1/12th scale recap
 

I am thinking about doing the 1/12th scale national up at Jarrow in november but then i realised, i have just about completely forgotten everything about setting it up to what tyres i need. So all help would be appreciated. but what i really need to know is how would i work out the ratio for pinion size as i have completely forgotten, will probably have a brand new set of fronts and rears.

i've found this on another site

For 12th scale:

Rear Tire size x 3.14159 / Spur Gear x Pinion

roll out charts

So what would be a good rollout for a 19turn motor as mine at the moment is around 48 but i dont know whether that is too high or not. My spur is 98, pinion is 32 and tyre size is 47mm. But if i put a new set of tyres on then the diameter would be 51mm.

I'm far from an expert, but based on what I've read a roll-out of 48 mm is in the right area for 19-turn.

To work out what pinion size you need, use the following formula:

Pinion size = [required roll-out / (Pi x tyre diameter)] x spur size

So assuming 48 mm of roll-out, a tyre diameter of 51 mm, and an 98-tooth spur gear, you will require a 29-tooth pinion (approximately).

Hope that helps.

Which 19T, they all need differing ratios

I have got a team orion Elite V2 19T. I believe they have a little more torque than the averge motor so they may be able to handle a slightly bigger pinion.

The following applies if running 64dp spurs
adjust pinion/spur accordingly for 48dp