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Old 10-28-2010, 11:23 AM   #646
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Most of the on-road people account for tire size also, so when he says 91mm the car move 91mm to 1 turn of the motor.
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Old 10-28-2010, 11:31 AM   #647
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Most of the on-road people account for tire size also, so when he says 91mm the car move 91mm to 1 turn of the motor.
WOW...they are geared WAY different than my B4/T4's are then. I mean if I understand it all correctly (found an article on how to calculate rollout) my B4 should have an approximate tire diameter of 3.5 inches and a final drive ratio of 5.35 (72 spur / 35t pinion x 2.6) giving me a rollout of 0.6542056 inches or 16.616822239982053 mm. Quite a bit different indeed!
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Old 10-28-2010, 11:34 AM   #648
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WOW...they are geared WAY different than my B4/T4's are then. I mean if I understand it all correctly (found an article on how to calculate rollout) my B4 should have an approximate tire diameter of 3.5 inches and a final drive ratio of 5.35 (72 spur / 35t pinion x 2.6) giving me a rollout of 0.6542056 inches or 16.616822239982053 mm. Quite a bit different indeed!
You're missing a very important variable.....PI (3.14)
The mathematical equation for ROLLOUT is-
Tire size (I like to use millimeters) X PI (3.14) X pinion / spur

41.10mm X 3.14 X 51(pinion) divided by 72(spur) = 91.41mm

We use rollout (NOT FDR) with FOAM tires because of our tires changing size from run to run.
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Last edited by JayBee; 10-28-2010 at 11:48 AM.
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Old 10-28-2010, 11:36 AM   #649
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Nevermind that...3.5 was the diameter not the circumference. That would make the circumference about 10.99, giving me a rollout of about 52.17682223994365 mm
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Old 10-28-2010, 11:38 AM   #650
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WOW...they are geared WAY different than my B4/T4's are then. I mean if I understand it all correctly (found an article on how to calculate rollout) my B4 should have an approximate tire diameter of 3.5 inches and a final drive ratio of 5.35 (72 spur / 35t pinion x 2.6) giving me a rollout of 0.6542056 inches or 16.616822239982053 mm. Quite a bit different indeed!
I believe most on-road cars fdr's are in the three's
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Old 10-28-2010, 11:41 AM   #651
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Originally Posted by JayBee View Post
You're missing a very important variable.....PI (3.14)
The mathematical equation for it is-
Tire size (I like to use millimeters) X PI (3.14) X pinion / spur

41.10mm X 3.14 X 51(pinion) divided by 72(spur) = 91.41mm
I found an I-phone app (Ratio Calc) that is free and does all the math for me.
I eat PIE instead of calculate it.
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Old 10-28-2010, 11:44 AM   #652
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Quote:
Originally Posted by JayBee View Post
You're missing a very important variable.....PI (3.14)
The mathematical equation for it is-
Tire size (I like to use millimeters) X PI (3.14) X pinion / spur

41.10mm X 3.14 X 51(pinion) divided by 72(spur) = 91.41mm
Okay that gives a wildly different result altogether. That would stack up like this -

88.9 (3.5 inches) x 3.14 = 279.146 x 35 (pinion) = 9770.11 / 72 (spur) = 135.695787 mm rollout.

Why is that so much different from the one that I had previously?
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Old 10-28-2010, 11:53 AM   #653
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Okay that gives a wildly different result altogether. That would stack up like this -

88.9 (3.5 inches) x 3.14 = 279.146 x 35 (pinion) = 9770.11 / 72 (spur) = 135.695787 mm rollout.

Why is that so much different from the one that I had previously?
Because you left out the all important PI (3.14).
And what you calculated above is exactly right...that's why you were way off. But why are you trying to use this formula with RUBBER tires? Rubber tires don't have the wear that FOAM tires do. Plus camber and caster changes the 'shape' of our tires on our 1/12th & 1/10th scale pancars. Most of us 're-true' (shave down) our tires, so the tire size changes and to maintain the same speed (rollout) pinion size has to increase. A couple of other factors are involved but this is it basically....
Still confused?
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Old 10-28-2010, 11:57 AM   #654
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Because you left out the all important PI (3.14).
And what you calculated above is exactly right...that's why you were way off. But why are you trying to use this formula with RUBBER tires? Rubber tires don't have the wear that FOAM tires do.
Still confused?
Pretty simple to figure out really. I read you all talking about it and wondered how it applied to me. I had no idea whether you were talking about street or dirt and nobody really said (so far as I could tell). As I said before...I'm new to this hobby and just want to get up-to-speed on the tech side of it all.

Make sense now? So I take it you are saying that I shouldn't be concerned with rollout at all then?
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Old 10-28-2010, 12:03 PM   #655
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Brah...calm ya nerves. Nothing that I've said and how I've type it should have came across as demeaning. If it has, I apologize. But whether your new or not....I'm explaining.
And yes....If you are running offroad w/RUBBER tires, ROLLOUT doesn't apply to that application.
(I'm smiling at you)
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Old 10-28-2010, 12:27 PM   #656
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Hey buddy, yep...had that in the endbell at first. Opted to try less endbell timing with throwing a couple more teeth at it. Final rollout of the night was 91mm.
I do everything in inches... You are at 3.58".... we run 3.4-3.5 usually.

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Old 10-28-2010, 12:31 PM   #657
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Well I know off-road or on-road the Murfdogg motors are freeking sweet.
Nice to see more and more local racers are running blue motors. The down side is my speed advatage is being matched by them now.
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Old 10-28-2010, 01:09 PM   #658
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Brah...calm ya nerves. Nothing that I've said and how I've type it should have came across as demeaning. If it has, I apologize. But whether your new or not....I'm explaining.
And yes....If you are running offroad w/RUBBER tires, ROLLOUT doesn't apply to that application.
(I'm smiling at you)
Oh I wasn't insulted at all...just explaining since you asked is all. (I'm smiling back).

From MY perspective your statement that you were trying to figure out why I was trying to figure rollout on an offroad car with rubber tires wasn't really explaining...it was confusing. So I felt the need to explain myself.

Sorry...text can be taken in so many different ways...I like to use caps and bolds and stuff to infasize things I think are important..it's not yelling or me being pissed or anything. If I was mad or insulted you would have no doubt in your mind, plus I'd probably use the RED smilies!
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Old 10-28-2010, 02:05 PM   #659
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I do everything in inches... You are at 3.58".... we run 3.4-3.5 usually.

PM me your ESC setup...

We will get you where you need to be!

Matt
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Old 10-28-2010, 10:42 PM   #660
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Originally Posted by Cameron Kellogg View Post
Well I know off-road or on-road the Murfdogg motors are freeking sweet.
Nice to see more and more local racers are running blue motors. The down side is my speed advatage is being matched by them now.
They may be matching speed but are they lasting as looooong. I know in WGT the MD motor is still pulling fast laps when everyone else is dropping off.

Great motor Matt, looking forward to your new 1S rotor version.
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