Does anyone understand what the effect of changing pulley sizes if pulley ratio remains the same? Ive come across an excel simulator and it suggests that increasing the pulley sizes while the ratio is held the same decreases the belt load (lb). Is this accurate/ does belt load impact performance?

 

My rudimentary understanding is that increasing the lower/crank pulley size (diameter) increases the belt load and reducing the upper/SC pulley size does the same, so it depends on which pulley you are talking about.
I also understand that if the pulley ratio remains the same (eg both pulleys larger or both pulleys smaller) the SC boost remains the same so nothing is achieved.

 

Boost wise nothing changes in theory, but there can be like an 100 lb difference in belt load. I’m wondering if that effects performance

Additional considerations:
Increasing the size of the upper pulley should change the angle of contact with the belt, and increase the area of contact with the belt, decreasing slippage. Both in theory should decrease the amount of torque needed to spin it

Increasing the size of crank should increase passive loss as every accessory attached to the crank would also spin faster

The automotive engineering aspect is truly intriguing

 

Just thinking about it a little more and having no idea what I am talking about, I reckon increasing the size of both pulleys (so as to retain the pulley ratio and not effect boost level) will decrease the belt load and decrease slippage.
Based on the fact that so far there have been few if any reports of slippage caused by a larger crank pulley but many reports of slippage from fitting a smaller SC pulley (not including the new VAP Grip-tec pulley).
My theory is the SC pulley has much less surface area for the belt to grip than does the much larger crank pulley so changing the size/diameter of the SC pulley has a much larger effect than changing the size/diameter of the crank pulley, even if the changes are the same percentage. Put another way, increasing the size of the crank pulley makes little or no difference to belt grip but increasing the size of the SC pulley could (should?) improve the grip quite a lot, so increasing the size of both should improve grip.

 

oh yes, i have the new grip upper pulley from VAP, only on my table, not in the car till yet.
But! When I test it with my new belt, the grip is mega good! I have a good feeling when all is installed,
the grip is good enough for no slipping I think! I will give an update after installing next week....
perhaps the 1470mm belt is the first choice, and i have less tight in the system. if this doesn't work,
I'll mount the new 1461mm