Rear brake usage?

[Mikkel]

OK, I'm totally out of my depth with physics terms; I never studied it.

That's cool not a worry. I was just trying to illustrate the point that the stickiness of your tyres and how they grip the road in a given situation is the only thing that determines you "maximum stopping force". As said, this is pretty academic when considering some situations as there are other concerns that will prevent you from applying that force.

Don't bother, he's talking engineering bollocks. What he is missing out on is the stability using the rear break as well gives.

If you had bothered reading what was written you'd see that you are actually not correct with that statement...

You can't achieve that maximum on a motorbike in the dry with warm sticky tyres because (since the braking force is applied at the ground and the c of g is above the ground) you will raise the rear wheel, at which point the braking force you can apply decreases. Using the rear brake can help the suspension squat, lowering the c of g, and therefore increasing the amount of braking force you can apply without raising the rear wheel.

I take that what you mean is that there's a limit as to how much braking force you can apply without flipping the bike head over heels...
And true, the larger the vertical height from the centre of your front wheel to the centre of gravity the less force is takes to hoist the rear and flip it.
I see your point that using the rear at first will help to compress the fork without raising the centre of gravity. How much of an impact this has upon your actual stopping length I can't guess at.
Another way to prevent hoisting the rear would be to have a longer front fork and/or a higher degree of rake (increase the horisontal distance between the centre of the front wheel and the centre of mass).

[Ocean1]

Ffriction = M*g*f

Where g is the gravitational acceleration (~9.8 m/s^2) and f is your static coefficient of friction. Unless there's a big difference between f for your front and rear tyre the magnitude of your braking force should remain unchanged regardless of the way weight is distributed between the two tyres.

Can you demonstrate how static COF is related to dynamic friction?
Is the relationship between g and f linear wrt rubber/asphalt?

[Hitcher]

Gahhh! Here come the engineers and the physicists! Run, run to the hills!

[Swoop]

Throw them some pocket protectors to distract them!!!

[Mikkel]

Can you demonstrate how static COF is related to dynamic friction?
Is the relationship between g and f linear wrt rubber/asphalt?

Due to popular demand I'll flick you a PM if you're truly interested. Just let me know...

[Ocean1]

Due to popular demand I'll flick you a PM if you're truly interested. Just let me know...

Apparently we're not in that much demand.

But don't bother dude, I've got some idea.

[sAsLEX]

If someone says you don't need them then smile and nod like you are agreeing

You are claiming you can beat some pretty handy racers then!

It's quite possible to recover from locking the front wheel

Try, on the gas at relatively low speed, locking the front. Most don't know what it feels lie and when it happens instead of relaxing will think something has gone wrong and do the completely wrong thing and squeeze harder!

About 400+km since I last touched the rear brake pedal.

I occasionally feather mine out and about, say once a week, to keep the surface rust away!

Using the rear brake, even on a sportsbike, will in effect lower the bikes cog giving more grip. It's not just a 'stamp on the brake pedal' thing, but controlled use of the back brakes.

Ah but do you need to use the brake to retard the rear wheel?

Due to popular demand I'll flick you a PM if you're truly interested. Just let me know...

Bugger it, lets have some mspaint physics!

[homer]

That's cool not a worry. I was just trying to illustrate the point that the stickiness of your tyres and how they grip the road in a given situation is the only thing that determines you "maximum stopping force". As said, this is pretty academic when considering some situations as there are other concerns that will prevent you from applying that force.



If you had bothered reading what was written you'd see that you are actually not correct with that statement...



I take that what you mean is that there's a limit as to how much braking force you can apply without flipping the bike head over heels...
And true, the larger the vertical height from the centre of your front wheel to the centre of gravity the less force is takes to hoist the rear and flip it.
I see your point that using the rear at first will help to compress the fork without raising the centre of gravity. How much of an impact this has upon your actual stopping length I can't guess at.
Another way to prevent hoisting the rear would be to have a longer front fork and/or a higher degree of rake (increase the horisontal distance between the centre of the front wheel and the centre of mass).

Maybe this was the actual point of safety of anit dive suspension

[Mikkel]

Apparently we're not in that much demand.

But don't bother dude, I've got some idea.

Yeah, beers would be awesome. But I have had someone mentioning that combining drugs and alcohol is not necessarily a good idea

Maybe this was the actual point of safety of anit dive suspension

I don't know. I guess you might loose some feeling with an anti-dive front suspension... That could be just a problematic, if not more so.

[terbang]

Don't bother, he's talking engineering bollocks. What he is missing out on is the stability using the rear break as well gives.

Yes there is a good arguement for stability, but what he fails to realise is that when you are doing a stoppie (intentional or not), the rear wheel, with its braking coefficient of "f" or not, is now just along for the ride.
I guess the manufacturers know a trick or two as well. Take a look at any sport bike and you will notice huge twin discs with multiple piston calipers on the front wheel and a token single disc (much smalller diameter) with only one or two pistons in the caliper on the rear. Its a pretty common theme across the spectrum of makers and sort of indicates where they think the braking should come from.. But hey, who are they and what would they know? They only build em eh...

[xwhatsit]

About 400+km since I last touched the rear brake pedal.

Did it fall off?

I seem to have taken a leaf out of Motu's book, and give my rear brake an absolute hammering. I trail brake with it in all corners, probably too much. I even find myself using it with the throttle on, which seems pointless, but I suppose it's a way of smoothing out the forces in the rear end. On gravel I barely take my foot off the pedal. The brake drum is usually very, very hot after a ride -- at one stage I was worried I'd rooted the rear wheel bearings and that's why it was so hot, so I went for a ride without touching the rear brake at all. How strange and awkward that was! Hub remained quite cool, however.

I don't know how people can ride around town without touching the rear brake. Trying to slow and change down gears smoothly, especially when you're not travelling dead-straight, is very hard. I find it hard to blip the throttle whilst squeezing the front brake, so the rear wheel tends to lock and skip from engine braking and no blip anyway.

[DEATH_INC.]

I see your point that using the rear at first will help to compress the fork without raising the centre of gravity. How much of an impact this has upon your actual stopping length I can't guess at.

Nope, you've missed it. Using the rear first compresses the REAR suspension as well as the front thereby lowering the cog, where using just the front extends the rear and compresses the front, moving the cog up and forwards. It works, on my old beast I hammer the rear to the point of overheating it, as the rear is so high that it stoppies too much without it....

[GaZBur]

You are claiming you can beat some pretty handy racers then!

Shhhheeeit No! I got back into racing again last year after a big break but I am assuming that because ALL asked this question he can't either. If he was expert enough to completely unweight the back without it losing control he would not need to ask. We are not all expert racers sadly. I use the back brake a lot - but for the control it gives as the stopping power is as we all know minimal.
Can someone enlighten me please on one point. Someone here said doing stoppies were the fastest way to stop, I always assumed that once the point of balance is passsed and the rear wheel is off the ground you had to ease up on the front brake to prevent a face plant situation, therefor it's less efficient than keeping the rear wheel down. If you can enlighten me please keep it realtively simple as I don't get the physics equations.
Thanks.
GaZBur

[All]

If he was expert enough to completely unweight the back without it losing control he would not need to ask.

I don't pretend to be a racing expert, but my only aim was to gauge opinion on what the fastest way to stop was. My ability to unweight the back without losing control is irrelevant.

[All]

Don't bother, he's talking engineering bollocks. What he is missing out on is the stability using the rear break as well gives.

Have a look at these...

http://www.sportrider.com/ride/146_9...ips/index.html

Interesting link. That certainly points to using both brakes being the best way to stop.