Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Dangerous Rear Sliding

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Dangerous Rear Sliding

Old 06-09-12, 04:06 PM
  #1  
Junior Member
Thread Starter
 
Join Date: Mar 2012
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Dangerous Rear Sliding

Hello,

I'm just got back from a errand and I was out biking on the streets in Chicago, where I live. I don't know if it's because of the heat on the pavement from the really hot day today (about 90 degrees in a big ass city that traps heat),or what. But the roads are absolutely insane today, and I have had to consistently do some quick braking to avoid the various ******* drivers who honestly don't care if you live or die, barring they are liable. I digress.

I was biking on an extremely bust street, clark st, which is insane today because of the weather and proximity to the beach. I was going along and a guy took a left hand turn right in front of me. I tries to brake hard and I slid right into the front of his car. Luckily, the immense 700c wheels I have bounced off his license plate and I was fine.

I tested them out afterwards when I got home and even when walking with my bike and applying the rear brake I could literally walk with it as it just slid along. When applying the front brake I couldn't.

The point is: What the hell is wrong with my rear wheel.

I have SUN Rhino Lytes, recently installed, perfect tension and true.

The brakes are cantilever and perfectly aligned. They are kool stop brake pads and are tensed correctly and lock the rim into place.

Now...my suspicions. The tire looks a little worn down but is only 2 months old!!

It's a Schwinn Kevlar comfort/hybrid tire. Is this true that it is the tire that is ****ty? It just slides along the pavement...and when I inspect the area that I slid it on it has a little worn streak.

Do I need a new tire or is it something else I'm overlooking?
qondamibuey is offline  
Old 06-09-12, 04:19 PM
  #2  
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,362

Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

Mentioned: 138 Post(s)
Tagged: 1 Thread(s)
Quoted: 5605 Post(s)
Liked 2,228 Times in 1,249 Posts
Nothing is wrong with your rear wheel or tire. Your problem is more one of physics than mechanics.

When you do a hard braking, there's a weight shift to the front which reduces the force holding the rear wheel down and therefore the traction. The more braking G's you generate, the lower the rear wheel traction, until the wheel skids and you cannot get any more Gs in the system. The same happens with cars which is why car brakes are proportioned with 60% or more braking power sent to the front wheels, and even then rear wheels always lock up and skid first.

In order to stop in the shortest distance you must bring the front brakes into play, but the physics here are trickier. Increased Gs increase the front wheel load and traction, making more Gs possible until the weight transfer is enough to flip you over the bars. So the key is to use both brakes and modulate them, to prevent rear wheel skids and/or endos. It's easily learned, but even very experienced riders can have an adrenaline rush and punch down the front brake causing a front end flip.

When I lived and commuted in Manhattan, I got so good at this that in an emergency stop (like behind a taxi cab) I could lock the front wheel, lifting the rear wheel, swing a leg over the handle bar, and step off the bike catching it behind me with my right hand. It looked spectacular when done perfectly, but I've also landed on a few trunks in my life.

The only thing I can suggest is to practice hard braking, until you can feel the point at which a flip is about to start, then ease off the front brake enough to prevent it. Do this at low speed and work your way up to the critical point by degrees, so you don't injure yourself learning to prevent injury. (the Catch-22 of learning good bike handling). It's important that good brake modulation is drilled so that it's totally automatic because you don't have time to thing about it during a 3 millisecond emergency.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

Just because I'm tired of arguing, doesn't mean you're right.

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.

Last edited by FBinNY; 06-09-12 at 04:22 PM.
FBinNY is online now  
Old 06-09-12, 05:16 PM
  #3  
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,319

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 1438 Post(s)
Liked 1,091 Times in 722 Posts
Locking the rear wheel without using sufficient braking on the front is the classic novice motorcycle rider pitfall. The same applies to bicycles. Try to get into the habit of using your front brake only for most of your riding; use the rear brake only as a "drag brake" to control speed on long downhills. In this way you will tend to react correctly in an abrupt stop situation, that is, using maximum front braking until you nearly lift the rear wheel. If you habitually use the rear brake you will tend to use it in an emergency as well. According to Sheldon Brown: "The fastest that you can stop any bike of normal wheelbase is to apply the front brake so hard that the rear wheel is just about to lift off the ground. In this situation, the rear wheel cannot contribute to stopping power, since it has no traction. "Here's his full article article about braking: https://sheldonbrown.com/brakturn.html

Another tactic which many folks do not use is to turn away from the danger while braking rather than just hit the brakes, continue to go straight and hope for the best. You may be able to turn and avoid the collision altogether or mitigate the impact by striking the object at a shallow angle rather than head-on. It is rare that you will be totally cut off and you may be able to scoot through a narrow opening once you have slowed enough.

