veganbikes

What?

cxwrench

That's funny. Most riders can handle a rear wheel locking up in a turn a WHOLE LOT better than locking the front. Locking the rear is most definitely not an instant crash...for nearly every one locking the front is.
I was reading along pretty much agreeing with everything you've written, except for this. It's just plain wrong. When the rear tire loses traction you ease off the rear brake to get the wheel rolling again. Not rolling=no traction. Rolling=traction.

Yan 

You didn't ready post carefully enough. I said during emergency braking during a turn. If you lock the rear during this you will crash instantly 100% of the time. There is no recovering from this. You disagree with this claim?

By " lock " the front do you mean skid it like skidding the rear? It's not possible to skid the front wheel on dry pavement. The whole bike will flip over first.

Iride01 

Then I must be the greatest cyclist of all time! Or at least I've got enough awareness of what's happening that I release the rear brake and let it roll again. I really believe others of us do too. I've locked up the back and went almost what felt 90° to my direction of travel during a emergency braking and then recovered. Had sense to keep my front wheel pointed in the direction everything was going.
Well now you are setting up specific conditions that don't apply to every ride. Have you never ridden on pavement with spots of sand or other loose material? Or even wet pavement, slimy areas that stay wet and grow algae or where a light sheet of mud from a recent rain washed over the road?

cyccommute 

Neither the friction force nor the force applied to the levers is “constant”. The friction force is close to constant but it can vary mostly due to contamination such as water and oils. The force applied to the levers varies even more widely due to many factors including how strongly the rider squeezes the lever but can also include other factors. Most people…even in an emergency situation…don’t go from full off to full on braking in an instant. Stopping the wheel from spinning that quickly will result in the rider going over the bars.

Going over the bars isn’t a function of gravity but of the friction between the road and tire. Bicycles don’t have enough weight nor a low enough center of gravity for the coefficient of friction cause the front wheel to slide. The brake stops the wheel from turning causing the center of gravity to go forward of the axle and the rider goes over the bars. Yes, gravity is involved in the friction between the tire and the road but “going over the bars” is due to momentum.

The “curve” I’m talking about is the time it takes from the brakes to slow the momentum of the system, i.e. the stopping distance. That said, there is also a curve for the brake’s effect on the wheel. It takes a small amount of time for the brakes to make contact with the brake surface and then to slow the spin of that brake surface.

No, there is no delay in weight transfer but it takes time for the weight to transfer forward and for the system to stop moving. That’s the stopping distance and is far slower than the speed of light. The stopping distance is a function of the square of the speed divided by the coefficient of friction between the road and the tire times the gravitational constant. The faster the vehicle is traveling, the longer it takes to stop. Up to the time where the rear wheel lifts…which is, again, far slower than the speed of light…the rear wheel is contributing stopping power but it does diminish as the center of gravity is moved forward. Keeping that center of gravity from moving forward can greatly increase the influence of that rear wheel’s braking power. Moving the CG rearward 4” and downward 2” can increase the possible deceleration of the bicycle from 0.5g to 0.9g

Do you always use the same amount of force on your brake levers in all situations? Of course not. Every time someone uses their brakes, they use a varied amount of force on the levers. Sometimes you even ramp up (or down) the force on the levers depending on the situation. That’s a curve.

I don’t follow. Your hands are independent of one another when it comes to braking. How much force the left hand applies has no influence on how much force the right hand applies. I don’t apply less force to the brakes because I’m using both brakes nor do I think most people do. Nor am I not saying to do that. There’s just not that much thought that goes into braking. If you do that much thinking, you are going to greatly increase the reaction time.

cyccommute 

The problem isn’t that the rear wheel is locked. The problem is that once the rear wheel starts to skid, the weight is transferred too far forward to the front wheel. Continuing to apply force to the front brake will just lift the bike more and decrease the contact of the rear wheel with the ground. Getting off the front brake, stops the weight transfer and puts the rear wheel back on the ground where it can roll again and not slide.

