[bowley]

Hi again sorry if this getting old but; refers to Scaleauto rs200 the original R series used 20000rpm 265cm/g motor & 9.27 gearing. Mew models have 18000rpm 310cm/g motor & 8.31 gearing. How much different will comparison be? I ask as my build has 20000rpm 216cm/g motor & don't know best gearing to start with 9.27 or 8.31 can anybody advise me please. Thankyou

[Kevan]

I'll be honest, for Rally I never look at the torque ratings when considering motors, I prefer short cans and always use 20-22k motors and always start at 2.6:1 gearing.

To me it seems logical that a 20k motor on 3:1 (27/9) gearing is going to have a higher top speed and lower rate of acceleration than a 18k motor on 3.875:1 (31/8)

[BAracer]

It's rare that a rally car will hit max speed on a traditional twisty track. I've started builds with 9/27 and then changed the 27 crown to 25 or 29 as I have learnt how the car performs on the tracks I have run it on.

[Kevan]

As the old saying goes...suck it and see 

[steveaca]

I think that your motor's torque (216 gm.cm.) is markedly less than the other two motors mentioned and for rallying, acceleration would be more important than top speed, a lower gear ratio (numerically higher) would be preferable. In this case, 3.875:1 (31/8) would be preferable to 3.000:1 (27/9). That's a big difference however, and you could possibly go for something in between, say 3.500:1 (28/8).

[Kevan]

In an ideal world you'd test a load of different motors and have a favourite that suits your driving style then simply stick to motors that are similar in performance.

As far as gearing there comes a point where driveability is more important than outright acceleration.  Don't forget if you go for large gear ratios i.e. over 3.5:1 I find you have way too much brakes and can't dial them out as I prefer a car that can still flow under braking without stopping on a sixpence...so that's how I find a preferred gear ratio by the amount of control it allows me to have on brakes.  

If the car is too slow with the gear ratio and brakes that feels best then it's time for a quicker motor...suck it and see 

We don't rally on magnetic track and high mag effect motors do have a big impact on a cars handling on magnetic track...good and bad.