need gearing help

2wd slash, mamba max pro, tekin 17.5 redline (2500kv). 7.4 trakpower lipo
haven't installed it yet.
well i'm trying to run a big track and a small track within days of each other. i want to use same motor/esc in both. ne body got some ideas on gearing for two different tracks. i want to keep temps in check via good advice, not trial and error. i've checked some other forums (traxxas) and it's so hit and miss i don't know what to beleive. practice day is tomorrow, qualify sat, race sunday. please help me. i bought a bunch of spurs/pinions today
thanks monster heads

i realize i'll have to change gears for other tracks (just need 2 setup plans)