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+--- Thread: Question for math boffs - serp belt size (/showthread.php?tid=8397)
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Question for math boffs - serp belt size - Stoney - 19-07-2019
jimxms So, if the belt makes contact with exactly half of the pulley
a = 64mm (2.55")
b = 57mm (2.25")
a/2 = 32mm
b/2 = 28.5mm
32-28.5 = 3.5mm
That right?
I'd have to say no mate. I don't think that is right
sprinter2012 Don't take this as gospel, but it makes sense in my head...
You need to work out the circumference of the part of the pulley that the belt will sit on for the old and new pulleys...
Old Pulley Circumference = a
New Pulley Circumference = b
Then half them both, so now you have a/2 and b/2
Then do (a/2)-(b/2) which will tell you how much shorter the belt needs to be :thumbup:
This method should work. Although the angle at which the belt comes up will have changed, this has an effect on the length too, in theory, though in practice this would be very small and probably negligible, so we'll forget about that!
a = 64.77mm * Pi = 203.48mm
b = 57.15mm * Pi = 179.54mm
a/2 = 101.74mm
b/2 = 89.77mm
Difference = 11.97mm or 12mm shorter
Question for math boffs - serp belt size - sprinter2012 - 19-07-2019
Aaah yes, well corected Stoney. I haden't realised the 2.55 and 2.25 were diameters.
Does make sense now I think about it because they would be some pretty small pulleys if they were the circumference!
But as you have rightly edited in the equation, just multiplying the values by Pi corrects the whole thing :thumbup1:
Question for math boffs - serp belt size - Stoney - 19-07-2019
sprinter2012 Aaah yes, well corected Stoney. I haden't realised the 2.55 and 2.25 were diameters.
Just imagine the boost from a 18mm pulley! (If circumference was 2.25") Christ!
Question for math boffs - serp belt size - sprinter2012 - 19-07-2019
Well at least now 2 of us have had an input and come to the same conclusion Jim should feel a bit more confident in getting his new belt
DISCLAIMER: I still take no responsibility for any wrong belt sizes and consequent profanities this may cause