ra272 wrote:First road test today, it runs very well but I don't know how to gear it correctly. I've tried a 25t pinion with 81t spur gear, but it seems a little slow on top speed.
I have a 13.5 Robitronic sensored motor and a Nosram Matrix Power esc.

Looks awesome and makes me want to find a DS project of my own.
Here's my 2 cents on gearing.
To get a higher top speed you want to go with a smaller spur and to get more low end punch you go with a larger spur.
You can find the happy medium by doing the following.
Check your motor temps with the gearing you have now.
If your temps are low under 150 degrees or so try increasing your motor timing by 5-10 degrees at a time all while checking your temps.
If it's not quick enough for you yet then try going to the smaller spur and play with different pinions ranging from 23-28. Again keep an eye on your temps. On the timing I wouldn't recommend is going above 30 degrees but most importantly just keep an eye on the motor temps.
There is more to it than this but it a start.