Topic: bench racing, rear F0 disc vs drum, drag race bike.

[Don R]

 On a sohc drag bike is there a mechanical advantage to either style of brake? The old school rule of thumb was a drum has less drag and may be lighter. Not sure if that's the same in our case. I have both types, the F0 is wrecked and cut up already.   

[dragracer]

I ran an  early F model disc brake set up on my F3 before installed the PM Chicanes.  I relaced the spoke hub to a wider aluminum Sun rim and installed a 5.5" slick. Started off with a 170/18 DOT tire but never could get that street tire to hook. Not certain how much weight I could have saved using a rear drum but I just prefer disc brakes for better stopping power-- just in case. 

[Sam Green Racing]

Don, the difference is not worth talking about but are you talking front or rear ?
If it's the front, go with the disc for the greater stopping power (if you have to stop Quickly).
When it comes to the weight, you would have to weigh both systems.

Sam.

[Don R]

 Rear, Sam. I'm a double disc fan on the front on a street bike. This question is more closely considering a drag race only situation. I just happened to have a rear disc setup and am thinking what's the best drag bike I could build from the parts I have.

[Sam Green Racing]

Don, my bike was only used for drag racing so if you're concerned about weight, why two discs up front ?
I had a single disc up front and never needed anything else, plenty enough for stopping quickly on a drag strip.
I had a disc on the rear also and being an Automatic, it was only used to stop the bike from creeping forward through the stage beam.
It was hooked up to a Bussa hydraulic clutch leaver so was just a case of letting it go when I was ready, I never touched it after that.

Sam.

[Don R]

  My double disc remark referred to a street bike, didn't mean to muddy the waters.
  I hadn't considered the use of the rear disc as a roll control on an auto bike, releasing with the left hand would be entirely natural.
  Holding an auto bike on the starting line using the front brake would compress the forks, that might affect the reaction time and I'd assume your right hand is busy with throttle control.
   

[HondaMan]

I can't remember a rear disc on these 'F' bikes that DIDN'T drag, and often a lot. Honda once said this was to keep the disc clear of water and chain lube, but who knows? The drum doesn't drag, and the sum weight of the parts is lighter with the drum as well.

[Don R]

I can't remember a rear disc on these 'F' bikes that DIDN'T drag, and often a lot. Honda once said this was to keep the disc clear of water and chain lube, but who knows? The drum doesn't drag, and the sum weight of the parts is lighter with the drum as well.

 Thanks Mark, that was the thought on the old drag cars too, the new drag cars have evolved to need some bad ass brakes.
    I needed to buy my dragster driver new Strange brakes and a new Stroud Super Gas chute, one size bigger than she was used to. (for mph recommendations) For the test I insisted she use the chute so the brakes had a chance to break in. I neglected to mention it was bigger and when I got to the end of the track she said holy crap Dad, I was hanging in the seat belts for a second there. We normally wouldn't replace two things at once but found two possible problems on mid season inspection day and had to.  I guess that's why we had to put in a half inch chute retainer bolt. 

[HondaMan]

I can't remember a rear disc on these 'F' bikes that DIDN'T drag, and often a lot. Honda once said this was to keep the disc clear of water and chain lube, but who knows? The drum doesn't drag, and the sum weight of the parts is lighter with the drum as well.

 Thanks Mark, that was the thought on the old drag cars too, the new drag cars have evolved to need some bad ass brakes.
    I needed to buy my dragster driver new Strange brakes and a new Stroud Super Gas chute, one size bigger than she was used to. (for mph recommendations) For the test I insisted she use the chute so the brakes had a chance to break in. I neglected to mention it was bigger and when I got to the end of the track she said holy crap Dad, I was hanging in the seat belts for a second there. We normally wouldn't replace two things at once but found two possible problems on mid season inspection day and had to.  I guess that's why we had to put in a half inch chute retainer bolt.

It sounds like you need a G-meter, too!

[dragracer]

Just retrofit modern brakes like I did on my F model before I went to the PM weeks and grimeca brakes. I used a ZX11 master cylinder. I realized it was the master cylinder causing my drag, not the caliper. It was holding pressure in the line for some reason keeping the piston pushed out. 

I can't remember a rear disc on these 'F' bikes that DIDN'T drag, and often a lot. Honda once said this was to keep the disc clear of water and chain lube, but who knows? The drum doesn't drag, and the sum weight of the parts is lighter with the drum as well.

 Thanks Mark, that was the thought on the old drag cars too, the new drag cars have evolved to need some bad ass brakes.
    I needed to buy my dragster driver new Strange brakes and a new Stroud Super Gas chute, one size bigger than she was used to. (for mph recommendations) For the test I insisted she use the chute so the brakes had a chance to break in. I neglected to mention it was bigger and when I got to the end of the track she said holy crap Dad, I was hanging in the seat belts for a second there. We normally wouldn't replace two things at once but found two possible problems on mid season inspection day and had to.  I guess that's why we had to put in a half inch chute retainer bolt.

[Don R]

It sounds like you need a G-meter, too!

[/quote]
 Oddly enough we normally do, but it drops out under 11.8 volts and with the 50 amp alternator and already huge electrical load, late season we added Holley super sniper EFI with an O2 sensor, 8 injectors and a twin motor fuel pump. I had to forgo the data until I could fit a bigger alternator, battery and appropriate wiring.
  This year it gets a 120 to 150 amp alternator and an Oddysey pure lead battery, I also replaced the nose weight with two 170 cca smaller oddyseys. I'm undecided whether to tie them to the main battery or use them total loss operating specific loads.