Measure diameter of chainring to know how many teeth?

[yoothgeye]

On vacation I went to a bike shop (something I don't get to do around here) and asked them if they had a single speed chainring with 30-32 teeth. The bike mechanic grabbed a tape measure and went to the back where I couldn't see what he was doing.

He came back with a chainring and I bought it, I was very curious about what the tape measure was for, but didn't ask.

Is there a known diameter of chainring to number of teeth chart somewhere? I searched and came up with a bunch of people doing math, I don't wanna do math, I wanna just know, "Oh, a 32 tooth chainring is 5.25" " (I just made that up).

Anyone know of a chart so I can quit counting teeth? I'm starting to feel like a pediatric dentist.

 

[yoothgeye]

:lol: Thanks, I needed that. :lol:

 

[kingfish254]

Oh man, that is classic!!!!!

For our international RRBers, this process also works, but you just have to extend you tape measure to 10cm and lock it.

 

[yoothgeye]

According to that chart I was actually pretty dang close with my made up example in the first post.

 

[Tater]

This is not an answer to your question, but having a marked length of chain in your tool kit is useful for getting a quick tooth count.

 

[CCR]

you can measure the circumfrence, since a 36t sprocket has a tooth every 1/2" it should be 36/2= 18"

18" diveded by 3.14 is the diameter ... so 18 /3.14 = 5.73 ... i would round up to 5- 3/4" diamter, should be a 36 tooth

I'm at work with no sprockets around, somebody check my math please :mrgreen:

roughly speaking if the above works

36 tooth / 5-3/4" D
39 tooth / 6-1/4" D
42 tooth / 6-5/8" D
44 tooth / 7 " D

looks like adding / subtracting 3 teeth are roughly adding/subtracting 1/2" of diameter.

so if 44t is 7"
41t should be roughly 6-1/2"
38t ... 6"

enough to eyeball it and have a good idea anyway :mrgreen:

 

[kingfish254]

That's fine for SWAGs, but CeeBee's method is still the most accurate one.

 

[CHAMPION123]

My bike buddies think I'm crazy but most of my sprockets hanging in the wall have the teeth number marked with a black sharpie on them. Plus I take more time to get a good riding radio and just not slap parts together and then try to figure out why the bike pedals hard. Those old ratios took some strong legs to pedal. Gary

 

[yoothgeye]

This is my favorite idea yet. (not a big fan of all the maths)

This is not an answer to your question, but having a marked length of chain in your tool kit is useful for getting a quick tooth count.

 

[axsepul]

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