Top Trumps - Brakes

[Dean Roberts]

Front Disk Brakes -

 

260mm vented VS 240mm grooved, drilled & vented.

 

Who wins?

[Guest mower man]

Fit what you like or need!

[Dean Roberts]

Drilled and grooved look pretty with painted calipers.

But bigger 260mm seem to sit better within a large alloy wheel.

 

Oh the choices.....

[maccavvy]

Bigger is better imo

[Dean Roberts]

Bigger is better imo

 

Isn't that what most women say?

[brumster]

Front Disk Brakes -

 

260mm vented VS 240mm grooved, drilled & vented.

 

Who wins?

 

At this risk of further building up the belief that cars like ours need 260mm discs, I'll say this.

 

Cross-drilled I have never, ever been sold on. It's removed material, which must be detrimental, and any thought that you'd get actual airflow through them has got to be *bleep*s. Coupled with the fact that I've only ever seen grooved discs on fellow competitors cars that I've held in any high regard, I've never been fussed for cross-drilled. I've no idea what the purported benefit is - naturally I could google it and spout it here, but then I'd be no different to every other internet warrior out there.

 

Short answer - I look to my fellow competitors, see what works well, and the general gist is grooved seems to work well for most.

 

Larger diameter disk will naturally give your brakes more strength in terms of the angular torque the brakes can put on the axle. Whether your car needs that is something I'll let you decide. Larger diameter means more weight, obviously, so it's a trade-off. And also it's got to fit under your rims of course, along with the caliper, so you need to bare that in mind.

 

Something you've also not talked about it disc thickness, which really comes into the life and heat dissipation properties of the disc. On the competition car I had the choice of 3 thicknesses; a respected colleague suggested the thickest possible for longevity and resistance to cracking, but it was something like a 500g difference per disc, so I opted for the middle choice and just swapping the discs more regularly if needed.

 

My one overriding point is that, we can talk all we like about brakes in a hard environment like racing, but most of this is moot for a road car.

 

But hey, if you want to put some big brakes on, don't let me stop you spending your money !

 

If it was my money, and I was after some sort of ultimate race setup on my Zero, I'd go 240mm grooved/vented discs, with some light aluminium calipers, and Performance Friction pads, braided lines and AP500 fluid. I don't think AP do a disc that small though, so I might be looking around at Alcon's catalogue/etc.

 

edit: I should have said, the grooving/slotting is I believe to scrape the pad surface at extreme temperature/use. It really is a race-focused approach, will obviously bring with it serious pad wear. Again, road benefits? Meh...

Edited June 15, 2016 by brumster

[brumster]

Here's a close-up of mine and one thing to note is the disc material - this can make such a massive difference. You want to know the difference between a £10 road disc and a proper race disc? Come run your finger over these - you can see it in the material. It's really abrasive. You can feel it just with your fingers. That's the difference between "Meh" brakes, and "bloody awesome" brakes. Not size alone; spend money on quality gear and you'll get a quality performance.

 

 

[Dean Roberts]

Here's a close-up of mine and one thing to note is the disc material - this can make such a massive difference. You want to know the difference between a £10 road disc and a proper race disc? Come run your finger over these - you can see it in the material. It's really abrasive. You can feel it just with your fingers. That's the difference between "Meh" brakes, and "bloody awesome" brakes. Not size alone; spend money on quality gear and you'll get a quality performance.

 

 

 

Nice bling

[brumster]

It's not so bling-shiny any more!

[richardm6994]

As always, I think Dan (brumster) is talking a lot of sense!

[Guest lotusPaul]

Mathematically speaking, if the larger disks "break" the coefficient of friction of your rubber then they will cause lock up. No good. But if they dont then its ok to use.

Personally I'd stick to the smaller disks anyway.

Larger disks tend to cause varnishing

Of the pads, the groves are there to prevent this but at low operating temps seldom do.

The cross drilling are there to allow cooling of hot disks which seldom get hot enough to use them, so they actually become a start point for cracks.

 

If your on a track day and drive to it, swap to a set of track disks and matching pads then bleed new fluid through.

 

After track action and when cool enough swap back to road disks and pads and again re bleed.

 

Or, if your just after improving braking and can put up with dirty wheels go for a softer pad and the 240mm disks,braided hoses and new fluid.

[brumster]

The cross drilling are there to allow cooling of hot disks which seldom get hot enough to use them, so they actually become a start point for cracks.

 

 

I seriously doubt air flow through a spinning disk is significant through these cross-drillings. Air flow is generally sucked in to the central back of the disk and vented through the internal gaps of the casting, exhausted out the edge of the disk (or is it the other way round?) - hence the directional vanes in the casting to draw air through. Putting holes through a disc to aid venting I just find incredibly hard to believe works, but I'm not a physics major in fluid dynamics so I can't really comment with any conviction ! A brief google search suggests they are indeed pointless on modern designs as they were originally introduced to combat gases cooked off brake pads back in the days before pad technology was what it is today. Whether that's true or not, I don't know, but it's backed up by the fact I see little by way of competition cars with cross-drilled discs last time I was walking round the paddock

 

I agree they are more likely to be a staring point for cracks; I'd rather have more meat in my disc than holes!

Edited June 15, 2016 by brumster

[Guest lotusPaul]

I think we're agreeing on same issue with the cross drills. Mine has solid disks and works fine..1970 elan plus 2. Gets driven to track and back too.

[speedtripledan]

240mm solid discs normal pads drums on the back with normal shoes and I can lock up. nice and progressive plenty of feel. Twin m/c and bias bar. The key is the pedal ratio, get that wrong and you are going to spend a fortune to compensate for it. I found this out yonks back in my 2b days.

[Bob Tucker]

Agree with Dan.....

various pedal ratios here between 5.1:1 and 7:1

 

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