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Old 08-10-2007, 01:51 AM   #1
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Default Rollout mysteries

Of late I have been trying to study the finer aspects of tuning gas touring cars. After months of just getting confortable with the driving, I am now at a point where I can have the luxury of considering topics litle roll centers, ackerman and rollout calculations.

I am confused about rollout calculation and the pinion to spur ratio. The following questions come to mind:

1. I understand how to calculate the Pinion to Spur ratio but how can I arrive at a single number for both 1st and 2nd gear? Most articles address the use of 1 pinion and 1 spur ...as if we all had single speed cars. How does it work for 2 speed transmissions? Or do you arrive at two seperate ratios ...one for first gear and one for second gear?

2. Considering that most of us use foams, and are forced (if we do not get the appropriate optional parts to arrive at a 1:1 torque split) to have a 2mm tyre diameter split front to rear, how can you arrive at a single Rollout figure for the entire car? Can you calculate the front, then the rear, ADD the two together and then divide by 2? Would this be a valid Rollout number?

Any input would be appreciated. Thanks
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Old 08-10-2007, 03:39 AM   #2
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My understanding is that most of the time you would want the FINAL ROLLOUT value. So you would use the second gear ratios for the calcuations.

I use the rear tires to calculate the rollout. In most cases, you are using a tire split that would create a 1:1 (or close to it) final drive ratio, because of the pulleys that make up the transmission. Also the rear tires are typically bigger and are what will be "driving" the car (more distance per rotation).

Below is a link to some good articles regarding transmission, rollout and overdrive calcuations.


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Old 08-11-2007, 12:15 AM   #3
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Thanks Doug!! Very helpful info!!
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