Final Drive Ratios

[Alex]

Ok, heres a bit of an embarassing and newbie question.. can someone please explain FDRs to me?? i mean what do the numbers mean exactly??

does a smaller number mean more torque, a higher number mean more speed? ie, is 9.66:1 slower than 10.14:1 or the opposite?

I know how to calculate it (spur divided by pinion x internal drive ratio)

but am not sure how it affects the life of the motor...

another words.. how to calculate and get the best speed to track type ratio to motor type! (without frying the motor!!)

I can prob google it..but would like to hear some views from local driver for running in WC / Rypers

cheers!! !bow

[PomAbroad]

OK, FDR is the number of turns the motor makes to turn the wheels once. Therefore 9.44:1 is higher top speed than 10:1 as the motor only has to turn 9.44 times to rotate the wheels once. Basically, the opposite to what you thought. 9.44:1 is a taller (higher) gearing than 10:1 or lower number less torque or any other of the confusing ways to put it. hope that hasn't made it worse.
<span class='smallblacktext'>[ Edited Tue Mar 28 2006, 08:59PM ]</span>

[Alex]

ok understand that..but how do u know where the limit is ...or the "sweet spot" with the motor (take running stock in offroad as an example)without frying / over cooking it first ;)

[Alex]

or is it a matter of trial and error?

[James]

the best way (to be honest) to get the ultimate FDR is to ask your local track pro/fast guy... im not joking.

if they deny you information, firstly, they suck.... for not helping a fellow racer..

your generally geared right when you appear to be a simular 'straightway' speed as your fellow racer.. your over geared when you blow motors or have a lack of performance.

i ran crazy stupid gearing at bunbury this weekend, but the track demanded it, it was absolutely massive...

I run a 7.5 FDR at ryper for onroad with a monster stock. if it's a hot day, maybe 7.8. if i was to run an 8.5 FDR i would be really fast out of corners (more torque)... but I would be lacking in 'top speed'. If i geared to 6.5, i would have huge top speed, but lacking in torque, I'd probably blow my motor, trying to go fast in technical sections...

etc.

[Alex]

ok. ok..thanks Kev and James...

so...

Im running a 14T Mod motor on the xxx4... the recommneded pinion size for the 14 is 22T by the book..

Im sure we all concur..but just to have it in my own language so it makes sense to me...sorry, feeling slow here. haha pardon the pun.

if i go with
92 (spur gear) / 22 x 2.1 (internal ratio) = 8.78:1
thats the starting point by the book

if i drop 1 pinion down...
92 (spur gear) / 21 x 2.1 (internal ratio) = 9.2:1
i gain more torque and lose top speed

if i go up a pinion...
92 (spur gear) / 23 x 2.1 (internal ratio) = 8.4:1
i gain more top speed and lose torque

and if i go crazy, like go up 4 pinion size than recommended...
92 (spur gear) / 26 x 2.1 (internal ratio) = 7.43:1
i gain super top speed and very little torque, with not much power tackling jumps and corners...with the possibly of over frying motor.

right? !burnout

[Alex]

it just seems a lot easier with a mod motor cos there s "recommended SINGLE pinion gear to start with" but when it comes to stock, there like a wide powerband to play with..

so... would anyone like to share their FDR for the Ryper offroad track :P ??

[Birky]

Shadow, its not so much torque but more acceleration.

A high ratio with give you good acceleration but your top speed, whereas a low ratio would give you great top speed but no acceleration.

Therefore you need a combination of both, acceleration for the infield and top speed for the straights.

[PomAbroad]

Mod easy.....Ha! A single pinion reccomendation is just a starting point. The powerband of a mod is in a completely different place if you change from a single to a double wind for example. It is all a bit trial and error, everysingle motor is slightly different. You just got to suck it and see, especially with stock, listen to the motor down the straight you WILL hear when you hit that sweet spot.
<span class='smallblacktext'>[ Edited Wed Mar 29 2006, 08:19AM ]</span>

[Alex]

gotcha gotcha.. i think i see the light now.. hmmm, or should i see the straight! hahhah thanks boys appreciate the brainstorm ;) !bow