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Update: this question is NOT about how to calculate the # of skid patches. I've always used http://www.bikecalc.com/skid_patch_calculator for that and the math is sound.

So, I'm already thinking ahead to next winter to see what I could do better with my fixed gear winter commuter. I'm running a pretty conservative gearing with a deliberately odd-numbered cog (21T I believe) to spread the skid patches all over my rear tire (update: I'm running 44x21 so 21 skid patches, which is a lot). This winter I tried the Schwalbe Marathons and was pleased generally, but after only two months of daily riding, the rear tire looks like the tonsure on a monk's head: completely bald in the middle and treads on both sides.

Why? Because I have SO MANY skid patches that it's a pretty uniform wear. And I hear that the Schwalbes use a pretty soft compound so they wear fast.

So, I'm wondering, what if I switched to an even gearing with **LESS* skid patches? Like a 45x20 for 8 skid patches. Obviously, some parts of the tire would wear more... but others would keep their tread... Has anyone tried this and is it a horrible idea? Or is there some merit? Again, I'm focusing on WINTER riding where I might want to preserve a little tread for grip.

And yes I run a front brake.

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    A good idea would be having a front brake on your bike and avoiding the skid patches altogether. A good front brake will stop you much faster than skid stopping or a rear brake, and save you money on tires. Not only that, but having two redundant braking mechanisms is a lot safer and actually required by law in many places.If you insist on going brakeless, you should be able to remove the wheel or tire and rotate it so that the skid patches move to a different point in the rotation. – Kibbee Mar 24 '16 at 14:27
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    +1 to Kibbee. If you ride on the road, you need a brake, period. – Mike Baranczak Mar 24 '16 at 23:08
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    Guys, what a disappointing set of responses. Did anyone actually read my post or are you just responding to the title? The comments are all "you should run a brake". Thanks. That wasn't my question and in fact I made a joke about it in the OP anticipating the do-gooders would get on me about brakes. I run a front brake year long. Happy? And all the answers are "here's how to calculate the number of skid patches". Guys, I obviously already know all that. I have deliberately chosen a gearing that spreads the patches across the whole tire. Can you guys please take the time to read the question? – Tom Auger Mar 26 '16 at 20:49
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    Well, if you have a brake and have problems with skid patches, you are doing something seriously wrong. The part about number of skid patches wasn't in the original question either. Seriously, ask the question you want answered. – ojs Mar 26 '16 at 21:04
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    If skidding 21 patches wears down all your tire within 2 months, then skidding only 8 patches will make holes in your tire within 1.5 months? – Alexander Mar 27 '16 at 6:55
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Less skid spots is going to mean uneven wear. Every time you try to stop, you'll be skidding on the more worn out parts. You're better off having even wear and replacing your tire as needed, less skid spots pretty much guarantees you'll need to replace your tires more often, with more chance of blowouts.

Good tread is most important on your front tire, especially for winter riding, so make sure that one is not super worn.

If you have a low number of skid spots, you can try and loosen your chain and rotate your wheel slightly to change where the skid spots hit as kibbee said. It can be hard to remember to do that though. Though, It will make the wear more even, causing the same issue you're already concerned about.

If your tire is bald on the center and tread on the sides, you may want to lower the pressure somewhat in your tires to widen the contact patch and allow more of the tread to contact the ground, providing a bit more stopping power and making for more even wear.

Barring all that, you may just want to switch up your tire to something that wears differently. I've had good luck with thick slicks and panaracer ribmo tires. Both have a bit of extra tread in the center and wear down to a flat profile over time.

  • The "Thick Slick" tyres I had were dreadful - they have zero tread and I have slid off a white-painted line in the dry on one. Slicks are for indoor tracks or hipsters only. You must mean something different. – Criggie Mar 26 '16 at 0:27
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    @Criggie tread pattern does not help much smooth hard surfaces, but the rubber compounds have huge differences. Try watch road racing in rain and check what equipment they are using. – ojs Mar 26 '16 at 11:30
  • Edited to more directly address the question. – Benzo Mar 28 '16 at 13:44
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    Thanks @Benzo this is all good advice. I service my bike twice a week, so not too worried about doing the two-link skip (to keep the small links on the same teeth if you see what I mean) every so often to spread out the patches. But I hear you about preferring even wear to alternating bald / tread areas on the tire. – Tom Auger Mar 31 '16 at 14:01
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To spread skid patches around the tire, you need to have chainring and cog that have mutually prime tooth counts, i.e. no common divisors. With a common 42 tooth chain ring, 21 is the worst possible choice because it produces a straight 2:1 ratio. If this did no seem to make sense, search for "skid patch calculator" to find interactive visualizations.

If you really want to avoid excessive tire wear at the cost of some style points, a front brake is great. Also, the current version of Schwalbe Marathons doesn't seem to wear that well.

Edit: After writing the answer, the question has changed. Having less skid patches is a good idea, if your aim is to wear the tire to cords faster. It will not help with braking because the tire has skid patch facing ground when you brake. It will also not help much with lateral grip, because the smooth patches will be even smoother.

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