Gear Ratio for RWD

So I converted my R31-FM to RWD and so far it's been good. Although, I haven't really done a full shake down with the car yet but I have tested it on my hardwood floor.

I noticed on RWD setup's that people don't mention any pullies that they have installed that would result in the change of a FDR. My guess is that a lot of the drivers that convert over to RWD are just leaving the gear/pullies as is. My question is does FDR really matter? I don't know how to calculate the setup that I have.

PS: I'll post pics up soon.

First off FDR does matter! You want to match a gear ratio to your motor. Finding the right gear ratio can change everything! I go by the recommendation for my motor in an awd touring car. Then play from there to make sure I am not overheating the esc and motor. To figure out FDR you need to calc all your gears and pulleys.

1 take rear diff pulley and divide by center pulley.
ie 34/20=1.7 <---We call this internal ratio

2 take the spur gear and divide by pinion
ie 120/30=4 that would be your external ratio

now times your external ratio by the internal ratio
ie 4x1.7=6.8 This number mean 6.8:1 so this information tells you that the motor will turn 6.8 times every time the wheels turn once.

A Higher FDR ie 10:1 Is less work for the motor and can cause over reving! Also gives a lot of torq but less wheel speed.

A lower FDR ie 5:1 would make the motor work harder to turn the wheels this would result in lower torq and more max wheel speed.

You really need to find the right gearing for your motor so the rpm and torq is in the right spot. I refer to a chart novak puts out.

http://teamnovak.com/tech_info/view_article/26

Been thinking about this too..
My thought is that although it changes the rpm of the rear wheels, it would be just as easy and probably cheaper to change the pinion/ spur ratio for the same effect?
Or is it about fine tuning?

yes it is cheepest to change fdr with spur and pinion. I am not sure what effect changing the internal ratio would be. I know you would have to compensate the external ratio with the spur and pinion.

Thanks, JustSiDEwayZ. So my guess is that I may need to change my gearing since I came from CS to RWD, because the front pulley is taken out of the equation. I'll need to crunch some numbers to determine that.

Also, how would you calculate this if there is a two belt setup for RWD applications? My R31-FM has a rear pulley that connects to a rear center pulley. Then the rear center pulley connects to the front center pulley that is on the same shaft as the spur and pinion. Sorry, I was spoiled with the CS Calculator that did everything for me and all I did was plug numbers in.

as long as the two belts on the rear center pulley doesnt have different tooth count for the middle and the rear belt, it doesnt matter.
It ´s the same number in as it is out it equates to 0.