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Old 09-17-2008, 09:37 PM   #1
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Default IDR vs FDR

pls explain what the difference between two kits with the same final drive ratios, but different internal drive ratios.


thanks!
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Old 09-17-2008, 09:44 PM   #2
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pls explain what the difference between two kits with the same final drive ratios, but different internal drive ratios.


thanks!
IDR is set by the pulleys in your car and thus the internal ratio. Two cars can have different size pulleys front and rear. Some cars you can change the IDR if they offer different size pulleys.

FDR is spur/pinion * IDR
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Old 09-17-2008, 10:09 PM   #3
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I think he's trying to ask what differences there would be in how the car drives etc between 2 cars with the same FDR but different IDRs.

I too would like to know from someone who has a good understanding of what this means as for me it seems like there would not be that much difference other than where in the drivetrain the torque would be applied etc.

My knowledge of this is limited to knowing that you can change the IDR of your car to allow for slight changes in the FDR of your car for the same given Spur/Pinion combinations.

Anyone care to elaborate on how different IDRs affect your car when the same FDR is obtained in the end?

-Mark
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Old 09-17-2008, 10:12 PM   #4
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yes, i would like to know the difference on their handling characteristics.
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Old 09-17-2008, 11:37 PM   #5
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the car with a lower IDR should be more efficient and might actually have better top end from lower rolling resistance due to having lower belt speed... I don't know if you will feel something a difference between a car with idr of 2.0 vs 1.9....
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Old 09-18-2008, 12:38 AM   #6
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the car with a lower IDR should be more efficient and might actually have better top end from lower rolling resistance due to having lower belt speed... I don't know if you will feel something a difference between a car with idr of 2.0 vs 1.9....

... and so will have lesser acceleration right?
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Old 09-18-2008, 01:02 AM   #7
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the car with a lower IDR should be more efficient and might actually have better top end from lower rolling resistance due to having lower belt speed... I don't know if you will feel something a difference between a car with idr of 2.0 vs 1.9....
Now when you think of it 3 for seconds longer, the belt speed does not depend on the IDR, it's only determined by diff pulley size. Smaller diff pulley = lower belt speed.
I think the main difference actually comes from layshaft speed and spoolup. With higher IDR, the layshaft has to rotate faster for the same car speed, meaning the spoolup will also take more effort.
Efficiency wise, the best of both worlds would be to have lower IDR by making the diffs smaller, not the layshaft pulley bigger. Then again, the belts run more efficiently on bigger pulleys, so in the end it's all a big mess
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