I was in Portland today and ducked in a bike shop in my spare minutes looking for SS stuff and a guy there mentioned something about having the chainring and rear cog being odd/even numbered teeth (i.e. not both even or both odd). He said because that would cause wear in the same place.

What does this mean? I'm trying to imagine and all I can come up with is that maybe on the downstroke of each pedal the same place would be getting the most friction. But why not with odd/even combos?

thanks...

It's more complicated than that. Search for skid patches and ratios. Has to do with when you lock the rear wheel up with your legs on a fixie, your cranks are usually in the same position. Depending on the gearing, your wheel could have 1 spot to I think like 30 spots to lock up and drag on the ground. If you hit the same spot too many times, you get a bald patch on your tire...

Oh...so this is a fixed thing? I'm doing an SS conversion, not fixed.

Then don't worry about.
It's something to consider if you skid/skip a lot.

yeah, it only applies to fixed gears, and specifically, to tire wear from skidding.
do what HereNT said, there's tons of info, but in a nutshell, the ideal configuration wrt to tire wear is to have the tooth-count on your cog and chainring be prime, relative to each other.

Sheldon Brown has an interesting on article on Extending Bicycle Chain and Sprocket Life. He says it only applies to "simple chain drives, as with singlespeed /fixed-gear bikes or bikes with internal gear systems". Now it does not touch upon the skidding which HereNT touched upon, which I had never thought about, but makes lots of sense. I guess it comes down to what you want to replace more b/c it sounds like something has to give, but since you are going SS you may want to go with Sheldon Brown's advice since you won't be skidding.

wow- i've never heard that. that's freakin cool.....

well if you think about whats actually going on, it makes sense. 17t cogs are my friend

Cool- thanks for the sheldon brown link. Just ordered my spacer kit, lockring, 16t cog and KMC chain+half link from misfit cycles. They better ship fast!

their order confirmation message made me wonder if maybe i should've taken my business elsewhere..(maybe harris)

"we have your money...and be assured we're spending it on bling bikes and beer...mostly beer"

plus their marketing seems like its geared for 13 year olds...ah well, hopefully they ship fast - their prices and selection are one thing i can't complain about as far as single speed stuff goes

we'll see if the magic gear configurator was right about the 36x16 with half link

So is 49/19 bad? Or good? I've never been able to figure that out. Both 49 and 19 are prime so there's only one skid patch per "foot forward" (right or left)?

I've never gotten this to work on my work computer, but a few quick pages reveal to me that MacG is, in fact, a genius:

https://www.basementfreaks.com/members/karl/gearing/

I don't think there's much that you could be looking for that's not in that calculator/table...

[edit]And I finally remembered to bookmark it.

benk0 :

49x19, 23c

67.83 inch
19 skid patches
99 rpm @ 20mph
21.2 mph @ 105rpm
[/edit]

Misfit cycles is good stuff with solid product. I wouldn't be worried. Personally, I'd be happy that their order confirmation message was actually written by a human and not just a generic template. Kind of like when you read the warning for a Surly cog or lockring: written in plain english, no lawyer-speak. It's nice when companies have a human face.

If your worried about the number of skid patches..theres no need to mess with your gearing. Periodically, take you chain off the chainring, rotate the cranks forward or back a bit...fresh skid patches!

I don't think what the OP asked about has anything to do with skid patches. If both the chainring and cog have even or odd teeth, the skinny links of the chain will always hit the same teeth, and those teeth will wear faster. If you have an odd/even setup, the skinny links of the chain will alternate on the ring/cog and make for more even wear. You can see this if you are running both even, every other tooth on your chainring will be dirty.

Woot! My planned 35x13 ratio (dictated by what I have to build with) gives me 13 skid patches and 70 gear inches. It was meant to be...........

You should re-read this entire thread, and then switch one of those numbers to be even. There was a lot of good advice about reasons not to run even/even or odd/odd ratios...

PS- I'm not trying to sound like an ass, I just think you might have missed something.

That page looks very helpful, but doesn't work for me. I can figure that stuff out on my own, but I would rather have the machine do it... any tips on getting it going?

select one of the checkboxes in the 'display' row and set the other parameters.

what are you trying to get it to calculate?

Sheldon Brown recommends an even/even for the same reasons that you recommend an odd/even.
From Sheldon Brown:
With even numbered sprockets, only the teeth that correspond to the "stretched" half links get deformed, and by doing so, they work fine with the elongated half links. The alternate teeth don't wear as much, since they are dealing with normal pitch half links.

Sheldon Brown talks about skidding (skip stopping) and gearing here:

https://sheldonbrown.com/fixed.html#skip

Reasons for EVEN/EVEN or ODD/ODD (what sheldon is saying):

Your entire drivetrain will wear together. This means that if you leave it on there, even when it is pretty worn, it should still work well together. This is a good idea for people who like to switch their ENTIRE drivetrain at once.



Reasons for EVEN/ODD:

Your drivetrain will wear EVENLY. Since the narrow links will be contacting alternate teeth, no teeth will be worn more than others. This is good if you like to change out parts of your drivetrain at different times. If you just change your chain and not your chainring and cog, it is better to have evenly worn CR/cog instead of every other tooth being worn and every other tooth being new.

An arguement could be made that if you are careful to put your new chain in the same orientation as the old (narrow links on worn teeth) then you can change out your DT at different times and still benefit from E/E or O/O. I'm not sure how this works in practice as you are replacing a worn chain with an unworn one, which could still contact the teeth differently.

I don't mean to be a jerk, but I feel compelled to point out that 49 is most certainly not prime (7x7)...

prime numbers have more to do with the cog than the chainring, but yes 49 is not prime.

Relatively prime numbers are not necessarily prime numbers themselves. In order for numbers to be relatively prime, the share no factors other than 1. For instance, neither 81 (3^4) and 100 (2^2*5^2) are prime, yet they are relatively prime. This ends your regularly scheduled math lesson.

Still..if you periodically remove your chain from the cog/chainring for cleaning or whatever, you don't need to worry about the number of skid patches or uneven tooth wear, since the chain will not go back on the exact same way every time. How many of us leave our rear wheel on the bike, without removing it, for the amount of time it takes for a drive train to wear out? I certainly don't. By chance, my ratio is even/odd, but if it was odd/odd or whatever, I'm quite sure that my chain gets moved around enough to circumvent either of these problems, so its just not something to be concerned about, except for maybe a few freak perfectionists.