Wednesday, July 14, 2010

Braking: Not Always Your Friend

The other day I was cycling on a busy road where the city has recently installed those raised-platform intersections to make the cars slow down before crosswalks. Ahead of me, I saw a cyclist brake just as she entered the intersection - probably hoping to reduce the impact of the bump. Watching her, I somehow knew what was going to happen next and winced. And then it happened: As her wheel hit the raised platform, her bicycle flipped over, and she with it. All this occurred at a slow enough speed, so that she wasn't hurt and was soon back on the bike. But I suspect that she has no idea why the fall happened, which means that it might happen to her again.

To me, it has always seemed self-evident that it is "bad" to brake while going over bumps, and watching the cyclist's fall confirmed that. But were there actually any facts behind this belief? I got home and looked it up, stumbling upon Sheldon Brown's explanation.
Bumpy surfaces. On rough surfaces, your wheels may actually bounce up into the air. If there is a chance of this, don't use the front brake. If you apply the front brake while the wheel is airborne, it will stop, and coming down on a stopped front wheel is a Very Bad Thing.
Okay, that makes sense. It has also since been pointed out to me that braking transfers the weight of the bicycle forward, so braking on the bump drives the front wheel right into it. Makes sense as well. So, we essentially have two forces working against us when braking over a bump.

When we find ourselves hurdling towards an obstacle n the road that we cannot avoid, naturally the reflex is to slow down. But this should be done before going over the said obstacle, not during. Braking is your friend, but only when done correctly (brake before the bump, then release before going over it). I would also venture to say that most casual cyclists who use handbrakes do not differentiate between front and rear.

Of course, this is just one more reason why I love coaster brakes for cycling in the city. If you're used to braking with a coaster brake in order to slow down, you do not rely on the front brake as much and are not likely to squeeze it while going over a bump. I know that some will not agree with me on that one, but that is how I see it, and the coaster brake has been a reliable ally for me in pothole-ridden Boston Metro.

35 comments:

  1. do u have any pics of these special intersections? never seen one before. btw, nice rear rack!

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  2. Anon - If you're local, it's Somerville Ave. I don't take pictures while cycling in traffic, but will pull over next time and photograph one of these babies when I have time!

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  3. I think I know which "raised intersections" you speak of... in that Camberville area.

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  4. Yes - am I using an incorrect name for them? They've installed about a dozen of these, and they are most definitely raised!

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  5. It's the new in-vogue traffic "thing" in Boston, to rework in red brick and raise all pedestrian crossings, surrounding "the box" with four raised pedestrian bridges. In theory, it discourages the cars from pulling into the pedestrian zone while waiting at a light, or turning on red, and generally tells traffic that they are crossing foreign terrain. It's a bit like a gentle speed-bump, but sometimes not so gentle.

    All negative aspects aside, I think it's a "good thing" for cyclists and pedestrians. The lower inner-city traffic speed, the better. I am not pro-bike and anti-car here, I think the same thing driving the car, (which I do a lot, by the way). The traffic pattern is better, I arrive at the same time, and in a more safe manner.

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  6. I need some of those in front of my house! I don't think I've ever seen them before, but they sound like they may just do the trick (or I'm going out in the middle of the night and installing logs or something.)

    I suppose it came second nature to me, but I've noticed that I always let go of the brakes whenever I approach a bump or pothole or anything that I can't go around. Maybe I had a learning experience as a kid. I've also noticed, and this must come from years of horseback riding (hunter/jumper) that I post (stand in the stirrups/pedals) when ever I go over speed bumps. As if they are very small jumps. :)

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  7. I agree that the platforms are a good thing; did not mean to suggest otherwise. To my eye the behaviour of cars on Somerville Ave has noticeably improved since their installation. Now to replace that enormous car-wash across from Starbucks with a flower market, and to plant some trees along that stretch!...

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  8. I think Somerville is pumping serious cash into road work, especially for today's economy, with--I guess--the emphasis of revamping itself by making prettier, tree-lined avenues. At least in this area, can't speak for other, further-away parts of Somerville.

