No, I haven't done it (yet), but ever since I started riding, I've wondered about this issue.
According to my MSF instructor and many other users in this board, if you lock the rear brake at high speeds and then release it, the bike will send you flying up the air to neverland... or something.
However, I am having trouble understanding the physics of this.
Let's say Im doing 50mph, and then I see a deer or some other furry animal crossing on my path and stopping in front of me, so then I step on the rear brake and lock the tire; and also grab the clucth all the way in... and then the furry animal decides to get the hell out of the way a fraction of a second later... so I release the rear brake leaving the clucth in...
the question is: WILL the BIKE send me to hell and back and forth?
if so, why?
It is common for the rear to come out to either side when it is locked up. If you are in anything but a straight line, there will be some violent reactions when the rear regains grip. The rear is going to want to roll in the direction it is pointed (sideways) when it grips, rather than go straight with the rest of the bike. This will most likely result in a highside, with the tires gripping and you getting flipped off the bike.
Since I made a fuss about this to BSD, I will add my $.02.
I think that when you lock the rear brake it starts to slide faster than the front of the bike.
If the back tire starts to move faster than the front tire it basically tries to "pass" the front tire. Since they are bound together by the bike it must pass on the outside. So the back tire must move out to one side. Which is fine. Unless you slow down the slide by releasing the rear brake. Which will quickly pull it back into line with the front tire. That rapid attitude change of the bike causes it to pitch. Usually resulting in what we call a high side.
You may have problems you may not. The higher the speed, the greater the risk. I've not done it. But I can see how it could happen.
That all could be wrong, but that is the best way I understand it.
I think I like Jake's explanation a little better :laugh:
ps. what kind of job are you lookin for subc?
When coming out of a lock situation, you still need to match tire speed with ground speed. So in your hypothetical situation, if you were to release the rear brake with the clutch in the rear tire should eventually speed up to match ground speed and regain a neutral traction. Then you need to match engine speed to wheel speed when you let the clutch out.
So the answer to your question is no.
I've always heard this but I've never understood it. I lock my rear all the time...or used to, I should say...to slide a little. It was especially fun on the motard and smaller bikes. Couple times it resulted in a near high-side, but it was never too violent.
Quote from: scratch on February 14, 2006, 01:49:50 PM
When coming out of a lock situation, you still need to match tire speed with ground speed. So in your hypothetical situation, if you were to release the rear brake with the clutch in the rear tire should eventually speed up to match ground speed and regain a neutral traction. Then you need to match engine speed to wheel speed when you let the clutch out.
So the answer to your question is no.
...I guess I should mention that I never just powered it back into line with the throttle...I always used the clutch to line the bike back up.
I never found the reaction to be violent when I was running the old excedra or whatever crap OEM tires, but when I switched to stickier rubber it got infinitely worse. Instead of gripping immediately, the old tires would lose traction when I released the brake and eventually come back into line with the front, but the newer stickier rubber (Sportec M1) grabs instantly and even at 10 MPH is very difficult to control. So the rubber you're running probably has something to do with it.
-Brian
I have locked the back wheel at more than 60mph and had the back wheel wiggle from side to side. I released some rear brake presure and managed to brake properly.
Thanks all for your replies. I now understand what could cause a high side. :icon_mrgreen:
Quote from: manofthefield on February 14, 2006, 01:04:32 PM
... ps. what kind of job are you lookin for subc?
I see you are looking for a job too 8) me? multimedia stuff. My experience is on video related stuff and broadcasting (some 8 years), and more recently in all things multimedia (html, php, 3d, video for the web, codecs, compression, new technologies, etc).
I think I need to move down south in california to get a decent pay.
Didn't read all the replies, but I will throw in my .02. When the rear begins to skid, the direction the tire is pointed changes compared to the direction the bike is moving. To make matters worse, the front wheel usually is pointed by instinct into the direction you want to go, in order to keep the bike upright. A skidding tire is something like only 20% of it's available grip, when you release the brake, suddenly it's able to freely turn and grip. the rear takes off in it's new direction but the front tire is pointed in the opposite direction, this causes an immense amount of countersteering and the bike whips up and tosses you over. A major factor in this is the loss of gyroscpic effect on the rear tire.
Do not confuse a skid with a spin or a slide. Many people that are aggressive riders took a page from Wayne Raineys book and began to roll on coming out of a turn to actually induce the rear to spin. this allows them to drift and the bike has to catch up with the tire instead of the tire catching up with the bike. Also, don't confuse this with the hopping skid you feel if you downshift too far, although downshifting in a turn can cause a highside, it's rare but not unheard of that hopping in a straight will lead to a highside.
Given a choice, I would lowside. I have been in a situation where I got on the rear too hard and was thinking that I was gonna lowside. Instinct is to let off and you have to force yourself to stay on it. At any rate, a lowside is far more manageable tan a highside, and no near as damaging. Most lowsides put the bike in front, sliding of you after you are seperated from it whereas a highside means the bike is behind you often in the air.
All that said, I rarely rarely rarely even use my rear brake.
I rarely use mine too. I push on it, but I don't know if it is even doing any good. I used to race mountain bikes and I was a front brake heavy guy then too. I'd say more like 80% front.
Uncontrolled sliding will put you on your head. Last 2 times I locked up the rear was around 60-70, both at the track. Once on my GS in the sand (yeah a little off track excursion) and the other in the rain on my TLR (stayed on the track). Plenty of back and forth sliding for well over 100 feet. Kept both under control. Never really cared for the rear, guess I need to soften it some.
I love using my rear brake on my mountainbike though, great for turning sharply and squaring off turns. hmmm...maybe I should try a thumb rear brake on my track bike.
I've locked the rear and released it while going about 30... I did it so fast that the rear only moved about a half inch to the right and popped back to center without a problem... But...
I can imagine that holding the locked rear tire for longer would allow the rear to slide more to one side...
I can also imagine that locking and releasing at a faster MPH would cause the rear to pop back to center a lot faster...
I wouldn't try it at 60... You might try it out in an empty lot and see what it feels like... But, don't crash. :nono:
I have locked up the rear a few times at ~40MPH but I have always been going straight and I was able to just keep the bike fishtailing tell I could let off the brake and regain control. I think it would be hard to high-side if your going in a straight line but I can see it easily happening in a turn.