Purple Pos / Blue Neg for the rpms ( started out with red/green combo but I would get smoked on the straight)
WOW -Is the Blue Spring Extremely LIGHT in tension?
Most blue springs are and I would pull it off right away.
With a 75ft straight that isnt much at all and I would actually gear the motor for the LONGEST PART of the track which is the infield stretched out.
If that blue spring is LIGHT like most manufacture's blue springs pull it out as fast as you can and either go another purple or a Red on the -.2 springs that far away can only mean brush bounce on one side of the motor which is really bad.
If you run purple/red then I would stay at 18.
If you run Purple/Purple you may try 18,19.
Red/Green works REALLY good in buggy on faster tracks but trucks dont seem to like the Green Spring on the -.If the BLUE spring your using is normal and VERY light in tension while it may feel ok I guarantee the motor doesnt like it.
Goodluck and if you need any other help just ask.
P.S.Great Choice in Motor's going with Team Br00d.
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Just wanted to say Thanks to RcTech for all these years of Great Information.