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  9. Irrespective of whether the wheel leaves the ground over a bump, braking transfers weight forward. If you brake into the bump you effectively drive the front wheel into the bump. Acceleration, on the hand, transfers weight to the rear, so:

    Brake before the bump. Release the brake just as you reach the bump and at the same time, drive a pedal forward and the front wheel will "float" over the bump.

    Or you could just show off and bunny hop the sucker.

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  10. Kfg gives a great tip . . . Maybe you can say it's about using speed and forward movement appropriately for the situation.

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  11. the raised crosswalks (also known as "traffic calming devices") are not normally dangerous to cyclists, and they're actually not supposed to be raised in somerville: what wasn't mentioned in the case of somerville ave is that the entire street is nearing completion of a major reconstruction. the current pavement is only the base layer, and is about 2 full inches below grade. the "raised" crosswalks in question are actually designed not to be raised above street grade, as opposed to cambridge, where they are like gentle speed bumps. the city still hasn't laid down the top 2" layer of pavement, and they've done a pathetic job of warning cyclists and motorists alike of the sudden 2" ledge at the edge of these walkways. when the project is finally completed, the new crosswalks should be like the ones in davis square-- brick-lined, but at grade with the pavement, not raised above it.

    i learned about not braking on bad bumps from my auto-crossing days, when doing so could cause a car to lose control near the car's handling limits... instinctively i always anticipate bumps, brake prior to them if necessary, then coast over them. it stabilizes the handling of the car. naturally, i carry over this same habit when cycling. my motto: brake now, coast later.

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  12. Interesting. I'd never thought about this, but it makes sense. At least with the type of roadsters we ride, we could never actually flip over...right? We just sort of slide over - at least, I do. :)

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  13. kfg: In my youth, I probably would have grabbed the front brake and done a bunny-hop, especially when I had a mountain bike with suspension. (Yes, I rode one of those!)


    Velouria: I know of the kind of intersection you describe. It's almost like a podium, really, and it's made of bricks. I don't think there are any in NYC. However, I've seen them on Long Island, and they're really not so bad to cycle through. If anything, pedestrians and motorists seem to be more conscious when crossing through them.

    I like the rear rack, too.

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  14. I guess it's about getting the experience to anticipate. Breaking before bumps, setting up your angle and speed before you hit the turn, checking parked cars for occupants before you pass them, rechecking the intersection before you respond to the green light, releasing your foot before you need it to balance. When you first start out all these things can take some real concentration. Then gradually riding with anticipation becomes automatic, which is great because the slight stress is replaced with a calm sense of control. It's the same lesson my brother taught me after he did an advanced driving course (way back in the age of the dinosaur). Anticipate, anticipate, anticipate. You can't argue moral high-ground with the side of a bus. :)

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  15. somervillain - I had no idea that an extra 2" of asphalt is coming and that the "raised" design is not intentional, wow!!...

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  16. Oh wow I'm so excited for some slick new asphalt! Feels so nice on my tired wheels, like the bike is making love to the road. Next they need to fix up Beacon Street in Somerville, especially where it leads into Somerville Ave. City cycling can be a bummer when it's so tough to find smooth pavement.

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  17. personally, i like raised pedestrian crossings like the ones being installed all around cambridge. when done properly, there is a gently ramp leading up onto and down off of the crossing, allowing cars and bikes alike to coast smoothly over, provided they aren't going too fast (which is the point making them raised). from what i've heard from all of our cambridge friends who have kids and do lots of walking, they are fantastic. they make crossing the street much less intimidating to pedestrians, and they force drivers to slow down and become more aware of the intersection and people who might be in it.

    i actually *wish* somerville designed their new crosswalks to be raised like cambridge's, but i suspect there were probably a lot of politics behind the decision to keep the design more "conservative" and not piss off the driving faction of the public (which is the majority, sadly).

    biking through cambridge, i rarely have to slow down to smoothly traverse the raised crossings.

    and MDI is right-- somerville is pumping a huge amount of money into somerville in an effort to make it more pedestrian, cyclist and family friendly, since historically there has been a "family drain" out of somerville as young professionals typically move into somerville because of its proximity to boston, then move out to greener suburban pastures once they have families. "family drain" actually hurts local economies in many ways, and somerville is smart to invest money into reversing that trend.

    anon-- beacon street was supposed to be repaved but that project got tabled because of the somerville ave project, and since both streets are major thoroughfares the city didn't want to disrupt both simultaneously. i think beacon is slated to be redone starting next year... and it may turn into a multi-year project the way that somerville ave did, with the brick crossings, new sidewalks, trees, etc. so... don't hold your breath!

