So this is awesome. I was riding across Humboldt Park in the rain last night and had a brilliant idea. There are lots of places where the paved path tees into another paved path, surrounded by grass. It occured to me that because the grass was wet I could probably skid really far if I hit it at full speed. Humbolt Park is huge, so I was able to accelerate for half a block before plowing off the path and locking up the wheel. I almost crashed so many times. When done right, I was skidding for well over a hundred feet. I was a half hour late for the party I was headed to, but it was worth it. I've heard that in Scottland they race track bikes on a flat grass track as part of a strong-man competition. Would anyone want to do that in Chicago? I think it would be fun. Let me know whose down and I'll organize it.

https://www.fixedgeargallery.com/perth.htm

Look at the sideburns and missing teeth on those gnarly ****ers!

why do you want to skid? It isnt a good stopping method, and it tears up trails and courses.

It is FUN. It comes from the same impulse as jumping in puddles. It's not environmentally conscious to skid on mtb trails, but there's practicaly zero impact on a huge flat city park.

Almost as fun but not nearly as destructive is the wet decaying leaves skid. We have had some major leaf blow-downs in the past couple days, followed by rain. This makes for a combo slicker than snot and conveniently located in the shoulders of most roads.

You really have to watch your balance though, as the stuff is so slick that your rear end will start to slide out very easily. I was able to execute a perfect bmx-style skid stop on this stuff just yesterday. Problem is, it was an accident.

Try it. Its fun.

Missing teeth, could it be because of the crashes riding on grass?

Thanks again for the chain-ring-bolt help on our last ride, Ira.

Also, 99.99999999++ fixie skidding is done on pavement.

which slowly but surly kills perfectly good tires.

and your point is. . . so does normal riding and skipping!

that said the best is skidding over those metal construction plates (the ones they put on the ground to cover up holes) right after it rained. man you can go soooooo far with a good series of them!!!

i'm glad someone has the courage to advocate for the tires. let's save the tires.

you can spread the tire wear from skidding most effectively if you select a chainring and a cog that have prime numbers of teeth. if you select a ratio that's an integer, you will skid a hole in that tire really quickly.

and pedro, godammit those wet leaves are gonna kill me some day this week!

a 3:1 ratio will wear your tire in the same 3 places if you're on a fixed if you have something more like a 46*16 your tire will wear more evenly at least that's what i've seen.

Nah, they're missing teeth 'cause they're SCOTTISH! That's not a cheap shot, I've just never seen more punched out faces than during the time I spent in Scotland. But god bless 'em!

And for the bolt, any time. Is that thing still holding?

I'm serious about grasstrack racing. Tell me if you want to do it and I'll set it up.

Yea, it's still holding.

I'll have to give the whole idea of grass racing a try by riding on some grass before I commit.

Going to the cyclocross races in two weeks?

Actually, a 3:1 will wear the tire in the same 1 place. A 1:3 would wear in the same 3 places. Any gear ratio that is relatively prime--that is, if you factor each gear, they should share no terms in common--will wear essentially randomly.

And you're a braver man than I for skidding on those steel plates. Them things is slippery as @#$% when they're wet. I try to stay completely away.

Okay, since I'm an artist and not a math freak, can anyone tell me if a 46x18 will wear my tire out in the same place?

Thanks.

i think that'll give you 9 skid spots on your tire.

the highest common factor of 46 and 18 is 2. 18/2 = 9.

did i remember the rule properly?

Arright, thanks for your help! Now, does that include if I skid in the same position, with my right leg only?

That sort of doesn't make sense (to me, anyway). 48/16 = 3 and 16/16 = 1. 48/16 = 3:1.

If my gear ratio is 3:1, that means that for every three revolutions of my crank, there is one rotation of my wheel.

As we all know, there are two power strokes for every revolution of a crank, thus, a 3:1 ratio wil give me 6 consistent contact patches, not one.

The rule would still apply, though, if the numbers were relatively prime (because there would never be an x number of crank revolutions that equal y wheel revolution(s)). I think the formula, given a ratio x:y would be:

x*2/y, where x and y are the greatest common factors of the gears in question.

Does this sound right to anyone else?

the other wy around. 1 revolution of crank, and 3 rotation of your wheel, unless you have 16 chainring and 48 cog.

That's right, my mistake. That makes a bit more sense than what I was saying.

So what is that, 2 contact patches? Since after each crank revolution, the tire returns to the same spot (after turning three times), that means that the power stroke (or leg-lock. I noticed after my previous post that we were talking about skids, not just pedaling) will always occur on the same two spots on the wheel.

Then how does the rule work? This might be more or a mathematics problem than a cycling problem, at this point. Do you multiply the first number in the ratio by 2? So 46/18 = 9:23, so there are 18 possible contact patches?

Clearly, at this point, I have no clue.

Same one spot if you always have the same foot back.

To determine the number of potential "skid patches", you start by factoring each gear. Find the least common multiple, which means multiplying all of the unique terms in each gear. So if I had a 48/16 ratio, my terms are 2*2*2*2*3 = 48, 16 = 2*2*2*2--The set for 48 actually contains all of the unique terms, so multiplying them = 48 = the LCM(48,16). On the other hand for 46/18, the terms are 46 = 2*23, 16 = 2*2*2*2, so the LCM(46,16) = 2*23*2*2*2 = 368. So whenever the number of teeth the chain passes over counts a multiple of 368, that means both the cranks and wheel have returned to the same position that they started in.

That comes out to 8 rotations of the crank, so on any given skid (assuming the same leg position), you have a 1-in-8 chance of hitting any given skid patch on the wheel.

If your ring and cog have relatively prime numbers of teeth (that is, they share no terms in common), then you have a best case scenario where the number of skid patches is equavalent to the number of teeth in the cog. My case, with a 47/16 ratio: LCM(47,16) = 47*2*2*2*2 = 752. 752/47 = 16 (big surprise) => 16 unique skid patches.

holy number theory! i should be busting out my old text for this thread... euclidean algorithms for all!! YAY!!!!

This thread made my brain bleed.

Pretty good explanation but you calculated the # of skid spots for 46/16, not 46/18 as SBL requested. Anyway, i still think that SBL has 9 possible skid spots; I drew it out this time.

Oops.

18 = 3*3*2, 46 = 2*23, LCM(18,46) = 3*3*2*23 = 414. 414/46 = 9. Incidentally, the shorcut for all of this is to take the set of unique terms and eliminate the terms from the chainring. So LCM(18,46) = 3*3*2*23. Drop the 2*23 and you get 3*3 = 9, the result of LCM(18,46)/46.

slick.

out of curiosity and to completely derail this thread, what's your educational background?