thanks op but i have found somethign rather interesting, i have viewed many calculators and using my T4 as an example with a 10.5T (3250KV) brushless the calcs all agree that a 17/84 ( 18/87 pinion spur is the way to go, HOWEVER, this makes esc and motor run hot, and is a poor gearing option. i am still playing with gearning however because the cold temps outside arent exactly a blessing LOL. right now i have a 23/84 in it and motor temps are 90 to 98 degrees F telling me i have more room and stay uner 150 F but that is with the weather being cool/cold. anyway, this gearing puts me way outside of the 17/84 18/87 ( or 1:1 ). i also recalculated for running an 8.5T (4000KV) brushless and found that gearing it 20/87 was the sweet spot for temps but was overheating slipper and ball diff under normal driving conditions.

it is also important to note that AE recommends a 21/84 for the T4.3 for a 10.5T 3500KV reedy setup.

now here is where things get interesting. if we factor in tire size, my tires are proline bowties and they physically measure 4" across and are what came on my T4, i also have another set of bowties that are brand new that also measure 4" across. now looking at the AE recommended gearing of 21/84 for a T4.3 it would be possible to acheive a 1:1 IF the bowtie tires measured 3.5". so tire size also plays a role however this recommended gearing is way conservative on the part of AE since the T4 stock tires are 4" not 3.5" and i would personally recommend a 22/84 combo for a T4, T4.1, T4.2, or T4.3 running the 4" tires but if you have 3.5" tires starting point would indeed be 21/84 for a 10.5T.

at the end of the day gearing isnt just pinion/spur, it is also tires, and any other gear ratios be it internal tranny ratio, multiple diffs with different ratios ( overdrive on front as an example). when it comes to brushless though and no standardization between brushless manufactures just gear for whatever works for your track and if you are just bashing gear to give you the best trifecta of speed, control, and temp, gear calcs can be useful for a starting point but most common reply i see when people ask for help gearing is ask the local racers at your track, followed by gear calc suggestions.