Regarding your rear brake locking when you are walking along, remember that the wheel has only the weight of the rear of the bike on it; when you are riding it has about 2/3 of your full weight added to that so it will have much more force to generate traction.
dsbrantjr is offline  
Old 06-09-12, 05:30 PM
  #4  
Mechanic/Tourist
 
Join Date: Apr 2007
Location: Syracuse, NY
Posts: 7,522

Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 486 Post(s)
Liked 11 Times in 11 Posts
FB is of course correct that there is nothing wrong with your rear brakes (at least not just because you can make the tire skid) but there is more involved than just modulating the front brake. The key is to use the rear wheel as an indicator, and to release pressure on the front brake when the rear wheel skids. But shifting one's body to the rear can greatly increase the braking rate without the rear wheel skidding. I'll not go into the full explanation of an "Instant Stop" here, as it's already done well at this link:
https://floridabicycle.org/chapter/firstcoast/?p=516

Please note that the above article and just about every other one that is similar owe much to John Forester, the originator of Effective Cycling. There are other very useful techniques and traffic strategies that commuters especially may find useful. I had the great fortune to take his Effective Cycling Instructor Course back in the late 70's. I also credit him with teaching me a more "effective" way to change a tire, even though I had been a mechanic for several years.

Sheldon also has some interesting views about brake usage at https://sheldonbrown.com/brakturn.html

Last edited by cny-bikeman; 06-09-12 at 05:34 PM.
cny-bikeman is offline  
Old 06-09-12, 07:00 PM
  #5  
Junior Member
Thread Starter
 
Join Date: Mar 2012
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I mean I understand the principal of sliding when sudden and tight pressure is put on a brake. I've experienced this in a car as a teenager and on my bike before hand. But the issue that is happening that I should have clarified more is the fact that it is literally sliding when I brake even at slow speeds. For example, I was inching behind a car at a stop light, and with hardly any speed I of course began to slide and had to dismount in order not to tap their rear bumper. In my head I was like, what the fu*k is this? I have never experienced this sensation of sliding on ice on perfectly good pavement and a new tire. The only thing I can honestly deduce is the tire because I have never experienced this and it's not like my riding style all of a sudden changed in a day. What I'm asking is if the tire being usually worn is a possibility. I'm not saying that I could do a better job at braking, and the way I ride, but today I got that, "I shouldn't even be on my bike in these conditions," feeling. I mean, it will virtually slide at almost any (harder) pulling I do of the brakes. I definitely do not think this is a normal phenomenon.

I may just be going crazy and be completely wrong here, but is it a possibility it's the tire?
qondamibuey is offline  
Old 06-09-12, 07:24 PM
  #6  
Insane Bicycle Mechanic
 
Jeff Wills's Avatar
 
Join Date: Mar 2008
Location: other Vancouver
Posts: 9,795
Mentioned: 34 Post(s)
Tagged: 0 Thread(s)
Quoted: 778 Post(s)
Liked 674 Times in 358 Posts
New tires often have a coating of release agent left over from the molding process. It's possible that this is the problem. The coating wears off pretty quickly. If you want to accelerate the process, a little soap and water helps.
__________________
Jeff Wills

Comcast nuked my web page. It will return soon..
Jeff Wills is offline  
Old 06-09-12, 09:18 PM
  #7  
Mechanic/Tourist
 
Join Date: Apr 2007
Location: Syracuse, NY
Posts: 7,522

Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 486 Post(s)
Liked 11 Times in 11 Posts
It is certainly understandable that you are concerned if you are convinced that you are doing the same thing with different results. However, walking the bike and being able to put on the rear brakes and drag/skid the tires is normal.

Tire wear is not a factor, as the tread on a bike tire has essentially no positive effect on traction when on pavement. You may even get better traction with a little wear. Assuming you are doing nothing different in technique and there is no significant weight change over the rear wheels, then the difference would have to be the pad/rim interface. I would think that the only thing there that would cause the problem is the brake pads grabbing too agressively due to some foreign matter. Try cleaning the pads with fine sandpaper, rinsing thoroughly afterward with something like Fantastic, 409 or similar. You could also try switching front and rear pads.

