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Commuting Bicycle commuting is easier than you think, before you know it, you'll be hooked. Learn the tips, hints, equipment, safety requirements for safely riding your bike to work.

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Old 03-01-07, 08:45 PM   #1
notfred
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Holy crap, look what I did to my tire.

I've been commuting to work almost every day (every work day, anyway) since I moved to San Francisco in December. I've taken the bus about 3 or 4 times, because of weather or whatever, but other than that I've done 5.5 miles each way every day on the bike.

What I wanted to mention is that my bike hasn't given me a single problem the whole time. I haven't done any maintenance at all, except to add some air to the tires once in a while... until yesterday. I was involved in a sort of panic stop that involved my skidding down the road (upright -- the bike was on its wheels and moving forward, it's just that the real wheel wasn't turning). Anyway, the stop turned out ok and I didn't hit anyone or anything, but I thought "wow, I wonder if I ruined my tire in that skid," so for the first time in months, I looked over my rear tire. This is what it looks like:





Those are three separate holes through the outer part of my tire, and I think only one (probably the biggest one) was caused by my skid yesterday. I've been riding around like that for probably weeks without even noticing. I'm almost surprised those tires still hold 110PSI of air.

Anyway, I bought some new tires today (Michelin Lithions) and I'll be installing them tonight. I hope they give me as long of a maintenance-free streak as the last ones.
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Old 03-01-07, 09:24 PM   #2
newbojeff
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How many miles did those tires have on them!? I'm getting that you only had about 600 miles on them. Had they been sitting around in the sun for a long time before you used them?
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Old 03-01-07, 09:36 PM   #3
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Try using your front brake more, it's about 70% of your braking ability. The reason the rear skids so easy is because when you brake, your weight shifts to the front and makes the rear end lighter, therefore it slides/skids easier. In fact, you could disconnect your rear brake and probably not notice any increased stopping distances (there are cases when you NEED to use it, but that's beyond the scope of this post) but please use that front brake more!

Another thing you can work on is threshold braking. It's just something to practice when you have some free time. Basically ride around on various surfaces and squeeze your brakes until the tires reach the limits (squeeze it like you would the trigger on a gun and you'll actually hear a VERY slight howl from your tires immediatly before they slide[this is the absolute limit of traction]) and just practice practice practice!

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Old 03-01-07, 09:51 PM   #4
notfred
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I tend to use both brakes pretty much equally. In panic stops (which happen infrequently, but once in a while in city traffic) I tend to lock up the rear wheel. Also, the bike is a fixed gear, and when stopping quickly I tend to also stop my feet, which forces a skid.

Also, the tires probably have 1000-1500 miles on them (I got the bike before I started working in SF) and I always keep the bike indoors out of the sun.
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Old 03-01-07, 09:58 PM   #5
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Quote:
Originally Posted by notfred
I tend to use both brakes pretty much equally. In panic stops (which happen infrequently, but once in a while in city traffic) I tend to lock up the rear wheel. Also, the bike is a fixed gear, and when stopping quickly I tend to also stop my feet, which forces a skid.

Also, the tires probably have 1000-1500 miles on them (I got the bike before I started working in SF) and I always keep the bike indoors out of the sun.

Not being knowledgeable of fixies I would head over to the fg/ss forum and search for gear ratios. It looks like you are skidding on one or two spots. By using a different gear you can spread the skids over the entire tyre.
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Old 03-02-07, 01:42 AM   #6
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What's your ratio notfred? it looks like you have only six skid patches.
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Old 03-02-07, 02:52 AM   #7
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Quote:
Originally Posted by notfred
I tend to use both brakes pretty much equally. In panic stops (which happen infrequently, but once in a while in city traffic) I tend to lock up the rear wheel.
When you feel the rear wheel locking up it is safest to ease up on the rear brake. Sheldon Brown has a good article on this.
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Old 03-02-07, 06:16 AM   #8
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i also find michelins, at least the pro race 2, to be ridiculously thin tires for skidding and whatnot.

i only use the rear tire to skip occasionally and i blew through one of them in about a month recently.

currently i have a conti gatorskin which is holding up much better. mostly because the casing is a little thicker. but realistically with riding fixed and trying to stop with the pedals (skipping/skidding) i don't see my tires ever lasting much more than 6 months. do i care so much? no it's fun.

for my next tire i plan to check out this guy...

http://www.somafab.com/tires_ev.html
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Old 03-02-07, 07:33 AM   #9
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Notfred:

Not checking on the condition of your bike regularly ... is reckless and potentially life threatening.
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Old 03-02-07, 09:49 AM   #10
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I understand the physics of why braking with the front is better. The problem is that for many of us a panic stop involves some actual panic. I've had cars pull out in front of me twice. The first time, I know I locked up the rear wheel and skid. Not sure what happened the second time. I remember there was no skid, but I wasn't going that fast either. I don't know how you practice a panic situation.
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Old 03-02-07, 10:11 AM   #11
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Whats the problem?
Thats how a street fixie's tire SHOULD look =D

You'll know when you've gone too far with a tire when you feel the bulge a couple revolutions before the tube blows out of the casing.
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Old 03-02-07, 11:23 AM   #12
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Quote:
Originally Posted by notfred
I've been riding around like that for probably weeks without even noticing. I'm almost surprised those tires still hold 110PSI of air.
Those are fixie skid wear patterns. You're supposed to rotate your tire every once in a while by removing the chain, turn it a fractional rotation and remount the chain to even out the wear. San Francisco streets are bumpy, but on smooth stretches you should be feeling the bumps of these lopsided tires.
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Old 03-02-07, 12:57 PM   #13
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Quote:
Originally Posted by richardmasoner
Those are fixie skid wear patterns. You're supposed to rotate your tire every once in a while by removing the chain, turn it a fractional rotation and remount the chain to even out the wear.
Some gear ratios are more prone to this than others. Check out:

http://sheldonbrown.com/gloss_sa-o.html#skidpatch

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Old 03-02-07, 01:22 PM   #14
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Fixies are great (I've used them as road bikes for training) but if I were to commute on one daily I'd be checking the rear tire every morning and night for tread wear. It sounds like your bike's equipped with two good brakes as well and that's a good thing but I've seen lots of cyclists sliding to stops wholly dependent on what looks like a worn out chain and pretty crappy tires. The failure rate of those two components alone and the consequences of their failure under certain circumstances can be sobering to say the least.

