[WestCoastHucker]

i've got a 40t front ring on order, and am making chainguide plates to fit it, so i need the diameter of a 40t ring with a chain wraped around it. i'd like to have the plates made by the time the ring shows, so i can just bolt it up and go. any help from you cats would be greatly appreciated......

 

[kidwoo]

Call mrp, e.thirteen, or truvative and ask what they use for plate diameters. That will be more accurate than someone here measuring theirs.

 

[- seb]

A chainring with a chain around it can be thought of as a 40-sided regular polygon. So split that up into 40 isosceles triangles.

Each triangle will have an acute angle of 360/40 = 9°. The shortest side is half a chain link = 0.5".

Each triangle can be split into 2 right angled triangles, angle 4.5°, opposite side 1/4".

We want the longest side (hypotenuse).

H = 0.25" / sin (4.5°) = 3.186"

Double that gives a diameter of 6.37" between the pin centres of the chain. Now add double the radius from pin centre to edge of chain (5/32" at a guess) and we get 6.69". (= 170mm)


Can you tell I'm bored?

Probably wrong too, I'll be interested to see what measurement someone comes up with

 

[dw]

Call mrp, e.thirteen, or truvative and ask what they use for plate diameters. That will be more accurate than someone here measuring theirs.

Or just buy a 40T supercharger kit for $34 and save the time and aggravation! hah

dw

 

[Tashi]

"Spam, spam, spam, toast and spam" (In your best man-impersonating-a-woman voice of course)

j/k

 

[WestCoastHucker]

Or just buy a 40T supercharger kit for $34 and save the time and aggravation! hah

dw

but, it would be more fun to mod my current plates down a few sizes.......
there is a lot of extra metal on the MRP plates and this causes a lot of chain rattle noise while in rough sections and i would like to shave some of this off......
i am not opposed to the supercharger kit, but i would still need to mod my inner plate anyway (dual rotaters on a mono)......

 

[dw]

I believe that a 40T inner MRP plate is about 180mm but Im not 100% sure

have fun!

dw

 

[WestCoastHucker]

I believe that a 40T inner MRP plate is about 180mm but Im not 100% sure

have fun!

dw

is this the approxamate diameter of the 40t supercharger as well?...... if so, about how far is the top of the chain within the exterior of the supercharger?

after i remove the extra metal of the plates, the mrp logo will dissapear, maybe i'll take my dremel and grind EVIL into it instead......

 

[ssaddict]

Does this give you an idea?

Here is a 39t ring behind a 40t SRS

This is the backside of a 40t ring behind a 42t Supercharger