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calculating FDR for OTA-R

Posted: Mon Sep 03, 2012 11:58 am
by DaveyZ
Hi guys,

I have heared several things about calculation your FDR on spur and Pinion.
that that isnt the same as like a 2 belt chassis, my qeustion now remains is this correct?
because I now drive with 3.2 FDR but I have a pinion 27T en Spur 118T what makes 4,37. is this correct or is it different because of the 3 way belt system?
because I want to have a spur pinion for short track and long tracks. :)

kind regards,

Davey Zoutenbier

Re: calculating FDR for OTA-R

Posted: Mon Sep 03, 2012 12:35 pm
by Davis
Did you use the CS calculator for that? - FDR also depends on the whole drivetrain, hence, which pulleys you use, not only on the spur and pinion.
CS calculator gives me a FDR of 5.46 on the OTA with 10.5t motor, that I used yesterday in the Hague. - I actually never change that, but it might be a good idea to keep an eye on that. :mrgreen:

But then, as long as the electronics and motor don´t get hot and the car has enough forward power it´s aok, i always say. :lol:

Re: calculating FDR for OTA-R

Posted: Tue Sep 04, 2012 5:45 am
by Stalwart
DaveyZ wrote:Hi guys,

I have heared several things about calculation your FDR on spur and Pinion.
that that isnt the same as like a 2 belt chassis, my qeustion now remains is this correct?
because I now drive with 3.2 FDR but I have a pinion 27T en Spur 118T what makes 4,37. is this correct or is it different because of the 3 way belt system?
because I want to have a spur pinion for short track and long tracks. :)

kind regards,

Davey Zoutenbier


118 / 27 = 4.37 is the External Drive Ratio
Rear Internal Drive Ratio on 1:10 touring/drift is usually between 2.0 (usual 50/50 touring setup) and 1.0 (CS conversion gone really wrong)

Recently, while working on my iOS app, i've noticed that some of the excel tables floating on forums are wrong at this

Re: calculating FDR for OTA-R

Posted: Wed Jan 09, 2013 3:54 am
by JyuRoku
I also have an OTA-R31 with the street jam CS kit running 1.8CS. My motor and ESC seem to get pretty hot after 10+ laps at the carpet track. My app is showing "FDR: 4.6". I'm assuming a hot motor is normal if i'm running a bunch of laps non-stop. Im using a Tamiya 450 sport tuned motor that came with my TT01. I plan on changing to a rear 20 and 36 or 37t diff pulley which will drop it to around 3.8 FDR. Is this a good idea?

Re: calculating FDR for OTA-R

Posted: Wed Jan 09, 2013 3:29 pm
by Stalwart
JyuRoku wrote:My app is showing "FDR: 4.6". I'm assuming a hot motor is normal if i'm running a bunch of laps non-stop.

Because 4.6 is quite low.

JyuRoku wrote:around 3.8 FDR. Is this a good idea?


No. Get bigger spur and smaller pinion, and/or underdrive front axle