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Old 01-25-2011, 06:35 PM   #1
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Default ROLLOUT CALCULATIONS -SOMEONE PLEASE HELP!

SO IF MY ROLLOUT CALCULATES TO BE 3.23, WHAT THE HECK DOES THAT NUMBER MEAN? AND HOW DO I APPLY IT??

IS IS THE NUMBER OF TEETH I SHOULD BE GOING UP AS MY TIRES WEAR DOWN??
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Old 01-25-2011, 06:38 PM   #2
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Rollout is how many inches your tire rolls for each turn of the motor. So your tires roll 3.23 inches for each revolution of the motor.

Here are a bunch of good calcs to calculate rollout and rollout adjustments. (There are also a ton of other useful tools on the site, I recommend them to everyone)

http://www.scriptasylum.com/rc_speed/rollout_ratio.html
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Old 01-25-2011, 06:40 PM   #3
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Old 01-25-2011, 06:47 PM   #4
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Awesome, thanks!! So basically, as the tires wear I need to maintain that distance in order to maintain my speed? And I would mauintain that distance with gearing?

How do I measure the distance? Lol

I'm not sure why I'm having so much trouble grasping this concept
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Old 01-25-2011, 06:50 PM   #5
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go to gearchart.com and print out a chart it will show you your rollout and gearing that you need to keep it
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Old 01-25-2011, 06:51 PM   #6
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Use the calculator I linked. You can enter the rollout, and also the changing tire diameter, leave the pinion blank, and it will solve for what pinion you need to maintain proper rollout as tires wear down. (You can also solve for the spur, but pinion is easier to change and most people have more pinion selection than spurs.)
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Old 01-25-2011, 07:01 PM   #7
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Use the calculator I linked. You can enter the rollout, and also the changing tire diameter, leave the pinion blank, and it will solve for what pinion you need to maintain proper rollout as tires wear down. (You can also solve for the spur, but pinion is easier to change and most people have more pinion selection than spurs.)

Excellent! thanks guys.

I have the gearit2 app for the phone, should work well
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Old 01-25-2011, 07:08 PM   #8
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If you're running rubber tires, they won't wear enough to require changing gearing. Foam tires do require gearing changes since they wear more than rubber tires.
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Old 01-25-2011, 09:14 PM   #9
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What is the difference btw FDR and rollout? The higher the FDR, the more acceleration? And the lower FDR, more top end speed?
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Old 01-26-2011, 05:18 AM   #10
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What is the difference btw FDR and rollout?
FDR only takes gear ratio and internal drive ratio (diff/spool pulleys and layshaft pulley) into account. No tire diameter involved in the calculation. Rollout also uses the tire diameter to figure out the distance the car rolls for one revolution of the motor shaft.

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The higher the FDR, the more acceleration? And the lower FDR, more top end speed?
Yes.
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Old 01-26-2011, 04:28 PM   #11
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I have just drawn a line on my set up board with a mark every mm for us in the UK and then a dot on the side of the pinion at the top and just roll the car 1 turn of the shaft and mesure how far it travelled.

Rollout is also track and motor turns specific for example most of the guys at our track run about 40/45 mm per revolution (mmpr) and we run 10.5 boosted 1s. But when I run 17.5 boosted I set my rollout much higher to achieve the same distance say 75 mmpr if motor temps allow.
Tonight after racing I measured all my foams that I rotate through out the night and the size had dropped to 43mm changing my pinion up buy 1 tooth.
The gear it app is great for these calculation i find.

I am by no means an expert but I have spent allot of time studying and trying to get my head around this concept, And also pestering racers on forums. And if it helps then great.

One more thing i do is true all my foams down to the same size now and again in order to not have to change roll out during a meeting. Or ride hight for that matter.
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Old 01-26-2011, 05:20 PM   #12
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So rollout is not for rubber tires? Why do people run foam if u constantly have to change setup?
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Old 01-26-2011, 06:56 PM   #13
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So rollout is not for rubber tires? Why do people run foam if u constantly have to change setup?
Sure, you could use rollout for rubber tires. But, people that run rubber tires are inherently lazy, so since the tires really don't wear that much, they skip the rest of the calculations.

People run foam because the grip is awesome. At the Halloween Classic, amateur drivers running 17.5 foam TC were turning faster lap times than Paul Lemieux and Keven Hebert were running rubber Mod TC.

If you had 4 sets of foam tires and only ran them once per race day (3 quals and the main), you wouldn't have to change gearing/ride height, etc except between race days.
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