I'm glad it was just the tire that took the abuse and not your body. I agree with those who suggest looking into a different gear ratio but also checking more habitually for tire wear.
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Old 03-02-07, 01:33 PM   #15
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Quote:
Originally Posted by Sheldon Brown
Ahh, I hadn't seen that one before. I've wondered idly if there was a way to determine the number of skid patches like this, and it makes sense.

I ride 42/16, which simplifies to 8 patches for me.

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Old 03-02-07, 02:54 PM   #16
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Learn to ambi-skid to get the maximum of skid patches you can. Skipping will help prolong the tire's life more than skidding, but skidding's fun so I'm not gonna tell you not to skid.
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Old 03-02-07, 03:17 PM   #17
Sheldon Brown
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Quote:
Originally Posted by jyossarian
Learn to ambi-skid to get the maximum of skid patches you can. Skipping will help prolong the tire's life more than skidding, but skidding's fun so I'm not gonna tell you not to skid.
"Ambi-skidding" is only beneficial if you have an odd number of skid patches.

Here's my Glossary entry on the topic:
--------------------------------------------------------------------------------------
Skid Patch

Fixed-gear riders who make a habit of doing "skip stops" you will wear the rear tire out considerably faster than those who use a brake. This problem is exacerbated by certain gear ratios, because they may tend to repeatedly skid on the same section of the tire.
Riders who plan to do a lot of skip stops should consider the ratio when selecting their chainring and rear sprocket. The mathematics of this is actually fairly simple:


Simplify the gear ratio to the smallest equivalent whole number ratio.
The denominator of the resulting fraction is the number of skid patches you will have on your rear tire.
Examples:
44/16 simplifies to 11/4, so there would be 4 skid patches.

45/15 simplifies to 3/1 so there would only be 1 skid patch.

42/15 simplifies to 14/5, so there would be 5 skid patches.

43/15 can't be further simplified, so there would be 15 skid patches.

This is based on the assumption that you always skid with the same foot forward.
If you are an ambidextrous skidder, and the calculation gives an even result, your number of skid patches will be the same.

If you are an ambidextrous skidder, and have an odd denominator, the number of possible skid patches will be doubled.

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Old 03-02-07, 03:27 PM   #18
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Hint for fixie riding. Ride a rear cog with a prime number of teeth (13,17,19,23) to make for an (almost) continuous wear patch with any chainring up front. I ride a 48/17 combo and the tire wears evenly.
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Old 03-02-07, 03:32 PM   #19
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So Sheldon, you're saying the upshot is that you should "ambi-skid", have chainring and cog sizes that are relatively prime, with and odd number of cog teeth to spread the wear better?

Edit: Dang it Brian R sorta beat me to it.
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Old 03-02-07, 03:35 PM   #20
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Quote:
Originally Posted by Brian Ratliff
Hint for fixie riding. Ride a rear cog with a prime number of teeth (13,17,19,23) to make for an (almost) continuous wear patch with any chainring up front. I ride a 48/17 combo and the tire wears evenly.
Primeness has nothing to do with it, as long as the front and rear have no common factors, for example 44/15, 45/16, 39/14, 53/20...

If _either_ the chainring or the rear sprocket is a prime, there cannot be any common factors, so the number of skid patches will equal the number of teeth in back.

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Old 03-02-07, 04:23 PM   #21
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My only point is that a prime numbered cog will allow any number of teeth in the front and maintain the maximum number of skid spots. But yes, if you change the gear ratio primarily by changing the cog in the back, you can put in a 43 or 47 tooth chainring in front and use any number of teeth in the back. I usually change the chainring because one can adjust the gear ratio more finely by changing the chainring by a tooth or two. (edit: Oh, and because with only a chainwhip and my lack of cog changing skill, it is much easier to change a chainring if I want a new ratio.)

I just said "continuous" because, in practice, 17 wear patches becomes a continuous strip around the tire.
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Old 03-02-07, 04:40 PM   #22
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Quote:
Originally Posted by Sheldon Brown
If _either_ the chainring or the rear sprocket is a prime, there cannot be any common factors
Huh? 44/11?
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Old 03-02-07, 05:02 PM   #23
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Originally Posted by chephy
Huh? 44/11?
Ah, I guess the chainring cannot be a multiple of the rear sprocket either. Actually, it kind of works, you either get the number of teeth for the skid patches, or a single one. BTW, 44/11 is a massive gear to be pushing fixed.
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Old 03-02-07, 05:06 PM   #24
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Apparently Sheldon himself isn't a mathematician, Cephy.

Quote:
The problem is that for many of us a panic stop involves some actual panic.
I've never seen you ride so it's hard to say, but I wonder if you ought to ride more conservatively. I certainly run into panic-inducing situations from time to time, but I think there are far too few panic stops to put any appreciable wear on my tires.
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