no tengo coche

I'm sporting a 48/17 gear ratio. So if my understanding of ratios is right, shouldnt I get somewhere between 17-34 skid spots?

Thats not what seems to actually happen. Instead I tend to get somewhere between 1-3 spots. I skip with both sides, but definitely prefer my natural for sustained skids.
Thanks

shapelike

You need to take a closer look at your bike, either with it on a repair stand or w/ the rear end lifted off the ground. Either your gearing isn't what you think it is or you're not noticing how many skid patches you actually have. 48x17 gives you 17(34) skid patches ... look carefully and test it a bit.

sivat

The easy way to test is to put the bike on a stand and mark the bottom of the tire every time one of the pedals reaches the 3:00 position. Remember that, just because you have 17 skid patches, theres no telling how many will really be used. its possible that perhaps 3 of the patches have been used for long skids more that any of the others, so thats where you notice the wear.

dirtyphotons

you sure your rear cog isn't a 16 or an 18? 48/16 gives one skid patch (or two for ambiskidding) 48/18 gives three (or six).

edit: by the logic described below, 48/18 gives three no matter what

sivat

When the rear cog is an even number of teeth, the patches don't double for skidding with either foot forward.

dirtyphotons

haha, we keep disagreeing about this!

and i'm loathe to get into a technical difference of opinion because i made such an ass of myself about the whole gear inches thing.

but think about it. with a 48 tooth chainring 1/2 revolution (of the cranks) = 24 teeth. on 48/16 (one skid patch, even teeth on the rear cog) 24 teeth equals 1.5 revolutions of the rear wheel. it seems like there must be a second patch if you're going to skid with your other foot forward.

it then appears (and sheldon brown seems to agree) that you can only double the skid patches for ambiskidding if you have an odd number of skid patches.

then i thought about it some more, and if you're running 48/24 (still one skid patch, even teeth on the rear cog) 1/2 revolution of the cranks (24 teeth) will land you back on the same spot so there's only one skid patch whether you skid with both feet or not. this means that not all odd skid patch configurations are doubled for ambiskidding.

so my current thinking is that if you divide out all the common factors of the cog and chainring (48/16 = 3/1, 48/24 = 2/1, 48/17 = 48/17 etc) and the numerator and denominator are both odd, then you double the skid patches for ambidextrous skidding. this seems to be slightly different from what sheldon brown has on his site, but i might just be reading it wrong.

dirtyphotons

and yes, i know that very few people care about such things. i'm a nerd, and i'm okay with that.

queerpunk

so, 17 skid patches really isn't going to be that helpful. in fact, any more than 8-ish, i think most people will find that their skid patches run together. unless you're super****in' precise when you skid. i thought i was, too, but i've got worn-thru spots almost all the way around my tire with my 16 skid patches.

no tengo coche

Its definitely a 48/17 ratio. Perhaps it is just the long skids that are wearing thru the tire quicker...
So let me ask, how long do peoples tires last (hand brakes don't count)?

queerpunk

you'll get very different answers out of people based on how much they ride, whether or not they skid in order to stop, and what kind of tires they use. in other words, too many variables for answers to mean much.

BoogerBike

https://www.basementfreaks.com/member...ring/index.php

done.

TNCLR

https://www.bikeforums.net/showthread...ght=skid+patch

and

https://www.bikeforums.net/showthread...ght=skid+patch

dirtyphotons

thanks, those threads are useful (especially the stuff i posted ) but they don't really get to the matter of when you double skid patches for skidding with both feet forward or not.

also, booger, that calculator doesnt seem to work for me.

edit: oh yeah, sorry to neglect you op.

tire choice, rider weight, etc. factor heavily into tire life. but unless you're skidding on pencil eraser, one or two long skids shouldn't make huge skid patches on their own. also, assuming you have 17 skid patches, it seems unlikely that you'd typically use one or three more than the others. unless you're subconsciously counting to 17 in your head or something...

TNCLR

I assumed that those charts take that into consideration. Meaning, if you only skid with your right foot forward, you would half the number skid patches. Right?

octopus magic

I had a seventeen tooth rear cog on my bike before I dropped to a 15, and I ended up having about 3 or 4 main patches, doing just mono skids (left foot pull, right foot push).

I was trying to figure out why that was happening, but eh... I'm going to worry less and ride more.

Boss Moniker

^ You probably have a chainring in the front with 45 teeth, or some other unlikely multiple of 15. I'd check for that.

dirtyphotons

sometimes. that's the thing, you only double if you have an odd number of skid patches. but you don't ALWAYS double (for instance 48/24 is one skid patch whether you ambi-skid or not). i'd be interested in hearing what sheldon thinks on the matter.

dirtyphotons

a good strategy in general i think.

octopus magic

I have a 44 up front.. And I got that number of patches with my 17 rear.

Sheldon Brown

See: https://sheldonbrown.com/fixed.html#skid

Sheldon "Front Brake Is More Fun" Brown

vobopl

...or unless the OP rides on the same path, starting in the same spot with the cranks in the same position and skid stops at the same lights.
Edit: beware, ROBOTS

dirtyphotons

ooh, that's really cool, i never thought of that.

dirtyphotons

hi sheldon,

thanks for responding, i was actually referring to this page in my earlier posts. i believe this is the relevant passage:

"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."

the thing is, if i'm an ambidextrous skidder, and i'm running 48/24, which simplifies to 2/1, it seems from your page that i'd have two skid patches (odd denominator, double my skid patches). in practice, however, one half revolution of the pedals (24 teeth) would get me back around to the same spot. therefore, i'd only have one skid patch, even though it is an odd denominator, and i skid with either foot.

i guess that's where we differ. i've tried to visualize this with more complex ratios (like 48/18 which simplifies to 8/3) and it still seems to hold. according to my thought experiments (yes, i'm sure einstein is rolling over in his grave) it seems to me that both the numerator and denominator need to be odd in order for skid patches to double.

i'll retroactively disclaim all of this with the fact that i really appreciate everything you've done for us. i'm happy to accept the fact that i might be wrong on this, as i frequently am, but it seems like something that can be definitively proven one way or the other.

lz4005

If you carry a travel size pack of baby wipes in your pocket, you can eliminate skid spots entirely.

thurstonboise

I'm trying to visualise this, but I don't believe you can have more skid patches then teeth on your rear cog, regardless of which foot is forward. I think they would all overlap.

In reality, when I was into tearing up tires with 42/16(21/8) I had 3 spots that seemed to come up a lot more then the other 5.