Home Forum Bike Forum Difference in Dia between 32T, 34T and 36T chainrings ?

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• Difference in Dia between 32T, 34T and 36T chainrings ?
• thomthumb
Member

chain is 1/2″ pitch.

so 2t will add 1″ (25.4 mm) circumference

diameter of 32t = 128 mm
diameter of 34t = 137 mm
diameter of 36t = 144 mm

* guessing

allthegear
Member

The number of teeth defines the circumference of the chainring so the difference in diameter will be the difference in circumference measured in teeth divided by ?

So, ((32/36)/?)*100 for percentage difference = about 28%

Wow – more than I thought!!

Rachel

gofasterstripes
Subscriber

My 40t Surly measures approx. 175mm Dia.

If we allow 10mm for the height of the teeth, we get: 165

165*Pi = 518

518/(25.4/2) = 40ish [it has 40T]
So (518-25.4)/Pi = 38T = 157mm ish
and (518-50.8)/Pi = 148mm….ish

ie for each 2T less than 40, you remove 25.4mm from the Circumference and then divide by Pi

I think

clubber
Member

No need for pi in the calc rachel – it cancels out for both sizes. It’s a straight percentage difference.

(32/36) x 100 = 89%

chillidave
Member

Think that may be a little off, I believe the diameter is directly proportional to the circumference. So a 36t would have 12.5% larger diameter than a 32 which I think is what Thom said up there.

And that’s the most I can remember from my degree. 🙂

cr500dom
Subscriber

Cheers everyone,
I shall have a measure up tonight but I suspect if I want to maintain a decent chainline then I shall have to go down on the rear sprocket instead

woody2000
Subscriber
jameso
Subscriber

Easy.

32-34-36 are ~134mm, 142mm and 150mm

(I’m not great at maths but I do have the shimano tech book..)

cr500dom
Subscriber

Nearly finished the commuter build and rode it in for the first time today (Rides nicely on 2.3 Supermotos)
It has an Alfine 8speed hub with an 18t sprocket fitted

I have just put a new 32T stainless front chain ring on and I could do with it being a bit taller geared.
I am limited for chainring clearance so was wondering if anyone knew the difference in Diameters of a 32T 34T 36t chain ring ?

Cheers
Dom

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