Hammerhead disc brake adapters

[fyrstormer]

...but, just like in a car, a bigger rotor setup does affect performance if you have the clearance for it...the larger rotor takes less pressure the further away from the axle, to stop it...some of the trails I ride xc, some are very technical and some also have very gnarly downhills in the mix, so for me the bigger rotors are definitely a bonus.

You can't get enough braking power out of the rear wheel to overburden even a normal 160mm rotor; that's why some companies actually make 140mm rotors for rear wheels. Furthermore, you need a certain amount of pressure on the brake pads to keep them clean, so they won't accumulate glaze that will make them noisy and ineffective. So a smaller rotor, perhaps with lower-friction pads as well, is actually a good idea so you can apply enough pressure to keep the pads clean without locking the rear wheel.

As for the front rotor, depending on your riding style you might be able to overburden a 160mm rotor, but it's not likely, because *unlike* a car, you don't have very much kinetic energy even when you're moving as fast as you can pedal in top gear. (even the best bicycle racers can barely generate power at a rate of .5 kilowatt, whereas the average car engine can generate power at a rate of 150 kilowatts -- *and* the car weighs 10-20x as much as you do.) The front disc will only really be in danger of overheating during long steep descents.

Compared to your weight, even small bicycle disc brakes have *tons* of stopping power -- you're not going to be squeezing the brake lever all the way to the handlebar while desperately hoping you can stop in time. Larger discs do provide more leverage, but their biggest advantage for downhill racing is the extra surface area -- stainless steel isn't very good at dissipating heat, so a wider-diameter rotor will have more surface area to cool off.

my front fork will have no problems whatsoever dealing with the largest rotors i can attach, but I don't want to run a 203 up front and have a 160 in the rear, IMO it'll feel unbalanced...lighter pressure used to brake the front and harder to stop the back does not make for good braking...

You'd be surprised. It actually takes very little time to adjust to the idea that the amount of force you apply to the brake lever delivers braking force relative to the maximum each wheel can provide, as opposed to braking force measured on an absolute scale. It actually feels more imbalanced if you can squeeze the crap out of the front lever without locking the wheel, but the most you can do to the rear lever is a light touch.

I've had a front disc on my 756 for about 10 years now, but I've only had a rear disc for about 4 years. During the first 6 years, I had a mixed setup with a disc in front and Shimano XT V-brakes in the rear. That felt funny at first, until I got Avid brake levers with adjustable leverage; then I was able to tune the leverage on each lever so the feel of each brake "made sense".

When I upgraded the rear brake to a disc, I ended up turning the leverage all the way down on both brake levers, and the amount of grip on the rear brake was still too much; I spent a couple years searching for good low-friction pads to use with the rear disc, so the brake feel would "make sense" again. I finally found a kevlar-and-copper (NOT kevlar-and-brass) pad made by DiscoBrakes that works just right. Now the rear disc once again has significantly less braking power than the front disc, which uses sintered bronze pads, and I can once again apply significant force to the rear brake lever without locking the wheel.

It actually feels quite natural to have different response from the front and rear levers, as long as the amount of force you apply to each lever is roughly the same.

[Colin]

Very informative response, as always, Fyrestormer!
so to be clear, what size discs are you running?
and what make ?

I have Avid BB7's on my XP-X set up for the road with 160mm discs and OEM Avid Pads and am very pleased with both the feel and stopping power under a loaded bike and on long Scottish road descents.

My next "disco" plans are for my OzM to be Avid Juicy 7's with 203mm front and rear, and for my wife's OzX to be Avid BB7's with 185mm front and rear, but have maybe overspec'd them both! <GRIN>

My only concern is wether the 203 (or even the 185) will foul the swing-arm? and maybe this is the thrust of Shaiitaan's original Q?

I have no idea when it comes to brake pads, as I say, I'm running the OEM one's on the XP-X at the mo' and have some Clarks Organic pads as spares, that I haven't needed to use so far, dunno what "sintered" or "organic" mean in real use terms............

Col.

[fyrstormer]

Very informative response, as always, Fyrstormer! so to be clear, what size discs are you running? and what make ?

I have Avid BB7's on my XP-X set up for the road with 160mm discs and OEM Avid Pads and am very pleased with both the feel and stopping power under a loaded bike and on long Scottish road descents.

I'm using Avid BB7 calipers front and rear, 160mm Magura VentiDiscs front and rear, and sintered-bronze pads in the front and kevlar/copper pads in the rear. (The copper shavings in DiscoBrakes' kevlar pads are softer than the brass shavings used in most kevlar pads, so it wears down smoother and doesn't produce an annoying grinding sensation when the pads touch the disc. Most people probably don't care, but I do.)

With saddlebags on your bike, that increases the maximum braking power of the rear wheel a bit, since the saddlebags push the rear wheel into the ground a bit harder. However, unless you're carrying lead-shot in the bags, there's no way it would put enough pressure on the rear wheel to make a 203mm rotor worthwhile.

My next "disco" plans are for my OzM to be Avid Juicy 7's with 203mm front and rear, and for my wife's OzX to be Avid BB7's with 185mm front and rear, but have maybe overspec'd them both! <GRIN>

My only concern is wether the 203 (or even the 185) will foul the swing-arm? and maybe this is the thrust of Shaiitaan's original Q?

It took me a minute to remember the definition of "fouling" that you meant. Are you asking whether there's enough clearance for a large rotor? A 185mm rotor is an inch wider than a 160mm rotor, and looking at my 756, it looks like there might be just barely enough clearance for that -- but definitely not enough clearance for a 203mm rotor. Maybe newer bikes with carbon swingarms have more clearance; I don't have my dad's 857 handy to look at.

