TobinHatesYou wrote: ↑
Tue Jun 25, 2024 12:39 am
If you can apply the rear brake without locking up the rear wheel, then your weight isn’t shifting forward – you aren’t braking as hard as you should!
See AlsoTrain descent skills - Page 5This statement is particularly belligerent. Shift the weight forward? Relative to what? You want to shift the weight low and back. There is a tipping point on extremely steep grades, like literally 40 degrees where you need to keep weight on the front tire, but you’re still shifting your weight back relative to your BB.
Yes, out of context that statement is over-the-top hyperbole. But the purpose of his test was to stop as fast as possible. In which case, if you can't easily lock up the rear wheel, you aren't braking as hard as possible.
His comment about the forward weight shift isn't that about the rider moving their CG forward (in fact, he suggests the rider shift their CG backwards). The forward weight shift Heine is referring the braking reaction force, which naturally shifts weight from the rear wheel to the front wheel when braking. This fundamental aspect of physics can't be avoided, and is why the harder one brakes, the less effective the rear brake becomes.
TobinHatesYou wrote: ↑
Tue Jun 25, 2024 12:39 am
But yeah, set up a ramp yourself and try it. Keep increasing the angle until you can no longer come to a complete stop with just your front brake. Then add rear brake and see if things improve. I guarantee it will.
How can you guarantee that when you have never tried it yourself? If you are really at the "tipping point", where any additional front braking would result in the bike bike flipping over, then there is no weight on the rear wheel, and therefore no rear wheel traction available to add any additional braking.
By the way, Jan Heine is not the only advocate of concentrating on the front brake. This is from Jobst Brandt's FAQ on descending:
https://www.sheldonbrown.com/brandt/descending.html
Once the basics of getting around a corner are developed, doing it fast involves careful use of the brakes. Besides knowing how steeply to lean in curves, understanding braking makes the difference between the average and the fast rider. When approaching a curve with good traction, the front brake can be used almost exclusively, because it is capable of slowing the bicycle so rapidly that nearly all weight transfers to the front wheel, at which point the rear brake is nearly useless.
In case you don't know, Jobst Brandt was a legend in cycling, and knew a thing or two about descending and cornering. Here he is right at the traction limit of his tires, at close 1 g of lateral force:
As far as maximum braking at the "tipping point", and also about learning/practicing maximum braking technique, there is a GCN video that has an illustration of this: https://www.youtube.com/watch?v=48BRZEzXtcA . The subject of the GCN video is get better stopping performance with 140mm or 160mm disc brake rotors. But it has a good illustration of braking at the maximum limits.
In the test, the same test rider does multiple test runs trying to brake from the same speed in the stopping minimum distance. As the test goes on, the rider's stops get shorter and shorter as he becomes more practiced. Although the 160mm rotors should be able to produce more braking torque, the rider's later braking distances with 140mm rotors are actually shorter than in his earlier tests with 160mm rotors, indicating that braking technique may often be more important than rotor size. However, we can see that he can brake the hardest with just his front brake, because his shortest stopping distances are accomplished by using the front brake alone. How do we know that he isn't using his rear brake? Because under the fastest stops, his rear wheel lifts off the ground during braking - so obviously his rear brake is completely ineffective during the shortest stops. In fact, the more time he spends with his rear wheel off the ground, the shorter his stops.
Now, obviously one shouldn't aim to brake so hard as to lift the rear wheel off the ground on a regular basis - the video was a test under controlled conditions. But it does illustrate that front brake has much more stopping potential than the rear brake. And more importantly, it illustrates that braking is a skill that needs to be practiced. While learning good braking technique, one should learn the use of both front and rear brakes, and why the faster one needs to stop, the more one should use the front brake, and the less one should use the rear brake. Too many riders are afraid of the front brake, and as a result are unable to slow/stop as fast as they could.
