Bike Forums > diameter of a 38-tooth ring?
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 10-05-07, 06:49 PM #1 erader Senior Member Thread Starter     Join Date: Feb 2006 Location: silicon valley Bikes: Posts: 1,774 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) diameter of a 38-tooth ring? does anyone know how much bigger a 38-tooth ring is compared to 36-tooth ring? i'm looking at replacing the 36-tooth ring on my 1 x 9 with the larger ring and i'm trying see if i have enough clearance. i have an MTB frame and i run the ring in the middle position and i believe the stays are bent to optimize a 34-tooth middle ring (i already had to move the BB over to get the 36 to clear). TIA ! ed rader Last edited by erader; 10-05-07 at 10:38 PM.
10-05-07, 07:21 PM   #2
MudPie
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 Originally Posted by erader does anyone know how much bigger a 38-tooth ring is compared to 36-tooth ring? i'm looking at replacing the 36-tooth ring on my 1 x 9 with the larger ring and i'm trying see if i have enough clearance. i have an MTB an mtb frame and i run the ring in the middle position and i believe the stays are bent to optimize a 34-tooth middle ring (i already had to move the BB over to get the 36 to clear). TIA ! ed rader
I believe the diameters are directly proportional to the number of teeth. For example, the diameter of a 32T is twice as large as a 16T.

If you measure the diam of your 36T, you should be able to calculate the diam of a 38T.

The ratio is constant: 36/38 = diam of 36/diam of 38.

 10-05-07, 07:30 PM #3 waterrockets  Making a kilometer blurry     Join Date: May 2006 Location: Austin (near TX) Bikes: rkwaki's porn collection Posts: 26,130 Mentioned: 2 Post(s) Tagged: 0 Thread(s) Quoted: 2 Post(s) c=2*PI*r c = 38/2 inches = 19 inches (teeth are 1/2 inch apart) 2 * PI * r = 19 r = 19 / (2 * PI) = 3.02 inches d = 2 * r = 2 * 3.02 = 6.04 inches That's along the chain centerline, and I'll bet the teeth are 1/16 of an inch proud of the centerline, so I'd say 6 1/8"
10-05-07, 10:36 PM   #4
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 Originally Posted by waterrockets c=2*PI*r c = 38/2 inches = 19 inches (teeth are 1/2 inch apart) 2 * PI * r = 19 r = 19 / (2 * PI) = 3.02 inches d = 2 * r = 2 * 3.02 = 6.04 inches That's along the chain centerline, and I'll bet the teeth are 1/16 of an inch proud of the centerline, so I'd say 6 1/8"

wow! that's some pretty fancy math ! i get 5 7/8" for the 36 so that would 1/4" difference. thanx to the both of you!