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Discussion Starter · #1 · (Edited)
When bikers talk about braking, the mantra "the front wheel provides 75% of braking force" invariably comes up. I thought this might be a good time to talk about why: it all boils down to weight transfer.

If you've ever been to a drag race, you'll notice that the middle classes (e.g. Stock and Super Street) often don't have the nose-down/tail high look of the more powerful classes: instead the cars are jacked up at both ends, sitting pretty much level but higher than they would be on the street.

It's all about Physics: the higher the center of gravity, the more weight will be transferred to the rear wheels when the driver nails the gas. The more weight on the rear wheels, the more traction, and the less wheel spin.

Obviously, it's a tricky balance: too high and the car will wheelie off the line, too low and your launch turns into a burnout.

When you brake, the opposite is true - the weight gets transferred to the front end, lightening the rear in the process. However, this weight transfer does not happen instantaneously. The quickest stops will occur when the operator progressively brakes the vehicle, in this case your bike.

When you apply the front brake, the forks compress and the downward force on the front tire increases as the CG shifts forward. As it does, you can increase the force on the lever, which will add more downward pressure to the front tire, which means you can add more force to the lever, which means.... you get the picture.

Conversely, if you apply your maximum braking force on first grab, chances are you'll break the front tire loose - it hasn't started to load yet so it will slide.

As with everything else, it's a balance: even though the CBR250 has a single disc and less-sticky tires than a lot of bikes, you can still do a stoppie (rear wheel in the air) if you take progressive braking to the extreme.

Note also that as the front tire loads, the rear tire is unloading. As a result, you can apply more force to the rear brake in the initial stages of braking, easing off as the weight shifts forward.

Getting the maximum braking force out of a bike takes practice: find a parking lot with clean, consistent pavement and practice stopping, first from 15-20 mph and then from higher speeds (be sure to wear all of your gear). If you do, you'll be amazed and how quickly your bike can stop.

Last but not least, don't be naive enough to believe that you don't need this knowlege if you have ABS. Study after study (as well as the Honda CBR250 manual) note that an experienced rider can stop in shorter distances than ABS. I'm not discounting ABS as a good safety feature (and don't want to turn this topic into an argument about ABS), but if you want the maximum protection, learn how to use your brakes. If anything, ABS lets you get closer to the limits of adhesion without worry.

Ride safe!
 

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Discussion Starter · #4 ·
There are essentially two schools of thought on downshifting.

If your main interest is mileage and/or wear/tear on the bike, pull the clutch in as you start to slow and let the bike coast. As the speed drops below 10-15mph, click down through the gears without ever releasing the clutch. Time it so you're in first just before the bike comes to a complete halt.

If you're downshifting and want power (say, a curve or a slow vehicle cleared or you just like to use engine braking), then clutch in, slight RPM increase, shift down, clutch out. Remember that shifting down one gear requires higher RPM to stay at the same speed - for instance on my CBR, ~60 mph is ~6000 rpm in 6th gear and ~7000 in 5th. So, if I'm running 60 in 6th and want to go to 5th, I'll blip the throttle up to around 7000 rpm before letting the clutch out. You CAN do this while braking - use your middle and index fingers on the brake and roll the throttle with the rest of your hand. It just takes a little practice.

You also want to find the engagement point on your clutch, and release the lever through that range slowly - this will allow the engine and tranny speeds to match up much less abruptly. Rember, you don't have to release slowly through the entire travel range - just the 1/4" or so where the clutch does most of it's engagement

Last but not least, remember that dumping the clutch on a downshift has the same effect as applying the rear brake - it can break the back wheel loose, especially in a turn or on loose material. You may have seen the phrase "slipper clutch" in articles about high powered sport bikes. This clutch is designed to lessen the abruptness of the clutch release to the rear wheel. We don't have those on the CBR, so good clutch lever technique is the answer.

Practice, Practice, practice - one day you'll wonder why you ever thought it wasn't easy.
 

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Discussion Starter · #6 ·
Would it be better to both brake and downshift (also known as engine braking)
That was the way i learned many years ago - but the reason was that the engine kept the rear wheel from locking. Not a bad idea still, but if you do a lot of engine braking you will see faster component wear.
 

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Discussion Starter · #8 ·
Yes - versus chain, sprockets, clutch, and reduced engine life. It's just logical... I had an F250 Ford Diesel truck with manual. As I approached stop signs, i would shift to neutral and coast to the stop (easy when the vehicle weighs 7700 lbs). I sold it at 160,000 miles with the original clutch and no trans / diff / driveline problems. The truck mechanic at Ford said that he'd never seen a clutch go that long in one of those trucks, that 80-100K was as high as they normally went.

I will nail the CBR250 - that's half the fun. However, when you're hearing a bike screaming in every gear, it's going to hurt somewhere along the way.

Another problem is that half the guys i know that use engine braking a lot don't use the brakes much. When i slow down, I want the brake light on to hopefully alert the idiot with the cell-phone behind me that I'm slowing.
 
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