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  18. Despite the bumpiness, I find Beacon St ridable, whereas Somerville Ave pre-construction used to be a scary place to cycle. Now it is much better, so the updates have made a big difference.

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  19. I recently learned that sand and breaks don't mix. I have a skinned knee to remind me.

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  20. kfg - Thanks for the additional info; I've added it to the post.

    dagmara - Oh yes, especially when cornering : ) Hope your knee gets better soon!

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  21. Amy, I do the same thing! Going over bumps reminds me so much of jumping. I rarely ride these days but it is a sense-memory one retains forever. The first time I rode my Pashley I was like oh, ok, pony, saddle, got it.

    I have never seen that kind of intersection here. In some residential neighborhoods where impromptu drag racing is common they are beginning to install speed bumps, though.

    Poor girl, to fall must be awful.

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  22. Velouria, how did you know what I was up to?:
    I was coming up to a corner on a slightly sandy bike path and my tire slid out from under me. I think had I been on a lighter bike I might not have lost my balance but the Pashley being a wee bit heavy meant I fell sideways on to my rear. The best part was that though I fell while I was nearly at a standstill so I didn't really sustain any injuries, in the process of holding on to the bike's handlbars I managed to elbow myself in the chest and knock the wind out of me. I guess this proves I'm still a newbie and have a lot to learn yet.

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  23. dagmara - nope, a lighter bike would have probably been worse; heavier bikes are more stable. Don't feel bad; sand has been the downfall of many a cyclist, even professionals. Best thing to do is to avoid it altogether, or cycle slowly and in a straight line.

    neighbourtease - Judging by the comments I've gotten on different posts over the past year, it is amazing how many women who get into bicycles have horseback riding experience. I wonder if there is a connection!

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  24. Velouria, a connection would definitely make sense to me, especially with an upright ride and a leather saddle-- I don't remember ever thinking of riding during all those high school years I spent on my mountain bike. I guess I needed the stately posture and heavier steel to get it.

    I think the sense of freedom is comparable, and the ability to carve one's own path. And the romance, too. It all makes sense to me. Horses were freedom when I was little and my bicycle is my urban version of that now.

    I used to cycle with my old velvet show helmet because at least it felt normal to wear, though now I am sans helmet.

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  25. Thank you for this post, I'm memorizing this for my ventures out on the road bike. I'm still new and hesitant to a road bike and I definitely am just feeling my way around the different posture and break system on it.

    I am 100% with you - I LOVE coaster brakes. When my husband got me a cruiser and told me it had coaster brakes, I was nervous about how I would adjust to them. Previously, I was riding an old mountain bike with hand brakes. I got used to the coaster brakes within a mile or two and now I miss them every time I'm on a different bike. I think they're brilliant.

    S.

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  26. Hi there, good post!
    I agree with Dottie that roadster bikes are less likely to flip over. Most of your weight in far behind the front wheel, and using a coaster brake puts even more weight on the pedals and less on the handlebars.

    I think the Dutch would agree with you too:
    I recently visited Groningen in the Netherlands and I would say that about 70% of the bikes in the city were fitted with coasters, even new bikes. I felt right at home with my coaster bike :)

    John I

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  27. Are they not 'road humps' or are they 'platforms'? If platforms - i.e. the side facing on-coming traffic is vertical,they are certainly treacherous to cyclists.
    I've come across and crossed over road-humps . To play safe I would slow down, whenever possible, before reaching one as you have so correctly suggested here ... but there were (just a few ..Thank G..!)occasions in dim-ligthed areas when I had not enough time to reduce speed - and had to go over them without applying any brakes ... applying brakes (especially the front one)(suddenly) would most likely bring about a tumble (on landing).
    L

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  28. I've never really thought about it, but the explanation you found about braking makes sense. I've just always coasted over bumps while standing slightly and haven't had an issue yet thankfully.

