Gear ratio calculations and formula...

[redsawacs]

I found this on the Axial site and wanted to walk throught it to see if I could make this a working thread...correct me if I made any errors and I'll edit as needed.

Find the Final Drive Calculator here –
Gear ratio...87t Spur ÷ 13t pinion = 6.69:1
Transmission ratio...52t output gear ÷ 20t input gear = 2.60:1
Axle diff ratio...38t Ring Gear ÷ 13t Pinion gear = 2.92:1
Spur/pinion(6.69) x Transmission(2.60) = 17.39:1
Trans. Final Drive(17.39) x Axle ratio(2.92) = 50.77 Final Drive at wheels is – 50.77 : 1


Another way to look at this data...
Spur ÷ pinion = Gear ratio
Output gear ÷ input gear = Transmission ratio (should be stardard across the board)
Ring ÷ pinion= Axle ratio (this will only change if you use under/over drive gears)

Gear ratio(pinion/spur under the dust cover) x Trans ratio (2.60 stock) = Total transmission ratio

Total transmission ratio x axle ratio (2.92 stock) = Final drivetrain gear ratio

If everything is stock an easier way to find your final drive ratio is...Spur ÷ Pinion x 7.59

IF you have changed any axle or transmission gears - you'll have to work through the formula above


There was a question from another individual who was questioning what gears they need to be running to keep their rig from over heating. First thing is to know that you're final drive ratio is (if stock) is 33.02...assuming you're running a 20/87 gear set up. If you change to an 87/15 gear ratio, you'll increast your final drive to 44.03 and if you change to an 87/10, you'll have roughly a 66.05 final drive ratio. Obviously, the larger the number, the more efficient your motor/gear setup will become; the easier the motor can push the weight of the car without generating excessive heat.

In my example above, all I did was change the pinion gear from a 20 to a 10. I didnt underdrive the axles, i didnt alter tire size.....I simply changed the pinion gear.

SO, if you're looking to move the extra weight of your truck, you'll have to make the drivetrain more efficient and increase your final drive...smaller pinion gear or larger spur gear. there are other ways to do this but this is the usual way.

Hope this helps

[BodiBuilt]

Good info... for future reference Robinson Racing has a nice Gear Ratio Chart as well!

[EeePee]

People like pictures. Doesn't Axial still put all that in the manuals? They used to. I posted a picture of it January 2009.

Axial tips and tricks

[crawlhog]

Originally Posted by EeePee

People like pictures. Doesn't Axial still put all that in the manuals? They used to. I posted a picture of it January 2009.

Axial tips and tricks

they still do, very last page has all the info.

[EeePee]

Originally Posted by crawlhog

they still do, very last page has all the info.

Did they correct the 15 and 16 tooth error?

[rc kraver]

thanks but what size pinion do you think i need for a 10 lb rig runnding 1.9's weighted running 3s lipo with tekin fxr and ccbec and a novak 55t motor?

[turtleone]

Depends how much wheel speed you like. I'm running a 23t and still want more speed. The 55t motor seems to give a good amount of low end power.

Sent from my PG86100 using Tapatalk 2

[rc kraver]

im using stock gearing and its pretty dang fast but i want it so it wont overheat

[redsawacs]

pinions are cheap - start with a small one - not sure what the smallest one that will fit, try something in the 10-15t range

[redsawacs]

The good thing about what I posted is, you can use it to calculate if you decide to start changing axle gears or tinkering with the transmission gears. the gear chart in the book (I couldnt find a pictures Online simply because my "Google-fu" is weak) only addresses stock final drive.

BUT, there was a TON of information in the above posts.....mmmmmmmmmm - "Feed Me More"!