing the stress raisers of the holes ??
Anyway, I had the wind put well and truly up me when I started cracking discs on a lowly Formula Ford which only weighs 500kg including driver and is very easy on brakes.

[rick130]

Dougal, only ever run Hayes pads on the mtb, what have you found the best, just for CC (average, not very good technically rider on an NRS ?)

[Dougal]

Dougal, only ever run Hayes pads on the mtb, what have you found the best, just for CC (average, not very good technically rider on an NRS ?)

Yes I've found the hayes sintered metallics (gold backing plate) work the best. My original set is 7 years old, second set of pads in the back, 3rd or 4th in the front.

Some of the riding I do involves a lot of vertical, have turned an 8" rotor blue/brown/purple from the heat.

Koolstops and fibrax are terrible, I bought a second hand set that had them fitted. They'd also glaze the rotors which resulted in a lot of squawking when swapping wheelsets between my bikes.
EBC reds stop well, but don't last. EBC green felt like they were covered in grease.
Hayes semi-metallic (black backing plates) stop well but don't last, I've heard reports of them chewing up rotors if run really hot. But haven't run them long enough to konw.

[rick130]

thanks mate. We're getting a bit OT here, but I funnily enough I found Fibrax pads on the roadie a step up from Dura Ace, which just chewed the sidewalls out on my OP rims and didn't slow me at all, but have always been happy with the Hayes pads on the mtb.
BTW, you aren't the famous kiwi 'Dougal' from the MTBR shock and brake boards are you ?
Used to be on the weight weenies board a lot till the board re-vamp about 3.5 years ago.
Small world if so.

[Dougal]

BTW, you aren't the famous kiwi 'Dougal' from the MTBR shock and brake boards are you ?

Possibly.:angel: