Front vs. rear brake panic stop?

[mecheic]

I don't know the answer to this one and maybe one of the younger MTBers with crash pads could test this for me.
I recall as a child that the old coaster brake cruisers could lock up the rear wheel and skid sideways or even do a 180* turn to stop. The skinny tire "English Racers" with front brakes could only stop going straight ahead in an upright position and were at risk of going OTB while doing it. It has occured to me that with fhe wide tires most of us run and the large front rear disc brakes modern bikes have this is still a valid question. The real question being is if one method is better than the other to say avoid a car that pulls out in front of you and stops, you only get one chance to choose which method you want to use.
Front brake- you're commited to staying upright and not going OTB.
Rear brake- you lock the rear and get it swung around ASAP but can lay the bike down.
Laying the bike down has the advantage that the bike takes the impact, OTB it's your head and neck.
I haven't used the rear brake technique since forever, but maybe it should still be in my bag of tricks.

[zebee]

Front suspension changes things, but on the whole most of the braking is from the front.

If you lock the back it is because the weight transfers to the front, even without suspension. That's the laws of physics: you slow the front down but forces are still there. Just like when the train slows suddenly and you keep moving.

I have had no problems hitting the front brakes hard on a skinny tyred drop bar bike until the rear skids. The front doesn't lock because it has all the weight on it. Experiment with sitting well back so you have all the weight on the back, then try to lock the back wheel with back brake only. Bet you find it's really hard to do with weight on the back and no front brake. On your cruiser you had to get off the saddle or jerk the bars to get it to slide.

If you have front suspension you need to do what motorcycle riders do: some back brake, slow take up on the front to take up the suspension travel, then hard braking. Most riders on modern motorcycles don't use the back at all. I do because I learned on (and still own) drum braked bikes where you need all the brake you have to stop before the middle of next week....

If you don't have suspension then some back and a lot of front. If the back skids then don't tense your arms just back off a bit and keep your head up and looking forward, keeping the front hard on. If you practice your emergency braking you soon learn how much rear to use to start and when to back off as the weight transfer happens.

My recumbent has more rearward weight than a diamond frame, especially a racer, but still slides the back pretty easily with hard braking. So I hit both brakes hard, if the back slides I can ease it up but usually don't bother I just ride it out. It won't slide out if I have my steering and balance under control. Mind you all that's on a grippy surface. Leaves or oil and you are going down....

[find_bruce]

With modern rim or disc brakes I can’t think of when it would be better to lock the rear or lay it down.

Much better to practice emergency front braking- ie weight back & hard enough to unweight the rear. An escape route is a great option to have

[mikesbytes]

When a tyre skids it provides less breaking force than when it is not skidding, that is why antilock brakes are being fitted to motorised vehicles. A tyre provides maximum braking where the braking force being applied is just at the point just before the tyre looses adhesion with the road surface

The front wheel permits more force to be applied to it before loosing adhesion and hence will contribute more to the total braking effectiveness than the rear wheel

Modern high quality tyres provide so much grip that the limiting factor in the front wheel is the point where one will go over the handlebars rather than limit of adhesion. The quality disparity is such that skinny racing tyres often produce more grip that bicycle tyres that are 4 times bigger. Also the grip of these high quality tyres is great enough that near maximal braking can be combined with an avoidance manoeuvre in the hands of an experienced rider

[chriso_29er]

I think the trick is to not panic brake at all.
Take a measured emergency response which should be full braking force while still allowing you to change direction if needed.

In dry weather you would find it very difficult to ever lock up the front even if turning slightly.
But also keep in mind that any front brake is going to stand you upright and make turning difficult, so depending on the situation you may need to slow agressively with front and rear in a straight line, then release front while still trailing rear which will allow you to set up and lean into a required swerve.

[bychosis]

Why not both brakes?

[find_bruce]

Why not both brakes?

[Mububban]

The real question being is if (front brake only or back brake only) method is better than the other to say avoid a car that pulls out in front of you and stops, you only get one chance to choose which method you want to use.

Both brakes. Why would you not use them together?!?

In an emergency, train yourself to stiffen your arms so you don't get thrown forwards, and quickly shift your weight over your back wheel while applying both brakes, like this:




Most of your braking is done on the front brakes, I think it's about 75/25 for front/rear? So if you only have one arm/brake, then go the front brake BUT you'll need to shift your weight back to avoid going over the bars.



This video from 0:12 - 0:40 shows the difference between back brake only (worst), front brake only (okay) and both brakes working together (clearly the best).