Changed the A/C compressor clutch assembly. Original pulley diameter was 125 mm. New one is 105 mm or 16% smaller. No I didn't measure before and only found out when the belt went on much easier than expected. Does this mean the compressor will spin 16% faster?
Math question about changing pulley diameters
- Thread starter atikovi
- Start date
Yes.
In addition to requiring a smaller belt.
In addition to requiring a smaller belt.
%19 faster. 125/105 = 1.19
Hmmmmmm. Shouldn't it be 105/125 = 0.84 which translates into 16%? Another way is: 125 - 105 = 20. 20/125 = 0.16. 20mm is 16% of 125mm.
The final confirmation is: 16% of 125 = 20 ................ 0.16 x 125 = 20
The math is simple. Understanding the relationship of the pulleys is required.
Think of it this way.
How much does the new [smaller] pulley have to rotate to pass the same amount of dive belt?
The new pulley must be multiplied 1.19 times to be the same size as the original.
Think of it this way.
How much does the new [smaller] pulley have to rotate to pass the same amount of dive belt?
The new pulley must be multiplied 1.19 times to be the same size as the original.
Surprisingly the mechanical belt tensioner took up all the slack and is good and tight. When I put a new belt on I might try and get a shorter one.
and no the belt isn't hanging off the edge, the pulley has extra ribs for a different application.
No. That is the pulley size difference. It will spin 19% faster regardless of the driving pulley diameter.
- Ken
This can be confusing.
The question was how much faster will it spin not the pulley diameter difference. The calculation is a bit more involved. But it will reduce down to what @WobblyElvis calculated in post#3
Clarification: @doitmyself your math works if we were discussing a driving pulley diameter reduction and a loss of driven pulley "speed' as the reciprocal of the ratio originall described - Ken 4JUN23_1236hrs
- Ken
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If you want to check you brain and your math, just use a mathematically simple, well understood relationship as a test.
Two 10" pulleys will spin at the same speed. If you reduce the driven pulley by 50% down to 5" diameter, it will spin 2x as fast as it circumference is half that of the driving pulley.
Easy to see here that the 50% diameter reduction does not related to a 50% speed increase.
Now if the 10" driving pulley is reduced by 50% to 5" the the driven pulley speed will will be reduced by 50%
Pulley speed is determined by the circumference ratio - just as in gearing. In the ratio, 𝝅 cancels out leaving d1/d2.
" If I could explain this any simpler, I might even understand it myself "
Two 10" pulleys will spin at the same speed. If you reduce the driven pulley by 50% down to 5" diameter, it will spin 2x as fast as it circumference is half that of the driving pulley.
Easy to see here that the 50% diameter reduction does not related to a 50% speed increase.
Now if the 10" driving pulley is reduced by 50% to 5" the the driven pulley speed will will be reduced by 50%
Pulley speed is determined by the circumference ratio - just as in gearing. In the ratio, 𝝅 cancels out leaving d1/d2.
" If I could explain this any simpler, I might even understand it myself "
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So does that mean it will drain more power from the engine as well? 70 hp isn't too much to begin with.