Just to be clear, I’m not saying to stop using the front brake. Releasing the front for a moment is usually enough to put the rear wheel back on the ground to reestablish the traction that is lost in a skid.

rydabent

But they scab up your high priced rims.

Rick

Keeping your body from moving forward over the bars by countering with your muscles while you brake in an emergency Is also a major point of weight transfer. After figuring this out I never went over the bars again.This is the first thing I taught my young children. I have owned and ridden motorcycles and letting off the front brake when the rear wheel skids Is equally important.

I can lock up both the front and rear wheel on my Burly bongo without going over the bars.

cyccommute 

Tandems are different. Too long and too heavy to endo. You can slide both wheels on a tandem, although control would be poor.

sweeks

I've been waiting for someone to go in this direction, and this comes close. Since in a hard stop the rider's weight is transferred forward increasing the risk of going over the bars, the rider can lift their butt off the saddle and shift it rearward. This moves the center of gravity back and reduces the tendency of the rear tire to lift off the pavement. Watch a mountain bike rider braking on a steep downhill... their belly button is practically on the saddle. This is a useful maneuver to practice on a road bike as well. If it's a familiar maneuver, it will come naturally in an emergency.

I remember learning to ride a motorcycle 50 years ago; one of my instructors said that the purpose of the rear wheel under hard deceleration is to provide just enough drag to keep the bike going in the desired direction. At another learning experience with off-road motorcycles the mnemonic for throttle action was "ON for control; OFF for traction". Also, "When in doubt, GAS it!"
As others have noted, the OP may *think* his rear brake provides enough stopping power... but at any reasonable road speed the front brake is the one to depend on.

Charlie Ky

​​​​​​What is a reasonable road speed ?

I'm not trying to look for reasons to justify using my rear brake primarily but I just don't ride that fast. And as I mentioned I can't because I've got several intersections I have to cross on my route. A steady 10 mph is just lovely for me. I just enjoy riding, and of course I'll use my front brake if I have to.

I'm sure you fellows with road bikes would get bored 10 minutes into a ride following me lol.

cxwrench

I don't care how slowly you're going, if you need to stop quickly the front brake is the one to use. If you're dawdling along at 10 mph and just need to come to a slow stop the rear is ok. That said if you use just the rear brake you'll wear out pads and rotors faster than if you just used the front because the front is so much more efficient at slowing you down.

Charlie Ky

I noticed the front brake has better stopping power the first ride on my new bike.

And looking back at my posts in this thread I don't see anything I've said to infer that I doubt it does.

What everyone that has described and argued over concerning these hypothetical situations one may find themselves in is informative but I just wanted to know about how long in general brake pads last under the conditions I described in my op as this is my first bike with disc brakes.

sweeks

Anything over walking speed.
FWIW, my average commuting speed is 10-12 MPH. The front brake is very handy at those speeds when a car pulls out of a driveway or I notice a pothole, or a light changes just as I get to the intersection.
Here's a test suggestion: Does your rear wheel ever skid? If not, you're probably OK using the rear brake only.

cxwrench

A looooong time. That's as accurate as anyone can get.

Charlie Ky

No, rear wheel never has locked / skid. I've come up on countless vehicles backing out of their driveways. Never been close enough to them to have to stop rolling. Watching up ahead has become second nature.

I like my bike and my skin, so I'm very safety conscious. When I cross the intersection of one or two 4 lane roads I wait for the crosswalk light and walk my bike across per state law. Traffic or no traffic. The law says stop for stop signs so I do. No big deal. Safest way to grab a swig of water or check my phone if need be while I'm at it.

My route on the access roads along the parkway have a few short stretches of narrow sidewalk. If I have to pass a pedestrian or a another cyclist going either direction I don't mind pulling off sidewalk and walking until I pass them. Elderly pedestrians appreciate that.

Charlie Ky

Good deal. I'm not a mechanic but I can pull and replace parts I can get to with the proper tools on my truck. Inside the engine or transmission, It'll go to the shop. I'm sure I won't have any issues working on my bike when the time comes.