Physical clearance aside, I don't know how strong the swingarm is against unbalanced torsional loads, though it certainly *feels* robust. While I would expect the adaptor to break first, I suppose there *is* the possibility that the bolt-holes on the swingarm could be damaged by extra torque from the larger rotor -- IF the rotor could be used to the maximum extent of its capacity. But that will never happen in real life, because the rear wheel will start skidding after only a small fraction of the 203mm disc's braking capacity is reached. You could have a rotor the same size as the wheel and it wouldn't be able to provide more braking power once the tire starts skidding.

<physics>
The sum of all forces acting on a bicycle (or any vehicle) can be visualized as a line hanging down from the bicycle's center-of-mass. There is a special name for the point where that line intersects the ground -- I don't remember if there's a scientific name, but I'll call it center-of-balance. In any event, I'm sure everyone here is familiar enough with basic physics to know this dangling line will tilt backwards when the bike speeds up, and tilt forwards when the bike slows down. When the bike slows down fast enough to push the center-of-balance forward of the front wheel, the bike can no longer balance on its wheels and it flips over. But even under slight braking, the center-of-balance slides forward a bit, which indicates the bike is trying to lean forward -- and that means there is *always* less pressure on the rear wheel than on the front wheel when the bike is slowing down.

Since friction is directly related to pressure between two objects, and since braking power is dependent on tire traction to transfer kinetic energy from the bike to the ground, the lower pressure on the rear wheel means it will *always* be less effective for braking. (though it may be safer in certain circumstances, like braking in a slow, sharp corner, or braking on a steep decline where the center-of-balance is already perilously close to the front wheel.) The harder you brake, the more you decrease pressure on the rear wheel -- so the harder you brake, the more you decrease the rear wheel's ability to provide any braking power at all. That is where the maximum limit on rear-wheel braking power comes from. There simply is no need for a huge rotor on the rear wheel.
</physics>

I have no idea when it comes to brake pads, as I say, I'm running the OEM one's on the XP-X at the mo' and have some Clarks Organic pads as spares, that I haven't needed to use so far, dunno what "sintered" or "organic" mean in real use terms............

Sintering means heating up a pile of metal shavings until they're almost melted, then squeezing them together so they stick to each other. It's a way of producing a high-friction brake pad out of metal, without unifying the crystalline structure of the metal which would result in resonance when braking. (in other words, it would squeal like a stuck pig.)

Organic pads are produced from soft fibers mashed together with some kind of resin. Often it has bits of metal shavings added to help scrape the rotor clean, but most of the braking work is done by the fibers and the resin. The most popular fiber to use is kevlar, which isn't actually organic, but it's strong and it has a high burn-point, which is what really matters.

[Colin]

Very good response, thanks!

yes "Foul" is being used in the context of the disc contacting the swing-arm when being assembled, not in the context of the warm wet feeling in one's baggies when descending at too fast a speed due to the failure of the bike's retardation system...............<GRIN>

Col.

[Spokes]

Just to add my bit to this, I've bought Hope X2's for my OZx build. They come with 182mm front and 160mm rear. These are billed as xc, free ride, race type set up.

The physics has always made perfect sense to me and the principle of needing a more powerful brake up front than the rear has always been self explanatory. In fact when I ride fast on my race motorbike I hardly use my rear brake at all. Just the lightest touch is all that's needed and that's a twin disc up front single on the rear.

Before discs were developed for bicycles and we all used canti and v's you didn't have a choice. Although I suppose you could have use one of each?

But I would think with discs there is definitely a chance of going too powerful. Whether you run different pads front to back as Fyrstormer does or run a bigger/smaller disc setup, it will achieve the same thing. 183mm up front or 160mm could be the same performance across different makes but the principles are still the same.

Anyway I would say don't go too big on back, as Fyrstormer says you will be locking up the rear everywhere.

Chris

[Jcshinkle]

Any blueprints available to make your own? I can't find them anywhere and would really like to upgrade to disc. I've tried EBAY, CL, and about every Google search I could try with no luck. 

[Spokes]

Mike Hammer was the only person making them commercially apart from Proflex/k2 so if he has stopped you might be out of luck. There are various drawings in previous threads so have a look back and see what you can find.

Chris

[Shaitaan]

yea the only way to find out is to send him a msg....he still has his account w/ ebay, that would be a good place to start

http://www.ebay.com/usr/racing_green_motorsports

I've sent him a message through his page there, so hopefully I'll hear back from him soon

[Jcshinkle]

Thanks, guys.

[Hammer]

Hello Chaps!

Hammer reporting for duty. :-)

I stopped listing them on ebay due to the listing fees and after an i itial rush there were some months where I would not sell any.

I still have some in stock (ask me) and once they run out I need to make batches of 10.

Email me a picture of your bike and the bike model if you need one and I'll try to help out.

The prices vary depending if it is new or old stock, but approx €50-60 each including shipping.

mike_billett@yahoo.co.uk

[Spokes]

As if by magic he appears! 
Cheers Mike, I might even buy another for myself as you still have some left.


Chris

[fyrstormer]

In a way, it's kind of a shame that these aren't consumable parts, because I'd be glad to buy more of them to support the cause if I had any use for more than one.

[Hammer]

Could try starting a rumour about age hardening and brittleness....

Replace every 5 years.

Haha......

Truth is.... They still be perfect long after our frames turn to dust...

[Hammer]

Hi guys,

I had a request for an x56 adapter but am out of them.

I can get 10 made if there is enough interest to sell 5 of them?

Adapters for the carbon bikes, 857/957 and the x000's are in stock.

Mike

[Shaitaan]

would work for me if others are game...one of the frames I wanted to retrofit was for my x56...