"bacon slicer" brake discs to adapt GZP wheel to CB500Four

[Joksa]

Hi,

Since my aftermarket ronal wasn't true, I was searching something similar to go with rear wheel and found a 5-spoke GPZ wheel. 240mm or 260mm Kawasaki discs where too small (vs. original 275mm) so I desided to have new discs cut with laser/water from 5mm Hardox steel.

Here's the "bacon slicer/cutter" desing I am going with (double discs front so I though I'll manage with those holes). I chose fewer bigger holes hat could be cut at the same time and also keep the cutting cost lower compared to lost of smaller holes.

 

[manchestermichael]

whats the price of cuting new discs ? and whos doing it i would love a wavey front disc but just looking in to useing a new sportsbike brake disc and just redrilling mounting holes to fit my hub

 

[locOleoN]

whao.. thats gonna look cool...

 

[Joksa]

whats the price of cuting new discs ?

The price will be 50 euro per disc from that material.
If you find decent 2nd hand sport bike wave disc, you could have a new carrier made.

 

[Joksa]

After first mock up discs look pretty good \o/
I still need to polish/brush them and have them zinc plated.

 

[steve]

I really like the enthusiasm and originality here, but I have to point his out:

The little holes that you often see in rotors are for cooling. When a disk brake is used to its limits, there is less and less stopping power (friction) due to the overheated rotor, so engineers started designing holes in the rotors to allow for greater air flow, and better cooling. The holes are deliberately made small so that many holes can be made without compromising strength and braking efficiency. Large holes would make a rotor weaker than an equivalent area of smaller holes. More importantly, it's possible that brake pads may "catch" on larger holes. That could lock up the brake, or damage the brake pads, or both. I have never seen a rotor drilled with large holes like yours. Your rotors have a substantial part of the brake pad contact area removed, whereas typical drilled rotors have the drilled-out areas spread more evenly over the surface of the rotor, leaving more contact area for the brake pads. Please test those rotors carefully before you really need to make a stop in traffic.

"Bacon slicers" were simply aluminum cooling fins added to drum brakes to help dissipate heat. Not that they were especially effective at dissipating heat, but in the early days of racing, builders didn't have any better options. I can see why you would emulate the look of bacon slicers (vintage appeal). But the large-hole bacon slicer design is probably a poor design to use on a rotor.

 

[Joksa]

Thanks for the comment. I have also been thinking this issue and even though my general rule is 'form follows function', I chose the design based more on aesthectics ( though the holes do lighten the discs). Since I am not going to race the bike and I do have duall discs, I probably won't run into any performance issues. Nevertheless I am going to test these in quiet environment before heading full speed in traffic. If this would have been a case of any higher performance bike, I would probably not have taken this design. I do also have couple of other design ready, I can quickly have another set made with different design.

What comes to the area: those 15 of 20mm diameter holes equals ~94 8mm holes.

 

[Koestum]

Actually when the brake pad material rubs against the disc a gas is created. This causes a barrier between the disc and pads thus reducing friction and braking. The holes and grooves that are cut into the discs allow an escape route for the gas. Cooling is a benefit but maximum braking is the reason for grooves and holes. I believe this technique was first used used on F1 race cars way back in the day.

Holes weaken the disc, so the smaller and fewer the better.