No matter what, it is a good idea to practice panic/instant stops before you need to stop quickly, and to practice in general using your front brake much more than the rear.
cny-bikeman is offline  
Old 06-10-12, 08:18 AM
  #8  
Lover of Old Chrome Moly
 
Myosmith's Avatar
 
Join Date: May 2011
Location: NW Minnesota
Posts: 2,949
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 143 Post(s)
Likes: 0
Liked 23 Times in 17 Posts
I got so good at this that in an emergency stop (like behind a taxi cab) I could lock the front wheel, lifting the rear wheel, swing a leg over the handle bar, and step off the bike catching it behind me with my right hand.
Video link, please
Myosmith is offline  
Old 06-10-12, 10:42 PM
  #9  
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,532

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1520 Post(s)
Liked 716 Times in 508 Posts
Ever noticed how cars and motorbikes have smaller brakes on the rear...?

This is why dual-pivot brakes on the rear of road bikes are silly. Single-pivot brakes are perfect for the back, being lighter and having less leverage, meaning it's easier to avoid skidding and control exactly.

With cantis, you can alter the geometry of the straddle cable to achieve the same effect. It sounds like your rear straddle cable is set too low, giving the brake way too much power.

Originally Posted by FBinNY
When I lived and commuted in Manhattan, I got so good at this that in an emergency stop (like behind a taxi cab) I could lock the front wheel, lifting the rear wheel, swing a leg over the handle bar, and step off the bike catching it behind me with my right hand. It looked spectacular when done perfectly, but I've also landed on a few trunks in my life.
Awesome. I'd love to see some vid of someone pulling that move.

The only thing I can suggest is to practice hard braking, until you can feel the point at which a flip is about to start, then ease off the front brake enough to prevent it. Do this at low speed and work your way up to the critical point by degrees, so you don't injure yourself learning to prevent injury. (the Catch-22 of learning good bike handling). It's important that good brake modulation is drilled so that it's totally automatic because you don't have time to thing about it during a 3 millisecond emergency.
When I first got a DP on the front, my first emergency stop sent me over the bars.

The next, my back wheel stayed in the air for a few metres, no problem. It was automatic once I realised I had as much braking as I wanted... can't do endos like that at will, though. Like I said, automatic...

Last edited by Kimmo; 06-10-12 at 10:53 PM.
Kimmo is offline  
Old 06-11-12, 05:29 AM
  #10  
aka Tom Reingold
 
noglider's Avatar
 
Join Date: Jan 2009
Location: New York, NY, and High Falls, NY, USA
Posts: 40,560

Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem

Mentioned: 505 Post(s)
Tagged: 0 Thread(s)
Quoted: 7210 Post(s)
Liked 2,238 Times in 1,319 Posts
Don't follow so closely. Anticipate people cutting you off. Be prepared to stop if people do inconsiderate and stupid things. Don't push your bike to its limit. And don't get too angry at the people who do stupid things.

Not every problem has a mechanical solution.

Francis, the description of your technique is impressive, but it would take a lot of practice. I don't mean to recommend against it; I'm just saying it's not for everyone.
__________________
Tom Reingold, tom@noglider.com
New York City and High Falls, NY
Blogs: The Experienced Cyclist; noglider's ride blog

“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author

Please email me rather than PM'ing me. Thanks.
noglider is offline  
Old 06-11-12, 04:24 PM
  #11  
Senior Member
 
DannoXYZ's Avatar
 
Join Date: Jul 2005
Location: Saratoga, CA
Posts: 11,736
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 109 Post(s)
Liked 9 Times in 6 Posts
Try rolling the bike backwards and doing the following:

1. applying front-brake
2. applying rear-brake

Please summarize the physics lesson you just learned.
DannoXYZ is offline  
Old 06-12-12, 12:15 AM
  #12  
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,532

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1520 Post(s)
Liked 716 Times in 508 Posts
Heh... nice one, Danno
Kimmo is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
DenBoy
General Cycling Discussion
79
08-01-19 01:29 PM
Nassa
Road Cycling
70
08-02-11 04:23 PM
vladuz976
Singlespeed & Fixed Gear
17
01-10-11 05:21 PM
Gege-Bubu
Road Cycling
132
12-06-10 08:18 AM
daven1986
Bicycle Mechanics
44
02-03-10 06:48 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.