A question about brakes, tires, and stopping power

[scotch]

currently i'm riding a 72 cb500/4 with stock brakes and standard tires and can lock both the front brake (disc) and the rear brake (drum) if i feel like it.

if my logic is correct, this would mean that i have reached the maximum stopping power possible out of this set up. right?

dual discs on the front would use less hydraulic effort than a single disc would, and a disc on the rear would likely react quicker than the drum, but it seems that the only way to get more stopping power would be to get more rubber in contact with the road.

am i correct in thinking this?

 

[VonYinzer]

Sort of...

But there are other things to think about. More rubber (Im assuming you mean wider tires) also increases drag (slower starts) and reduces cornering. Too wide and you effectivly make the bike unsafe.

Good braking is about technique as much as it is about the equipment. Good braking means stopping in the shortest time without ever locking up the brakes (at which point you are no longer in control of the bike). Modern brake setups allow for more brake control without locking them up.

Thats a real laymans description, but Im sure ya get what Im saying.

 

[scm]

... can lock both the front brake (disc) and the rear brake (drum) if i feel like it.
if my logic is correct, this would mean that i have reached the maximum stopping
power possible out of this set up. right?

Probably, but not neccessarily.
A very sudden front brake operation can lock it if there's not yet
sufficient weight shift to the front axle even if the brake was
"too weak" to lock with all the weight to the frontl.
On the other hand, a weak rear brake can easily lock if the
rear wheel has no normal force...

... the only way to get more stopping power would be to get more rubber in contact with the road.

Contact area doesn't affect friction, only normal force and frictional coefficient.
So what you need ain't wider but stickier tires.

Best regards
Sven

 

[Nanahan Man]

You need tires with more grip and a better braking technique to load up the front tire to get better traction. It's all in the "squeeze".
I have not been able to "lock up" the front tires on any of my bikes unless I snatched the front brake too fast.
Maybe you have really crappy tires...I don't know.
Dual discs will give you more stopping power from high speeds or with a heavier load.
I have duals on my ST1100 but that's a heavy bike. Installed duals on my XS650 and it's overkill.
Still, proper technique is the key.

 

[crazypj]

By 'standard tires' you don't mean standard in 1972?
Fit some decent high grip rubber and you'll see how crap the single disc really is on a bike weighing around 600lbs with rider
I fitted dual discs, wider rims and 'grippy tyres to my CB550 and never locked front on a dry road
I also have dual discs fitted on my XS650, but, I used two standard sized XS discs. (standard dual disc 'euro' type XS use smaller diameter discs than single disc bikes)
It isn't overkill, it's just about right

 

[teazer]

PJ, Imagine a pair of those large XS disks lightened and on the front end on a TZ350 with a stock master cylinder. That was stupid and had zero degree of modulation it was on or off and no good for trail braking.

Braking consists of more than one step. First step is to apply small amount of brake to generate weight shift.
Bike starts to dive at the front end as weight shifts
progressively apply more brake pressure as the front wheel nails itself to the ground.

Or grab brake, wheel locks, you fall down.

It's all in the touch. The technique.

 

[crazypj]

I used Suzuki 4 pot calipers and master cylinder with Yamaha rotors

 

[scotch]

Yeah, they're modern tires. And i now understand that grippier tires and a higher coefficient of friction would make a bigger difference than "wider tires." It's not like my brakes lock up every time i touch them, it's only if i feel like screeching to a stop that i lock them up. They've got a very good feel and amount of play.

Thanks everyone for all the great info! I'm putting together a dual disk setup for my next 550/4 project and this has given me a lot to take into consideration.