    Atlanta's solution for everything is to install speed bumps - not just those raised areas at intersections or crosswalks, but in practically every residential neighborhood (and parking lot) around. I absolutely hate them from a bike perspective because the slope on many is not so gentle. There is one street that I especially hate and have no idea why they even installed speed bumps. It's very hilly AND has 2 or 4-way stop signs every few blocks! So not only do you have to slow for the speed bumps, you have to prepare to completely stop at the signs and then try to make it up the hills - horrible!

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  29. It should be noted that about 70% of your stopping power comes from your front wheel break. Should you need to come to an emergency stop,just using your rear break or coaster breaks will "skid out" resulting in more distance till your bike actually stops moving.

    The most effective way to come to a quick and complete stop (say somebody opens their car door in front of you) is to firmly squeeze both front and rear breaks while shifting your weight backwards. Standing up and moving your butt over your rear fender will help insure you don't "endo".

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  30. neighbourtease - I am imagining you cycling through Brooklyn with an equestrian show-helmet! Great stuff : ))

    hubs - in theory that is so, and Sheldon Brown actually recommend using front brake only, from what I understand. But I think these things only apply if you are going fast enough. At the speed most Dutch bikes or Roadsters cycle in a densely-trafficky city, just the coaster plus putting a foot down is sufficient. Those who own or try this type of city bike will actually notice that the front brakes on them are very weak compared to the rear brake; so I doubt the 70% stopping power rule applies to these bikes - what do you think?..

    Simply Bike - Roadbike! I will head over to your site in hopes of pictures!

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  31. Re horse-riding background: there's a blog http://cyclingwithoutahelmet.blogspot.com/
    by an American expat living in Leiden in the Netherlands. She recently visited the Velorama bicycle museum in Nijmegen and shot this photo of a draisine from 1819: http://www.flickr.com/photos/aliannack/4803539021/
    What more can I say?

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  32. Re coaster brakes on city bikes: bikes with roller brakes front and rear have the same brakes on both wheels. In case of a coaster brake, it is incorporated in the speed hub and less powerful than the front brake. Shimano say their IM-70 and -80 roller brakes are on a par with mechanical disc brakes; maybe, maybe not.
    Exploded views can be found on http://www.komponentix.de/onlineshop/index.html?shimano.htm
    under Getriebenabe mit R├╝cktrittbremse and Rollenbremse. All in German but the drawings are clear enough. Prices are informative, too.

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  33. I find that many shops seem to "de-tune" the front brakes, and this was even turned into a product by Shimano, in the form of "power modulators", which are just a bit of spring that limit the amount of force that can be applied. I'm also told roller brakes have a break-in period during which their power increases, so if you never use it, it's possible it's just not broken-in.

    The roller brakes on my Opus Lugano (which isn't exactly a lightweight bike) are just strong enough to lift the rear wheel, but I have to go at a good speed, and squeeze the brakes really hard (I'm fairly comfortable with lifting the rear wheel in an emergency stop).

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  34. Sheldon is quite correct about the front being the better brake to use to stop in the shortest possible distance.

    Once you start to brake, the weight of the bike, car, bus or any other wheeled vehicle will transfer to the front. If you are using the back brake only, it will most probably lock up as the weight transfers. Try stopping a heavily loaded two wheel drive tractor on wet grass. It only brakes from the back and the wheels lock up almost instantly. Disconnect the back brakes on your car and you won't really notice any difference in normal driving but try stopping a car from even moderate speed using the hand brake (which usually only works on the back wheels) on it's own. It takes skill and the stopping distance is appalling.

    I can prove this with an old Peugeot touring bike that I have. The front rim is the original chrome plated steel rim whereas the back wheel is a modern alloy rim. Rim brakes on chrome plated steel rims is never very powerful in the dry an absolute shit in the wet, as most people know. But even in the wet, it will stop in a shorter distance using the front brake alone than it will using the back brake alone, despit the fact that the back brake should be the more powerful because of the alloy rim.

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  35. @Velouria

    Unless there is something wrong with your bike, Sheldon's advice holds true regardless of speed.

    How quickly you can stop is limited by the grip of your tyres, it is nothing to do with your brakes. All "better" brakes do is reduce the amount of force you have to apply to achieve that minimum stopping distance.

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